Terahertz (THz) technology is one of emerging technologies that will change our life. A lot of attractive applications in security, medicine, biology, astronomy, and non-destructive materials testing have been demonstrated already. However, the realization of THz emitters and receivers is a challenge because the frequencies are too high for conventional electronics and the photon energies are too small for classical optics. As a result, THz radiation is resistant to the techniques commonly employed in these well established neighbouring bands.

https://www.degruyter.com/document/doi/10.2478/s11772-011-0033-3/pdf

Terahertz detectors and focal plane arrays

Using an organic molecular crystal as gain medium allows a maser to be operated in pulsed mode in air, at room temperature and in the terrestrial magnetic field, so avoiding many of the obstacles that have previously hindered the application of masers The maser is the microwave-frequency precursor of the now ubiquitous laser — or 'optical maser', as it was once known But it has had little technological impact compared with the laser, in large part because of inconvenience: masers typically require vacuum and/or low-temperature operating conditions Overcoming these obstacles would pave the way for significant maser-based innovations, including drastically more sensitive measurements across a range of scientific disciplines, from molecular biology to radio astronomy And, if the history of the laser is any indication, applications not yet dreamt of Mark Oxborrow, Jonathan Breeze and Neil Alford have now developed a solid-state room-temperature maser, based on an organic molecular crystal, that should enhance the potential of the maser as a tool for science and technology The invention of the laser has resulted in many innovations, and the device has become ubiquitous However, the maser, which amplifies microwave radiation rather than visible light, has not had as large an impact, despite being instrumental in the laser’s birth1,2 The maser’s relative obscurity has mainly been due to the inconvenience of the operating conditions needed for its various realizations: atomic3 and free-electron4 masers require vacuum chambers and pumping; and solid-state masers5, although they excel as low-noise amplifiers6 and are occasionally incorporated in ultrastable oscillators7,8, typically require cryogenic refrigeration Most realizations of masers also require strong magnets, magnetic shielding or both Overcoming these various obstacles would pave the way for improvements such as more-sensitive chemical assays, more-precise determinations of biomolecular structure and function, and more-accurate medical diagnostics (including tomography) based on enhanced magnetic resonance spectrometers9 incorporating maser amplifiers and oscillators Here we report the experimental demonstration of a solid-state maser operating at room temperature in pulsed mode It works on a laboratory bench, in air, in the terrestrial magnetic field and amplifies at around 145 gigahertz In contrast to the cryogenic ruby maser6, in our maser the gain medium is an organic mixed molecular crystal, p-terphenyl doped with pentacene, the latter being photo-excited by yellow light The maser’s pumping mechanism exploits spin-selective molecular intersystem crossing10 into pentacene’s triplet ground state11,12 When configured as an oscillator, the solid-state maser’s measured output power of around −10 decibel milliwatts is approximately 100 million times greater than that of an atomic hydrogen maser3, which oscillates at a similar frequency (about 142 gigahertz) By exploiting the high levels of spin polarization readily generated by intersystem crossing in photo-excited pentacene and other aromatic molecules, this new type of maser seems to be capable of amplifying with a residual noise temperature far below room temperature

https://home.uni-leipzig.de/pwm/teaching/ep5_ws1213/literature/Oxborrow_Breeze_Alford_2012_room-temperature_solid-state_maser.pdf

Room-temperature solid-state maser

In the paper, issues associated with the development and exploitation of terahertz (THz) radiation detectors are discussed. The paper is written for those readers who desire an analysis of the latest developments in different type of THz radiation sensors (detectors), which play an increasing role in different areas of human activity (e.g., security, biological, drugs and explosions detection, imaging, astronomy applications, etc.). The basic physical phenomena and the recent progress in both direct and heterodyne detectors are discussed. More details concern Schottky barrier diodes, pair braking detectors, hot electron mixers, and field-effect transistor detectors. Also the operational conditions of THz detectors and their upper performance limits are discussed.

https://www.degruyter.com/downloadpdf/j/oere.2010.18.issue-1/s11772-009-0029-4/s11772-009-0029-4.xml

