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Proceedings ArticleDOI

Modal simulation framework for the design and verification of future few-mode far-infrared spectrometers

28 Jun 2022-Vol. 12190, pp 121901T-121901T
TL;DR: In this paper , the spectral and photometric imaging receiver (SPIRE) was used as a case study to highlight calibration issues observed in-flight, while including straylight. And the authors developed a modal framework to model, analyze, and address these issues.
Abstract: The next generation of astronomical space-based far-infrared (FIR) missions require ultra-sensitive spectroscopy as a diagnostic tool. These instruments use ultra-sensitive detector technologies to attain unprecedented levels of spectral observing sensitivity. The reception patterns of the individual detectors consist of individually coherent orthogonal field distributions, or equivalently, they are few-mode (5 to 20), to increase the spectral-spatial coupling to the astronomical source. However, the disadvantage of few-mode detectors is an increase in coupling to external (from the sky or warm telescope optics) and internal (from the instrument itself) straylight, which can greatly affect the measurement of the source spectrum. Therefore, understanding the spectral-spatial few-mode behavior of these systems in detail, and developing verification and calibration strategies, are crucial to ensure that the science goals of these future mission are met. Since conventional modelling techniques are less suited to address this problem, we developed a modal framework to model, analyze, and address these issues. In this paper, we use Herschel’s spectral and photometric imaging receiver (SPIRE) as a case study, because its optical design is representative for future FIR missions and illustrative to highlight calibration issues observed in-flight, while including straylight. Our analysis consist out of two part. In the first part, we use our modal framework to simulate the few-mode SPIRE Fourier transform spectrometer (FTS). In the second part, we carry out a end-to-end frequency-dependent partially coherent analysis of Herschel-SPIRE. These simulations offer a qualitative explanation for the few-mode behavior observed in-flight. Furthermore, we use the Herschel-SPIRE case-study to demonstrate how the modelling framework can be used to support the design, verification and calibration of spectrometers for future FIR missions. The modal framework is not only limited to the spectrometers discussed, but it can be used to simulated a wide range of spectrometers, such as low-resolution gratings and high-spectral resolution Fabry-Pérot interferometers.

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References
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Book
01 Jan 1968
TL;DR: The second edition of this respected text considerably expands the original and reflects the tremendous advances made in the discipline since 1968 as discussed by the authors, with a special emphasis on applications to diffraction, imaging, optical data processing, and holography.
Abstract: The second edition of this respected text considerably expands the original and reflects the tremendous advances made in the discipline since 1968. All material has been thoroughly updated and several new sections explore recent progress in important areas, such as wavelength modulation, analog information processing, and holography. Fourier analysis is a ubiquitous tool with applications in diverse areas of physics and engineering. This book explores these applications in the field of optics with a special emphasis on applications to diffraction, imaging, optical data processing, and holography. This book can be used as a textbook to satisfy the needs of several different types of courses, and it is directed toward both engineers ad physicists. By varying the emphasis on different topics and specific applications, the book can be used successfully in a wide range of basic Fourier Optics or Optical Signal Processing courses.

9,800 citations

Journal ArticleDOI
Matthew Joseph Griffin, Alain Abergel1, A. Abreu, Peter A. R. Ade2  +186 moreInstitutions (27)
TL;DR: The Spectral and Photometric Imaging REceiver (SPIRE) is the Herschel Space Observatory's sub-millimetre camera and spectrometer as discussed by the authors, which is used for image and spectroscopic data acquisition.
Abstract: The Spectral and Photometric Imaging REceiver (SPIRE), is the Herschel Space Observatory`s submillimetre camera and spectrometer It contains a three-band imaging photometer operating at 250, 350 and 500 mu m, and an imaging Fourier-transform spectrometer (FTS) which covers simultaneously its whole operating range of 194-671 mu m (447-1550 GHz) The SPIRE detectors are arrays of feedhorn-coupled bolometers cooled to 03 K The photometer has a field of view of 4' x 8', observed simultaneously in the three spectral bands Its main operating mode is scan-mapping, whereby the field of view is scanned across the sky to achieve full spatial sampling and to cover large areas if desired The spectrometer has an approximately circular field of view with a diameter of 26' The spectral resolution can be adjusted between 12 and 25 GHz by changing the stroke length of the FTS scan mirror Its main operating mode involves a fixed telescope pointing with multiple scans of the FTS mirror to acquire spectral data For extended source measurements, multiple position offsets are implemented by means of an internal beam steering mirror to achieve the desired spatial sampling and by rastering of the telescope pointing to map areas larger than the field of view The SPIRE instrument consists of a cold focal plane unit located inside the Herschel cryostat and warm electronics units, located on the spacecraft Service Module, for instrument control and data handling Science data are transmitted to Earth with no on-board data compression, and processed by automatic pipelines to produce calibrated science products The in-flight performance of the instrument matches or exceeds predictions based on pre-launch testing and modelling: the photometer sensitivity is comparable to or slightly better than estimated pre-launch, and the spectrometer sensitivity is also better by a factor of 15-2

2,425 citations

Journal ArticleDOI
TL;DR: In this article, the cross-spectral density of a steady-state source of any state of coherence may be expressed in terms of certain new modes of oscillations, each of which represents a completely spatially coherent elementary excitation.
Abstract: It is shown that, under very general conditions, the cross-spectral density of a steady-state source of any state of coherence may be expressed in terms of certain new modes of oscillations, each of which represents a completely spatially coherent elementary excitation. Making use of this result, a statistical ensemble of strictly monochromatic oscillations, all of the same temporal frequency, is then introduced that yields the cross-spectral density as a correlation function in the space–frequency domain. From these results two new expressions for the Wiener–Khintchine spectrum of the source and also a new mode representation of the cross-correlation function of the source follow at once.

531 citations

Journal ArticleDOI
Paul F. Goldsmith1
01 Nov 1992
TL;DR: The basic theory of quasi-optical Gaussian beam propagation and beam transformation by simple optical elements is summarized, and coupling to and between Gaussian beams is briefly discussed Guidelines for Gaussian optics system design are reviewed, the most important being beam truncation and matching Passive components in the terahertz frequency range based on quasioptical propagation, including polarization processors, filters, diplexers, and ferrite devices, are examined as mentioned in this paper.
Abstract: The basic theory of quasi-optical Gaussian beam propagation and beam transformation by simple optical elements is summarized, and coupling to and between Gaussian beams is briefly discussed Guidelines for Gaussian optics system design are reviewed, the most important being beam truncation and matching Passive components in the terahertz frequency range based on quasi-optical propagation, including polarization processors, filters, diplexers, and ferrite devices, are examined Some active quasi-optical devices, including multielement oscillators, frequency multipliers, and phase shifters, are described Some specific applications of quasi-optical systems are briefly described >

312 citations