Putley detector

Hot Electron Bolometer, Putley Detector. Whether it is more appropriate to include the hot electron bolometer and Putley detector in a list of detectors employing photon effects, or to instead list them with thermal effects, is somewhat arbitrary. Both employ photon effects in that incident photons interact with free electrons in a semiconductor. However, they are thermal (as the name bolometer implies) in that the effects are explainable in terms of a change in the effective temperature of the free electrons. Because the interpretation is mainly from the viewpoint of a photon-electron interaction, they are included here in the list of photon effects. 

E. H. Putley, The Pyroelectric Detector Norman B. Stevens, Radiation Thermopiles... 

P. R. Bratt, Impurity Germanium and Silicon Infrared Detectors E. H. Putley, InSb Submillimeter Photoconductive Detectors... 

W. L. Eiseman, J. D. Merriam, and R. F. Potter, Operational Characteristics of Infrared Photodetectors P. R. Bratt, Impurity Germanium and Silicon Infrared Detectors E. H. Putley, InSb Submillimeter Photoconductive Detectors... 

The electrical impedance of a pyroelectric detector is almost that of a pure capacitance. Hence an output signal only appears when the input radiation is changing. For maximum output the rate of change of the input radiation should be comparable with the electrical (RC) time constant of the element. Figure 3.10 is the equivalent electrical circuit of a pyroelectric detector (Putley [3.11, 51J). Assume that the element receives radiation over an area A normal to the polar axis of the material and that this produces a modulated temperature rise (3.4). 

One of the most useful detectors of recent origin is the pyroelectric one, proposed by Chynoweth [2.93] and reduced to practice by Cooper [2.94,95] and others. Many investigators have contributed to the development of pyroelectric detector technology in the past decade, among whom are Astheimer and Schwarz [2.96], Beerman [2.97,98], Glass [2.99], Liu et al. [2.100-103], Lock [2.104], and Phelan et al. [2.105]. Putley [2.106] and Liu [2.107] have reviewed the theory of operation and state-of-the-art of pyroelectric detectors. 

X 10 Jcm" K" /c= 1.38 x 10 JK" and assuming 7 = 290 K, a = 1 cm and the electronic bandwidth Af = Hz). This value is used as a reference to compare the performance of actual detectors. The best room temperature thermal detectors approach within about one order of this value. It will be noted that this calculation has been made without reference to the readout mechanism. It does assume a perfectly noiseless mechanism—the noise level is set by processes outside the detector. An alternative way to perform this calculation is to consider the fluctuations in the background radiation incident upon the detector Putley [3.8]). It would then be found that (3.11) corresponds to the fluctuation associated with the total background radiation incident on the detector from a complete hemispherical field of view. 

E.H. Putley, Thermal Detectors, in Optical and Infrared Detectors, ed. by RJ. Keyes ( Springer, Berlin, 1983)... 

Since Johnson noise is not present in the imaginary part of an electrical impedance, only noise due to the loss tangent of the capacitor, the load resistor, and the amplifier input resistor contributes to Johnson noise. However, the basically capacitive nature of the element shunts Johnson noise to some degree. As a consequence the NEP [W Hz 5] of p5ux)electrical detectors due to Johnson noise is only proportional to the square root of frequency (Putley, 1977). Pyroelectric detectors can, therefore, be used to relatively high modulation frequencies. Temperature noise, due to thermal conduction and radiative exchange, is also present, as in all... 

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