What detectors are available for mid infrared work?
There are a wide variety of detector types available – it really depends on the application. For power measurements not requiring a time response faster than 100 msec, pyroelectric and thermopile detectors are a good choice. Both are relatively inexpensive and can be operated at room temperature. For extremely low light levels (< 10 uW), LN2 or TE cooled semiconductor detectors are a must. Semiconductor material and type (PC vs. PV) depend on the application. Common materials include HgCdTe (MCT) over the 1 to 28 µm range, PbSnTe from 2 to 18 um, and InSb from 1 to 5.6 µm. For power levels achievable with QC lasers (1 to 10 mW), room temperature variants of the above detectors are usable. For QC power levels greater than 10 mW, semiconductor detectors are not useful: they either saturate or in some cases can be damaged. It is recommended that pyroelectric or thermopile power meters designed for these power levels be used for power levels greater than 10 mW.
