Golay cells

Millimetre wave Klyston (frequency multiplied) backward wave oscillator Mica polymer None Crystal diode Golay cell thermocouple bolometer pyroelectric... 

Mid- and near-infrared Nernst filament globar NaCl or KBr Grating interferometer Golay cell thermocouple bolometer pyroelectric photoconductive semiconductor... 

A commonly used detector is a Golay cell, in which there is a far-infrared absorbing material, such as aluminium deposited on collodion, inside the entrance window of the cell. 

The aluminium absorbs the radiation, heats up and transfers the heat to xenon gas contained in the cell. As the temperature of the gas varies the curvature of a flexible mirror of antimony-coated collodion, forming a part of the cell, changes. Reflection of a light beam from this mirror, which is on the outside of the Golay cell, indicates its curvature and therefore the intensity of radiation absorbed by the cell. 

Defectors are similar in fype fo fhose for fhe far-inffared, namely fhermocouples, bolomefers, Golay cells or phofoconducfive semiconductors. 

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. 

Golay cell Infrared detector that uses expansion of a gas in a blackened chamber to deform a flexible mirror. Deflection of a beam of light by the mirror changes the power impinging on a phototube. 

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). 

Detectors are similar in type to those for the far-infrared, namely thermocouples, bolometers, Golay cells or photoconductive semiconductors. 

Some detectors employ the optothermal effect the absorbed modulated infrared radiation heats the sample and its environment, thus producing sound waves which are recorded with a microphone. They can be combined with scanning spectrometers and interferometers. A Golay cell (Golay, 1949) measures the optothermal pressure change by a light beam which is deflected by a reflecting membrane. The first infrared process spectrometer, the URAS, alieady employed the absorption bands of a detector gas to specifically analyze the concentration of this particular gas in a sample. This is a non-dispersive spectrometer already mentioned in Sec. 1. 

The time constant of this system depends on its electrical impedance. A typical value is t =40 /[Pg.173]

The Golay cell uses the distortion of a reflecting Sb-coated collodion membrane, closing one of the ends of a so-called pneumatic chamber. This distortion is caused by the thermal expansion of a gas heated by the radiation incident in the cell, and produces the deflection of a beam of visible light, which is detected by a photocell. The Golay cell was used, fitted with a diamond window, with the first far IR FTS and its responsivity and response time were comparable to those of the radiation thermocouple. For more details on these detectors, see [15]. 

Rad. optical filter Golay cell solarimeter solar cell photographic... 

The type of detector used in an FT-IR spectrometer is highly dependent upon the bandwidth (i.e. the spectral frequencies), the modulation rate of the interferometer, and the intensity of the radiant flux. Several types of detectors are used in the infrared regions photoconductive, photovoltaic, bolometers, pyroelectric and Golay cells. A detailed discussion of detectors may be found elsewhere.12 In general, the photovoltaic and photoconductive detectors can be used in the near- and mid-infrared regions as rapid response, high sensitivity detectors. Usually the bandwidths are limited and will not cover the total ran passed by the beamsplitter. Examples of such detectors are given in Table I. As can be seen from the... 

Other detectors that are useful in the near- and mid-infrared regions are bolometers and pyroelectric detectors. Both these detectors have very large bandwidths and can operate at room temperature however, they have long response times compared to the photodetectors and they have low D s. Pyroelectric detectors are useful in the far-infrared region with rapid-scanning spectrometers whereas Golay cell detectors are often used with slow scanning far-infrared interferometers. These cells are modulated at or below 20 Hz. 

Golay cell after Hickey and Daniels [3.20], Stafsudd and Stevens [3.21], and Gill [3.22]... 

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