Design And Construction Of Axial Slow Flow Cw Co2 Laser

[ماجستير هندسة ليزر]

السلام عليكم ورحمة الله وبركاته

سوف نعرض في هذا الموضوع مشروع بعنوان:

DESIGN AND CONSTRUCTION OF AXIAL SLOW FLOW CW CO2 LASER
(تصميم وبناء منظومة ليزر CO2 طولي بطيء الجريان المستمر)
وهذه الرسالة مقدمة الى:
معهد الليزر للدراسات العليا / جامعة بغداد
كجزء من متطلبات نيل شهادة الماجستير في علوم الليزر/ هندسة الليزر
من قبل :
المهندسة زينب قاسم محمد الشيخلي

في هذا البحث سيتم بحث كيفية تصميم هذا النوع من ليزر ثنائي اوكسيد الكاربون حيث تكلمت الباحثة وناقشت الاتي:

يمثل هذا البحث تصميم نظري وعملي وبناء منظومة ليزر ثنائي أو كسيد الكاربون الطولي بطي الجريان المستمر المتعدد المسارات المستخدم في التطبيقات الصناعية حيث يمثل نموذج جديد يختلف عن التصاميم السابقة.
التصميم الميكانيكية و البصرية والكهربائية ومنظومة التبريد لهذا الليزر تم عرضها بشكل تفصيلي و القياسات النظرية المتمثلة اعتماد كل من 1) القدرة الخارجة على طول أنبوب التفريغ الكهربائي وقطر ه. 2) فولتية التفريغ الكهربائي على طول أنبوب التفريغ الكهربائي والضغط داخل الأنبوب.3)سرعة جريان الماء داخل الأنبوب على قطر الأنبوب الخاص بالتبريد .تم عرضها أيضا.
تم تصميم بناء وتشغيل منظومة ليزر ثنائي أو كسيد الكار بون ذات المسار الواحد و ذات المسارين (أحادية الأنبوب وثنائي الأنبوب )باستخدام أقطاب مختلفة الأشكال حيث تم تسجيل أعلى قدرة خارجة بقيمة (37-25.5) W لنمط TEM01 عند طول موجي 10.6 μm بالتعاقب. أعلى كفاءة للمنظومة كانت 16,2% عند ضغط 16ملي بار وتيار تفريغ 40ملي امبير .
وأخيراً,تمت مقارنة النتائج النظرية والعملية والتي أعطيت نتائج جيدة بالنسبة لمنظومة أحادية الأنبوب بينما لوحظ بعض الانحراف عن المطلوب في منظومة الثنائية الأنبوب.


وهذا البحث يتضمن الفصول الاتية:


Chapter one:Introduction
Introduction.
Thesis contents
Types of CO2 Lasers
Historical Background
Lasing Transition in CO2 Laser
Energy Transfer in the Discharge
Glow Discharge in CO2 Laser
Normal Density of Current at Cathode
Normal Anode Current Density
Self –Sustained Glow Discharge
Output Stabilization by the Opto –Voltaic Effect
Effect of E/N Parameter
Parameter Affecting the CW Gain in CO2 System
Current
Gas Kinetic Temperature
Helium Molecule
Tube Diameter
Gas Composition
Efficiency
Optical Material for CO2 Laser
Optical Cavity Types
Resonator
(High Power System( Folding
Cooling of CO2 Laser
Diffusion-Cooled CO2 Laser
Connective-Cooled CO2 Laser
Output Power Design Equation

Chapter two:Co2 laser system

Introduction
Mechanical Design
Optics
Gas and Vacuum System
Cooling System
Laser Discharge tube
The CO2 Laser Power Supply
CO2 Laser System Configuration



Chapter three:Results and disscusion

Introduction
Effect of the Pressure on the Discharge Voltage
Effect of the Pressure and Flow Gas on the Output Power
Effect of the Current on the Power Output
Effect of the Input Power on the Output Power
Efficiency of the System

Conclusion
Proposal for Future Work
Reference

وسيتم عرض كل فصل على حدة ساقوم بتقسيم كل فصل الى اجزاء لتسهيل قراته

انتظرونا

[ماجستير هندسة ليزر]

chapter one

i1.1 Introduction
Carbon Dioxide (CO 2) laser is the gas discharge device .It operates by electric excitation of an active medium that is a mixture of helium, nitrogen, and carbon dioxide .The excited CO2 has many energy levels it can drops to, allowing emission on groups of lines around (9.6) and (10.6) µm..
All CO2 lasers are rated in Watts or kilowatts. The distinguishing characteristic of the CO2 lasing process that make these sustained power levels possible is its relatively high efficiency at least compared to most other common gas lasers. The typical electrical power into optical power out efficiency of a CO2 laser may be any, where from 10 to 30 percent [1].

Unlike the other lasers producing visible or near IR light, the output of a CO2 laser is medium IR radiation at 10.6µm .At this wavelength, normal glass and plastic are opaque, and water completely absorbs the energy in the beam .The 10.6 µm energy is ideal for cutting, engraving, welding, heat treating and other industrial processing of many types of materials including:
****ls, ceramics, plastics ,wood ,paper ,cardboard fabric ,composites.

The CO2 laser represents the classic heat ray of science fiction .The basic construction of CO2 laser is a gas filled tube between a pair of mirrors excited by an electrical discharge. ****l coated mirrors (e.g. solid molybdenum, gold or copper coated glass) may be used for the high reflector (totally reflecting mirror). Germanium or zinc selenide which have very low losses at 10.6µm are often used, but must be cooled to minimize losses for high power.


There are many different types of design for CO2 laser divided into different groups but the basic principles are the same.
We can summarized the properties of these lasers as fallow:
1
i1. High output power. Commercial CO2 Lasers produce more than 10kW continuously.
i2.Output spectrum is in the infrared (IR) spectrum.
i3. Very high efficiency (up to 30%).
i4.Can operate both continuously or pulsed.
i5.Average output power is 50 [W/m] for slow flow of gas, and up to few hundreds [W/m] for fast gas flow.
i6.Very simple to operate, and the gasses are non-toxic.


i1.2 Thesis Contents
In this thesis, the basic theory of CO2 laser and the parameters that effects on its reviewed in this chapter. Chapter two represents the basic design aspects for slow flow CO2 laser. The details of the laser system design and construction are described in chapter three. Results, discussion, conclusion and suggestions for further works will be present in chapter four.


i1.3 Types of CO2 Lasers:

There are many types of CO2 lasers, all based on the same physical principles. The difference between them is in their structure, excitation mechanism, and the output power radiation. CO2 laser can be separated into six categories[2] :

i1. Flowing CO2 gas lasers
a.The Slow Flow CO2 Laser.
b.Fast Flow CW CO2 Laser.
i1.Fast Axial Flow.
i2. Fast Transverse Flow.

i2. Sealed-off CO2 Laser.
i3. The Gas Dynamic Laser.

In these lasers a fresh gas mixture is flowing continuously through the laser tube while lasing lasts. Flowing gas is used when the maximum power is needed out of the CO2 laser. The gas flows along the tube and is released out into the atmosphere (since it is non-poisonous)
These lasers are very simple, and the requirements from the gas purity are small. Hundreds of watts can be achieved at the output of these lasers. There are two different types of flowing gas CO 2 laser slow flow and fast flow [3].

The slow flow of CO2 laser reliable, robust, easy to operate, and are produced by the industry in many versions with powers ranging from tens of watts to a kilowatt . Figure .1.1 shows a typical setup of a conventional diffusion cooled (slow flow type) CW CO2 laser.
http://www.iraqup.com/uploads/3j2nV-ByV331015.JPG


Figure (1.1) Schematic Drawing of Slow Flow CW CO2 Laser [3].i

In these systems, the heat generated by the electrical discharge is removed by heat conduction through a water jacket surrounding the laser discharge tube .In order to continuously refresh the mixture, the gas is slowly pumped through the tube. Laser out put power can be done only by increasing the tube length [4]. i

For a fast flow system, mass transfer or the flowing gas removes the heat produced by the electric discharge. The output power is largely dependent on the mass flow rate (amount of the laser gas medium flow rate per second )of the gas, which can be as high as 120 to 150 W of output power for each gram per second of mass flow .The fast flow system can be divided into two major types as the fast-axial –flow and transverse –flow system .
Summary of CO2 lasers according to groups:
•Gas laser.
•Emit in the infrared (IR) spectrum (λ = 9-11 [μm]).
•Electrical excitation.
•Four level laser
•Continuous wave, although pulsed operation is possible.

