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.

We have designed, fabricated, and tested superconductor-insulator-superconductor (SIS) mixers based on Nb/AlN/NbN twin tunnel junctions for waveguide receivers operating in a frequency range of 790-950 GHz. Electromagnetic simulations and measurement results of the mixer performance are presented. The junctions have a high gap voltage of 3.15 mV and a high current density of about 30 kA/cm , providing a wide receiver band, which was confirmed by Fourier transform spectrometer (FTS) and noise temperature measurements. The corrected receiver noise temperature varies from 240 K at low frequencies to 550 K at the high end of the band. The influence of the SIS junction heating on its characteristics has been studied and compared to another similar high current density technologies. The heating does not have a critical impact on the mixer performance.

We report on the phase locking of a 3.4 THz third-order distributed feedback quantum cascade laser (QCL) using a room temperature GaAs/AlAs superlattice diode as both a frequency multiplier and an internal harmonic mixer. A signal-to-noise level of 60 dB is observed in the intermediate frequency signal between the 18th harmonic of a 190.7 GHz reference source and the 3433 GHz QCL. A phase-lock loop with 7 MHz bandwidth results in QCL emission that is 96% locked to the reference source. We characterize the QCL temperature and electrical tuning mechanisms and show that frequency dependence of these mechanisms can prevent phase-locking under certain QCL bias conditions. V C 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4817319]Since the development of the first THz quantum cascade lasers (QCLs), 1 there has been considerable progress made in their development. They are compact and offer lasing at any frequency between roughly 1 and 5 THz with high output power in the range of tens of milliwatts, making them highly suitable for many applications from local oscillator (LO) sources for high resolution heterodyne spectroscopy to gas sensing and terahertz imaging.One of the key applications driving the development of the THz QCL is heterodyne spectroscopy in the superterahertz which is loosely defined as 2 to 6 THz. For frequencies beyond 2 THz, there are few solid state sources available. The commonly used LO below 2 THz is the multiplier based source which, to date, has demonstrated output power of a microwatt at up to 2.7 THz. For an LO source, single mode emission is crucial. A 3rd order distributed feedback (DFB) laser, as to be explained, can offer not only a robust single mode operation, but also a relatively narrow single-lobe beam. The latter is of practical importance for efficient coupling of the radiation to a mixer or mixer array.Frequency locking of a THz QCL was first demonstrated by Betz et al. 2 in 2005. Since then, it has been well established that to apply a QCL as an LO in a real receiver system, either frequency stabilization or phase locking is required. For this reason, many frequency or phase locking experiments have been reported in the literature. Those demonstrations can be mainly divided into a few cases: (a) phase locking of Fabry-Perot (FP) based QCLs with the use of a cooled superconducting detector as the mixing element 3-5 or by the use of a frequency comb generated from a mode-lock femtosecond laser. 6,7 The latter is operated at room temperature but requires relatively bulky and high power consumption electronics; (b) frequency locking of an FP or 3rd order DFB laser using a gas absorption line as the reference; 8 (c) frequency locking of an FP laser using a Schottky-diode harmonic mixer, 9 which was operated at room temperature, but requires high THz input power from the QCL in the order of several mW and has so far been demonstrated only below 3 THz.In this paper we report on a phase locking demonstration of a 3.4 THz 3rd order DFB laser QCL using a roomtemperature component,...

In this report an overview of the results on the development of a single-chip superconducting integrated receiver for the Terahertz Limb Sounder (TELIS) balloon project intended to measure a variety of stratosphere trace gases is presented. The Superconducting Integrated Receiver (SIR) comprises in one chip a planar antenna integrated with a superconductor-insulator-superconductor (SIS) mixer, a superconducting Flux Flow Oscillator (FFO) acting as Local Oscillator (LO) and a second SIS harmonic mixer (HM) for FFO phase locking. As a result of the FFO design optimization a free-running linewidth between 9 and 1.5 MHz has been measured in the frequency range 500-710 GHz resulting in phase-locking of 35 to 95% of the FFO power correspond- ingly. A new generation of the SIR devices with improved FFO performance and optimized interface between FFO and SIS/HM has been developed and comprehensively tested. As a result all required TELIS parameters were demonstrated. Phase-locked FFO operation over entire SIR channel frequency range has been realized, spectral resolution below 1 MHz has been confirmed by gas cell and CW signal measurements. An uncorrected double side band (DSB) noise temperature below 250 K has been measured with the phase-locked FFO. The intermediate frequency bandwidth 4-8 GHz has been realized. To ensure remote operation of the phase-locked SIR several procedures for its automatic computer control have been developed and tested.Index Terms-Phase-locked oscillators, submillimeter wave integrated receivers, superconducting integrated circuits.