John Anthony Murphy

SCUBA: A common-user submillimetre camera operating on the James Clerk Maxwell Telescope

SCUBA, the Submillimetre Common-User Bolometer Array, built by the Royal Observatory Edinburgh for the James Clerk Maxwell Telescope, is the most versatile and powerful of a new generation of submillimetre cameras. It combines a sensitive dual-waveband imaging array with a three-band photometer, and is sky-background-limited by the emission from the Mauna Kea atmosphere at all observing wavelengths from 350 μμto 2 mm. The increased sensitivity and array size mean that SCUBA maps close to 10 000 times faster than its single-pixel predecessor (UKT14). SCUBA is a facility instrument, open to the world community of users, and is provided with a high level of user support. We give an overview of the instrument, describe the observing modes, user interface and performance figures on the telescope, and present a sample of the exciting new results that have revolutionized submillimetre astronomy.

Second and Third Season QUaD Cosmic Microwave Background Temperature and Polarization Power Spectra

We report results from the second and third seasons of observation with the QUaD experiment. Angular power spectra of the cosmic microwave background are derived for both temperature and polarization at both 100 GHz and 150 GHz, and as cross-frequency spectra. All spectra are subjected to an extensive set of jackknife tests to probe for possible systematic contamination. For the implemented data cuts and processing technique such contamination is undetectable. We analyze the difference map formed between the 100 and 150 GHz bands and find no evidence of foreground contamination in polarization. The spectra are then combined to form a single set of results which are shown to be consistent with the prevailing LCDM model. The sensitivity of the polarization results is considerably better than that of any previous experiment—for the first time multiple acoustic peaks are detected in the E-mode power spectrum at high significance.

Medical applications of terahertz imaging: a review of current technology and potential applications in biomedical engineering

Terahertz (THz) imaging is in its early stages of development but already the potential clinical impact of this new imaging modality is clear. From cancer research to DNA analysis THz technology is improving or even making possible imaging of hitherto inaccessible phenomena. In this paper we present a short review of THz imaging from the point of view of biomedical engineering. We discuss the current state of the art in terms of THz imaging systems; describe current applications, future potential and our own approaches to harnessing this novel technology. We draw attention to open problems in the area with respect to the limitations of the technology before concluding with descriptions of our future work in the area.

First Season QUaD CMB Temperature and Polarization Power Spectra

QUaD is a bolometric CMB polarimeter sited at the South Pole, operating at frequencies of 100 and 150 GHz. In this paper we report preliminary results from the first season of operation (austral winter 2005). All six CMB power spectra are presented derived as cross spectra between the 100 and 150 GHz maps using 67 days of observation in a low foreground region of approximately 60 deg2. These data are a small fraction of the data acquired to date. The measured spectra are consistent with the ΛCDM cosmological model. We perform jackknife tests that indicate that the observed signal has negligible contamination from instrumental systematics. In addition, by using a frequency jackknife we find no evidence for foreground contamination.

Small Angular Scale Measurements of the Cosmic Microwave Background Temperature Power Spectrum From QUaD

We present measurements of the cosmic microwave background (CMB) radiation temperature anisotropy in the multipole range 2000 < l < 3000 from the QUaD telescopes second and third observing seasons. After masking the brightest point sources our results are consistent with the primary ΛCDM expectation alone. We estimate the contribution of residual (un-masked) radio point sources using a model calibrated to our own bright source observations, and a full simulation of the source finding and masking procedure. Including this contribution slightly improves the χ^2. We also fit a standard Sunyaev-Zeldovich (SZ) template to the bandpowers and see no strong evidence of an SZ contribution, which is as expected for σ_8 ≈ 0.8.