[ماجستير هندسة ليزر]

chapter one

1.4i Historical Background
It was some time after discovery of gas laser that special properties of the mixture of gases used in the CO2 laser were recognized .Patel et al [5].(Patel 1964 )observed laser action in pure CO2 at 10.6μm .using a 5-m laser he obtained outputs of 1 mW CW with DC excitation and 10 mW peak with 1 μse excitation pulses [6].This report was rapidly followed by the observation of laser action in a CO2-N2 mixture (Patel 1964)[7].In this case a stream of N2 was passed through high frequency discharge and the active nitrogen so formed was mixed with CO2 in an interaction region between the mirrors of a Fabry-Perot resonator; an output of over 1mW was observed with a 20-cm long interaction region .i

Further work by Patel (1965)[8] led to the direct excitation of the gas within the laser resonator and the attainment of 12 watts from a 2-m tube containing a mixture of CO2 and air. He observed oscillation on R branch lines as well as P branch lines and noted that the flow rate of the mixture effected the gain .Moeller and Rigden (1965) [9]reported 10Wm-1 from a sealed tube containing a CO2-He mixture and also mentioned,with no details ,that a flowing mixture of CO2,N2 and He gave good results ,but the simultaneous report by Patel (1965) gave a detailed account of a water–cooled tube using a flowing CO2-N2-He mixture which produced over 50 Wm-1 [10].i


Pulse energies of 1.1mj were reported in the first study of a Q-switched CO2 laser (Kovacs et al 1966)[11].i

The year1969 marked attuning point in the development of high –power CW and pulsed CO2 laser .By 1969 a 750 –f t long CW CO2 laser based on the design of Patel et al (1965) had been built and operated at a power output of 8.8 kW (Horrigan et al., 1969)[12]. Subsequently, the development of electric discharge convection and gas dynamic laser has been resulted in the generation of CW laser powers in excess of 100 kW.i

The same year also saw the development of lasers based on convective cooling (Lavaini et al., 1969; Deutsch et al., 1969;Cool and Shirley ,1969)[13] and a report was published describing the operation of a compact closed system CW laser using rapid transverse gas flow capable of generating output powers of 1kw (Tiffany et al., 1969)[14]. i

Late in 1969 ,Bealieu (1969)[15] reported that CO2 laser emission could be obtained at atmospheric pressure and above by exciting the gas transversely so that the discharge passed perpendicular to the optical axis .i

The extraordinary in powers obtained from CO2 lasers in the 10 years, 10-15 kW CW CO2 can be purchased (Locke and Hella, 1974)[16].i

Al-aobaidi A.R M., in 1981[17] discussed the design and construction of CO2 CW laser and its application in the detection of the absorption line in some gases using opt.-acoustic technique. The designed laser has been operated with TEM00 mode with an output power of 27 W, and gas mixture ratio of CO2: N2: He /12:14.3:73.7% respectively .He used a grating to tune the laser emission for the required lines. i

Noory Z.T.,(1989)[18]described the design and construction of continuous waves fast flow CO2 laser system ,the total electric discharge consist of two equal parts 112cm with DC of 15kVand 600mA power supply output power was 30 W at pressure 60mbar and gas flow rate of 240l/min.
Al-Yaseen U. A.,(2001)[19] constructed a CW CO2 laser system .The laser cavity of different lengths 50,60,70and 80cm.The maximum output power was 60 W at flow rate 150 l/min .i

Kazim Kh. N.,(2002)[20]constructed a CW CO2 laser system of different lengths60, 70 cm with internal diameter of 2cm.The maximum output power and efficiency obtained of 83 Wand 8.5% respectively at resonator length 204 cm..i


1.5i Lasing Transition in CO2 Laser:

Lasing transitions in CO2 laser occur when the molecule is going from higher energy level of the asymmetric mode into one of the following modes see figure 1.2.i

1. The transitions to the symmetric stretching mode correspond to the wavelength of 10.6 [µm].i2. The transitions to the bending mode correspond to the wavelength of 9.6 [µm].i


http://www.iraqup.com/uploads/ED1on-6N4w36236.JPG

Fig. 1.2 : Energy Level Diagram of CO2 Laser [22 ].i
Each of the vibrational energy level is subdivided into many rotational levels. Transitions canoccur between vibrational energy levels with different rotational levels, so there are many lasing lines around the main vibration transitions [20].i

The carbon dioxide molecule is liner asymmetric triatomic molecule. The molecule has three normal modes of vibration and the three atoms are situated on a straight line with the Carbon atom in the middle. i

In figure 1.3 the three vibration modes of CO2 molecule are illustrated: i

i1.Symmetric stretch mode (υ1). i
i2.Bending mode (υ2). i
i3.Asymmetric stretch mode (υ3). i

Vibration levels are designated by three numbers representing the number of vibration quanta in each mode associated with the particular level and written in the form (υ1,υ2,υ3 ). The molecule can simultaneously vibrate in more than one mode and can have more than one quantum of vibration energy in each mode [21].i


Electric discharge is created in the laser tube. The energy of the accelerated electrons is transferred by collisions to the Nitrogen molecules and to the CO2 molecules. .i

Nitrogen molecules help in the process of the excitation of the CO2 molecules. The first vibrations energy level of the Nitrogen molecule is very similar to the asymmetric stretching mode of the CO2 molecule (see figure 1.4), so energy can be easily transferred from the excited Nitrogen molecules to the CO2 molecules [22]..i


http://www.iraqup.com/uploads/im6L0-j3YE6932.JPG

Figure 1.3: Oscillation Modes of CO2 Molecule [22]..i

The (00˚1) upper laser level of CO2 at 2349.3cm-1 lines 18.6 cm-1 above the υ =1 level of N2 .The (10º0) and (02º0) lower laser levels for the 10.4µm and 9.4µm bands of CO2 lie at 1388.3 and 1285.5 cm-1 , respectively .These two levels are in Fermi resonance and vibration levels belonging to different vibrations have nearly the same energy .The mixed states denoted as (100,020) lying at 1388.3 and 1285.5 cm-1 respectively .The (01º0) bending mod of CO2 lies at 667.3cm-1 For exhibit laser action ,(00º1)(100,02º0) near 9.4µm,consist of an R-J is the rotational quantum number .iThe IR transitions between various levels are governed by the selection rules [24]. .i

ΔV= ±1
ΔJ= ±1
Where, J is the rotational quantum number.i
V is the vibration quantum number.i

[HazemSakeek]

بارك الله فيك ماجستير هندسة ليزر على هذه السلسلة الرائعة من المواضيع المتعلقة بالليزر وموضوع ليرز ثاني اكسيد الكربون من الليزرات التي لها تطبيقات عديدة جدا

اشكرك على هذا الشرح الوفي والواضح والسلس وان شاء الله سيفيد كل من يدرس مقرر الليزر


تحياتي

[HazemSakeek]

توضيح واستفسار

نلاحظ من الشكل الذي يوضح مستويات الطاقة التي تنتج الليزر في ثاني اكسيد الكربون ان هناك 3 انتقالات تعطي 3 اطوال موجية لليزر. وهذا يعود للحركة الاهتزازية لذرتي الاكسجين بالنسبة لذرة الكربون حيث يكون هناك 3 انماط اهتزازية هي الموضحة في الشكل

http://www.iraqup.com/uploads/im6L0-j3YE6932.JPG


كيف يمكن الحصول على ليزر بطول 10.6 µm فقط

ما فائدة النيتروجن المخلوط مع ثاني اكسيد الكربون


تحياتي

[ماجستير هندسة ليزر]

السلام عليكم ورحمة الله وبركاته

حياك الله

شكرا دكتور على المرور

حلو مرورك والسؤال احلى


كيف يمكن الحصول على ليزر بطول 10.6 µm فقط

اهتزاز الذرة ضمن مستوياتها يتحكم بنوع الليزر والطول الموجي المنتج فمثلا الانتقالات الاهتزازية والدورانية تؤدي الى تكوين ليزر ضمن مدى تحت الحمراء (IR) او قريب هذا المدى (near IR). كما موضحة في الشكل المذكور فلذرة (Co2) ثلاث حركات اهتزازية كما لها ايضا انتقالات دورانية.اي انتقالته هي اندماج لهذين الانتقالين.

اما الانتقالات الاهتزازية لوحدها فتنتج طول موجي مرئي ( visible).

ما فائدة النيتروجن المخلوط مع ثاني اكسيد الكربون

ان اول ليزر ثنائي اوكسيد الكاربون اكتشف في عام 1964 بواسطة عالم اسمه بتل لم يكن يستعمل النتروجين فقط غاز ثنائي اوكسيد الكاربون ولكن كانت الطاقة الناتجة قليلة جدا وكذلك كفائة الليزرحيث كانت الطاقة بحدود (1 ملي واط), فائدة النتروجين يستعمل كعامل مساعد مع الهليوم ولكل وضيفته,حيث يستعمل النتروجين في عملية التهيج ونقل الطاقة الى جزيئات ثنائي اوكسيد الكاربون حيث ان النتروجين لا يوجد له عزم كافي ليهبط الى المستوى الاوطىء لعدم وجود محصلة عزم كهربائية لتهبط لذلك تبقى في حالة رنين وتهبط الى مستويات قريبة من مستويات Co2 وبذلك سوف يحصل انتقال رنين من النتروجين الى ثنائي اوكسيد الكاربون مما يؤدي الى انتقال الطاقة.

وهناك اضافة اخرى وهو غاز الهليوم وهذا الغاز لا يشارك في عملية التهيج او في عملية التفريغ (discharge)وانما يستعمل من اجل عملية التبريد حيث انه يحاول نقل الحرارة الناتجة بسبب التفريغ (discharge) الى جدران الانبوب الحاوي.

وطبعا تختلف نسبة استخدام كل منهما كما انه باختلاف النسب سنجد اختلاف بعض عناصر ومميزات الليزر الناتج.

