TABLE OF CONTENTS Dr. Thomas Kenny, Department of Mechanical Engineering, Stanford University
This chapter offers an overview of the basic types of sensors used to detect optical and near-infrared radiation.
Detection of light is a basic need for everything from devices to plants and animals. In the case of animals, light detection systems are very highly specialized, and often operate very near to thermodynamic limits to detection. Device researchers have worked on techniques for light detection for many years, and have developed devices that offer excellent performance as well.
Clearly, the military has been a major sponsor of light detection device research. 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 c=3 10 8 m/s, a frequency 
, energy 
where h=6.67 10 ?34 Js, 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 may be broken into two basic 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...
