I. Furniss

The Long Wavelength Spectrometer (LWS) for ISO

A spectroscopic instrument for the ESA Infrared Space Observatory is described, covering the wavelength range 45 to 180 microns and with operating modes offering a choice of two resolving powers. The lower resolving power of around 230 is given by a diffraction grating system, with the spectrum recorded by a line of 10 detectors. The high resolving power of around 1.5E4 is achieved by switching a Fabry-Perot (F-P) interferometer into the parallel part of the instrument beam. Either of two F-Ps can be selected, one optimised for the 45 to 90 micron wavelength range and the other for 90 to 180 microns. The operating modes offered include differential measurement, using wavelength switching and synchronous detection, and absolute measurement with an internal chopper/reference. Development aspects of the instrument are also discussed.

Design and performance of cryogenic, scanning Fabry-Perot interferometers for the Long-Wavelength Spectrometer on the Infrared Space Observatory.

The design of cryogenic, scanning Fabry-Perot interferometers for the Long-Wavelength Spectrometer on the ESA Infrared Space Observatory is presented. The interferometers were designed to provide a spectral resolving power of 10(4) over the wavelength range 45-180 µm, with the highest possible transmission efficiency consistent with this requirement. Metal meshes, custom designed with the aid of a theoretical model of metallic reflection, were used as the reflecting elements. The scanning mechanism featured a spring-suspended plate, which was servocontrolled by moving coil actuators and monitored by capacitance micrometers. The spectroscopic performance of the interferometers was measured in the laboratory and is compared with the model developed for the interferometer design. Although the measured resolving powers were somewhat lower than expected because of the laboratory measurement conditions, the transmission efficiencies were in approximate agreement with the design specification.

A method of determining the flatness of metal mesh elements of a far infrared Fabry-Perot interferometer

Abstract A simple and inexpensive method is described for determining the flatness of metal mesh elements of a far infrared Fabry-Perot interferometer.

Laboratory evaluation of the fabry-perot interferometers for the long wavelength spectrometer of the infrared space observatory

Abstract An optically pumped molecular laser has been used as a diagnostic tool to study the spectroscopic performance of a far infrared astronomical Fabry-Perot interferometer for the Long Wavelength Spectrometer of the Infrared Space Observatory. Experimental results are presented and, through comparison with theory, used to derive fundamental parameters of the metal mesh elements of the Fabry-Perot.