وسوف توضح في بقية البحث ان شاء الله

Co2+He+N2---------------->Co2

التوضيح فائدة كل منهما تاتي ان شاء الله

انتظرونا

سلامي

[ماجستير هندسة ليزر]

chapter one

1.6:i
Energy Transfer in the Discharge:i

The most commonly observed laser transition in the CO2 molecule, barring the use of any frequency tuning mechanisms, are from the CO2 asymmetric stretch transitions, from the (00*1) to the (100*0)(10.6) micron and (02*0) (9.6) micron states, using the notation (v1v2*v3), where v1 refers to the symmetric stretch quantum number, v2 refers to the asymmetric stretch quantum number and v3 refers to the asymmetric stretch quantum number. There are literally dozens of other lasing transition. Which employing an interactivity grating .In a CO2 laser, depending on instantaneous gain medium and resonator conditions can easily choose.:i

Any single possible laser line can be forced through the use of an interactive grating. Rotational structure, having energies clustered very close to one another, may exist at any time. Nonradiative decay to short-lived lower lying states followed by Nonradiative decay to the ground state follows .N2 is added to the laser gas to more efficiently transfer energy from electron impact to the CO2 upper vibrations laser level. The glow discharge is a very effective mechanism for vibration excitation of nitrogen. Since N2 is ahomonuclear molecule, dipole radiate de-excited is forbidden. This allows for long-lived vibration states, which makes excited N2 molecules more readily available for collision excitation of CO2.:i

De-excitation is only accomplished collisionally with the wall or other gas constituents, the most beneficial of which is the CO2 molecule .The N2 (v=2) state is only 18cm-1 (2.2E-3 eV) from the upper laser level of the CO2 molecule .This makes resonant energy transfer between N2 and CO2 more likely.This energy is much smaller than the average kinetic energy of the molecules in the surrounding glow ,so vibration energy can easily be supplied to the CO2 molecules .:i

Energy transfer occurs from vibration levels up to v=4 in N2,because the ensuing anharmonicity of these states ,due to bond stretching ,is still well blow the average molecular kinetic energy .CO is isoelectronic with N2 and also has vibration levels easily excited in the glow discharge [24].:i

Thermal poisoning can occur, which is build up of lower lasing level populations in CO2.This results in a reduction in laser output power due to a clogging of the path from the upper lasing level to the ground state, where the CO2 upper lasing level is most efficiently populated through collisions with N2 these lower levels are cooled by the addition of He to the gas mix helium energy levels are much higher than the molecular energies of N2and CO2, above 20 eV.:i

For typical electron energies in the glow discharge of 1 to 3 eV, the discharge is not significantly affected by the addition of He other than to raise the electron temperature of the discharge [25].:i

Since the first ionization level of the He is higher than that of the other gas components, high energy impacts (higher “voltage”) is required to make it apart of the glow conducting path. Only a small amount of energy is lost from the discharge due to inelastic collisions with He and subsequent collisions with the walls. Thermal conductivity in gases is independent of pressure and since thermal conductivity of the He is roughly six times that of CO2 and N2, He makes an efficient transporter of waste heat to the walls of the discharge tube. The efficiency of heat transfer resulting from the addition of He to the mixture allows for higher discharge current before radiation saturation [23].:i

CO may also be added to the laser mix to improve efficiency, but it dose not transfer vibration energy as efficiently as N2, due to a difference between the CO v=1 level and the CO2 upper lasing level of 170 cm-1 . CO also has a dipole moment which creates a radiative decay channel to depopulate the electron impact excited CO, thus making CO less available for the job of CO2 excitation. CO is also a component in the dissociation equilibrium of CO2, so when using added CO with CO oxidation catalysis, larger concentrations of CO effect the CO2 concentration not always in a predictable manner. :i With these drawbacks, CO still adds to more efficient CO2 vibration excitation than electron impact alone. H2O can be added as a heat transfer enhance but is less efficient at cooling than He. H2O, in small concentrations, also has the beneficial side effect of homogeneous catalytic recombination of the dissociated CO2 products, CO and O.H2O in a larger concentration overwhelms the beneficial catalytic effects and effectively depopulates the upper lasing levels of CO2 .:i

Xe may also be added to a laser gas mix to effectively cool the electron temperature of the discharge for a given current, thereby reducing the amount of electron impact dissociation of CO2. The prohibitive cost of laboratory grade Xe prevented this investigator from utilizing it [25].:i

[ماجستير هندسة ليزر]

chapter one

1.7i Glow Discharge in a CO2Laser
Brown`s classification of discharge [27 ]is shown in fig.(1-4) .A glow discharge is characterized by a relatively high specific electric power (1-10 W/cm3 )and by “gab” between the electron temperature Te (Te 1-2 eV) and the gas temperature Tg (Tg=300 –600 K).These two feature are important for the use of glow discharge to excited nitrogen –molecule vibrations and to pump the vibrational (001) level of the CO2 molecule.i
The glow discharge in a tube, the from investigated detail before the invention of the CO2 laser, is divided in to three regions: the cathode drop re (its value in N2 is 340 V, and its length d=0.4 /p, where d is in cm and p in Torr), the anode drop region (the voltage drop is several times ten volts definite (for the given gas ) electric –field strength E proportional to the pressure and weakly dependent on the tube diameter and on the current flowing through the column .For nitrogen we have E/P= 5 V/cm. Torr..i

The current density in the column has a maximum at the tube center and drops to zero at the wall .In a round tube of radius a it varies with the column radius in proportion to the Basal function J0 (2.4 r/a)[26]..i

1.7.1.i Normal Density of Current at Cathode
The current distribution on the cathode surface is different: at low currents the cathode emission (observed at those where current flows) covers a cathode area fraction proportional to the total current ,i.e., the current density on the cathode is constant –this is called the normal density , proportional to the esquire of the gas pressure and equal to 0.240 mA/(cm.torr)2 for nitrogen and copper cathode .As the current is increased and the emission covers the entire cathode area the current density increases in proportion to the current , and the cathode drop increases slowly (it doubles approximately when the current density is increased by two orders above the normal value )[26]..i

1.7.2.iNormal Anode Current Density
Glowing spots were observed also on a solid anode at place s where current flowed into the anode . This phenomenon was observed in animmobile gas both at low pressure and at pressures of several times ten torr in air and in nitrogen. Measurements of the normal current density ja in a stainless steel anode in this pressure range yielded ja =4.2 10-4p2 ja in A/(cm.torr)2 and p in torr for nitrogen ,and ja =2.6*10-4 p2 for air .glowing layer were observed on an anode placed in a laminar produced by introducing gauze grids (at a velocity 30 m/sec and pressures 20-70 torr of the air ,N2, and CO2 )[27]..i


http://www.iraqup.com/uploads/0qgE0-8rKT50127.JPG

[ماجستير هندسة ليزر]

chapter one

1.8i Self –Sustained Glow Discharge:
When along cylindrical glass tube with plane electrodes at its ends is filled with a gas at a pressure of ≈mmHg and the potential difference “V” between the electrodes is slowly raised, then a small current of about 10-12 A can be observed to flow through the gas.i
This current causes the ionization process in the gas .As V increases ,the ionization by collision in the gas beings to increase as well as the current rises . When the potential difference across the discharge tube reach the ionization by collision in the gas being to increase as well as the current rises. When the potential difference across the discharge tube reaches the breakdown value VB as determined by the gas, its pressure ,and the electrode spacing ,the current jumps to about 10-6 through it varies with the potential difference in a complicated way. .i

A resistor, of high resistance R, is connected in series with the discharge tube to limit the current at value of the supply voltage E. The current then takes such value that the voltage drop across the series resistor is equal to the difference between the supply voltage and the potential difference VB across the tube..i

The self-sustained glow discharge is, used to pump the longitudinal and transverse CO2 laser systems for different pressure [27]. Fig.(1-5)shows the various regions of the self –sustained glow discharge ,,which can be classified into very narrow dark space (Aston )close to the cathode. This is followed by a thin relatively weak luminous layer (the cathode glow) ,which in turne is followed by the cathode dark space ..i

Aston’s dark boundary separates the cathode glow are not always clearly visible .A sharp boundary separates the cathode dark space from the negative glow, which becomes progressively dimmer towards the Faraday Dark Space. The positive end of this is the positive column. It is either the region of uniform luminosity or regularly striated. At the positive end of this positive column there is sometimes visible an anode dark space followed by the anode glow close to it [27]..i



http://www.iraqup.com/uploads/faQA5-0S0u87499.JPG

Fig.(1-5):Distribution of the visible and dark regions, electrical field ,charges and current density in the normal glow discharge[27]..i

Consider an electron emitted from the cathode, which is accelerated in a strong field, however it performs few ionizing collisions due to its sufficient energy. Further from the cathode, the field has become weaker, the electron ionizes more efficiently. Near the boundary between the cathode space and the negative glow , the field has become very weak ,thus only the fast electron , which have not lost energy by inelastic collisions, will be able to ionize in that region .However ,a large number of electrons will cross the boundary and enter the negative glow [24]..i

In the negative glow occurs the recombination process between the electrons, which have low energy with positive ion produced from the collision between the electrons of high energy and this recombination produce the electron ion pairs. The negative glow is not affected by discharge tube dimension but effected by the cathode cross-section and the discharge voltage and current density .In the positive column the axial component of the electrical field is found to be constant at any point, it follows that the net space charge is zero (i.e. n+=n- )[20]..i

At the anode side of the positive column the anode attracts the electrons ,and the positive ions are repelled . A negative space charge is set up in front of the anode this lead to an increase of electric field as well as a rise in potential. The anode is therefore covered with a luminous sheath “the anode glow “[24]. .i

[ماجستير هندسة ليزر]

chapter one

1.9i Output Stabilisation by the Opto –Voltaic Effect:
The phenomenon of static resistance fluctuation in a CW laser discharge due to the intra-cavity coherent radiation is well known as opt. -Voltaic or opt. galvanic effect .It can be used successfully for stabilising a single –line CO 2 laser with high accuracy, the alignment of a laser cavity, and the detection of radiation in CO2 laser.i
In general, the resistance fluctions of the discharge due to stimulated emission in a current stabilised or ballast resistor regime result in fluctuations of the power that is dissipated in the discharge, and hence in temperature variation of the plasma and the discharge tube. The relative changes of static resistance of the laser tube due to changes of the tube voltage V (or longitudinal electric field) and the discharge current I..i


http://www.iraqup.com/uploads/8BUUb-47jv39113.JPG

where:.i
:http://www.iraqup.com/uploads/83uNa-U0Kb52282.JPG
Changes of the static resistance of the laser tube..i

: http://www.iraqup.com/uploads/7BRew-2X8n14840.JPG
Static resistance of the laser tube..i

:http://www.iraqup.com/uploads/06kBF-ja5K92275.JPG
Changes of the tube voltage..i

:http://www.iraqup.com/uploads/d1M2k-gQ3X31379.JPG
Discharge tube voltage..i

:http://www.iraqup.com/uploads/8B8lX-sL5j57676.JPG
Change of the tube current..i

:http://www.iraqup.com/uploads/2o5AF-an3Y37146.JPG
Tube current..i

We shall consider the discharge laser tube as a nonlinear resistance with parametrical change of its voltage –current characteristic by the coherent radiation in the discharge tube .The operating current and voltage on the characteristic are determined by the voltage Ua of the power supply and the serial ballast resistor Rb ,the value of which must be larger than the absolute value of the negative dynamic resistance of the discharge tube ..i
The operating values of V and I0 change with the radiation power along the working –line determined by ballast resistor Rb and supply voltage Ua. .i


http://www.iraqup.com/uploads/G55c8-YbPm78854.JPG

The impedance of the discharge tube, however, increases with radiation produced. This means that the variation of the discharge voltage ,called the opt-galvanic effect ,is in phase with variation of the radiation power and simultaneously the variation of the current ,called the opt-galvanic effect,has the opposite phase[27]. .i

.i 1.9.2 Gas Kinetic Temperature.

