| temperature. Both a room temperature and TE cooled devices are offered. TE cooled gives better performance but it is also more bulky and needs appropriate handling. For more details on TE cooling see the chapter on TE Cooling and Cooler Controllers. Optical Area: A It is an area where the incident radiant power is collected. For rectangular devices it is a contact width(w)-length(l) product where length is a distance between contacts. Optimum Wavelength: ^,opt The wavelength for which a device was optimized for. For near IR detectors Xopt is close to A^eak. In contrast, for uncooled long wavelength detectors Xopt can be even larger then Xco. For example the A,opt=10.6 um detector has \,eak=610 7 Peak Wavelength: ^peak ^peak *s a point where a specified device has a maximum response. Photocurrent: Iph The current signal from a photovoltaic device when exposed to incident radiant power. It is described by photovoltaic current equation: I ph=r)QADe-g where: r| is the quantum efficiency, Q is the number of incident photons, AD is the active area, e is the electron load, g is the photoelectric gain Photoelectric Gain: g The parameter describing the photocurrent gain due to special construction of photoconductors. In photovoltaic devices g it is close to 1. Photoelectromagnetic Devices (PEM) Photovoltaic devices that employ a photoelectromagnetic effect based on spatial separation of the optically generated electron and holes in the magnetic field. They do not require electrical bias and show no flicker noise. The devices are typically used as fast uncooled detectors of the long wavelength radiation. Photoconductive Devices (PC) Photon IR detectors based on photoconductive effect. They conductivity is changed by incident radiation power by generating additional charge carriers. Photovoltaic Devices (PV) Photovoltaic devices (photodiodes) are semiconductor structures with p-n junction or more complex heterojunctions. Absorbed photons produce electron-hole pairs resulting in external circuit as photocurrent. Reverse bias is frequently applied to improve high frequency performance. PV devices are typically faster then PCs. There are usually more fragile than photoconductors. | Resistance - Area Product In typical photodiodes (PV series) a resistance decreases proportionally to their area. Therefore the normalize resistance can be expressed as the R - A product. In contrast the PVM series devices are characterized by the constant sheet resistance. Response Time: t t is time that takes a detector with zero bias to reach 1/e of the initial value of the signal after switching off the irradiation. It is related to the cut-off frequency (fc): 1 |