Electromagnetic and Quasi-Optical Analysis of Cavity Coupled Bolometers for Far-Infrared and Terahertz Receivers

The primary concern of this thesis is the development of theoretical and computational techniques for the modelling of cavity coupled bolometric detectors for future millimetre wave and terahertz astronomical receivers. Hypersensitive bolometer based receivers will be required to answer current open questions in astronomy concerning star and planetary formation, solar system physics as well as galaxy evolution and interaction. As part of the work for this thesis, fast and efficient Python code, GAMMA (Generalised Absorber Mode Matching Analysis), was developed and applied to existing and proposed future systems. One of the main goals of GAMMA was to analyse the performance of the proposed multimode pixel for the SAFARI instrument on the next generation SPICA terahertz space telescope. The pixels contain a free space gap between the horn and the cavity. The array of detectors will lie on a chip with an array of horns feeding them from the frontside and an array of backshort cavities behind them. The beam patterns for a SAFARI-like pixel were computed, using a direct calculation of the power absorbed by the bolometer in free space. This shows how the formalism can be used to directly calculate the power absorbed by a detector in a realistic terahertz receiver system. The impact of the various potential manufacturing tolerance levels for the feed horn on the predictions of the beam on the sky were also analysed for a millimetre-wave system. The specific example considered was the new 4 mm receiver on the Onsala Space Observatory 20 m millimetre-wave telescope. Mode matching, Gaussian Beam Mode Analysis and Physical Optics were used to determine the behaviour of the optical relay system. GAMMA was also applied to the multimode 857 and 545 GHz ESA Planck HFI channels. Agreement between previous predictions and both laboratory and in-flight measurements reported in literature was improved on

PoPSAT (Polar Precipitation SATellite)

The terrestrial water cycle is a unique system on planet Earth. It is directly influenced by our changing climate with most drastic effects in the polar regions. A main element of the water cycle is precipitation, and it is only very sparsely observed at high latitudes. We propose a new satellite mission, POPSat, to observe snow and light rain at high latitudes, as well as snowfall at mid latitudes. The satellite will be equipped with a dual band (Ka and W bands) phased array antenna radar and provide 3D information about precipitation and clouds. The horizontal resolution of 2 km will exceed all other observations, and the measurements at high latitudes, together with the capability to monitor snowfall, will complement the GPM mission’s observations. By filling this gap, POPSat will provide essential data for improving global weather and climate models

Electromagnetic and Quasi-Optical Analysis of Cavity Coupled Bolometers for Far-Infrared and Terahertz Receivers

The primary concern of this thesis is the development of theoretical and computational techniques for the modelling of cavity coupled bolometric detectors for future millimetre wave and terahertz astronomical receivers. Hypersensitive bolometer based receivers will be required to answer current open questions in astronomy concerning star and planetary formation, solar system physics as well as galaxy evolution and interaction. As part of the work for this thesis, fast and efficient Python code, GAMMA (Generalised Absorber Mode Matching Analysis), was developed and applied to existing and proposed future systems. One of the main goals of GAMMA was to analyse the performance of the proposed multimode pixel for the SAFARI instrument on the next generation SPICA terahertz space telescope. The pixels contain a free space gap between the horn and the cavity. The array of detectors will lie on a chip with an array of horns feeding them from the frontside and an array of backshort cavities behind them. The beam patterns for a SAFARI-like pixel were computed, using a direct calculation of the power absorbed by the bolometer in free space. This shows how the formalism can be used to directly calculate the power absorbed by a detector in a realistic terahertz receiver system. The impact of the various potential manufacturing tolerance levels for the feed horn on the predictions of the beam on the sky were also analysed for a millimetre-wave system. The specific example considered was the new 4 mm receiver on the Onsala Space Observatory 20 m millimetre-wave telescope. Mode matching, Gaussian Beam Mode Analysis and Physical Optics were used to determine the behaviour of the optical relay system. GAMMA was also applied to the multimode 857 and 545 GHz ESA Planck HFI channels. Agreement between previous predictions and both laboratory and in-flight measurements reported in literature was improved on

Electromagnetic and Quasi-Optical Analysis of Cavity Coupled Bolometers for Far-Infrared and Terahertz Receivers