It is important that the gas kinetic temperature of the CO2 laser plasma be kept as low as possible. This follows both from Patel’s treatment of the gain of molecular laser (Patel 1964) which shows that the gain αT-3/2.The wall temperature, gas pressure and discharge current all affect the gas kinetic temperature, which varies radically, being maximum on the tube axis [15]. .i



1.9.3.i Helium Molecule.
The cooling of discharge gas is effectively obtained by the addition of He .The first excited state of the helium occurs at 159850 cm-1 , which is above the upper laser level (001) in only 2349 cm-1 above the ground level .The thermal conductivity of the He is about six times as large as that of CO 2 and N2.The difference between the temperature of the gas and the wall of the tubes cased by the discharge heat is inversely proportional to the conductivity of the gas .The considerable increase of heat transfer obtained by the addition of He means that the radiation production of the system saturate at higher discharge current [29]..i

As a result of the laser action, population of the (0110) level increases steadily. Since this level is close to the ground state, and since (k T) at room temperature is 210 cm –1 (where k is Boltzman constant (k=1.3805 *10-23 JK-1),and T Is absolute temperature in Kelvin ),it acts as bottleneck which prevents molecules transition down to the ground level .Such problems are overcome by the addition of He to the CO2 ,N2 gas mixture .Its addition effects the rat of dissipation of heat in the discharge tube that consequently effects the gas temperature ,and the rat of the thermal relaxation of each laser level .the effects of adding helium can be summarized by the following reactions :.i

CO2 (10˚0) + He → CO2 (00˚0) + He + K.E

He are added to the gas mixture in order to:.i

1.Empty the lower laser energy level so that population inversion is maintained. .i
2.Stabilize the electrical discharge by taking heat away from the lasing area. .i
((Advanced: (The specific heat (which determines the thermal conductivity) of He (1.24 [cal/gr* 0K] is five times that of Nitrogen (0.249 [cal/gr* 0K]).)) .i
Gas pressure inside the CO2 laser tube is 5-30 [Torr], of which 10% CO2 gas, 10% N2 and the rest is He [36][37]. .i

[ماجستير هندسة ليزر]

chapter one

1.10i Effect of E/N parameter:

An important parameter in the electron –induced population of both CO2 and N2 levels in a discharge is the ratio of the electric field E to the total density of neutrals N.The average electron energy in creases steadily as E/N increases from 10-16 V-cm2 , reaching ~3eV at E/N~6*10-15V-cm2 in atypical CO2,N2,He laser mixture .This value of E/N is that at which part of the incident discharge power first starts to be used in producing electronic excitation of N2 in pure N2 .i

Optimum pumping of the CO2 (001) level in pure CO2 occurs when E/N s~2.5*10-16 V-cm2 .It should be noted that E/N in typical high-pressure pulsed discharges is usually in the range (2*10-16ˉ─8*10-16 ) V-cm2.In electron –beam –controlled lasers E/N may be (1*10-16 -2*10-16) V-cm2 .The possibility of controlling E/N to tailor this ratio to the value most effective, since with optimized E/N ,as much as possible is being done to adjust the discharge to yield direct electron impact excitation of CO2 (001).Thus laser in which E/N can be controlled will be inherently more efficient that those in which the values of E/N tend to be relatively uncontrollable and high[28].i
The following equation shows the relation between the E/N ratio to the pressure gas temperature , gas density and discharge voltage at optimum pumping in pure CO2 when E/N equal 2.5*10-16 V.cm2

http://www.iraqup.com/uploads/4btPn-JV211014.JPG

http://www.iraqup.com/uploads/wQLo1-03Nf92512.JPG

where

http://www.iraqup.com/uploads/4YmHx-Bh5763981.JPG

http://www.iraqup.com/uploads/0aD5D-cIc385753.JPG


1.11 Parameters Affecting the CW Gain in CO2 Systems (D.C Excitation.].i

It is difficult to separate completely the influence of the various parameters on the gain of the CO2 laser, even when it is operating in the CW, D.C. excitation regime. This is primarily because many of the parameters are inter-related, e.g. change the current in the discharge will also change the balance of the components in the optimum mixture in a given tube, etc. Although one can predict the optimum operating parameters of the a system moderately well, it is almost always necessary to experimentally trim them to achieve the peak performance of the system [28].].i

].i 1.11.1 Current:

All CO2 laser mixtures show current saturation of output; as the current increases the laser output increases steadily to maximum and then decreases slowly as the current rises above the optimum .The current for maximum CW output depends on gas pressures and tube diameter .The axial gain behaves in a similar manner but the optimum current is much lower, generally (10-20) mA.].i

As the current is increased above this value the center of the gas becomes too hot for the gain to remain optimum so the radial gain profile in the tube dip in the center .The larger the current, the deeper is the dip and nearer to the walls are the points of maximum gain .].i

The efficiency of the laser also varies with current flowing through the tube, maximum efficiency and maximum output power cannot be obtained at the same time, the current which gives greatest efficiency being lower than that which gives the best output [28].[].i

http://www.iraqup.com/uploads/VtALx-277r51353.JPG


Figure (1.6): Optimum Current and Total Pressure for Maximum CW Oscillator Output Power as A function of Tube Diameter [28].].i

].i1.11.4 Tube Diameter.

It already been mentioned that the tube diameter influences the optimum gas pressures and the currents (The larger the diameter, the lower the optimum gas pressures and the larger the current). ].i

The maximum output power obtainable is, however, virtually independent of tube diameter (up to 2-inch diameter at least) if all the other parameters are properly optimized for each tube diameter [28]. ].i

The peak gain attainable in the laser dose depends on tube diameter (see figure 1.6) [30]. The precise manner depends on the gas mixture, but the peak gain always decreases as the diameter increases.].i

To a first approximation the maximum axial gain for N2-CO2-He mixture varies inversely with the diameter.].i

1.11.5].i Gas Composition.
A wide variety of different three –component gas mixtures have been investigated in conventional flowing CO2 laser systems but the highest output power is obtained from a mixture of CO2 ,N2 and He .Generally ,the output power is not too sensitive to changes in the [CO2,N2]:[He] ratio but will depend quite strongly on CO2 pressure and the [CO2]:[N2] ratio .In practice ,to determine optimum operating conditions one would set the [CO2]:[N2] ratio constant at about 0.8:1 and then vary [CO2,N2]:[H2] until peak power was obtained .The [CO2]:[N2]ratio would then be “fine tuned” by varying the N2 flow rate to find a point at which the system was optimized[11].].i

1.11.6].i Efficiency:

The efficiency of conventional CW CO2 laser discharges may approach 30% at low laser output .it is shown that the efficiency depends strongly on wall temperature and the flow rate. It is also usually true that maximum efficiency of practical system may not occur at the same discharge parameters as the point at which maximum power output is optioned [30]. ].i

[ماجستير هندسة ليزر]

chapter one

1.12i Optical Material for CO2 Laser

For optical materials are commonly used for CO2 laser. These are listed in table (1) Germanium (Ge) is the most common output coupler material for lower –power models (<100W) because of the cost advantage .It cannot be used on higher- power lasers as it absorbs significant amount of the laser beam and experiences thermal runaway at approximately 50&ordm;C.This means that ,as the temperature of the substrate increases ,its until the mirror is destroyed by fracture .i

Gallium arsenide (GaAs) and zinc selenide (ZnSe) are used as output couplers for higher power CO2 lasers. Gallium arsenide has a lower absorption coefficient than germanium and a higher thermal runaway point .It is also resistant to damage from high peak power and thus is popular for pulsed CO2 lasers. Zinc selenide has an even lower absorption coefficient, but its thermal conductivity is also low..i


http://www.iraqup.com/uploads/61gdI-X7Hu49178.JPG

Zinc selenide has the advantage of transmitting visible light. This makes optical alignment of the laser much easier. Both of these materials are widely used ,with zinc selenide being more popular in high-power kilowatt range for CW CO2 lasers.Because the index of refraction of these materials is high,antireflaction coatings are required for all transmitting optical components[8] ..i

1.13.i Optical Cavity Types.

