QMC-Cooled and room temperature THz detectors

http://www.terahertz.co.uk/index.php?option=com_content&view=article&id=204&Itemid=583

THz detector systems 

QMC Instruments Ltd. has nearly forty years experience in the design and manufacture of cryogenic Terahertz detectors. Our unique combination of technologies permit the creation of individually designed systems resulting in 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. By cryogenic we mean that they operate at temperatures of 4 K (-269 °C) and below, either using liquid helium or a mechanical cooler. While the thought of cryogenic operation may be off-putting, operatirng a mechanically cooled system is extremely straightforward.

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 are listed below; select a link for more information. Example detector system manuals are also available, and please contact us if you cannot find what you are looking for.

Cooled detectors

• Superconducting bolometer
• Indium antimonide HEB (hot electron bolometer)  
• Magnetically enhanced indium antimonide HEB
• Doped germanium photoconductor

Room temperature detectors

• Pyroelectric detectors

Choosing a detector

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. These cryostats offer the convenience of very long run-times. Cryostat operation is straightforward, and detector systems come with a comprehensive range of safety devices as standard.  The photograph to the right shows a fully assembled bolometer system. The bolometer is cooled to 8 K by a mechanical (pulse tube) cooler. It views the outside world through a vacuum window. The system has its own low-noise preamplifier.   When the lower sensitivity of pyroelectric detectors is acceptable, they provide a less expensive alternative to cryogenic detector systems.

QMC Instruments-Filter technology for the Terahertz (mm and sub-mm) spectral region

 

http://www.terahertz.co.uk/index.php?option=com_content&view=article&id=113&Itemid=537
We offer a unique multi-mesh filter technology which allows extremely precise wavelength selection. Our range has been developed over more than 30 years by our astronomical academic colleagues, and is now a cornerstone technology used in all major sub-millimetre and Terahertz astronomical projects on the ground and in space.
We offer the following types of filters:

• Low-pass
• High-pass
• Band-pass
• Band-stop (notch)

If you are interested in our filters, please contact us so that we can use our extensive experience to discuss the best solution to meet your requirements. You can see examples of the performance of our filters here; these are our standard filters, produced in quantity and often available in stock. These are the lowest cost option and we would look to provide these filters in the first instance. If these are not suitable, we can custom design filters to your precise requirements. Both standard and custom designed filters can be produced to your choice of size and shape, with a maximum diameter of 300 mm.

Properties of our filters include:

• High in-band transmission efficiency
  • 90% transmission in a typical low-pass filter
  • 80% peak transmission efficiency in band-pass filters
• Low absorption and scatter; almost all non-transmitted power is reflected
• High broadband out of band blocking
• High frequency definition
• Negligible polarisation sensitivity in transmission (at near normal incidence)
• Robust construction
• Clear aperture diameters from 6 to 300 mm.
• Operation from room temperature down to temperatures below 1 K (-272 °C).
• Operating wave numbers between 1 cm^-1 (30 GHz, 10 mm) and 700 cm^-1 (21 THz, 10 um)

The majority of our filters use a dielectric spacer to separate the meshes forming the filter; we refer to them as "hot-pressed" filters. Low frequency, hence thicker, filters can be provided as free-standing filters, and are available at any size up to 300 mm and in arbitrary shapes. The higher frequency filters are quite thin and are difficult to keep flat, hence we recommend that they be purchased ready mounted in a frame. We offer several standard frame sizes up to 120 mm outer diameter. If you require a size greater than this, please contact us and we will see what we can do. The large aperture 30 GHz low pass filters manufactured for the Korean Astronomical Observatory (see picture) were up to 250 mm outer diameter.
On rare occasions, "air-gap" filters in which there is no dielectric spacer can be more suitable than hot-pressed filters; these can be provided if necessary, and we would advise you if we thought they would be appropriate for your application.
Our filter technology was originally developed for astronomical applications, where the need exists both for high in-band transmission efficiency and excellent out-of-band rejection in order to select the extremely low astronomical signal levels between intense atmospheric emission lines. An additional requirement of these filters is that they must cycle reliably between ambient and cryogenic temperatures for use with cooled bolometers and photodetectors, whilst maintaining their performance. These properties also make the filters of great value to the wider scientific community

Focus on QMC Instruments Ltd & Thomas Keating Ltd

MY NOTE: SO MANY EXCELLENT COMPANIES WORK WITH THZ, THAT IT'S HARD TO KEEP UP WITH THEM. HERE'S ONE MORE FOR READERS TO BE AWARE OF,  QMC Instruments Ltd & Thomas Keating Ltd


http://www.terahertz.co.uk/

• QMC Instruments Ltd develops instrumentation for the detection and processing of electromagnetic radiation at wavelengths ranging from microwaves to the near infrared. Our products include a long-established range of cryogenic detectors and associated components and instruments. These are used in diverse applications such as atmospheric remote sensing, astronomy, semiconductor materials characterisation, hot plasma fusion diagnostics and electron spin resonance (ESR) spectroscopy.

