I have 2 Qs I could not solve them



If you had a laser that emits blue light at 480 nm wavelength and 100mW power, how wide must the beam be if it is to be safe when shone at a human eye for up to one minute?




For the grating you used (1.66µm groove spacing), is there a wavelength for which you cannot get any diffracted orders?



what do u think answers would be

Thanks