Magnus Svensson

Facility heterodyne receiver for the Atacama Pathfinder Experiment Telescope

APEX, the Atacama PAthflnder Experiment (APEX) Telescope, is a partnership between Max Planck Institut fur Radioastronomie (in collaboration with Astronomisches Institut Ruhr Universitat Bochum (AIRUB)), Onsala Space Observatory and the European Southern Observatory. The telescope antenna, supplied by VERTEX Antennentechnik, is a 12 m antenna with a 17 mum rms surface accuracy operating at the Atacama Desert in the Chilean Andes at a 5100 m altitude. The APEX heterodyne facility receiver is placed in the telescope Nasmyth Cabin A. The receivers are coupled to the antenna via relay optics allowing the operation of two different Pi-type instruments and a 6-channel facility heterodyne receiver to cover approximately 210 - 1500 GHz frequency range while providing frequency independent illumination of the secondary. In this report, we present details on the optics for the APEX facility heterodyne receiver and details of its design. The report includes a very brief review of the APEX Band 1, 211 - 270 GHz, Band 2, 270 - 370 GHz, Band 3, 385 - 500 GHz, all based on sideband separation SIS mixer technology and Band T2, 1250 - 1390 GHz, a balanced waveguide HEB mixer, all developed by GARD.

Effects of nitro substituents on the properties of a ferroelectric liquid crystalline side chain polysiloxane

The syntheses of chiral liquid crystalline side chain polysiloxanes with lateral nitro substituents in the mesogenic core are described. The influence of the substituents and substituent positions on phase behaviour and electro-optical properties are investigated and compared. The lateral nitro groups strongly affect the phase behaviour of the side chain precursors as well as the liquid crystalline polymers. Properties in smectic A and C* phases are discussed with respect to substituent position. One side chain precursor exhibits very large spontaneous polarization of ∼700 nC cm–2 .

Synthesis and electro-optical behaviour of a new chiral smectic side-chain polysiloxane

SummaryA new chiral side-chain polymer was prepared by hydrosilylation of a dimethylsilane-methyl-hydrosilane copolymer. The chiral group of the mesogenic side-chain was (+)2-chloro-3-(3-nitro-4-hydroxyphenyl)propionic acid butyl ester while the main part of the aromatic nucleus consisted of 4′-hydroxybiphenyl-4-carboxylic acid. Phase behaviour was studied by DSC and polarizing microscopy, and correlated with dielectric measurements. Alignment properties and ferroelectricity were studied in cells with surface-induced alignment and in shear cells. The polymer exhibits chiral C-and A-phases. The spontaneous polarization is 130 nC/cm2 at 60°C and the polymer shows ferroelectric switching at room temperature.

The metabolic cost of various occupational exposures

This paper reports on the oxygen uptake in seated volunteers subjected to 5 Hz sinusoidal vibration at 2ms−2, axial rotation alone and axial rotation in combination with vibration. Compared to non-vibrated, non-twisted tests, the axial rotation and vibration exposure increased the oxygen uptake by 32%.

Influence of molar mass parameters on electro-optical switching in ferroelectric liquid crystalline polysiloxanes

Three ferroelectric copolysiloxanes with different molar mass have been synthesized. Mechanical measurements and electro-optical switching behaviour in both cell and thin film geometry are reported. Removal of short chains doubled M n and slowed down electro-optical switching but the mechanical properties were not affected. A further twofold increase in M n by chain extension did not affect electro-optical switching times but improved the mechanical properties markedly.

Optical second-harmonic generation in ferroelectric chiral smectic polysiloxane

The second-order nonlinear optical properties of ferroelectric liquid crystalline polymer have been studied. Angular phase-matched Second-Harmonic Generation (SHG) is observed in the chiral smectic C (SmC*) phase of siloxane copolymer with chiral mesogen in the side chain. The effective nonlinear optical coefficient deff under the phase-matching condition is determined. The intense SHG is observed even in the crystalline phase by cooling down from the SmC* phase under the electric field. The effective coefficient of SHG in the crystalline phase is more than ten times larger than that of the phase-matched SHG in the SmC* phase. The enhancement of SHG in the crystalline phase is observed only in a homeotropically aligned cell and maintained even in the non-biased state for at least several days. The angular dependence of the SHG in the crystalline phase is confirmed.

Phase properties in relation to mesogen length in chiral side-chain polysiloxanes

Abstract The synthesis of a series of side-chain liquid crystalline siloxane copolymers is reported, and comparative studies of physical properties of members of the series with different side-chain length have been attempted. All the five members show smectic C∗ and smectic A phases. Measurements of ferroelectricity, relaxation times and electroclinic properties have been carried out, aiming at finding structure-property relationships for the longer side-chain members. A relationship between electroclinic coefficient and side-chain length was also found.

CHIRAL LIQUID CRYSTALLINE SIDE-CHAIN POLYMERS: EFFECTS OF SIDE-CHAIN LENGTH ON PHYSICAL PROPERTIES

Abstract The synthesis of a series of side-chain liquid crystalline siloxane copolymers is reported, and comparative studies of physical properties of members with different side-chain length have been attempted. Measurements of ferroelectricity and relaxation times aimed at studying structure-property relationships for the longer side-chain members. It was found that the stability of the chiral smectic C phase decreases with decreasing length of the terminal alkyl ester.

Scalar beam pattern measurements for characterization of sub-millimeter receivers

The scalar beam measurement concept presented in this article is based on scanning the receivers beam with an isotropic radiating source at three to four parallel cross planes along the presumable optical axis. The receiver is operated in heterodyne mode and the output IF power is recorded for each coordinate point of the radiating source. The collected data provides information for the Gaussian beam profile at the particular distance from the receiver. According to the properties of the fundamental Gaussian beam, the maximum power value is located on the axis of the beam. Therefore, obtaini.ng the coordinates of the beam center (of the maximum intensity) for each measured beam profile allows for the determination of the beam axis orientation. The location of the beam waist and its size can be calculated by solving a system of equations derived from the Gaussian beam theory.

Gaussian beam measurement for HIFI instrument: Herschel Space Observatory

The Heterodyne Instrument (HIFI) is part of the ESA Herschel Space Observatory Project. The instrument is intended for high-resolution spectroscopy and has a frequency coverage from 480 to 1250 GHz band in five receiver bands and 1410 to 1910 GHz in two additional bands. HIFI is built based on a modular principle: the mixers together with their respective optics are integrated into Mixer Sub-Assemblies (MSA). Each frequency band has two MSAs allocated for horizontal and vertical polarization. In this paper, we present the work done on the design and construction of a Gaussian beam measurement range. One of the unique features of the developed method is a possibility to measure the beam parameters of the MSAs in the absolute coordinate system referred to the device under test. This along with other methods should allow integration of the entire HIFI with the best possible coupling of the antenna beam to the receivers and achieving ultimate performance in such a complicated optical system. The range houses the measured MSA, which is at 4 K ambient temperature, and a continuous wave source placed on a precise scanner entirely under vacuum. Developed triangulation system provides mechanical reference data on the MSA, in-situ, after the entire system is evacuated and the cooling is finished. We adopted a scalar measurement approach where the test source scans the receiver input beam and the mixer IF power is measured. The data collected from 3-4 planar scans are used to calculate the orientation and position of the optical axis. We present results from the first beam measurements for MSA HIFI bands 1 and 2 (480 and 640 GHz), the measurement system performance and accuracy analysis.