Cryogenic Terahertz Detectors
QMC Instruments Ltd. has nearly forty years experience in the design and manufacture of cryogenic Terahertz detectors. This experience, enables us to develop and build detector systems that are uniquely tailored to the needs of the customer, resulting in a performance that is optimised for each experiment.
We offer a range of cryogenic detectors which are sold as stand-alone items, or as systems packaged with our own cryostats, optics, filters and amplifiers. These detectors operate at temperatures close to 4K, using liquid helium or a mechanical cooler. Operating at this temperature enables us to make extremely sensitive detectors that would not be possible at room temperature.
For applications that do not require as high sensitivity, we offer an excellent pyroelectric detector that operates at room temperature.
All of our products are optically calibrated and come with a two year guarantee. Our detector types and their detection range are shown in the graphic below:
Choosing a detector
Which detector you choose really depends on your requirement. Superconducting bolometers are sensitive to a wide range of wavelengths. Their bandwidth ranges from 3 mm (100 GHz or 3.3 cm-1) to 15 microns (20 THz or 600 cm-1). As well as extremely high sensitivity, these detectors offer a linear dynamic range over 50 dB and constant sensitivity as a function of wavelength. The use of our unique multi-mesh filters means that observation bandwidth can be carefully and accurately controlled and detectors operate with optimised sensitivity as they are not unnecessarily degraded by exposure to background power at unwanted frequencies.
Indium Antimonide (InSb) hot electron bolometers (HEBs)and doped Germanium photoconductors offer a much greater speed of response than composite bolometers with no reduction in sensitivity. The disadvantage of these detectors is that the range of frequencies to which they are sensitive, is somewhat smaller. The two detector types are useful over different frequency ranges. InSb detectors are useful at frequencies up to 500 GHz or 2.5 THz depending on type, while photoconductors are useful at frequencies above approximately 1.5 THz.
The photograph above is of one of our InSb hot-electron bolometers. The detector area and volume is quite large compared to other detector technologies. This leads to good sensitivity at long wavelengths and high linear dynamic range.
Our detectors can be purchased as stand-alone units or as a fully assembled, tested and calibrated system ready for use. Cooling can be either using liquid helium or mechanical coolers. Mechanicaly cooled systems cool to operating temperature with no user intervention. Our liquid helium cryostats are designed and built to our specifications by our sister company, Thomas Keating Ltd.
We also offer pyroelectric detectors when a wide wavelength range is required, but less sensitivity is acceptable. They do not require cooling, thus provide a less expensive alternative to cryogenic detector systems.
Cryogenics
To gain the most sensitivity from, for example, a superconducting bolometer, indium antimonide hot electron bolometer or Ge:Ga photoconductor, it is necessary to cool the detector to cryogenic temperatures to reduce the noise present in the device and detector circuit, and hence maximise the signal that can be seen at that particular temperature. To do this the detector can be mounted in a suitable cryogenic vessel which is evacuated and then cooled to around 4 K i.e. liquid helium temperature.
Cryogenic techniques are often viewed as technically daunting, time-consuming and expensive. While this is was undoubtedly true to a degree when liquid bath cryostats were the only option, the introduction of mechanically cooled systems means that cooling is as simple as pressing an "on" button. Thus orders of magnitude more sensitivity than available from a room temperature detector can be provided with little increase in complexity of operation.
Of course, we still continue to offer detector systems using liquid helium cooled cryostats. We provide full colour instruction and operating manuals with all our products, and we calibrate and guarantee all aspects of the performance of our detectors and detector systems.
