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One of the instruments on board the Herschel Space Observatory is the Spectral and Photometric Imaging Receiver (SPIRE). SPIRE employs a Fourier transform spectrometer with feed-horn-coupled bolometers to provide imaging spectroscopy. To interpret the resultant spectral images requires knowledge of the wavelength-dependent beam, which in the case of SPIRE is complicated by the use of multimoded feed horns. In this paper we describe a series of observations and the analysis conducted to determine the wavelength dependence of the SPIRE spectrometer beam profile.

An optical alignment tool is described, which acts like an optical tee to produce two collinear beams whose direction can be adjusted. The device can be used to align optica subsystems.

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 humidity-dependent birefringence in a poly(methyl methacrylate) waveguide has been observed. This dependence was determined by coupling both a transverse electric and a transverse magnetic mode into a waveguide and then measuring the relative phase at the output. With this method, values for δ(TM) - δ9(TE) were found within the range of 5-90% relative humidity (RH). From the obtained data, Δ(n(TE) - n(TM))/ΔRH as a function of humidity was calculated and plotted.

A numerical method for eliminating channel spectra from data obtained with a bandlimited infrared Fourier transform spectrometer is developed. The method is compared with others in common use on a synthetic model spectrum.

A method is presented for using a Fourier transform spectrometer (FTS) to calibrate the metrology of a second FTS. This technique is particularly useful when the second FTS is inside a cryostat or otherwise inaccessible.

A novel instrument has been designed to measure the nighttime atmospheric water vapor column abundance by near-infrared absorption spectrophotometry of the Moon. The instrument provides a simple, effective, portable, and inexpensive means of rapidly measuring the water vapor content along the lunar line of sight. Moreover, the instrument is relatively insensitive to the atmospheric model used and, thus, serves to provide an independent calibration for other measures of precipitable water vapor from both ground- and space-based platforms.

We present a simple, inexpensive, and effective method of applying antireflection coatings to zinc selenide windows designed to operate in the thermal infrared wavelength region.

A simple, compact and inexpensive optical system is described which allows the dihedral angle of a roof-top mirror to be measured accurately. The system fits on a desktop and can be used to set and monitor the dihedral angle of the mirror. The ability to make adjustments while monitoring the angle is particularly useful when epoxy is used to secure the two plane mirrors that form the roof-top, since epoxy will tend to shrink as it cures.

A thermally induced birefringence in a poly(methyl methacrylate) waveguide has been observed. From polarization measurements made at the output of a waveguide in the range 20-60 degrees C, a value for Delta(n(TE) - n(TM))/DeltaT of 1.1 x 10(-6) degrees C(-1) has been calculated. After waveguide preparation the underlying substrate was found to have a bow. By measuring changes in the bow caused by temperature in the range 20-60 degrees , we have calculated a value for the change in stress in the polymethyl methacrylate film of 0.18 MPa/ degrees C. By relating polarization to stress, changes in stress as small as 90 kPa can be measured.

A new design for fabricating low-loss ridge waveguides by anisotropically etching two parallel V-grooves on a silicon substrate is proposed and demonstrated. Polymethyl methacrylate is used as the waveguide medium, with silicon dioxide and air as the lower and upper cladding, respectively. Because of the smooth sidewalls of the ridge structure, transverse confinement within the double V-groove ridge waveguide, with scattering losses of ~ 1.0 dB/cm are observed.