Device researchers have worked on techniques for light detection for many years, and have developed devices which offer excellent performance as well. Clearly, a major sponsor of light detection device research has been the military. Devices for light detection are of fundamental importance throughout military technology, and the maturity and widespread availability of inexpensive photosensors is a direct result of this DOD research investment over many years. Light is a quantum-mechanical phenomena. It comes in discrete particles called photons.
Photons have a wavelength , a velocity , a frequency , energy , and even a momentum .
Among all of this, it is important to remember the relationship between energy and wavelength. In all cases, the energy of the photon determines how we detect it. Light detectors essentially may be broken into two categories. The so-called Quantum detectors all convert incoming radiation directly into an electron in a semiconductor device, and process the resulting current with electronic circuitry. The Thermal detectors simply absorb the energy and operate by measuring the change in temperature with a thermometer.