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This paper discusses the development of a cryogenic grating spectrometer that has been used to evaluate the performance of a post-dispersed polarizing FTS over the range of 285-500 µm.

The performance of a prototype far-infrared post-dispersed polarizing FTS has been measured using a source module consisting of unresolved emission and absorption lines and the results are compared with theoretical simulations.

We describe the engineering development unit of a novel cryogenic scan mechanism suitable for post-dispersed polarizing FTS instruments. Compliance to the stringent SPICA mission requirements is demonstrated through analyses and results from proof-of- concept activities.

This paper describes the development and status of a cryogenic, far-infrared, post- dispersed, polarizing FTS (PDPFTS), a candidate instrument concept for the next generation of far- infrared astronomical space telescopes.

The high spectral resolution mode of the SpicA FAR-infrared Instrument (SAFARI) is enabled by inserting a Fourier Transform Spectrometer (FTS), based on a Martin-Puplett interferometer, into the signal path of the instrument. The cryogenic mechanism (FTSM) enables linear scans of two back-to-back rooftop mirrors sharing a common apex. ABB Inc. is under contract with the Canadian Space Agency to develop and test at 4 K an FTSM Engineering Demonstration Unit (EDU) for TRL-5 demonstration. The main SAFARI FTSM performance drivers are the stringent mechatronic demands (position stability of roof-top mirrors

Recent advances in far-infrared detector technology have led to increases in raw sensitivity of more than an order of magnitude over previous state-of-the-art detectors. With such sensitivity, photon noise becomes the dominant noise component, even when using cryogenically cooled optics, unless a method of restricting the spectral bandpass is employed. One method is to use a low-resolution diffraction grating spectrometer to post-disperse the signal from a high-resolution instrument, such as a Fourier transform spectrometer (FTS). This concept has been adopted for the SAFARI instrument on the SPICA mission. This paper discusses the development of a prototype cryogenic grating spectrometer that has been used to evaluate the concept of a post-dispersed polarizing FTS over the range from 285-500 μm.

Over half of the light incident on the Earth from the Universe falls within the Far-Infrared (FIR) region of the spectrum. Due to the deleterious effects of the Earth's atmosphere and instrument self-emission, astronomical measurements in the FIR require space-borne instrumentation operating at cryogenic temperatures. These instruments place stringent constraints on the mechanical and thermal properties of the support structures at low temperatures. With high stiffness, tensile strength, strength-to-mass ratio, and extremely low thermal conductivity, carbon fibre reinforced polymers (CFRPs) are an important material for aerospace and FIR astronomical applications, however, little is known about their properties at cryogenic temperatures. We have developed a test facility for exploring CFRP properties down to 4 K. We present results from our ongoing study in which we compare and contrast the performance of CFRP samples using different materials, and multiple layup configurations. Current results include an evaluation of a cryostat dedicated for materials testing and a custom cryogenic metrology system, and preliminary cryogenic thermal expansion measurements. The goal of this research is to explore the feasibility of making CFRP-based, lightweight, cryogenic astronomical instruments.

Nature is such that observations at far-infrared wavelengths are optimal for exploring both the nearby and distant Universe. The minute amount of energy carried by far-infrared photons, however, requires extremely sensitive instrumentation for their detection. Moreover, the instrumentation itself must be cooled to

The SPICA mission will employ ultra-sensitive superconducting detectors. In this case the multiplex disadvantage of Fourier transform spectroscopy dictates the use of a post-dispersed, diffraction grating detection system. The challenges of reconstructing astronomical spectra will be reviewed.

Imaging applications at terahertz frequencies are, in general, limited to relatively low spatial resolution due to the effects of diffraction. By using a subwavelength aperture in the near-field, however, it is possible to achieve subwavelength resolution, although low transmission through the aperture limits the sensitivity of this approach. Plasmonic lenses in the form of bullseye structures, which consist of a circular subwavelength aperture surrounded by concentric periodic corrugations, have demonstrated enhanced transmission, thereby increasing the utility of near-field imaging configurations. In this paper, the design, fabrication, and experimental performance of plasmonic lenses optimized for 300 GHz are discussed. While nanofabrication techniques are required for optical applications, microfabrication techniques are sufficient for terahertz applications. The process flow for fabricating a double-sided bullseye structure using a precision micromilling technique is described. Transmission and beam profile measurements using a customized terahertz testbed are presented.

