New developments in waveguide mode-matching techniques for far- infrared astronomy

Murphy, J. Anthony; Doherty, Stephen; Trappe, Neil; Bracken, Colm; Peacocke, T.; O'Sullivan, Créidhe M.

doi:10.1117/12.908068

Cited by 4 publications

(7 citation statements)

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“…These relationships are also affected by the guide impedance appropriate for the modes at the absorber. This theory has been described previously 2,3,6 and we summarise the main points here. The resulting scattering matrices for the case when the absorber is partially, or completely, filling the surrounding waveguide (or cavity) cross-section can be derived and are given by:…”

Section: Absorber Cavitiesmentioning

confidence: 87%

“…TES detectors) 3,4,5 . The difference in the tangential magnetic fields at the two surfaces (left and right) of the absorber are related to the current flowing in the current sheet by = − ×̂ (where ̂ is a unit vector in the direction of propagation and K is the surface current density).…”

Section: Absorber Cavitiesmentioning

confidence: 99%

“…One improvement to the accuracy of such mode matching simulations is to model the bolometer as a thin current sheet of finite surface resistance, in which lossy currents are induced by the fields at its surface 3,4,5 . Then, any real power that is not reflected back into propagating modes in the horn plus waveguide feeding the cavity must have been converted into Joule heating of the effective power absorbing sheet.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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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.

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Section: Absorber Cavitiesmentioning

confidence: 87%

Section: Absorber Cavitiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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“…However, in practice the size will normally be limited by the scaling of the required computational power with the number of modes, or by the point at which it becomes more computational favorable to employ methods from geometric optics. The proposed scheme is similar in numerical and computational complexity to existing modeling methods for multimode horns [9], and consequently we do not foresee any problems in this regard in its application to current and planned detectors. Additionally, increases in available computational power will only serve to alleviate this issue and to open up larger systems to analysis.…”

Section: Introductionmentioning

confidence: 90%

“…In Section 3, we employ this model to calculate the scattering matrix representation of the absorber, allowing its inclusion in mode-matching codes. Two different numerical schemes will be presented, developing work by Withington and Thomas [8] and Murphy et al [9]. Subsequently, in Section 4 we will show how to calculate the power dissipated only in the absorber when there are other lossy components in the assembly.…”

Section: Introductionmentioning

confidence: 99%

Optical modeling techniques for multimode horn-coupled power detectors for submillimeter and far-infrared astronomy

Thomas

Withington

2013

J. Opt. Soc. Am. A

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An important class of detectors for the submillimeter and far-infrared uses a multimode horn to couple incident radiation into an absorbing film made from a thin conductor. We consider how to model the full, partially coherent, optical behavior of these multimode detectors using extensions of mode-matching techniques. We validate modeling the absorber as a resistive sheet, and demonstrate the equivalence of mode-matching and Green's function methods for calculating the scattering matrix representation of the film. Finally, we show how the scattering matrix of the film can be cascaded with those of the other components, as determined by mode matching, so as to calculate the overall optical response of the detector. Simulations are presented of the optical behavior of a square absorbing film in a circular waveguide.

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A novel, highly efficient cavity backshort design for far-infrared TES detectors

Bracken

Lange

Audley

et al. 2018

Infrared Physics & Technology

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New developments in waveguide mode-matching techniques for far- infrared astronomy

Cited by 4 publications

References 0 publications

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

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

Optical modeling techniques for multimode horn-coupled power detectors for submillimeter and far-infrared astronomy

A novel, highly efficient cavity backshort design for far-infrared TES detectors

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