One of the 66 Atacama Large Millimeter Array (ALMA) telescopes in Chajnantor in the Chilean Andes; we are currently supplying windows and cooled polarisers for this project.

• Thomas Keating - Toolmaking has a 60 year history of making high precision tooling (press tools, gauges and injection moulds). We aim to give a complete tool-making service, from initial design to tool tryout and maintenance support, combining traditional skills with modern machining techniques and management procedures. The introduction of CNC Jig Grinding has significantly widened our scope. We produce precision components in areas such as medicine, aerospace, racing cars, and packaging.

CNC Jig Grinding of racing car parts at TK Toolmaking.

• Thomas Keating - Instruments draws on tool-making skills to design and develop quasi-optical Terahertz systems and subsystems. We have growing activity in High Field Electron Spin Resonance (ESR) spectroscopy and remote sensing instrumentation, including space-borne projects. These newer areas compliment our more established applications like Plasma Fusion diagnostics and material characterisation. Our space-borne work has included the High Frequency Instrument (HFI) feeds for the Planck space telescope mission launched in May 2009, and the multiplexer on the 94 GHz pulsed cloud radar on the EarthCARE climate monitoring satellite.

The 94 GHz HiPER Pulsed ESR Spectrometer at St. Andrews University in Scotland, built by TK Instruments.

Further information on products, abilities and contact details for all three companies can be obtained by following the links above and on the menu to the left. If you have any queries, please contact us.

Far Sighted Space Technology Finds Practical Uses On Earth

http://nanopatentsandinnovations.blogspot.com/2011/04/far-sighted-space-technology-finds.html

Technology developed for space missions to study the most distant objects in the Universe is now finding a host of practical applications back on Earth. QMC Instruments Ltd., in partnership with the Astronomical instrumentation Group at Cardiff University, has built instruments for many major space missions, including Herschel and Planck. Now, expanding on that experience they are developing KIDCAM, a kind of detector that could have applications in hospitals, factories and airports. Ken Wood will present the project at the RAS National Astronomy Meeting in Llandudno, Wales, on Tuesday 19th April.

QMC Instruments Ltd was involved in the design and manufactured the Corrugated horns for the HFI Instrument on Planck, ESA's Space based Cosmic Microwave Background experiment.

Credit: TK Instruments

The part of the Electromagnetic Spectrum including the far infra red and microwave is also called 'terahertz' radiation. Astronomers use this kind of radiation to study the Cosmic Microwave Background and the huge dust clouds where stars are born. The sensitive detectors they use will only operate at temperatures very close to absolute zero (minus 273C.) In Terahertz cameras like KIDCAM, those low temperatures are accessible in compact and less expensive ways using relatively new cooler technology. KIDCAM therefore has many potential day-to-day applications.

QMC Instruments Ltd was involved in the design and manufactured the Corrugated horns for the HFI Instrument on Planck, ESA's Space based Cosmic Microwave Background experiment.

Credit: ESA (Image by AOES Medialab)

"We are all familiar with optical images of the surface of objects and X-ray images which penetrate through soft tissue to reveal bone structure. Terahertz observations give us something in between the two. For example, most clothing and packaging materials are transparent to Terahertz radiation, whereas skin, water, metal and a host of other interesting materials are not. This gives rise to some important day-to-day applications: detecting weapons concealed under clothing or inside parcels; distinguishing skin and breast cancer tissue; quality control of manufactures items and processes in factories. Our KIDCAM detectors are also very sensitive, and so we can look at the natural radiation emitted by the target. This means there are no safety issues like those associated with other imaging techniques which shine radiation, including X-rays, at the target," said Mr Wood.

Until recently, there have been many practical obstacles to using terahertz detectors. Terahertz sources have only become available to the non-specialist in the last 10 years and cooling the detectors to very low temperatures using liquid cryogens is costly and complicated.

The Herschel and Planks satellites are used by astronomers to map the furthest reaches of the Universe. UK business partnerships could soon ensure that similar technology is used back on Earth to keep our airports secure or diagnose breast cancer.

Credit: ESA (Image by AOES Medialab)

"The instruments aboard the Herschel and Planck satellites need to be cooled to temperatures close to absolute zero so that emissions from the spacecraft don’t drown out the faint signals that come from the very edge of the observable Universe," said Ken Wood.

"For KIDCAM, we have developed a kind of detector that can be operated in electrical coolers and therefore without the use of liquified gases. KIDCAM can be tuned to specific frequencies for specific applications, for instance to, enhance the contrast between skin and plastic explosive for airport security scanners. Unwanted frequencies can be blocked to increase the camera’s sensitivity. The experience that we gained working on astronomical missions has been invaluable in helping us do this. The race is now on around the world to produce devices that will realise the enormous potential of terahertz science and thanks to the ingenuity of UK astronomers we have made a great start."

Source: Royal Astronomical Society