The primary concern of this thesis is the development of theoretical and computational techniques for the modelling of cavity coupled bolometric detectors for future millimetre wave and terahertz astronomical receivers. Hypersensitive bolometer based receivers will be required to answer current open questions in astronomy concerning star and planetary formation, solar system physics as well as galaxy evolution and interaction. As part of the work for this thesis, fast and efficient Python code, GAMMA (Generalised Absorber Mode Matching Analysis), was developed and applied to existing and proposed future systems. One of the main goals of GAMMA was to analyse the performance of the proposed multimode pixel for the SAFARI instrument on the next generation SPICA terahertz space telescope. The pixels contain a free space gap between the horn and the cavity. The array of detectors will lie on a chip with an array of horns feeding them from the frontside and an array of backshort cavities behind them. The beam patterns for a SAFARI-like pixel were computed, using a direct calculation of the power absorbed by the bolometer in free space. This shows how the formalism can be used to directly calculate the power absorbed by a detector in a realistic terahertz receiver system. The impact of the various potential manufacturing tolerance levels for the feed horn on the predictions of the beam on the sky were also analysed for a millimetre-wave system. The specific example considered was the new 4 mm receiver on the Onsala Space Observatory 20 m millimetre-wave telescope. Mode matching, Gaussian Beam Mode Analysis and Physical Optics were used to determine the behaviour of the optical relay system. GAMMA was also applied to the multimode 857 and 545 GHz ESA Planck HFI channels. Agreement between previous predictions and both laboratory and in-flight measurements reported in literature was improved on

Electromagnetic and Quasi-Optical Analysis of Cavity Coupled Bolometers for Far-Infrared and Terahertz Receivers

The primary concern of this thesis is the development of theoretical and computational techniques for the modelling of cavity coupled bolometric detectors for future millimetre wave and terahertz astronomical receivers. Hypersensitive bolometer based receivers will be required to answer current open questions in astronomy concerning star and planetary formation, solar system physics as well as galaxy evolution and interaction. As part of the work for this thesis, fast and efficient Python code, GAMMA (Generalised Absorber Mode Matching Analysis), was developed and applied to existing and proposed future systems. One of the main goals of GAMMA was to analyse the performance of the proposed multimode pixel for the SAFARI instrument on the next generation SPICA terahertz space telescope. The pixels contain a free space gap between the horn and the cavity. The array of detectors will lie on a chip with an array of horns feeding them from the frontside and an array of backshort cavities behind them. The beam patterns for a SAFARI-like pixel were computed, using a direct calculation of the power absorbed by the bolometer in free space. This shows how the formalism can be used to directly calculate the power absorbed by a detector in a realistic terahertz receiver system. The impact of the various potential manufacturing tolerance levels for the feed horn on the predictions of the beam on the sky were also analysed for a millimetre-wave system. The specific example considered was the new 4 mm receiver on the Onsala Space Observatory 20 m millimetre-wave telescope. Mode matching, Gaussian Beam Mode Analysis and Physical Optics were used to determine the behaviour of the optical relay system. GAMMA was also applied to the multimode 857 and 545 GHz ESA Planck HFI channels. Agreement between previous predictions and both laboratory and in-flight measurements reported in literature was improved on

Electromagnetic and Quasi-Optical Analysis of Cavity Coupled Bolometers for Far-Infrared and Terahertz Receivers

The primary concern of this thesis is the development of theoretical and computational techniques for the modelling of cavity coupled bolometric detectors for future millimetre wave and terahertz astronomical receivers. Hypersensitive bolometer based receivers will be required to answer current open questions in astronomy concerning star and planetary formation, solar system physics as well as galaxy evolution and interaction. As part of the work for this thesis, fast and efficient Python code, GAMMA (Generalised Absorber Mode Matching Analysis), was developed and applied to existing and proposed future systems. One of the main goals of GAMMA was to analyse the performance of the proposed multimode pixel for the SAFARI instrument on the next generation SPICA terahertz space telescope. The pixels contain a free space gap between the horn and the cavity. The array of detectors will lie on a chip with an array of horns feeding them from the frontside and an array of backshort cavities behind them. The beam patterns for a SAFARI-like pixel were computed, using a direct calculation of the power absorbed by the bolometer in free space. This shows how the formalism can be used to directly calculate the power absorbed by a detector in a realistic terahertz receiver system. The impact of the various potential manufacturing tolerance levels for the feed horn on the predictions of the beam on the sky were also analysed for a millimetre-wave system. The specific example considered was the new 4 mm receiver on the Onsala Space Observatory 20 m millimetre-wave telescope. Mode matching, Gaussian Beam Mode Analysis and Physical Optics were used to determine the behaviour of the optical relay system. GAMMA was also applied to the multimode 857 and 545 GHz ESA Planck HFI channels. Agreement between previous predictions and both laboratory and in-flight measurements reported in literature was improved on

