colm bracken

Multimode horn antennas can be utilized as high efficiency feeds for bolometric detectors, providing increased throughput and sensitivity over single mode feeds, while also ensuring good control of beam pattern characteristics. Multimode horns were employed in the highest frequency channels of the European Space Agency Planck Telescope, and have been proposed for future terahertz instrumentation, such as SAFARI for SPICA. The radiation pattern of a multimode horn is affected by the details of the coupling of the higher order waveguide modes to the bolometer making the modeling more complicated than in the case of a single mode system. A typical cavity coupled bolometer system can be most 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 that includes the power absorption by the absorber. In this paper we present how to include a cavity coupled bolometer, modelled as a thin absorbing film with particular interest in investigating the cavity configuration for optimizing power absorption. As an example, the possible improvements from offsetting the axis of a cylindrically symmetric absorbing cavity from that of a circular waveguide feeding it (thus trapping more power in the cavity) are discussed. Another issue is the effect on the optical efficiency of the detectors of the presence of any gaps, through which power can escape. To model these effects required that existing in-house mode matching software, which calculates the scattering matrices for axially symmetric waveguide structures, be extended to be able to handle offset junctions and free space gaps. As part of this process the complete software code 'PySCATTER' was developed in Python. The approach can be applied to proposed terahertz systems, such as SPICASAFARI.

The next generation of space missions targeting far-infrared wavelengths will require large-format arrays of extremely sensitive detectors. The development of Transition Edge Sensor (TES) array technology is being developed for future Far-Infrared (FIR) space applications such as the SAFARI instrument for SPICA where low-noise and high sensitivity is required to achieve ambitious science goals. In this paper we describe a modal analysis of multi-moded horn antennas feeding integrating cavities housing TES detectors with superconducting film absorbers. In high sensitivity TES detector technology the ability to control the electromagnetic and thermo-mechanical environment of the detector is critical. Simulating and understanding optical behaviour of such detectors at far IR wavelengths is difficult and requires development of existing analysis tools. The proposed modal approach offers a computationally efficient technique to describe the partial coherent response of the full pixel in terms of optical efficiency and power leakage between pixels. Initial wok carried out as part of an ESA technical research project on optical analysis is described and a prototype SAFARI pixel design is analyzed where the optical coupling between the incoming field and the pixel containing horn, cavity with an air gap, and thin absorber layer are all included in the model to allow a comprehensive optical characterization. The modal approach described is based on the mode matching technique where the horn and cavity are described in the traditional way while a technique to include the absorber was developed. Radiation leakage between pixels is also included making this a powerful analysis tool.

C. Bracken, 2 J.R. Hance, ∗ and S. Hossenfelder Dept of Experimental Physics, Maynooth University, Maynooth, Co. Kildare, Ireland Astronomy & Astrophysics Section, School of Cosmic Physics, Dublin Institute for Advanced Studies, Fitzwilliam Place, Dublin 2, D02 XF86 Quantum Engineering Technology Laboratories, Department of Electrical and Electronic Engineering, University of Bristol, Woodland Road, Bristol, BS8 1US, UK Frankfurt Institute for Advanced Studies, Ruth-Moufang-Str. 1, D-60438 Frankfurt am Main, Germany (Dated: December 2, 2021)

C. Bracken,1, 2 J.R. Hance,3, ∗ and S. Hossenfelder4 Dept of Experimental Physics, Maynooth University, Maynooth, Co. Kildare, Ireland Astronomy & Astrophysics Section, School of Cosmic Physics, Dublin Institute for Advanced Studies, Fitzwilliam Place, Dublin 2, D02 XF86 Quantum Engineering Technology Laboratories, Department of Electrical and Electronic Engineering, University of Bristol, Woodland Road, Bristol, BS8 1US, UK Frankfurt Institute for Advanced Studies, Ruth-Moufang-Str. 1, D-60438 Frankfurt am Main, Germany (Dated: November 19, 2021)

This thesis focuses on EM (electromagnetic) modelling methods for simulating the behaviour of receivers and detectors for far-IR (far-infrared) astronomy and CMB (cosmic microwave background) applications, toward an optimum design for SAFARI (the Spica Far-Infrared Instrument) on the proposed space based telescope SPICA (Space Infrared Telescope for Cosmology and Astrophysics). The computational methods required for modelling SAFARI-like receivers are described, and sophisticated conical waveguide mode matching theory is derived. Generic far-IR systems are investigated, including analysis of SAFARI-like multi-mode feed horns, and the absorber coupled superconducting TES (transition edge sensor) bolometers that are typically used in far-IR receivers. Special attention is given to the integrating cavity backshorts that serve to increase pixel efficiency, and new designs for improved cavity geometries, which provide high coupling between the detector and the incoming signal while reduc...

