Bolometer, as detector

Fig. 1.30 Optothermal spectroscopy in a molecular beam with a helium-cooled bolometer as detector and two optical systems, which increase the absorption path length...

Whisker contact diodes have much faster response times than InSb hot-electron bolometers and may be used as detectors or mixers. A good discussion of the behavior of near-millimeter band cat-whisker diodes... 

IR Detector. As with sources, detectors used in the ultraviolet and visible regions do not work in the infrared region. But infrared radiation possesses the property of heat, and heat detectors that transduce heat into an electrical signal can be used. Thermocouples and bolometers are used as detectors. A thermocouple consists of... 

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. 

Figure 7.2 shows a 2D detector array mounted ( hybridized ) to the ROIC to form the SCA. The SCA is common in most infrared array configurations today. In monolithic structures, the detector is an integral component of the ROIC there is no separate detector. Examples of monolithic structures are visible CMOS imagers used in commercial camcorders, cameras, and cell phones, and uncooled infrared devices that utilize temperature sensitive resistors (bolometers) as the sensing component. 

The noise is expressed as noise density in units of V/(Hz), or integrated over a frequency range and given as volts rms. Typically, photoconductors are characterized by a g-r noise plateau from 10 to 10 Hz. Photovoltaic detectors exhibit similar behavior, but the 1/f knee may be less than 100 Hz and the high frequency noise roU off is deterrnined by the p—n junction impedance—capacitance product or the amplifier (AMP) circuit when operated in a transimpedance mode. Bolometers exhibit an additional noise, associated with thermal conductance. 

Bolometers. The bolometer (23) has made a comeback as a popular detector thanks to advances in micromacbining technology. When appHed... 

In a cryogenic experiment, one or several detectors are used for a definite goal for which they have been optimized. For example, in CUORE experiment described in Section 16.5, the sensors are the Ge thermistors, i.e. thermometers used in a small temperature range (around 10 mK). One detector is a bolometer made up of an absorber and a Ge sensor. The experiment is the array of 1000 bolometers arranged in anticoincidence circuits for the detection of the neutrinoless double-beta decay. Note that the sensors, if calibrated, could be used, as well, as very low-temperature thermometers. Also the array of bolometers can be considered a single large detector and used for different purposes as the detection of solar axions or dark matter. 

Because of their high heat capacity, only few of the thermometers described in Chapter 9 can be used as sensors for detectors. Resistance (carbon) sensors were used for the first time in a cryogenic detector by Boyle and Rogers [12] in 1959. The carbon bolometer had a lot of advantages over the existing infrared detectors [13]. It was easy to build, inexpensive and of moderate heat capacity due to the low operating temperature. 

The astronomical calorimeters for the detection of the infrared radiation (usually called bolometers) do not conceptually differ from the cryogenic detectors used in nuclear physics as those just described for CUORICINO. 

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. 

Detection of the middle and far range of infrared radiation requires thermal detectors, the simplest of which is a thermocouple, in which the change in temperature at one junction of the thermocouple results in a small voltage being produced. Although simple in design, thermocouples lack sensitivity. Bolometers are more sensitive and are based on the fact that as the temperature of a conductor... 

The traditional source in IR absorption spectroscopy is a glowing rod or wire heated by the passage of an electric current the hot body emits radiation over a continuous frequency range. The radiation is dispersed using a prism NaCl, which is transparent over much of the IR region, is commonly used for IR prisms and windows. The sample may be a solid, liquid, or gas. Various detectors are used the most common are thermocouples, photoconductive materials such as PbS, bolometers (which are temperature-dependent resistors), and the Golay cell (which uses the thermal expansion of a gas contained in a chamber). 

The modulated beam is directed through either the sample or reference side of the sample compartment and is finally focused on the detector. For most mid-infrared work, a triglycine sulfate (TGS) pyroelectric bolometer is used as the detector because of its very high frequency response (> 1 MHz). 

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