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A series of far infrared (FIR) spectra of Mars between 43 and 196 μm was taken with the Long Wavelength Spectrometer (LWS) on board the European Space Agency's Infrared Space Observatory (ISO). Analysis of these medium-resolution data reveals a rotational modulation of the disk-averaged FIR brightness temperature. The observed variability of ±1.5% in the LWS wavelength range compares favorably with the predictions of a thermophysical model of the martian surface. A surface emissivity of ∼0.90 gives good agreement between the measured and the modeled brightness temperatures and leads to an improved estimate of the LWS photometric calibration uncertainty.

The short-wavelength spectrometer for the Infrared Space Observatory (ISO) is a cryogenic instrument operating at wavelengths from 2.45 to 45 μm, containing a grating spectrometer and a scanning Fabry-Perot interferometer. Some of the techniques used to build and test the instrument are described and some test results are presented, all from the viewpoint of cryoengineering.

International audience; Aims: This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI) that was launched onboard ESA's Herschel Space Observatory in May 2009. Methods: The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480-1250 GHz with SIS mixers and the 1410-1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 km s-1. Results: After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

We describe a planar antenna structure consisting of two half-wave dipoles, which are backed by a metallic reflector to create an image of two more elements. The array produces rather a wide main beam, and is therefore used with a dielectric lens. The far-field pattern of the dipole liens antenna has cross-pol better than −20 dB, and side lobes below −13 dB over an octave band. The impedance at the feedpoint of the antenna is approximately 70 - j10 Ω at the center of the band.

In the far-infrared (FIR) / THz regime the angular (and often spectral) resolution of observing facilities is still very restricted despite the fact that this frequency range has become of prime importance for modern astrophysics. ALMA (Atacama Large Millimeter Array) with its superb sensitivity and angular resolution will only cover frequencies up to about 1 THz, while the HIFI instrument for ESA'a Herschel Space Observatory will provide limited angular resolution (10 to 30 arcsec) up to 2 THz. Observations of regions with star and planet formation require extremely high angular resolution as well as frequency resolution in the full THz regime. In order to open these regions for high-resolution astrophysics we present a study concept for a heterodyne space interferometer, ESPRIT (Exploratory Submm Space Radio-Interferometric Telescope). This mission will cover the Terahertz regime inaccessible from the ground and outside the operating range of the James Webb Space Telescope (JWST).

In the far-infrared (FIR) / THz regime the angular (and often spectral) resolution of observing facilities is still very restricted despite the fact that this frequency range has become of prime importance for modern astrophysics. ALMA (Atacama Large Millimeter Array) with its superb sensitivity and angular resolution will only cover frequencies up to about 1 THz, while the HIFI instrument for ESA'a Herschel Space Observatory will provide limited angular resolution (10 to 30 arcsec) up to 2 THz. Observations of regions with star and planet formation require extremely high angular resolution as well as frequency resolution in the full THz regime. In order to open these regions for high-resolution astrophysics we propose a heterodyne space interferometer mission, ESPRIT (Exploratory Submm Space Radio-Interferometric Telescope), for the Terahertz regime inaccessible from ground and outside the operating range of the James Webb Space Telescope (JWST).

A review is given of different types of quarter wave plates as presently used in the optical and microwave spectral range, with a view to their application in the sub-mm wave-length range. Two types of quarter wave plates have been constructed and results of measurements at 640μm are given.

We report the results of a series of experiments on the use of an extrinsic silicon photoconductor for heterodyne detection at 10.6 μm. An arsenic-doped sample was for these measurements, having a donor density of 3 × 10 16 cm −3 . The measurements were made at approximately 5 K, with a CO 2 laser providing the local oscillator power, and a calibrated blackbody at 900 K providing the signal. The signal-to-noise ratio was measured as a function of detector bias voltage for local oscillator powers ranging from 30 to 280 mW. The measured signal-to-noise ratio was found to be within 4 dB of the theoretically expected value. The 3 dB roll-off frequency was measured from the signal roll-off and from the laser-induced generation-recombination noise roll-off. Both measurements agreed closely. The detector response time determined from this measurement varied between 4 and 10 nsec, depending on the laser power and bias voltage.

A heterodyne receiver is described in which an InSb hot electron bolometer is used as a mixer. The local oscillator power is obtained by doubling the frequency of a backward wave oscillator. The receiver operates between 460 and 500 GHz (0.65–0.6 mm). Noise temperatures amount typically to 1000 K.