In the absence of 50 m class space-based observatories, sub-arc-second astronomy spanning the full far-infrared wavelength range will require space-based long-baseline interferometry. The long baselines of up to 10’s of meteres are necessary to achieve sub arcsecond resolution demanded by the science goals. Also, practical observing times command a field of view toward an arc minute or so, not achievable with a single on-axis coherent detector. This paper is concerned with an application of an end-to-end instrument simulator PyFIInS, developed as part of the FISICA project under funding from the European Commission’s 7th Framework Programme for Research and Technological Development (FP7). Predicted results of wide field of view spatio-spectral interferometry through simulations of a long-baseline, double-Fourier, far-infrared interferometer concept are presented and analysed. It is shown how such an interferometer, illuminated by a multimode detector can recover a large field of vi...

Microwave Kinetic Inductance Detector (MKID) arrays are currently being developed and deployed for astronomical applications in the visible and near infrared and for sub-millimetre astronomy. One of the main challenges of MKIDs is that large arrays would exhibit a pixel yield, defined as the percentage of individually distinguishable pixels to the total number of pixels, of 75 80 %.1 Imperfections arising during the fabrication can induce an uncontrolled shift in the resonance frequency of individual resonators which end up resonating at the same frequency of a different resonator. This makes a number of pixels indistinguishable and therefore unusable for imaging. This paper proposes an approach to individually re-tune the colliding resonators in order to remove the degeneracy and increase the number of MKIDs with unique resonant frequencies. The frequency re-tuning is achieved through a DC bias of the resonator since the kinetic inductance of a superconducting thin film is current ...

Bolometric integrating cavities have been used with great success in previous far-infrared space missions, and are planned for extensive use in future missions where ever increasing sensitivity is required. It is critical for the purposes of design and the interpretation of results that these systems are thoroughly understood and optically characterised fully. Such systems, for manufacturing and mechanical reasons, may contain free space gaps between the feed horn antenna and the integrating cavity, and so it is necessary to include the effect of these waveguide openings in simulations. Since these pixels are electrically large, it is more feasible to model them by using the computationally efficient mode-matching approach. In this paper we discuss the elements required to model such pixels within the mode-matching approach and apply it to a typical pixel containing a free space gap, based on an experimental Transition Edge Sensor (TES) cavity waveguide pixel at SRON Groningen.

We discuss issues associated with diffraction effects in far-infared space interferometers, particularly wide field spacio-spectral space interferometers now being proposed. We present examples of the application of various useful quasi-optical approaches in such instruments.

At DIAS, in collaboration with Trinity College Dublin, we are developing visible and near-infrared Microwave Kinetic Inductance Detectors (MKIDs) for astronomical applications. By designing an array of MKIDs with different resonant frequencies, an array of thousands of detectors can be readout with inherent frequency domain multiplexing (FDM). The Xilinx ZCU111 Radio Frequency System on Chip (RFSoC) Evaluation Kit is a very promising option not only for Microwave Kinetic Inductance Detector (MKID) readout systems, but also for any application relying on frequency domain multiplexing. The board's on-chip data converters provide ample bandwidth for reading out up to 8,000 MKID resonators, with 2 MHz spacing, at a 1 MHz pixel sampling rate. Without additional resources, we roughly estimate the ZCU111’s field programmable gate array (FPGA) can analyse ~ 4,000 MKID pixels, at a cost of about €4.75 per pixel. We present initial progress from developing firmware for this MKID readout s...

M. Costa (1), T. Nordheim (2), L. Provinciali (3), J. Feng (4), S. Gasc (5), T. Hilbig (6), C. Johnson (7), F. B. Lisboa (8), A. Maier (9), D. E. Morosan (10), A. Morschhauser (11), C. Norgren (12), J. Oliveira (13), L. Salvador (14) (1) Technical University of Madrid, Madrid, Spain, (2) University College London, London, United Kingdom, (3) University of Pisa, Pisa, Italy, (4) Technology University of Delft, Delft, Netherlands, (5) University of Bern, Bern, Switzerland, (6) Thuringer Landessternwarte Tautenburg, Tautenburg, Germany, (7) Aberystwyth University, Ceredigion, United Kingdom, (8) University of Lisbon, Lisbon, Portugal, (9) Austrian Academy of Sciences, Space Research Institute, Graz, Austria, (10) Trinity College Dublin, Dublin, Ireland, (11) DLR, Berlin, Germany, (12) Uppsala University, Uppsala, Sweden, (13) Laboratoire de Planetologie et Geodynamique de Nantes, Nantes, France, (14) University of Liege, Liege, Belgium. (marc.costa@sciops.esa.int / Fax: +34-918131325)

The next generation of space missions targeting far-infrared wavelengths will require large-format arrays of extremely sensitive detectors. The development of Transition Edge Sensor (TES) array technology is being developed for future Far-Infrared (FIR) space applications such as the SAFARI instrument for SPICA where low-noise and high sensitivity is required to achieve ambitious science goals. In this paper we describe a modal analysis of multi-moded horn antennas feeding integrating cavities housing TES detectors with superconducting film absorbers. In high sensitivity TES detector technology the ability to control the electromagnetic and thermo-mechanical environment of the detector is critical. Simulating and understanding optical behaviour of such detectors at far IR wavelengths is difficult and requires development of existing analysis tools. The proposed modal approach offers a computationally efficient technique to describe the partial coherent response of the full pixel in ...

