Golay detectors

Fig. 49. The Polytec FIR 30 Fourier spectrometer (No. 5c in Tables 2, 3, 4) Optical diagram (lower part) and the possibilities of using the sample chamber (upper half). M 2, M 3, M 5, M 6 plane mirrors M 1, M 4 paraboloid mirrors M 7 spherical mirror M8 elliptical mirror C Chopper S high pressure Hg-lamp BS beamsplitter D mirror drive IS Moird system G Golay detector S sample...

Now, let us concentrate on the mode of propulsion of the movable mirror in various Fourier spectrometers. Among the discussed 13 instruments, there are three spectrometers (for the far-infrared ) where the movable mirror is driven by a synchronous motor (No. 1, 3, and 5c in Table 3) and where the speed of the mirror can be varied from 1 to 25 m/sec. These are the socalled "slow-scan instruments. They employ a slow Golay-detector (cf. Table 2), and the radiation of the source is chopped at a certain frequency as was pointed out already in context with the optical diagram (cf. Fig. 49). In the other ten instruments listed in Table 3 (No. 2a, b, 4a—e, 5a, b, and 6), the movable mirror is driven by an electromagnetic device like a linear motor and where the speed can be varied... 

Figure 16.27 in practice approximates the error only for instruments with Johnson or thermal noise-limited detectors, such as photoconductive detectors like CdS or PbS detectors (400 to 3500 nm) or thermocouples, bolometers, and Golay detectors in the infrared region. Johnson noise is produced by random thermal motion in resistance circuit elements. 

There are three types of thermal detectors the thermocouple, the bolometer, and the Golay detector. The thermocouple, the most widely used infrared detector. 

The fourth and final effect is essentially calorimetry which is used in radiometry but does not find application in analytical spectrophotometry. However, one particular detector, the Golay detector, was formerly used in the infrared. This consisted of a chamber containing xenon gas to which was attached a mirrored membrane. Deformations in the mirrored surface caused by heat absorption were measured optically. These detectors were very expensive to make and were temperamental, and have largely been superseded. 

Estimated by comparison between a Golay detector and calorimeter. 

Another problem unique to this type of detector is its susceptibility to destruction on exposure to high levels of radiation, such as normal room radiation. In general, problems relative to durability and sensitivity to microphonics tend to be somewhat more severe for Golay detectors than for other thermal detectors. 

Whereas it is usual to require many hours of signal averaging to obtain a reasonable quality spectrum in the far I.R. using a Golay detector, this same spectrum can be obtained in minutes with a well prepared liquid Helium cooled bolometer. 

Hickey, J. R. Daniels, D. B. (1969). Modified optical system for the Golay detector. Review of Scientific Instruments, 40, 732-3. 

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