Research Interests

I am involved with various projects in the field of submillimetre astronomy. Please follow the links on the left for more detailed information on specific projects.

1. Fourier Transform Spectroscopy

Based on early work in baloon-bourne FTS research, a variety of imaging and single-pixel FTS systems have been built in the group for lab spectroscopy and ground-based astronomy, covering wavelengths of ~20 to 2000 microns, with Michelson, Martin-Puplett (MP), and Mach-Zehnder (MZ) configurations. A polarizing MP instrument operated at the James Clerk Maxwell Telescope (JCMT) from 1991 to 2000, followed by a MZ instrument which operated until 2008. These instruments were successfully used for measurements of atmospheric gases, solar physics, planetary atmospheres, and galactic and extragalactic astronomy. The MZ spectrometer was built using the same basic design as the Herschel-SPIRE instrument, and its use both at the JCMT and at the U of L labs enabled the novel SPIRE beamsplitters to be tested. The SPIRE data reduction software written by the group was based on experience gained with this instrument. Also part of the CSA contract for participation in the SPIRE mission was the construction of an FTS for testing of the SPIRE spectrometer flight model. This instrument was built in the U of L labs and delivered to Rutherford Appleton Laboratory in the UK for flight model instrument verification tests between 2005 and 2007. Simultaneously, the group has also been involved with the SCUBA-2 imaging FTS project, beginning in 2002. This MZ instrument, also sharing the basic SPIRE design, was designed, built and tested in the U of L labs and delivered to the JCMT in 2010 where it is currently being commissioned. The group is also involved in the preliminary development phases of the SAFARI instrument for the proposed ESA SPICA mission, where it is providing cryogenic test facilities for detector and translation stage testing. The SPIRE, SCUBA-2 FTS, and SAFARI instruments represent the first large format imaging Fourier spectrometers for submillimetre astronomy.

2. Atmospheric Water Vapour Measurement

Atmospheric water vapour is the dominant cause of degradation in long wavelength astronomical signals measured from the ground, due to absorption, emission and phase distortion. An understanding of the spectroscopic properties of atmospheric water vapour is required for correction of data collected by ground based instruments, and the group has been involved in the development of radiative transfer models and radiometer instruments for this purpose.
Large arrays of telescopes operating in the submillimetre and millimetre wavelength ranges are currently under development. As each telescope in such an observatory looks through a different column of the atmosphere, non-uniform distribution of water vapour in space and time creates different phase delays in the astronomical signal for each telescope. By measuring the amount of water vapour in the path between each telescope and the source on short timescales (1 second or less), the measured signals can be corrected for the path change due to the water vapour in order to sharpen the image. Each telescope will therefore require a water vapour radiometer. Our group has developed an Infrared Radiometer for Millimetre Astronomy (IRMA) that provides the fast and accurate measurements of atmospheric water vapour required for such telescopes.

3. Far-IR Bolometers

The bolometer is the detector of choice for broadband far-IR and submillimeter photometers and FTS spectrometers. Our group and collaborators have designed, built and operated some of the most sensitive bolometer systems in existence at these wavelength ranges. Traditionally, bolometers have been hand-built in small quatities using a composite design of thermally isolated radiation absorbers coupled to small semiconductor thermistors. The state of the art is now moving towards superconducting transition edge sensors (TES) and kinetic inductance detectors (KID) operating below 0.1 K, which have orders of magnitude higher sensitivity than earlier composite bolometers and lend themselves to lithographic fabrication in dense arrays. We are currently fabricating TES devices which, while they have much lower sensitivities than required by current space-bourne applications, can be operated at 4K using much simpler closed-cycle liquid cryogen-free coolers.