Abstract In order to investigate the formation and evolution of galaxies, stars and planetary systems, it is necessary to carry out astronomical observations in the far-infrared portion of the electromagnetic spectrum. Missions such as the Herschel Space Observatory (European Space Agency) have already completed observations in this region with great success. Proposed high resolution spectrometer instruments such as SAFARI (a joined European/Japanese (ESA/JAXA) proposal as part of the SPICA mission), aim to build upon the work of previous missions by carrying out observations in the 1.5–10 THz band with unprecedented levels of sensitivity. Spica (SPace Infrared telescope for Cosmology and Astrophysics) is currently a candidate mission as part of ESA’s Cosmic Vision 2015–2025. Future far-IR missions must realise higher levels of sensitivity, limited only by the cosmic microwave background. One solution in achieving these sensitivity goals is to use waveguide coupled Transition Edge Sensor (TES) detectors, arranged in a densely packed focal plane. Additionally, multi-mode pixels can be used in order to maximise the optical throughput and coupling while still defining a definite beam shape. For the SAFARI instrument multimoded horns coupling into integrating waveguide cavities that house the TES detectors and associated absorbing layer are envisioned. This represents a significant technological challenge in terms of accurate manufacture tolerances relative to the short wavelength, however in the case of the SAFARI instrument pixel much work has already been carried out, with prototype pixels having undergone extensive testing at SRON (Space Research Organisation of the Netherlands) Groningen. In order to fully characterise the experimental results, it is necessary also to carry out comprehensive electromagnetic modelling of these structures which is also computationally intensive and requires novel approaches. These waveguide structures (horn and cavity) are typically electrically large however, and so analysis techniques using commercial finite element software prove inefficient (particularly as the structures are multimoded). The mode-matching technique with new analytical features offer a computationally efficient and reliable alternative to full electromagnetic solvers, and in this paper we outline the additions to this technique that were necessary in order to allow typical SAFARI far-infrared pixels to be modeled, including the complete optical coupling calculation of the measurement test setup at SRON and the inclusion of the free space gap within the horn antenna and the integrating cavity. Optical coupling efficiencies simulated using this developed technique show excellent agreement with the experimental measurements.

Multimode horn antennas can be utilized as high efficiency feeds for bolometric detectors, providing increased throughput and sensitivity over single mode feeds, while also ensuring good control of beam pattern characteristics. Multimode horns were employed in the highest frequency channels of the European Space Agency Planck Telescope, and have been proposed for future terahertz instrumentation, such as SAFARI for SPICA. The radiation pattern of a multimode horn is affected by the details of the coupling of the higher order waveguide modes to the bolometer making the modeling more complicated than in the case of a single mode system. A typical cavity coupled bolometer system can be most 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 that includes the power absorption by the absorber. In this paper we present how to include a cavity coupled bolometer, modelled as a thin absorbing film with particular interest in investigating the cavity configuration for optimizing power absorption. As an example, the possible improvements from offsetting the axis of a cylindrically symmetric absorbing cavity from that of a circular waveguide feeding it (thus trapping more power in the cavity) are discussed. Another issue is the effect on the optical efficiency of the detectors of the presence of any gaps, through which power can escape. To model these effects required that existing in-house mode matching software, which calculates the scattering matrices for axially symmetric waveguide structures, be extended to be able to handle offset junctions and free space gaps. As part of this process the complete software code 'PySCATTER' was developed in Python. The approach can be applied to proposed terahertz systems, such as SPICASAFARI.

In this paper I will describe work done as part of an EU-funded project ‘Far-infrared space interferometer critical assessment’ (FISICA). The aim of the project is to investigate science objectives and technology development required for the next generation THz space interferometer. The THz/FIR is precisely the spectral region where most of the energy from stars, exo-planetary systems and galaxy clusters deep in space is emitted. The atmosphere is almost completely opaque in the wave-band of interest so any observation that requires high quality data must be performed with a space-born instrument. A space-borne far infrared interferometer will be able to answer a variety of crucial astrophysical questions such as how do planets and stars form, what is the energy engine of most galaxies and how common are the molecule building blocks of life. The FISICA team have proposed a novel instrument based on a double Fourier interferometer that is designed to resolve the light from an extended scene, spectrally and spatially. A laboratory prototype spectral-spatial interferometer has been constructed to demonstrate the feasibility of the double-Fourier technique at far infrared wavelengths (0.15 - 1 THz). This demonstrator is being used to investigate and validate important design features and data-processing methods for future instruments. Using electromagnetic modelling techniques several issues related to its operation at long baselines and wavelengths, such as diffraction, have been investigated. These are critical to the design of the concept instrument and the laboratory testbed.

