5 research outputs found
Terahertz Spectroscopy of Gas Absorption Using the Superconducting Flux-Flow Oscillator as an Active Source and the Superconducting Integrated Receiver
We report on the first implementation of a terahertz (THz) source based on a Josephson flux-flow oscillator (FFO) that radiates to open space. The excellent performance of this source and its maturity for practical applications has been demonstrated by the spectroscopy of gas absorption. To study the radiated power, we used a bolometric detection method and additionally calibrated the power by means of pumping the superconductor–insulator–superconductor (SIS) junction, integrated on a single chip with the FFO. For calibration, we developed a program using the SIS-detected power calculations in accordance with the Tien and Gordon model. The power emitted to open space is estimated to be from fractions of µW to several µW in the wide region from 0.25 THz up to 0.75 THz for different designs, with a maximum power of 3.3 µW at 0.34 THz. Next, we used a gas cell and a heterodyne superconducting integrated receiver to trace the absorption lines of water and ammonia with a spectral resolution better than 100 kHz. Our experiment for gas absorption is the first demonstration of the applicability of the FFO as an external active source for different tasks, such as THz spectroscopy, near-field THz imaging and microscopy
Direct Experimental Observation of Harmonics of Josephson Generation in the Flux-Flow Oscillator
We present an experimental observation and a study of harmonics of radiation from a flux-flow oscillator (FFO) based on a long Josephson junction. An integrated microcircuit consisting of the FFO, the transmitting antenna and a harmonic mixer (HM) was used to provide the phase-locked emission in the terahertz (THz) range to open space. Both the FFO and the HM were made of superconductor–insulator–superconductor (SIS) trilayers based on Nb/AlOx/Nb. Two independent techniques were used for detecting of the output emission: a THz Fourier transform spectrometer with a wideband detector based on an 4.2 K silicon bolometer, and a THz spectrometer based on the heterodyne SIS receiver with a high spectral resolution. The FFO spectral composition obtained using the FTS demonstrates the main Josephson frequency and clear higher harmonics. Following that, the spectral characteristics of the 2nd harmonic at a frequency of 600–670 GHz (corresponding to the main frequency of 300–335 GHz) were carefully studied with a spectral resolution better than 0.1 MHz using the SIS receiver. To our knowledge, this is the first direct high-frequency observation of Josephson harmonics carried out at the true frequency of oscillations, which is in contrast to dc measurements
Superconducting Integrated Terahertz Spectrometers
A superconducting integrated receiver (SIR) comprises all of the elements needed for heterodyne detection on a single chip. Light weight and low power consumption combined with nearly quantum-limited sensitivity and a wide tuning range of the superconducting local oscillator make the SIR a perfect candidate for many practical applications. For the first time, we demonstrated the capabilities of the SIR technology for remote operation under harsh environmental conditions and for heterodyne spectroscopy at atmospheric limb sounding on board a high-altitude balloon. Recently, the SIR was successfully implemented for the first spectral measurements of THz radiation emitted from intrinsic Josephson junction stacks (BSCCO mesa) at frequencies up to 750 GHz; linewidth below 10 MHz has been recorded in the high bias regime. The phase-locked SIR has been used for the locking of the BSCCO oscillator under the test. To extend the operation range of the SIR well above 1 THz, a new technique for fabrication of high-quality SIS tunnel junctions with gap voltage Vg up to 5.3 mV has been developed. Integration of a superconducting high-harmonic phase detector with a cryogenic oscillator opens a possibility for efficient phase locking of the sources with free-running linewidth up to 30 MHz that is important both for BSCCO mesa and NbN/MgO/NbN oscillators
Development and characterization of the superconducting integrated receiver channel of the TELIS atmospheric sounder
The balloon-borne instrument TELIS (TErahertz and submillimetre LImb Sounder) is a three-channel superconducting heterodyne spectrometer for atmospheric research use. It detects spectral emission lines of stratospheric trace gases that have their rotational transitions at THz frequencies. One of the channels is based on the superconducting integrated receiver (SIR) technology. We demonstrate for the first time the capabilities of the SIR technology for heterodyne spectroscopy in general, and atmospheric limb sounding in particular. We also show that the application of SIR technology is not limited to laboratory environments, but that it is well suited for remote operation under harsh environmental conditions. Within a SIR the main components needed for a superconducting heterodyne receiver such as a superconductor-insulator-superconductor (SIS) mixer with a quasi-optical antenna, a flux-flow oscillator (FFO) as the local oscillator, and a harmonic mixer to phase lock the FFO are integrated on a single chip. Light weight and low power consumption combined with broadband operation and nearly quantum limited sensitivity make the SIR a perfect candidate for use in future airborne and space-borne missions. The noise temperature of the SIR was measured to be as low as 120 K, with an intermediate frequency band of 4-8 GHz in double-sideband operation. The spectral resolution is well below 1 MHz, confirmed by our measurements. Remote control of the SIR under flight conditions has been demonstrated in a successful balloon flight in Kiruna, Sweden. The sensor and instrument design are presented, as well as the preliminary science results from the first flight
Integrated SubmmWave Receiver: Development and Applications
A superconducting integrated receiver (SIR) comprises in a single chip a planar antenna combined with a superconductor-insulator-superconductor (SIS) mixer, a superconducting Flux Flow Oscillator (FFO) acting as a Local Oscillator (LO) and a second SIS harmonic mixer (HM) for the FFO phase locking. In this report, an overview of the SIR and FFO developments and optimizations is presented. Improving on the fully Nb-based SIR we have developed and studied Nb–AlN–NbN circuits, which exhibit an extended operation frequency range. Continuous tuning of the phase locked frequency has been experimentally demonstrated at any frequency in the range 350–750GHz. The FFO free-running linewidth has been measured between 1 and 5MHz, which allows to phase lock up to 97% of the emitted FFO power. The output power of the FFO is sufficient to pump the matched SIS mixer. Therefore, it is concluded that the Nb–AlN–NbN FFOs are mature enough for practical applications. These achievements enabled the development of a 480–650GHz integrated receiver for the atmospheric-research instrument TErahertz and submillimeter LImb Sounder (TELIS). This balloon-borne instrument is a three-channel superconducting heterodyne spectrometer for the detection of spectral emission lines of stratospheric trace gases that have their rotational transitions at THz frequencies.
One of the channels is based on the SIR technology. We demonstrate for the first time the capabilities of the SIR technology for heterodyne spectroscopy in general, and atmospheric limb sounding in particular. We also show that the
application of SIR technology is not limited to laboratory environments, but that it is well suited for remote operation under harsh environmental conditions. Light weight and low power consumption combined with broadband operation and nearly quantum limited sensitivity make the SIR a perfect candidate for future airborne and space-borne missions. The noise temperature of the SIR was measured to be as low as 120K in double sideband operation, with an intermediate frequency band of 4–8GHz. The spectral resolution is well below 1MHz, confirmed by our measurements. Remote control of the SIR under flight conditions has been demonstrated in a successful balloon flight in Kiruna, Sweden.
Capability of the SIR for high-resolution spectroscopy has been successfully proven also in a laboratory environment by gas cell measurements. The possibility to use SIR devices for the medical analysis of exhaled air will be discussed. Many
medically relevant gases have spectral lines in the sub-terahertz range and can be detected by an SIR-based spectrometer. The SIR can be considered as an operational
device, ready for many applications