ABSTRACT
This chapter deals with the sources of radiation and the detectors that are used in optical metrology. It provides a brief description of radiometric and photometric units. Incoherent light sources include incandescent lamps, discharge lamps, and light-emitting diodes (LEDs). In discharge lamps, the gas is ionized and the light emission is due to the collisions between accelerated electrons and ions resulting in electronic transitions between energy levels of the material of the ionized gas. LEDs are the most efficient light sources. Lasers are the coherent sources, the most common being a helium-neon laser. Detectors detect the radiation and usually produce an electrical output, which is processed using additional devices. Photon detectors include photoemissive, photoconductive, and photovoltaic detectors. The thermal detectors produce an electrical signal in response to the change in its bulk temperature. Dichromated gelatin is an ideal recording material for volume phase holograms as it has large refractive index modulation capability, high resolution, low absorption, and scattering.