The FP7 project, FISICA (Far Infrared Space Interferometer Critical Assessment), called for the investigation into the suitability of Carbon fiber Reinforced Plastic (CFRP) for a 2m primary mirror. In this paper, we focus on the major challenge for application, the development of a mirror design that would maintain its form at cryogenic temperatures. In order to limit self-emission the primary is to be cooled to 4K whilst not exceeding a form error of 275nm PV. We then describe the development of an FEA model that utilizes test data obtained from a cryogenic test undertaken at the University of Lethbridge on CFRP samples. To conclude, suggestions are made in order to advance this technology to be suitable for such an application in order to exploit the low density and superior specific properties of polymeric composites.

A cryogenic FTS is being developed at the University of Lethbridge based on a commercial rotary arm system. Measurement of optical path difference is accomplished using a fiber-fed laser interferometer system internal to the cryostat.

Imaging applications at terahertz (THz) frequencies are limited to relatively low spatial resolution due to the effects of diffraction. A subwavelength aperture can be used to improve the resolution at the cost of low transmission. Plasmonic lenses in the form of bullseye structures, consisting of a single subwavelength circular aperture surrounded by concentric periodic corrugations, have shown enhanced transmission and beam confinement. In this paper, we discuss the design and performance of plasmonic lenses optimized for transmission at 325 GHz., 2015 40th International Conference on Infrared, Millimeter, and Terahertz waves (IRMMW-THz), August 23-28,2015, Hong Kong, China

A major limitation in terahertz (THz) imaging applications is the relatively poor diffraction limited spatial resolution. A common approach to achieve subwavelength resolution is near-field imaging using a subwavelength aperture, but the low transmission efficiency through the aperture limits the sensitivity of this method. Bullseye structures, consisting of a single subwavelength circular aperture surrounded by concentric periodic corrugations, have been shown to enhance transmission through subwavelength apertures. At optical wavelengths, the fabrication of bullseye structures has been traditionally achieved by lithographic or chemical processes. Since the scale of plasmonic structures depends on the incident wavelength, precision micromilling techniques are well suited for THz applications. In this paper we describe a diamond micromilling process for the fabrication a plasmonic lenses operating at 325 GHz. Theoretical simulations are obtained using an FDTD solver and the performance of the lens is measured using a customized THz test bed., New Developments in THz, RF, Millimeter-Waves, and Sub-Millimeter Waves III, February 1 2014, San Fransisco, CA, Series: Proceedings of SPIE; no. Vol. 8985

The design and performance of a dual polarizing bolometer detector system for use with a polarizing Fourier transform spectrometer to conduct broadband astronomical spectroscopy at submillimeter wavelengths is presented. The system features a fully differential electronics design which virtually eliminates common mode noise. The optical design efficiently rejects unwanted radiation, both spectrally and spatially, while minimizing the effects of resonant optical cavities. The system is cooled by an efficient, closed cycle 4He–3He refrigerator which is cycled under computer control. The noise performance of the system is determined from analysis of electrical, optical, and spectral measurements, and the results are compared with a theoretical bolometer model.

The spectral imaging capabilities of the Herschel-SPIRE imaging Fourier Transform Spectrometer are discussed. The process of data reduction and results from sample observations are presented.

We report on the fabrication and characterization of a voltage-biased superconducting bolometer (VSB) in a cryogen-free 4 K cryostat for applications at far-infrared wavelengths. The VSB is made using standard microfabrication techniques. An optical NEP of 0.83 pW/√Hz has been measured with a T c ∼7.12 K.

We present the use of undersampling with a narrow band FTS operating in the step-and-integrate mode. Spectra can be unambiguously retrieved from interferograms sampled at less than the DC band-limited Nyquist sampling interval.