The optical design of the cavity must taking into account the actual path of the light rays (geometric optics), mirror losses (such as absorption), diffraction (physical optics), and the density inhomogeneities of the flowing gas that cause phase distortion in the laser beam [29]..i

1.13.1.i Resonators

The most simple optical resonator consists of a pair of plan or spherical mirrors located opposite one another .They are center to a common optical axis and are perpendicular to this axis ..i

There are basically three types of optical resonators : plane parallel resonator (A),hemispherical resonator (B), spherical resonator (C)..i

For laser in the low to medium power range (1 mW-500W) ,the hemispherical resonator is mainly used .Its features include high output powers with relatively uncritical mechanical adjustment. The output power depend on how much of the laser- active material use ..i

For the plane parallel resonator (A),in which the light beam is only refected and not modified in shape ,it must be ensured that both plane parallel mirrors are adjusted exactly parallel to another .This type of resonator is the most difficult to adjust and to maintain in a correctly adjusted condition [2]..i



http://www.iraqup.com/uploads/h0LSh-4u7Q78392.JPG
Figure 1.7: Types of resonator [2]..i

The spherical resonator (C) is the most simple to adjust; but has the advantage that undesired transverse modes can easily start to oscillate .This means that the laser power is split up over a number of modes which are separated spatially from one another and which cannot be focused to acommon point as with longitudinal modes ..i

The hemispherical resonator has become very popular since it exploits in special manner the desired mode characteristics of the plane parallel resonator and the advantages of adjustment associated with the spherical resonator [32]. .i

[ماجستير هندسة ليزر]

chapter one

1.14i High Power System. (FOLDING)

The use of very log tube can introduce problems not encountered in smaller systems.practically log tube are usually divided into sections(with alternate anodes and cathodes )to keep the excitation potential to reasonably low value .However ,great care must be taken to eliminate all possibly reflections ,particularly wall reflections. It is necessary to break the system up into optically isolated sections each with smaller gain .Further problem encountered with very long systems is the negative lens effect produced by the refractive index gradients in the discharge plasma [30][31] .i

The folding methods which have been used are illustrated in figure 1.8 ,the most widely used is a pair of plan mirrors each set at 45˚ to the primary beam direction which reverse and laterally displace the beam .A variant of this idea is to use a corner cube in place of pair of mirrors .This configuration is exceptionally stable against mechanical vibrations ,through it dose involve an extra reflecting surface

http://www.iraqup.com/uploads/e14RL-4hBd98229.JPG

(a)Two mirror or rooftop prism fold

http://www.iraqup.com/uploads/0IROy-11qn15619.JPG


(b)Corner cub fold

Figure (1.8):Schematic diagram of two-mirror and corner-cube folds[31].


1.15.i Cooling of CO2 Laser:
There are two basic ways of disposing of the waste heat .The first is to use the heat conductive properties of the gas and the structure containing it to carry off the heat Conductive –cooling is simple but ineffective because of the low thermal conductivity of the gas .Laser that use this cooling method generate an output of about 50 W/m of active length and therefor, must be relatively long to produce industrially interesting power level ..i

The second way to remove waste heat is to hot gas and replace it with cool gas by forced convection. Such flow –cooled laser are often called often called fast-flow lasers. Where as almost no heat leaves the active region of conduction –cooled lasers except through the tube walls with flow cooled lasers no significant heat flows to or through the tube walls compared with the amount of heat carried out of the active region of the gas flow .Power output for this type is not dependent on the length of the active region .It depend only on the mass flow rate of the gas and can be as high as 120 to 150 W of power output for each gram per second of mass flow [33][34]..i


A. Diffusion – Cooled Laser..i
In a diffusion cooled laser, waste energy is rejected in a characteristic time approximately that of the diffusion time (τD). If an electrical discharge column of diameter D is assumed, the number of mean free paths during which the energy diffuses is given by D/ where is the mean free path of the CO2 molecules in the gas mixture .The mean free time between collision is given by the ratio of D to the molecular speed. Since diffusion is a random- walk process, http://www.iraqup.com/uploads/xfS6T-36Re43630.JPG is not equal to http://www.iraqup.com/uploads/dL58x-7YkV19893.JPGbut is equal to

http://www.iraqup.com/uploads/o5WFu-U5x47304.JPG

Since the power achievable from a laser is approximately inversely proportional to such characteristic cooling time ,the power (PL ) of a diffusion- cooled laser is proportional to

http://www.iraqup.com/uploads/7F58h-HgaS8115.JPG
Where

http://www.iraqup.com/uploads/MPPr6-fp1250271.JPG
is the gas density.


B.Connective –Cooled Laser..i
If the gas is moved at speed is rejected in a characteristic time (τF ) which is given [35]..i


http://www.iraqup.com/uploads/hErL4-4oN136934.JPG

For the same active volume and gas density ,the ratio of the laser power achievable with a diffusion-cooled (PLd ) and with convection–cooled(PLc)laser is simply proportional to the ratio of the characteristic cooling times :.i

http://www.iraqup.com/uploads/07sHQ-Qxu748332.JPG

Since eq. (1-8) is much than unity for even relatively slow gas flow velocity, the advantages of convective cooling over diffusion cooling are readily apparent. .i

Assume that we have a rectangular volume of gas as schematically illustrated in figure(1-9),having a cross-sectional area A and a thickness χ .We dissipate PE watts of electrical power in the volume .We extract PL watts of laser power from the volume and PH watts of heat by convectively flowing the gas through the volume .If the laser extraction efficiency is η ,then

http://www.iraqup.com/uploads/qJ4yO-L5h783241.JPG

And

http://www.iraqup.com/uploads/63mVd-5IGr68986.JPG

Where,.i

http://www.iraqup.com/uploads/e8pI8-oBR240400.JPG

Where
http://www.iraqup.com/uploads/MPPr6-fp1250271.JPG is the gas density,
http://www.iraqup.com/uploads/5vvA8-7uQS13776.JPG is the specific heat of the gas ,
http://www.iraqup.com/uploads/7R2Tg-Mn0m36587.JPG is the velocity of the flow, and is the volume .Substituting (1-7) into (1-8 ) we obtain:

http://www.iraqup.com/uploads/cb1FY-05yG93113.JPG

http://www.iraqup.com/uploads/hgXK7-q7J44270.JPG

Figure (1.9): Schematic of Volume of Gas of Length x and Area A[36] .i

[ماجستير هندسة ليزر]

chapter one

1.16i Output Power Design Equations:

The first aspect to be consider is the dependence of the output power ,P(w) on the cavity ,the output mirror transmission T ,and the saturation I, the output power is given by[37] :i


http://www.iraqup.com/uploads/4jHp5-AE8t11541.JPG

Where, :i

A is the cross sectional area of tube diameter (cm2):i

Iο the output intensity(w/cm2):i

K an empirically determined factor relating the effective uniform output intensity I to actual output intensity.:i

It is found experimentally that for TEMοο mode operation the proportionality constant K is 0.8.:i

It is convenient to write the expression for Iο in equation (1-13) as product of the ratio of the effective intensity Io /Is times the saturation intensity Is, the resulting output power is : :i



http://www.iraqup.com/uploads/H232c-HroL80586.JPG

where,:i

dt is the tube inner diameter (m):i

a general expression for Io/Is as a function of the signal gain ,active laser cavity length La (length of discharge providing gain )in m, mirror transmission T ,and losses l is given by::i


http://www.iraqup.com/uploads/O0q02-aDGx54045.JPG

So, the output power is ::i


http://www.iraqup.com/uploads/cO872-QxeL16136.JPG


http://www.iraqup.com/uploads/16l1h-PcBU1687.JPG

Where
And


http://www.iraqup.com/uploads/mK3l3-I7dL83500.JPG

Where,:i

. ℓ is the active medium loss
is the absorbing confession.http://www.iraqup.com/uploads/2iSXt-xO8465858.JPG:

i


انتهى الفصل الاول

انتظروا الفصل الثاني

[ماجستير هندسة ليزر]

السلام عليكم ورحمة الله وبركاته

استكمالا للبحث سوف نبدأ باذن الله بالفصل الثاني:

chapter two

Co2 laser system

2.1i Introduction:

The first start to design CO2 laser system that we should know the relative optical output power that we wont to get it and the efficiency of the system that we should work with it .i

In this project the target optical power was 500W and the efficiency that we assume to work in 10%.So, the input electrical power should be of about 5000W and because we work in slow flow this mean that the available output power with respect to the length of the discharge tube of about 50 W/m.. So for 500W the overall active medium length of about 10m.i

The use of very long tube can introduce problem not encountered in smaller systems. So, long tube were divided into section with alternate anode and cathode to keep the excitation potential to reasonably low value .It divided into seven folds each folds consists from two discharge double jacket tubes with parallel input discharge voltage ( see figure 2.1) .By using stability condition of the optical resonator we found that the radius of curvature of the higher reflector mirror should be greater than or equal to 10m we chose hemispherical stable resonator to provide higher gain and easy in the alignment process..i

Using the above input parameters to the system and by using eq: (1-16) ,(1-17),(1-18),(1-22) and (1.23). at different variable parameter a compromise has been made between these parameters of the optical resonator using forward and backward calculation to specified the optimum values of diameter ,the best radius of curvature of higher reflector mirror ,the beam waist of the output window gain coefficient , Frenal number and the best output power that we can get from all these variable parameter (see table 2-1)..i

We found from the above calculation that the best discharge tube length equal to 0.75m, tube inner diameter equal to 0.17m. the best mirror reflectivity of 60%. Assume that we work at an output beam of TEM00 mode ..i



http://www.iraqup.com/uploads/Vc6YG-fs6129990.JPG

Fig.(2.1):Multi Folds Structure for Our Design System ..i

Table (2-1): Theoretical Calculation for Output Power at Different Variable..i


http://www.iraqup.com/uploads/oNR77-m1hJ25244.JPG
http://www.iraqup.com/uploads/Mx3Rb-K7w278636.JPG

In the present work five different electrodes shapes and discharge tubes have been designed and constructed .The details for these terminals, discharge tubes and power supply unit, cooling system, vacuum circuit and gas supply have also been described. .i