Scientific optimization of a ground-based CMB polarization experiment

We investigate the science goals achievable with the upcoming generation of ground-based cosmic microwave background polarization experiments, focusing on one particular experiment, QUaD [QUEST (Q and U Extragalactic Submillimetre Telescope) and DASI (Degree Angular Scale Interferometer)], a proposed bolometric polarimeter operating from the South Pole. We calculate the optimal sky coverage for this experiment, including the effects of foregrounds and gravitational lensing. We find that an E-mode measurement will be sample-limited, whereas a B-mode measurement will be detector-noise-limited. We conclude that a 300 deg2 survey is an optimal compromise for a 2-yr experiment to measure both E and B modes, and that a ground-based polarization experiment can make an important contribution to B-mode surveys. QUaD can make a high significance measurement of the acoustic peaks in the E-mode spectrum, over a multipole range of 25 < ? < 2500, and will be able to detect the gravitational lensing signal in the B-mode spectrum. Such an experiment could also directly detect the gravitational wave component of the B-mode spectrum if the amplitude of the signal is close to current upper limits. We also investigate how QUaD can improve constraints on the cosmological parameters. We estimate that combining two years of QUaD data with the 4-yr Wilkinson Microwave Anisotropy Probe (WMAP) data can improve constraints on ?bh2, ?mh2, h, r and ns by a factor of 2. If the foreground contamination can be reduced, the measurement of r can be improved by up to a factor of 6 over that obtainable from WMAP alone. These improved accuracies will place strong constraints on the potential of the inflaton field.

Shaped corrugated horns for cosmic microwave background anisotropy measurements

Novel corrugated horn have been modelled, manufactured and measured which give low-sidelobe patterns required by CMB Anisotropy experiments. These horns have a Back-to-Back structure with mode filtering at their centres. They are corrugated to give axial symmetric low-sidelobe patterns, profiled to reduce their length, and have a Gaussian flare at their entrance apertures to further suppress sidelobes to -40dB. Modelling and experimental results show excellent agreement to well below 50 dB.

COSMOLOGICAL PARAMETERS FROM THE QUAD CMB POLARIZATION EXPERIMENT

In this paper, we present a parameter estimation analysis of the polarization and temperature power spectra from the second and third season of observations with the QUaD experiment. QUaD has for the first time detected multiple acoustic peaks in the E-mode polarization spectrum with high significance. Although QUaD-only parameter constraints are not competitive with previous results for the standard six-parameter ΛCDM cosmology, they do allow meaningful polarization-only parameter analyses for the first time. In a standard six-parameter ΛCDM analysis, we find the QUaD TT power spectrum to be in good agreement with previous results. However, the QUaD polarization data show some tension with ΛCDM. The origin of this 1σ-2σ tension remains unclear, and may point to new physics, residual systematics, or simple random chance. We also combine QUaD with the five-year WMAP data set and the SDSS luminous red galaxies 4th data release power spectrum, and extend our analysis to constrain individual isocurvature mode fractions, constraining cold dark matter density, αcdmi < 0.11 (95% confidence limit (CL)), neutrino density, αndi < 0.26 (95% CL), and neutrino velocity, αnvi < 0.23 (95% CL), modes. Our analysis sets a benchmark for future polarization experiments.

Gaussian beam mode analysis of standing waves between two coupled corrugated horns

In this paper we present the theoretical analysis of the effects of standing waves between coupled horn antennas that can occur in terahertz quasi-optical systems. In particular we illustrate the approach for the case of two coupled horn antennas as the distance between them is varied. The full mode matching scattering matrix approach is based on combining a standard waveguide mode description of the horn antenna and a quasi-optical Gaussian beam description of the free space propagation. Track is kept of both the backward and forward going components of the propagating fields. We compare theoretical predictions with actual experimental test results for a quasi-optical system operating at a frequency of 0.480 THz.

Fast Physical Optics Simulations of the Multi-Beam Dual-Reflector Submillimeter-Wave Telescope on the ESA PLANCK Surveyor

We present physical optics simulations of the multi-beam dual-reflector submillimeter-wave telescope on the ESA PLANCK surveyor designed for measuring the temperature anisotropies and polarization characteristics of the cosmic microwave background. The telescope is of a non-conventional Gregorian configuration, with two ellipsoidal reflectors providing a very large field of view at the focal plane where the array of 76 horn antennas feeding low-temperature detectors is located. We analyse the defocusing effects of the system, the polarization properties of the telescope, and the optical performance of the high-frequency channels based on special multi-moded horns operating at 545 and 857 GHz.