THz radiation sensors

We present a multiwavelength study of five methanol maser sites which are not directly associated with a strong ($>100$ mJy) radio continuum source: G 31.28+0.06, G 59.78+0.06, G 173.49+2.42 (S231, S233IR), G 188.95+0.89 (S252, AFGL5180) and G 192.60-0.05 (S255IR). These radio-quiet methanol maser sites are often interpreted as precursors of ultra-compact \ion{H}{ii} regions or massive protostar sites. In this work, the environment of methanol masers is probed from mid-IR to millimetre wavelengths at angular resolutions of $8''-34''$. Spectral energy distribution (SED) diagrams for each site are presented, together with mass and luminosity estimates. Each radio-quiet maser site is always associated with a massive ($>50$ M$_{\odot}$), deeply embedded ($A_v>40$ mag) and very luminous ($>10^4$ S L$_{\odot}$) molecular clump, with $L_{total}{\propto}M_{gas}^{0.75}$. These physical properties characterise massive star-forming clumps in earlier evolutionary phases than \ion{H}{ii} regions. In addition, colder gas clumps seen only at mm-wavelengths are also found near the methanol maser sites. These colderclumps may represent an even earlier phase of massive star formation. These results suggest an evolutionary sequence for massive star formation from a cold clump, seen only at mm wavelengths, evolving to a hot molecular core with a two-component SED with peaks at far-IR and mid-IR wavelengths, to an (ultra-compact) \ion{H}{ii} region. Alternatively, the cold clumps might be clusters of low-mass YSOs, in formation near the massive star-forming clusters. Finally, the values of the dust grain emissivity index ($\beta$) range between 1.6 and 1.9.

/pdf/star-forming-protoclusters-associated-with-methanol-masers-ajshvu2r2s.pdf

Star-forming protoclusters associated with methanol masers

Terahertz (THz) technology is one of emerging technologies that will change our life. A lot of attractive applications in security, medicine, biology, astronomy, and non-destructive materials testing have been demonstrated already. However, the realization of THz emitters and receivers is a challenge because the frequencies are too high for conventional electronics and the photon energies are too small for classical optics. As a result, THz radiation is resistant to the techniques commonly employed in these well established neighbouring bands.In the paper, issues associated with the development and exploitation of THz radiation detectors and focal plane arrays are discussed. Historical impressive progress in THz detector sensitivity in a period of more than half century is analyzed. More attention is put on the basic physical phenomena and the recent progress in both direct and heterodyne detectors. After short description of general classification of THz detectors, more details concern Schottky barrier diodes, pair braking detectors, hot electron mixers and field-effect transistor detectors, where links between THz devices and modern technologies such as micromachining are underlined. Also, the operational conditions of THz detectors and their upper performance limits are reviewed. Finally, recent advances in novel nanoelectronic materials and technologies are described. It is expected that applications of nanoscale materials and devices will open the door for further performance improvement in THz detectors.

We have presented theory and experimentally demonstrated an efficient method for drastically reducing the power consumption of the rf/microwave amplifiers based on HEMT in unsaturated dc regime. Conceptual one-stage 10 dB-gain amplifier showed submicrowatt level of the power consumption (0.95 μW at frequency of 0.5 GHz) when cooled down to 300 mK. Proposed technique has a great potential to design the readout amplifiers for ultra-deep-cooled cryoelectronic quantum devices.

Note: Ultra-high frequency ultra-low dc power consumption HEMT amplifier for quantum measurements in millikelvin temperature range.

The paper describes a 3mm cryogenic mixer receiver using high doping density (“room-temperature”) Schottky diodes The measured equivalent noise temperature Teq of the diodes is 109 K at 20 K, which is much higher than the Teq of the low doping density (“cryogenic”) diodes In spite of this, the double-sideband (DSB) noise temperature of the cryogenic receiver developed is 55 K at 110 GHz, owing to the low conversion loss of the mixer and ultra-low noise of the PHEMT IF amplifier This is the lowest noise temperature ever reported for a Schottky diode mixer receiver The results obtained are useful for the development of submm receivers in which high doping density Schottky diodes are used

High Doping Density Schottky Diodes in the 3MM Wavelength Cryogenic Heterodyne Receiver

Extra-low power consumption amplifier based on HEMT in unsaturated mode for use at subkelvin ambient temperatures

PHEMT as a circuit element for high impedance nanopower amplifiers for ultra-low temperatures application

We developed a high-sensitivity receiving and measuring facility designed for observations of the ozone O3 and carbon monoxide CO spectral lines by the method of ground-based remote sensing of the atmosphere in the 90–116 GHz frequency range. The measurement and calibration procedure is described in detail. The results of observations of the O3 and CO emission lines at frequencies 110.836 amd 115.271 GHz, respectively, are presented. The sensitivity level of the receiving and measuring facility, which was implemented in the experiment using a filter-bank analyzer and a Fourier spectrum analyzer is determined.

A. M. Korolev

Papers

Note: Ultra-high frequency ultra-low dc power consumption HEMT amplifier for quantum measurements in millikelvin temperature range.

High Doping Density Schottky Diodes in the 3MM Wavelength Cryogenic Heterodyne Receiver

Extra-low power consumption amplifier based on HEMT in unsaturated mode for use at subkelvin ambient temperatures

PHEMT as a circuit element for high impedance nanopower amplifiers for ultra-low temperatures application

3-mm wave spectroradiometer for studies of atmospheric trace gases