Light sources and detectors for near-infrared analysers

2 Light sources and detectors for near-infrared analysers 

DTGS device will be slow, but can extend into the kHz range, which fits well with the amplitude modulation audio frequencies typical of an FT instrument. 

The pyroelectric DTGS detector is a very useful, low-cost, general purpose, wideband NIR detector well suited for use in FT-based analysers. It is not normally used in scanning monochromators where higher sensitivity detectors are needed to match the lower optical throughput and discrete wavelength scanning requirements. 

Both photoconductive and photodiode detectors are semiconductor devices. The difference is that in the photoconductive detector there is simply a slab of semiconductor material, normally intrinsic to minimise the detector dark current, though impurity-doped materials (such as B-doped Ge) can be used for special applications. By contrast, the photodiode detector uses a doped semiconductor fabricated into a p-n junction. 

Typical materials used in NIR photoconductive detectors are PbS, PbSe, InSb and InAs (lead sulphide, lead selenide, indium antimonide and indium arsenide). 

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