ABSTRACT The planet Uranus is one of two ice giants in the solar system, both of which have only been visited only once by the Voyager 2 spacecraft. Therefore, a dedicated mission to an ice giant is crucial to deepen our knowledge of the formation, evolution and current characteristics of such a planet and its system. We present the science objectives, architecture rationale and system design for a mission to the Uranian system. We conducted a detailed study on how to best fulfill the primary science goal, namely: To investigate Uranus and its system as an archetype for ice giants. To this end, we formulated specific science questions leading to measurement requirements and, finally, instrument requirements and suitable instruments. The primary science questions relate to investigating Uranus' deep interior and outer layers as these are directly related to the primary science goal. Additionally, investigations of the moons, rings and the magnetosphere will provide complementary observations of the Uranian system specifically and icy giants in general. A trade-off between several mission architectures was performed, such as an orbiter with an atmospheric entry probe and a flyby mission. In this process, the relative importance of the science questions, the capabilities of each concept to carry a certain payload and its capability to answer the science questions in the given architecture were traded off. Similarly, the feasibility of each concept from an engineering point-of-view was assessed, taking into account matters such as complexity, cost and risk. The results are presented as a function of relative engineering and science score weights, providing an envelope of optimal mission selections over a range of mission scenarios. We conclude that a Uranus orbiter with a single entry probe and an extended moon tour fulfills the primary science goal in an optimal manner. The mission scenario is based on a launch date in 2026 on an Ariane 5 ECA launcher and arrival at Uranus in 2044 using conventional high-thrust systems. The first two years of the mission are dedicated to observations of Uranus. In this phase, the periapsis is very close to Uranus and the apoapsis is outside the bow shock, specifically for performing magnetospheric studies. Subsequently, the periapsis is raised allowing for a nominal nine flybys for each of Uranus' largest moons. Dry mass in Uranus orbit is 2052 kg taking into account both system and subsystem margins. The probe's mass (350 kg), however, is not included. The spacecraft will be powered by four Advanced Stirling Radioisotope Generators (ASRGs) which are currently under development. A set of batteries is included, capable of covering the loss of one ASRG through the peak power phase. It will have about a 100 Gbit data storage capacity for optimizing the science return through careful selection of transmitted data. Data transmission is performed by a 3.5m high gain antenna transmitting in X-band for communications and Ka-band for tracking. Possibilities exist for mission extension at the final orbit which crosses the orbit of the moon Oberon, to extend even further the science return about this ice giant from the proposed mission.

Astronomical observations in the far-infrared are critical for investigation of cosmic microwave background (CMB) radiation and the formation and evolution of planets, stars and galaxies. In the case of space telescope receivers a strong heritage exists for corrugated horn antenna feeds to couple the far-infrared signals to the detectors mounted in a waveguide or cavity structure. Such antenna feeds have been utilized, for example, in the Planck satellite in both single-mode channels for the observation of the CMB and the multi-mode channels optimized for the detection of foreground sources. Looking to the demands of the future space missions, it is clear that the development of new technology solutions for the optimization and simplification of horn antenna structures will be required for large arrays. Horn antennas will continue to offer excellent control of beam and polarization properties for CMB polarisation experiments satisfying stringent requirements on low sidelobe levels, symmetry and low cross polarization in large arrays. Similarly for mid infrared systems multi-mode waveguide structures will give high throughput to reach the required sensitivities. In this paper we present a computationally efficient approach for modelling and optimising horn characteristics. We investigate smooth-walled profiled horns that have a performance equivalent to that of the corrugated horns traditionally used for CMB measurements. We discuss the horn optimisation process and the algorithms available to maximise performance of a merit parameter such as low cross polarisation or high Gaussicity.

New developments in waveguide mode matching techniques are considered, in particular the efficient modeling of waveguide cavity coupled detectors. This approach is useful in far-infrared astronomical instrumentation and cosmic microwave background experiments in which bolometers feeding horn antennas or Winston cones are often employed for high sensitivity, good control of stray light and well behaved beam patterns. While such systems can, in theory, be modeled using full wave FEM techniques it would be desirable, especially for large structures in terms of the wavelength, to exploit more efficient mode matching techniques, particularly for initial design optimization. This would also be especially useful for cavities feeding partially coherent multi-mode horns or Winston cones. The mode matching approach also allows for straightforward modeling of the complete coupling structure including the horn, waveguide cavity and absorbing layer of the bolometer, thus marking a significant ad...