In this paper some aspects of two of the most important components of a previously described submm heterodyne are discussed: the InSb mexer and the backward wave oscillator. The (known) properties of the InSb mixer and our method of fabrication will be briefly discussed. The aspect of matching this mixer to the waveguide is treated more extensively both in theory and practice. Finally the performance of InSb as a mixer at higher frequencies is briefly considered. Some properties of the backward wave oscillator which are of special relevance when using it in combination with an InSb mixer, have been measured and they are discussed in the last section.

Planar Nb-Nb Josephson Junctions (JJ's) have been developed to be used in submillimeter heterodyne mixers. Experimental mixing results show a System Noise Temperature around 1000 K with a best result of 800 K at an operating temperature of 1.5 K. Preliminary results at 900 GHz are reported. A strong temperature dependence of the mixer noise temperature has been observed.

For wavelengths 50μm the available detectors are far from ideal. Research and development of far infrared detectors for the mixing purpose are highly recommended.

The observation and quantative measurement of optical heterodyne detection at 337 μm using a HCN laser and an epitaxial n-type GaAs photoconductor are reported. The measured NEP amounted 1.4 × 10−14 W Hz−1.

THE possibility of applying heterodyne detection techniques in astronomy is now becoming well known1-3. Earlier observations made in this way in the visible region of the spectrum4,5 have indicated that its importance for astronomy lies primarily in the infrared. Preliminary measurements with a 10 µm system for solar heterodyne interferometry were recently published by Gay and Journet6. In August and September 1973 we carried out heterodyne detection measurements of planets, stars and the Moon at wavelengths around 10.5 µm. The observations were made at the Coude focus of the 1.5-m spectrographic telescope of the European Southern Observatory at La Silla in Chile. Figure 1 shows a block diagram of the experimental equipment. The local oscillator was a linearly polarised single line, single mode CO2 laser (Sylvania, model P941) tunable to different laser transitions around 10.5 µm. Tuning is achieved by changing the temperature of the cooling water and thereby varying the cavity length of the laser tube. Two different types of detectors were available as photomixing elements: a liquid nitrogen-cooled HgCdTe photodiode (Societe Anonyme de Telecommunications, quality B1) and a liquid helium-cooled Ge : Cu photoconductor (Santa Barbara Research Center, type HS). The detector signals were amplified by radiofrequency amplifiers and subsequently rectified by a quadratic detector. For amplifying the diode signals we used two CA1003 E + M amplifiers with a pass band between 10 and 300 MHz; the photoconductor signals were amplified by two AWL-1200 M Avantek amplifiers having a pass band between 0.1 and 1,200 MHz. A high-pass filter was used to produce a flat frequency response over the largest possible bandwidth. This resulted in an effective bandwidth of about 250 MHz for the photodiode system and of 1,000 MHz for the photoconductor system. The application of a chopper allowed synchronous detection. A rotating mirror (MC in Fig. 1), which chopped the source against the sky background, was used when observing planets or stars, whereas a plastic chopper (PC) was used in the calibration measurements and in the observations of the Moon to chop against room temperature (291 K). The sensitivities of both heterodyne detection systems were measured with the aid of a calibrated blackbody source. Heterodyne detection with a photodiode of an extended blackbody of absolute temperature T should have an associated signal-to-noise ratio (SNR)

A submillimeter receiver, to be used as common-user receiver for UKIRT and the UK-NL mm telescope at Mau-na Kea, Hawaii, is here described. The receiver operates at two submm frequency bands using one backward wave oscillator (carcinotron) and a doubler. It utilizes a bath cryostat coupled to a closed cycle cooler for cooling of the mixers and preamplifiers. All main receiver components are microprocessor controlled in order to provide reliable and efficient operation at the high altitude observatory.

An optical single-sideband mixer, operating at 6328 A and utilizing two balanced heterodyne mixers, has been constructed. The sideband suppression ratio was measured to be typically about 25 dB and an optimal ratio of 54 dB was achieved.

Josephson junctions (JJ) mixers have been developped and in the millimeter (185-270 GHz) and in the sub-millimeter range (345 GHz, 1000 GHz). Pointcontact devices have shown the best noise temperatures (Tsys = 420 K at 230 GHz) but are unreliable for practical operations. The developped planar junctions have gown so far competitive performance with respect to cooled Schottky barrier diode mixers e.g.. Tsys = 1600 K at 345 GHz.