[ماجستير هندسة ليزر]

chapter two

2.2i Mechanical Design:
Mechanical design represents the base for constructing the system because we take all basic principle for CO2 laser in to a count and related on it to design the system which include the size of system, type of material that must be used in each part of the system. Make sure that all quit good for optimal performance and min cost.i

The mechanical design includes five different forms of electrodes configuration. One made from Bakelite and the other from Aluminum..i

1.i . The first Type Aluminum electrode used as the output couplers mirror holder that consists from four parts. The first part use as mirror holder, which has central hole of 20 mm in diameter for laser output. The output window has been placed in the hole of 52mm diameter and thickness equal 5mm and water surrounding the mirror from every direction except the face for cooling the mirror. Tape screw holes of 8mm in diameter for inlet and outlet cooling water have been used. .i

An O-ring groove of 4mm thickness is made in front of the mirror for fitting and safety the mirror from broken and not let water to drain in front of mirror that because ZnSe mirror coating affected by water. Another O-ring groove of 4mm thickness has been made and used between first part and second part. This O-ring is important in the alignment of mirror. .i


The second part is the mirror adjustment plates Three screw holes are placed 120 degree apart is made for mirror adjustment and thick O-ring groove to provide both high vacuum seal and enough play for mirror adjustment .It has a central hole of 21 mm in diameter..i


The third part represents the cathode and tube holder that has central hole of 21 mm in diameter and hole of 10 mm in diameter from top of view of the electrode to enter the gasses to the plasma discharge tube. There is also groove of 4mm thickness for O-ring from one side and from far side there is cut of 45&ordm; for O-ring.An O-ring has been used for tightening the connection between the tube flange which is the fourth part of this electrode and with cathode to provide both high vacuum seal and decrease the pressure surrounds the tube..i


The fourth part is the circular flange of central hole of 21 mm in diameter and three screw holes placed 120&ordm; for easy work and to providing high vacuum seal ..i

2.i . The second electrode is the aluminum rear mirror (HR) electrode which consist also from four parts .All parts of this electrode like the first electrode except the first part has one different from first electrode that the mirror cooled from back and also from sides..i

3.i . The third electrode is also made from Aluminum and have the same parts of second electrode except that it has the central hole of 61mm in diameter in third and fourth that because we use Pyrex tube of 60 mm in diameter and 80 mm length for joining these parts with the fourth electrode. .i

4.i . The fourth electrode (see figure 2.2) is the corner holder tubes electrode that represents new design shape for multi fold CO2 laser. Designing this shape depend on corner of 20&ordm; .It consist form main part that is used as cathode and holed two discharge tube with one connecting tube. At top view of this part there is hole of 12 mm in diameter for outlet the gas..i

Also, there are three holes (one of 61mm in diameter and two of 21mm in diameter), the center of last one make a corner of 10&ordm; with strata line from face of the mirror on the third electrode..i

Light should enter from center of one hole of inner diameter (ID) of 20 mm pass through tube ID of 60mm touch the center of the mirror (which represent the center of the corner) and then reflected back to the second hole of ID of 21mm. .i

5.i . The last and fifth electrode (see figure 2.3) is Bakelite electrode which is made from Bakelite material .It is very high electrical insulation .The main part (A) of this electrode has a cylindrical shape of diminution (100×100) mm with central hole of 21 mm inner diameter for holding two discharge tubes [one from each side]. Both tubes enter to 10 mm distance in the Bakelite. .i

This part also has tip hole of 8mm inner diameter as inlet of gas from top view of electrode and there are two tips holes of 6mm diameter use for discharge pins where the last are made from stainless steel for high conductor and corrosion resistance..i

The discharge pine have length of 60 mm. About10mm of it length left on top of the electrode used for connected anode wire comes from power supply with system..i



http://www.iraqup.com/uploads/O7B34-awMd74200.JPG

Fig.2.2: Top View Section with Dimension for Holder Tubes Electrode
(New Design)..i


http://www.iraqup.com/uploads/21N8w-EouU91756.JPG

Fig.2.3: Sides View Section with Dimension of the Bakelite Electrode.

[ماجستير هندسة ليزر]

chapter two

2.3i Optics:
The optical cavity has two main cavity mirrors (output window and rear mirror). A ****l coated gold mirror has been used as the higher reflector mirror, The radius of curvature of it is 10m, 98% reflectivity and dimension of (50 ×10) mm. Another ****l gold coated mirror, plane, 98% reflectivity and has been used just as reflector.i
[’’’’The output widow is made from more exotic material Zinc Solenoid (ZnSe) for its low absorption at 10.6 μm and high thermal resistance .It is reflectivity was 60%, absorption coefficient was 0.005cm-1 and its plane which made with HR mirror hemispherical resonator that represents the best type for slow flow CO2 laser.i

2.4i Gas and Vacuum System:
We have been used premixed CO2 gas of the ratio (8%CO2: 8%N2: 82%He:i
2%CO) and flow meter of the maximum scale of flow rate equal to 50 liter /min.i
Oil sealed mechanical pumps has been used in which the gas is trapped, compressed and removed bodily from low pressure to the high pressure side of the pump, hence it is expelled to the atmosphere .The rotary that has been used have speed of (50 L/min) type Leybold –Heaves S8A and we measured the pressure by using absolute gage of maximum rang 27 mbar and tolerance of 0.9 percent. i
2.5i Cooling System :

In order to find the best radius of the jacket tube we have studied the effect of change tube radius on the water flow rate and instead of that it effect on the water temperature degree by using few relations as shown below:i


http://www.iraqup.com/uploads/l7PuF-Xq5169094.JPG


http://www.iraqup.com/uploads/yL5xS-vG5725172.JPG


http://www.iraqup.com/uploads/Or70X-mW8e1833.JPG


http://www.iraqup.com/uploads/4wKQe-n1V025487.JPG

http://www.iraqup.com/uploads/uA4CO-a0q090264.JPG

From above equation we found that the best radius of the jacket tube equal to 0.02 m at flow rate equal to 10 liter /min (1.6666×10-4m3/s) and rate of change of water temperature equal to 8.556*10-3˚C (see table 2-2).i

Table (2.2): Effects of variation radius of jacket tube on the water velocity and temperature. i


http://www.iraqup.com/uploads/x7I1g-fY8U59617.JPG


2.6i Laser Discharge Tube Fabrication:
Pyrex glass double jacket has been used as plasma tube or discharge tube. Several tubes have been made. Each double jacket tube has two concentric tubes, one of them has 17 mm inner diameter and 750mm length used as a plasma discharge tube and the second one of 40mm inner diameter and 670 mm length used for getting rid of excess heat (see figure 2.11) i


http://www.iraqup.com/uploads/RNe72-flV459339.JPG

Fig.2.11: Dimension of One of Tubes used as Laser Discharge Tube.i
A comprehensive check was regularly done to be sure that water circulation paths are well insulated from high voltage and that all fittings are securely grounded.i

Cooling system consists of chiller type (Leybold 20 AR ) having flow rate of 20 L/min was used. A connection of plastic tubes to let the water reaching the double jacket tubes and to the mirror cooling area.i

[ماجستير هندسة ليزر]

chapter two

2.7i The CO2 laser Power Supply:
Gas mixture pressure plays a dominant role in determining the gas laser output. This parameter may affect directly on the lasing action. The gas pressure is a function of the applied discharge voltage.i

So, the increase of the gas pressure means increase the discharge voltage and that lead to increase the output laser power to a certain limit..i

Calculations by using equations (1-3), (1-4) and (1-6) have been observed to find the optimum discharge voltage for each pressure (see table 2-3). Figure (2-4), which depicts the increasing of the discharge voltage with the pressure inside the cavity of the present system which has discharge length of 0.75m and total active length of 1 m at room temperature..i

The figure reflects the depend of the pressure inside the active medium on the discharge voltage within the working conditions. There is a linear increase between the pressures with the discharge voltage..i

Table2.3: The effect of increasing molecule density on the discharge voltage at different pressure..i


http://www.iraqup.com/uploads/1Fv1o-T5Rx36719.JPG


http://www.iraqup.com/uploads/s1HR8-yTx853958.JPG

Fig. 2.4: Theoretical Calculation of the Ignition Supply Voltage (kV) Variation with Pressure..i

The power supply has been designed and constructed to supply high and variable D.C.voltage required to break down the gas impedance and to and to provide glow discharge voltage. The circuit diagram is shown in figure 2.5 and the operation concept can be summarized as follows:.i

The input AC voltage connected to a variac device, in order to control the input voltage to the transformer. On the other hand it will control the output D.C voltage. This device has been chosen to allow high output current..i

The output of the variac was connected in parallel to the transformer that will raise the input voltage from 220V to 30 kV and it has turn ratio equal 1:135. The transformer specification has been selected to give maximum current of 100 mA and maximum voltage to 30 kV..i



http://www.iraqup.com/uploads/2SgK4-cL5v74165.JPG

Fig.2.5: Block Diagram of the D.C. Power Supply for Laser CO2 Constructed in Our Work..i

The transformer is connected to a set of three H.V diodes of 10kV and 1mA for each one, which represent half wave bridge rectifier, which is used to remove the ripple of the A.C. compound and make it right for D.C electronic circuit. The output of the rectifier is connected to a C-filter of the characteristic of 30 kV and 2.42μf in order to modify the output voltage..i

Also the output cathode of the rectifier is connected to the Ballast resistor or limiting resistor use for limiting the output current in order to protect the power supply from high current may be delivered due to discharge process and has been used to control the input current to the discharge tube (see chapter one (1.9)). The value of ballast resistance 500kΩ and it has maximum power of 1000W..i

[ماجستير هندسة ليزر]

chapter two

2.8i CO2 Laser System Configuration:

