Carbon resistor bolometers

Early bolometers used, as thermometers, thermopiles, based on the thermoelectric effect (see Section 9.4) or Golay cells in which the heat absorbed in a thin metal film is transferred to a small volume of gas the resulting pressure increase moves a mirror in an optical amplifier. A historical review of the development of radiation detectors until 1994 can be found in ref. [59,60], The modern history of infrared bolometers starts with the introduction of the carbon resistor, as both bolometer sensor and absorber, by Boyle and Rogers [12], The device had a number of advantages over the Golay cell such as low cost, simplicity and relatively low heat capacity at low temperatures. 

Nevertheless the heat capacity of a carbon resistor was not so low as that of crystalline materials used later. More important, carbon resistors had an excess noise which limited the bolometer performance. In 1961, Low [61] proposed a bolometer which used a heavily doped Ge thermometer with much improved characteristics. This type of bolometer was rapidly applied to infrared astronomy as well also to laboratory spectroscopy. A further step in the development of bolometers came with improvements in the absorber. In the early superconducting bolometer built by Andrews et al. (1942) [62], the absorber was a blackened metal foil glued to the 7A thermometer. Low s original bolometer [61] was coated with black paint and Coron et al. [63] used a metal foil as substrate for the black-painted absorber. A definite improvement is due to J. Clarke, G. I. Hoffer, P. L. Richards [64] who used a thin low heat capacity dielectric substrate for the metal foil and used a bismuth film absorber instead of the black paint. 

Carbon resistor First bolometer Historical Easy to model Easy to make Need LHe (4 K)... 

IR detection by bolometers and microbolometers depends on the change in electrical resistance of a material as the temperature of the material changes. The electrical resistance of carbon increases exponentially with l/T as its temperature is reduced below 5 K. This allows it to be used as an inexpensive cryogenic thermometer, and any material that can make a thermometer is a candidate for use as a thermal detector. The behavior of carbon resistors at low temperatures and their use as thermometers and bolometers are described by Clement and Quinell (1952), Boyle and Rogers (1959), and Shephard (1964). 

The first bolometers are of interest for historical reasons and because the first-order models that describe their performance also apply to modern microbolometers. The first bolometers were made from thin chips cut from a carbon resistor, connected to a plate at near-liquid-helium temperatures by 2-mil-diameter gold wires (Putley, 1963). The gold wires provided a path for the bias current, and also provided thermal impedance between the active element and the helium bath - see Figure 3.2. 

Carbon bolometers have been made of slices of material used in the construction of electrical resistors (Boyle Rodgers, 1959) however, far better results have been achieved with doped germanium elements (Low, 1961). Single crystals of... 

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