ABSTRACT
Grating efficiency is defined as the fraction of incident monochromatic light diffracted into a specific order. It is one of the most important and basic attributes of a grating – there are few applications where it is not a factor in the functioning of a spectrometric instrument. What generates so much concern is that efficiency is rarely constant, but varies considerably as a function of wavelength. Thus a typical UV-VIS monochromator could start at the short wavelength end with an efficiency of 50%, increase to a maximum of 75%, and gradually decrease to 10% at longer wavelengths, clearly variations that cannot be ignored. This behavior is not due to any lack of quality, but is the natural result of the interaction of light with a modulated metallic surface and the fact that light will always be diffracted into a minimum of two orders whenever there is useful dispersion. The number of orders can increase to as many as 100 or even more. One can imagine a silent competition between orders for photons. Just how this works out for a wide variety of practical gratings will be shown in this chapter.