Three CO2 laser system configurations have been built in this project . The first configuration in our work (as shown in figure 2.6) consist from higher reflected electrode works as an anode terminal and output coupler electrode works as cathode terminal with one plasma discharge tube 0.75m long joining between them. The above system represented only one fold laser type.i

The second configuration consists from three blocks HR electrode and OC electrode both of them works as cathode terminal and the third block is the Bakelite electrode, which has two-anode pins terminal..i

There are two double jacket discharge tubes represent optical active medium joining between the two aluminum electrode with Bakelite terminal (see figure 2.7)..i

In both of the above system we have been used the same hemispherical resonator consist from plane, 60% ZnSe (OC)output coupler mirror and 10 m radius of curvature gold coated mirror as HR back mirror..i

The third and last configuration is the (v-configuration) which consists of two parallel folds, which consist from four electrodes. OC electrode and HR electrode both of them works as anode and joining the corner holder tubes electrode, which represent cathode by two discharge tubes..i

Then the corner holder tubes electrode connected with corner electrode by using Pyrex tube of 0.6m outer diameter and length of 0.8m(see figure 2.8).In this system we use the same hemispherical resonator with adding Gold coated plane mirror in the corner electrode use just as reflector..i

In the above three systems configuration we use the same CO2 gas mixture and cooled by the same chiller..i

HeNe laser has been used to perform the mirror alignment and we do the initial alignment once every thing for each part of the system and after evacuating the system..i



http://www.iraqup.com/uploads/XQ323-cShe12395.JPG
.Figure 2.6: Picture of One Fold of The System



http://www.iraqup.com/uploads/sW877-MCfr95720.JPG

Fig.2.7: Two Folds CO2 Laser System as Being Builds in the Lab..i


http://www.iraqup.com/uploads/3uPDq-77Cd74966.JPG

http://www.iraqup.com/uploads/l6Mg5-g1MM19675.JPG

Figure 2.8: Corner Electrode Joining with Holder Tubes Electrode..i


انتهى الفصل الثاني

ان شاء الله الفصل الثالث ياتيكم لاحقا

سلامي لكم

[ماجستير هندسة ليزر]

chapter three

3.1i Introduction:

In this chapter, the results for the design and construction have been analyzed and discussed where different parameters are varied.i
3.2 Effect of The Pressure on The Discharge Voltage:i

Gas mixture pressure plays a dominant role in determining the gas laser output. This parameter may affect drastically on the lasing action. The gas pressure is a function of the applied discharge voltage. So, the increase of the pressure means increase the discharge voltage and that lead to increase the output laser power to a certain limit.i

Figure 3.1 presents the practical results obtained in the laboratory for the present designed at an active length 0.75 m. The required discharge voltage for normal glow discharge increases as the pressure increases. The normal glow discharge obtained at high vacuum (pressure in the tube less than 0.1mbar) for 0.75m tube length was 3.5kV and at steady state was 2kV. For both one and two fold and because the input voltage to the folded system are parallel but the current is series , So the input current for each fold was 10mA.The discharge in the two fold system configuration was successful obtained in both tubes (see figure 3.2)i



http://www.iraqup.com/uploads/O8ivt-U4K368992.JPG


Fig. 3.1: Practical Result for One Fold and Two Folds Discharge Voltage Variation with Pressure at Active Laser Media Length 0.75m.)i



http://www.iraqup.com/uploads/mT8p6-6CLb49834.JPG

http://www.iraqup.com/uploads/xGt4C-lM5182570.JPG

http://www.iraqup.com/uploads/2Et6I-w4vH33896.JPG

Figure 3.2:Picture of the Two Folds at Discharge.)i



http://www.iraqup.com/uploads/6jRU4-o1pX95208.JPG

Fig.3.3:The Behavior of The Discharge Current as Function of Discharge Voltage For Tube Length 0.75 m at Different Pressure and Flow Rate 50liter/min.)i


As we can see from the chart that increasing the pressure for a certain value will decrease the knee of discharge point, which obey the Pachen curve. )i


3.3)i Effect of the Pressure and Gas Flow Rate on The Output Power:)i

The variation of the output power of our conductive cooled CO2 laser as function of pressure and gas flow rate is illustrated by figure 3.4.)i

To optimize the output power ,we fixed the gas flow rate and change the pressure. The maximum output power obtained was at 16 mbar with 50 liter /min flow rate as shown in figure 3.4 This means that by increasing the flow rate , the power increases
The above result represent the practical result obtained in the lap where, the maximum output power obtained for only one fold =23.5W,discharge voltage =8 kV, discharge current =28mA at flow rate =50 liter /min and at pressure = 16 mbar.)i


http://www.iraqup.com/uploads/T6HKr-7s0y27939.JPG

Fig.3.4: Relative Output Power of CO2 Laser as Function of Pressure for Several Gas Flow Rates.)i



http://www.iraqup.com/uploads/11X1e-aSGj18319.JPG

Fig. 3.5: Output Power Behavior as Function of Pressure at Different Discharge Current for Only One Fold.
As we can see from the fig.3.5, increasing the pressure of the inner gas will decrease the knee point at the pachen curve which will reduce the input power , the thing that affect the output power positively.)i

3.4)i Effect of The Discharge Current on The Power Output:)i

All CO2 laser mixtures show current saturation of the output power, as the current is increased the laser output increases steadily to maximum and the decreases slowly as the current rises above the optimum value.)i

In general the small signal gain of the convectively cooled CO2 laser increases linearly as a function of discharge current for given gas flow rate .A point is finally reached where the small signal gain saturates, and as the discharge current increased beyond this point , the small signal gain begins to decrease .)i


[The decrease of the small signal gain with increasing discharge current an indication of excessive gas heating due to the inability of the gas flow to sufficiently cool the discharge .As the gas flow rate increased , the saturation of the small signal gain peaks successively reaches higher values and at higher discharge currents. )i



http://www.iraqup.com/uploads/b3r3O-4dFR41497.JPG

Fig. 3.6: Output Power Behavior as A function of Discharge Current at Different Gas Pressure.)i

The small signal gain is relatively insensitive to gas flow rate variation at low –discharge current. Fig.3.6 illustrates experimental results of output power as a function of discharge current at various gas pressure. we can notice that as soon as the ignition start, the voltage will drop and the current will build up and therefor the output power will increase till a saturation point where there is no longer increasing in the power, and after a while the power will start to fall reaching the sustain current condition.)i

The maximum output power obtained at discharge current of 28 mA, flow rate of 50 liter /min and pressure=16mbar, for only on fold is 23.5W and for the two fold (V-configuration see fig.3.2) at current 40 mA and pressure of 16mA at flow rate of 50liter/min the maximum output power is 37W.

[ماجستير هندسة ليزر]

chapter three

3.5i Efficiency of the System:

The efficiency of the system can be defined as the ratio of the output power to the input power at 100%.The output power of our system has been measured by using IR power meter [heat sink detector( coherent ) ]of type LTD, model 542]maximum scale power measurement of 1000 W.i
The efficiency of the laser varies with the current flowing through the tube..i

Maximum efficiency and output power might not be obtained at the same time, the current which gives greatest efficiency might being lower than that which gives the best output. .i


The maximum efficiency comes out to be in our work equal 16.2% at input power equal of 90W, discharge current of about 20 mA, discharge voltage 11kV and output power equal 14.6 W at a plasma tube pressure of 15mbar.These measurement were carried out for only one fold design ..i

But the maximum output power has been recorded at an efficiency equal 10% and input power equal 235W which is equal 23.5Wat pressure of 12mbar input discharge current 28mA Figure 3.7 shows the variation of the efficiency with input power at different pressure..i

It is clear from the figure that the efficiency depends on the input current being used..i
In two fold (V- configuration) the maximum laser output power was 37 W at input power of 400 W, discharge voltage was 13kV at pressure 16mbar and discharge current 30mA. The efficiency of such design is about 9% the total discharge length of the system equal 1.5m and cavity length of 2m .This value considered to be very low with the expected value which is about 75 W because the available input current compare with the current that we need is very low .The min required value of the current should be not less than 100mA..i



http://www.iraqup.com/uploads/1g5CM-q4rO75635.JPG

Fig.3.7: The Effect of Efficiency by Input Power at Different Pressure..i

So, the resultant of our work slow axial flow CO2 laser multi folds work in TEM01 mode (as we have see in the lap when the laser drop at the different material basis) .i

Conclusion :.i

Usually, from every experiment, there are results. These results lead to conclusions that consider as rules of thumb.Our experiments guided us to our own rules of thumb as follow:-.i

1.Seeking for reliability of CO2 system starts from its power supply. The ballast resistance that should be used to control the amount of the current that enter to the discharge tube and to protect power supply from the high current delivered due to discharge processes..i

2.Three main parameters affecting on the output power of CO2 laser are pressure, current and discharge voltage, where the current affects by the cross-section area of the discharge tube and the voltage affects by the active discharge length. Controlling the discharge needs to control gas pressure..i

3.Its possible to get uniform excitation in a multi folds CO2, V-configuration so this design proved to be quite reliable as the have no vacuum troubles and an other excepted problems during the construction and operation as well as minimize size and cost of the system..i

4.It is possible to get uniform excitation of the V-shape multi fold..i


Proposal for Future Work:-.i

1.A compact power supply should take the priority of the future work,due to fact that ,controlling the power supply and its current will control the whole system easily .There fore anew power supply of higher current(1A-2A) should be design and implemented before any farther improvements in the CO2 laser system ..i

2.Completing the system by groups the different configuration that have been design into one system and increase the number of folds to five tube at each fold to increase the power to 500 W..i

3.Using this laser in the industrial application like wielding, drilling, melting and cutting for ****l and non****l..i