Optical design and verification of the 4mm receiver for the 20m telescope at Onsala Space Observatory

The work of this research is the design, analysis and verification of the optical performance of a 4 mm receiver channel for the 20 m telescope at Onsala Space Observatory, Onsala, Sweden. The 4 mm (75 GHz) receiver is a newly proposed channel designed to be installed parallel to the existing 3 mm (100 GHz) channel targeting new science at that longer wavelength. Gaussian beam mode analysis is used to produce the fundamental optical design of the system. The design is then analysed more accurately with the physical optics approximation. We report on the comparison of simulation and measurement and verification of the system design

Radiation patterns of multimode feed-horn-coupled bolometers for FAR-IR space applications

A multimode horn differs from a single mode horn in that it has a larger sized waveguide feeding it. Multimode horns can therefore be utilized as high efficiency feeds for bolometric detectors, providing increased throughput and sensitivity over single mode feeds, while also ensuring good control of the beam pattern characteristics. Although a cavity mounted bolometer can be modelled as a perfect black body radiator (using reciprocity in order to calculate beam patterns), nevertheless, this is an approximation. In this paper we present how this approach can be improved to actually include the cavity coupled bolometer, now modelled as a thin absorbing film. Generally, this is a big challenge for finite element software, in that the structures are typically electrically large. However, the radiation pattern of multimode horns can be more efficiently simulated using mode matching, typically with smooth-walled waveguide modes as the basis and computing an overall scattering matrix for the horn-waveguide-cavity system. Another issue on the optical efficiency of the detectors is the presence of any free space gaps, through which power can escape. This is best dealt with treating the system as an absorber. Appropriate reflection and transmission matrices can be determined for the cavity using the natural eigenfields of the bolometer cavity system. We discuss how the approach can be applied to proposed terahertz systems, and also present results on how the approach was applied to improve beam pattern predictions on the sky for the multi-mode HFI 857GHz channel on Planck

Optical modelling and analysis of the Q and U bolometric interferometer for cosmology

Remnant radiation from the early universe, known as the Cosmic Microwave Background (CMB), has been redshifted and cooled, and today has a blackbody spectrum peaking at millimetre wavelengths. The QUBIC (Q&U Bolometric Interferometer for Cosmology) instrument is designed to map the very faint polaristion structure in the CMB. QUBIC is based on the novel concept of bolometric interferometry in conjunction with synthetic imaging. It will have a large array of input feedhorns, which creates a large number of interferometric baselines. The beam from each feedhorn is passed through an optical combiner, with an off-axis compensated Gregorian design, to allow the generation of the synthetic image. The optical-combiner will operate in two frequency bands (150 and 220 GHz with 25% and 18.2 % bandwidth respectively) while cryogenically cooled TES bolometers provide the sensitivity required at the image plane. The QUBIC Technical Demonstrator (TD), a proof of technology instrument that contains 64 input feed-horns, is currently being built and will be installed in the Alto Chorrillos region of Argentina. The plan is then for the full QUBIC instrument (400 feed-horns) to be deployed in Argentina and obtain cosmologically significant results. In this paper we will examine the output of the manufactered feed-horns in comparison to the nominal design. We will show the results of optical modelling that has been performed in anticipation of alignment and calibration of the TD in Paris, in particular testing the validity of real laboratory environments. We show the output of large calibrator sources (50 ° full width haf max Gaussian beams) and the importance of accurate mirror definitions when modelling large beams. Finally we describe the tolerance on errors of the position and orientation of mirrors in the optical combiner