Mr. George Saklatvala Profile

George Saklatvala

at Univ of Cambridge

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Publications (3)

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Proceedings Article | 27 June 2006 Paper

Optical physics of imaging and interferometric phased arrays

Stafford Withington, George Saklatvala, Michael Hobson

Proceedings Volume 6275, 62750Q (2006) https://doi.org/10.1117/12.669509

KEYWORDS: Phased arrays, Interferometry, Interferometers, Sensors, Telescopes, Antennas, Imaging arrays, Astronomy, Scattering, Phased array optics

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Microwave, submillimetre-wave, and far-infrared phased arrays are of considerable importance for astronomy. We consider the behaviour imaging phased arrays and interferometric phased arrays from a functional perspective. It is shown that the average powers, field correlations, power fluctuations, and correlations between power fluctuations at the output ports of an imaging or interferometric phased array can be found once the synthesised reception patterns are known. The reception patterns do not have to be orthogonal or even linearly independent. It is shown that the operation of phased arrays is intimately related to the mathematical theory of frames, and that the theory of frames can be used to determine the degree to which any class of intensity or field distribution can be reconstructed unambiguously from the complex amplitudes of the travelling waves at the output ports. The theory can be used to set up a likelihood function that can, through Fisher information, be used to determine the degree to which a phased array can be used to recover the parameters of a parameterised source. For example, it would be possible to explore the way in which a system, perhaps interferometric, might observe two widely separated regions of the sky simultaneously.

Proceedings Article | 27 June 2006 Paper

Simulations of multimode bolometric interferometers

George Saklatvala, Michael Hobson, Stafford Withington

Proceedings Volume 6275, 62750R (2006) https://doi.org/10.1117/12.671879

KEYWORDS: Interferometers, Telescopes, Sensors, Space telescopes, Interferometry, Bolometers, Michelson interferometers, Modeling, Signal to noise ratio, Fizeau interferometers

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We describe a modal theory of interferometry, suitable for the modelling of multimode bolometric interferometers, and present the first simulations of such an interferometer. The motivation for the work is the wish to combine the low noise properties of bolometers with aperture synthesis techniques to design far-infrared and sub-mm interferometers, without the need for single-mode components that restrict the power throughput and therefore reduce the signal to noise ratio. The analysis of such interferometers has proved impossible in the past because optical systems at sub-mm wavelengths are partially coherent, and bolometers respond not only to the intensity but also to the correlations in the field. In order to assess the viability of bolometric interferometers, we therefore require a multimode theory of interferometry. We show that the appropriate modes for describing an interferometer are the Hilbert-Schmidt decompositions of the kernels of the integral operators describing the individual telescopes, and demonstrate that these modes provide both a clear conceptual understanding of the operation of an interferometer and an extremely fast method of computation. We present simulations of idealized Michelson and Fizeau interferometers, and show that the normal behaviour of such interferometers is recovered. We show simulated sources, and dirty maps obtained from uv data for a simulated Michelson interferometer. We discuss the application of the theory to real instrument design.

Proceedings Article | 27 June 2006 Paper

A coupled-mode theory for infrared and submillimeter wave detectors

George Saklatvala, Stafford Withington, Michael Hobson

Proceedings Volume 6275, 62750W (2006) https://doi.org/10.1117/12.671942

KEYWORDS: Sensors, Signal to noise ratio, Imaging arrays, Polarization, Modeling, Signal detection, Infrared sensors, Systems modeling, Scattering, Lithium

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We present a new theory for the description of detectors in terms of modes. Although the theory is very general, it is expected to be of particular use in the modelling of far-infrared and submillimeter instruments. Such a theory is needed because at far-infrared frequencies, both optical systems and detectors show partially coherent behaviour. That is to say, even when the instrument is illuminated by an incoherent source, the resultant field at the detector is partially coherent, and the detector itself is sensitive to the coherence properties of the field and not just the intensity. We have previously developed a modal description of optical systems at far-infrared wavelengths; here we describe a modal theory for the detectors themselves. The theories can be combined to provide a complete modal description of far-infrared instruments. The theory presented here applies equally well to pulsed or ergodic radiation, and incorporates polarisation effects. We also show how the statistics of the detector output can be determined from the theory. This is important for instruments such as bolometers, where the internal noise of the detector is very low, and either sky noise or radiation from the optical components dominate. We illustrate our work with a number of simulations, showing signal to noise ratios for different detector types, and we show how how the theory may be applied to the array packing density problem.

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