4.Use Teflon material instead of Bakelite for higher thermal resistive..i

[ماجستير هندسة ليزر]

References


1i.Sond B.S, ”TATA MC Graw –Hill Company Limited”Vol.5, 1980, PP.6-15.i
2i.Luha W., and Schuber W.,”CO2 Laser Work Station ”,MEOS Corporation (Merdingen ,Germany ), No.9, 1997.i
3.i.Leonard Migloiore, ”Laser Material Processing “, Marcel Dekker,Inc.,1996..i
4.i.Svelto O.,” Principles of Lasers”, 3rd edition ,Plenum Press(New York),1998..i
5.i.Patel, C. K. N, Phys. Rev. Lett.12, 588.(1964 a)..i
6.i.Patel, C. K. N. Phys. Rev. Lett.13, 617(1964b)..i
7.i.Patel, C. K. N, Phys. Rev. 136, A1187. (1964 c)..i
8.i.Patel, C. K. N. Appl. Phys. Lett.18, 25,(1965)..i
9.i.Moller and Rigen ,Appl.Phys.Lette.,No.7 ,PP(274-276),1965..i
10.i.Bridges and Patel, C. K. N, Appl. Phys. Lett.7, 244, (1965)..i
11.i.Horrigan, F., Klein, C., Rudko, R., and Wilson, DMicrowave 8, 68(1969)..i
12.i.Cool, T. A. and Shirley, J. A., Appl. Phys. Lett. No.(14), 70,(1969)..i
13.i.Tiffany ,W.B., Targ, R., and Foster, J. D.Appl.Phys. Lett. 15.91.(1969 )..i
14.i.Beaulieu, A. J. Appl. Phys.Lett16, 504.(1970)..i
15.i.Lock, E.V. ,and Hella, R. A.IEEE J.Quantum. Electronic No.10,179,(1974)..i


16.العبيدي,عبد الرحمن رشيد "تصميم و تصنيع ودراسة خواص ليزر ثاني اوكسيد الكاربون المستمر " رسالة ماجستير ,كلية العلوم ,جامعة بغداد,(1981)
17. زيدون طارق محمد نوري " تصميم و بناء منظومة ليزر ثاني أو كسيد الكار بون ذات الجريان السريع "الكلية الهندسية العسكرية ،ايلول( 1989).
18. عدي عطا "تصنيع وتشغيل ليزر ثاني أو كسيد الكار بون المستمر لقطع البلاستك"،الجامعة التكنولوجية ،أطروحة ،نيسان2003.
19. خلدون ناجي "بناء منظؤمة ليزر ثاني أو كسيد الكار بون المستمر ذى التهيج المستعرض"،قسم العلوم التطبيقية –الجامعة التكنولوجية،أطروحة ،حزيران 2002.


20.i. Cheo,P.K.,”CO2 Laser “,in Lasers, edited by A. K. Levine and A. J. De Maria, Marcel Decker, , pp111-267, Inc. (New York)1971..i
21.i. Divide R Whit house “Understanding CO2 Lasers “Laser Kinetics, May 1999..i
22.i.Bessley M.J., ”Laser and Their Application “,Taylor and Francis LTD,1976..i
23.i.“Course 3 Module 9, CO2 Lasers System”, Internet source,[File //A:/htm.].i
24.i.Howatson A.M., ”An Introduction to Gas Discharges”,2nd edition, Pergamon Press Ltd.,1965..i
25.i.Gross R. and Bot J., ”Hand book of Chemical Lasers”, John –Wiley and Sons (New York), 1976..i
26.i.Jeovine A. S. A., “Carbon Dioxide Laser DC. Type “, Serves Electric Research Laboratory, Baldack Hertforshine, England 1968..i
27.i.Towsen J.A.E.,” Journal of Soviet Laser Research” Vol.8, No.(1), January(1987).
28.i.Witteman W.J ,“The CO2 Laser “, Spring-Verlag 1987..i
29.i.Duley W.W. “CO2 Laser Effact and Applications” Academic press (New York) 1976..i
30.i.Huxley L. G.and Crompton R.W., “The Diffusion and Drift of Electrons in Gases”, New York, John Wiley and Sons ,Inc.,(1966)24..i
31.i.Verdeyen Joseph T. “ Laser Electronics”, Prentice –Hall 2nd edition 1989..i
32.i. John D.A. “Gas Dynamic Laser Introduction “,Q.E (1976)..i
33.i. losev S.A. “Gas Dynamic Laser” , Chemical Physics ,No .12,pp52-57,(1977). .i
34.i.Stanley C. R “Carbon Dioxide Lasers-an Introduction to their clc.& Design”,Optics & Laser Technology,1971..i
35.i.Theodore T.H. ”Temperature Rise and Radial Profiles in CO2 Laser “,Vol.42 ,No (8),July 1971..i
36.i. Yariv Ammon ”Quantum Electronics”, John Wiley and Sons1975..i
37.i. Theodore S. Fahlen “CO2 Laser Design Procedure” , Applied Optics Vol.12, No.10, 1973..i
38.i. Thiebeau C., Delahaigue A, D. Courtois and P.Jouve “Design of A Low Pressure CW Carbon Dioxide Laser” ,Infrared Physics Vol.21,pp41, 1981..i
39.i.i.Internet Source “Carbon Dioxide Lasers “,Copy Right ( 1994 –2000),www,Sams Laser FAQ-Home –built..i
40.i. Kolg.,H. and Bridge J.J. IEEE.QE-3,pp(95-06) ,1967..i
41.i.Holman J.P.,”Heat Transfer”,8th edition ,McGraw-Hill Companies.Inc.,(1997)..i
42.i. Joseph J.Carr.,”DC Power Supplies: Technicians Guide “,Mc Graw-Hill- Company,(1996)..iانتهى البحث اتمنى انه سوف تتم الاستفادة منه........

مع اطيب التحية

سلامي لكم

[HazemSakeek]

رائع صنيعك هذا يا ماجستير هندسة ليزر وجعله الله في ميزان حسناتك

ساطلع عليه ان شاء الله واذا كان لي تعليق او استفسار ساعود




وبالمناسبة اقوم هذا الفصل بتدريس كورس الليزر وسادعوا طلابي للاستفادة من هذا الموضوع

بارك الله فيك وشكرا لك

تحياتي

[ماجستير هندسة ليزر]

السلام عليكم ورحمة الله وبركاته

حياكم الله


"]رائع صنيعك هذا يا ماجستير هندسة ليزر وجعله الله في ميزان حسناتك

ساطلع عليه ان شاء الله واذا كان لي تعليق او استفسار ساعود


حياك الله دكتور حازم وبارك فيك

ان في الخدمة من اجل نشر العلم ان شاء الله

ان شاء الله يكون البحث مفيد باذن الله وان شاء الله استطيع الرد على اي تعليق او استفسار

ننتظر عودتك........


"]

[COLOR="DarkSlateBlue"]وبالمناسبة اقوم هذا الفصل بتدريس كورس الليزر وسادعو طلابي للاستفادة من هذا الموضوع

بارك الله فيك وشكرا لك

تحياتي

ان شاء الله موفق دكتور وان شاء الله يستفيد طلابك من هذا البحث كما استفد منه في مختبر تصاميم الليزر في المرحلة التحضير في الماجستير حيث لنا في هذا المختبر منظومة ليزر كامة مع مجهز القدرة مصممة من قبل اثنين من حاملي شهادة الماجستير في قسمي وهما من كان يعطينا محاضرات هذا المختبر وقد طلبا من كل طالب تصمميم منظومة ثنائي اوكسيد الكاربون كاملة بعد ان اعطونا القياسات الاساسية التي يجب استخدامها لاتمام التصميم وقد كان لكل طالب قياسات وشكل للرنان مختلف وقد استفدت من هذا البحث وبحث اخر لثنائي اوكسيد الكاربون لباحث اخر......

ان شاء الله تتم الاشتفادة والمنفعة

بارك الله فيك دكتور

سلامي

[بنوته تنقط ع]

ماجستير هندسة ليزر

الله يعطيك الف عافيه اخوي على الموضوع الروعه .صحيح اهل بغداد ذوي العقول الصافيه

ماقصرت يادكتور والله انك كفيت ووفيت بالشرح وماقصرت

لكن عندي مشكله اني مااعرف كيف اقرا الموضوع بالانقلش .لانو التدرس حقي كلوه بالعربي

ودكتور الماده اعطانا بحث عن ليزر co2 والحمدلله لقيتوه هينا لكنوه مو بالعربي

ممكن يادكتور تساعدني ببحثي بحيث يكون عربي

وبضل شاكره لك ..وتسلم يمينم على ماخطته يدك من معلومات مفيده

أختك: بنوته

[iraq-x]

ماجستير هندسة ليزر

الله يعطيك الف عافيه اخوي على الموضوع الروعه .صحيح اهل بغداد ذوي العقول الصافيه

ماقصرت يادكتور والله انك كفيت ووفيت بالشرح وماقصرت

لكن عندي مشكله اني مااعرف كيف اقرا الموضوع بالانقلش .لانو التدرس حقي كلوه بالعربي

ودكتور الماده اعطانا بحث عن ليزر co2 والحمدلله لقيتوه هينا لكنوه مو بالعربي

ممكن يادكتور تساعدني ببحثي بحيث يكون عربي

وبضل شاكره لك ..وتسلم يمينم على ماخطته يدك من معلومات مفيده

أختك: بنوته


تكدرين تترجمين البحث عن طريق الترجمة

http://translate.google.com/

[xrayphy]

الف شكر لكل الاعضاء
معلومات قيمة

[الادميرال الثال]

فد شي رووووووووووعة اتمنالك المزيد من الابداع وكلش مميز من بنت بلدي