An end-to-end Far-infrared Interferometer Instrument Simulator (FIInS)
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FIRI (Far Infra-Red Interferometer) is a concept for a spatial and spectral Space interferometer with an operating wavelength range of 25-400 µm and sub-arcsecond angular resolution, and is based on the combination of Stellar Interferometry and Fourier Transform Spectroscopy to perform spectroscopy at high angular resolution in the Far Infrared. The resulting technique is referred to as Double Fourier Spatio-Spectral Interferometry (Mariotti and Ridgway 1988). To study the feasibility of a FIRI system the Far-Infrared Interferometer Instrument Simulator (FIInS) has been developed. To demonstrate its functionality, the simulation of an observation of a circumstellar disk around a Herbig Ae star is presented.Keywords:
Spectral resolution
Fourier transform spectroscopy
We propose a novel photonic spectral processor which overcomes current 0.8GHz spectral resolution limitation. The new spectral processor uses a Fabry Perot interferometer array located before the dispersive element of the system, thus significantly improving the spectral separation resolution, which is now limited by the Fabry Perot interferometers' full width at half maximum rather than the dispersive element's spectral resolution. A proof of concept experiment was performed utilizing two Fabry-Perot interferometers and a diffractive optical grating with a spectral resolution of 6.45GHz, achieving high spectral resolution of 577MHz. Further improvement of the experimental setup can result in resolution of about 50MHz.
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The HEAO1 A4 satellite hard X-Ray sky survey, performed in the late '70s, has discovered a crowded and complex hard X-Ray sky in the range 10 180 keV. This intrigued scenario has been recently confirmed by high quality balloon borne experiments. These experiments in spite of their good spectral capability have been generally unable to provide good positional resolution and large sky coverage because of the use of passive collimators with wide field of view (f.o.v.) (typically 3 ÷ 15 degree). It is now evident the scientific need for a new generation of hard X-Ray instruments providing high imaging and spectral resolution over a wide energy range to study the spectral behaviour of different classes of cosmic sources and to identify these X-Ray emitters with their counterparts at optical, infrared and radio wavelenghts. In this note we will describe a new type of position sensitive MultiWire Proportional Counter (MWPC) recently designed and built at the prototype level in our Institute. This detector, expected to be fully operational in two years, will be assembled with a coded mask, employed as the imaging device, and flown on-board a balloon borne experiment as a high-resolutionwide-angle hard X-Ray telescope. The main scientific goal is to produce sky images in the range 15 + 180 keV with arcminute angular resolution, good spectral resolution (λ/Δλ=20) and milliCrab sensitivity, during a typical observation time of 104 seconds. A space qualified version of this instrument operative in the range 2.5 ÷ 180 keV has been proposed on-board the Soviet mission "Spectrum X-Famma" expected to fly in the mid '90s.
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The spectral resolution of broadband Fourier-transform coherent anti-Stokes Raman spectroscopy is limited by the maximum optical path length difference that can be scanned within a short time in an interferometer. However, alternatives to the Fourier-transform exist which can bypass this limitation with certain assumptions. We apply one such approach to broadband coherent Raman spectroscopy using interferometers with short delay line (low Fourier spectral resolution) and large delay line (high Fourier spectral resolution). With this method, we demonstrate broadband coherent Raman spectroscopy of closely spaced vibrational bands is possible using a short delay line interferometer, with superior spectral resolution to the longer delay line instrument. We discuss how this approach may be particularly useful for more complex Raman spectra, such as those measured from biological samples.
Fourier transform spectroscopy
Spectral resolution
Coherent spectroscopy
Optical path length
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High resolution Fourier transform spectroscopy at the University of Oulu is based on the double-beam Fourier transform spectrometer constructed here. The instrument works between 20 and 1200 cm-1 with a practical resolution of better than 0.010 cm-1. The maximum optical path difference in the interferometer is 1.5 m giving a theoretical resolution of about 0.004 cm-1. The wavenumber precision of the instrument was found to be ±0.0005 cm-1. The practical resolution is limited by a signal-to-noise ratio accepted in spectral analysis. In the far infrared noise mainly originates in the detector and radiation source (black body radiator). Some new techniques aimed at eliminating these disadvantages will be presented. Also, some new computation methods will be pointed out.
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Abstract The Re I (527. 55 nm, 18955 cm−1) emission line from a hollow cathode lamp (HCL) is proposed as a standard for wavenumber accuracy and precision, resolution accuracy and precision and intensity precision. The Los Alamos Fourier transform spectrometer measured the HCL emission at high resolution (0. 026 cm−1). The advantages of this spectral line to other emission standards is discussed.
Hollow-cathode lamp
Fourier transform spectroscopy
Spectral resolution
Wavenumber
Ultraviolet
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Radiant intensity
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The development of a new time-resolved Fourier transform spectrometer that is capable of 0.25 cm−1 spectral resolution and better than 10−7 s temporal resolution in the visible is reported. The time-resolved capability of the spectrometer is achieved by coupling a step-scan interferometer to a transient digitizer/laser system. The operation of the spectrometer is described in detail, and scattered light and laser-induced fluorescence spectra from an I2 gas cell are presented to demonstrate the temporal and spectral resolution of the spectrometer.
Fourier transform spectroscopy
Spectral resolution
Temporal resolution
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A mechanical ``symmetrizer'' has been built for use with far infrared interferometers driven by stepping motors. It allows convenient and consistent setting of the position of zero phase difference and thereby permits straightforward Fourier analysis of the measured one-sided (even) interferogram.
Position (finance)
Zero (linguistics)
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Abstract Fast (sub-second) spectroscopy with high spectral resolution is of vital importance for revealing quantum chemistry kinetics of complex chemical and biological reactions. Fourier transform (FT) spectrometers can achieve high spectral resolution and operate at hundreds of ms time scales in rapid-scan mode. However, the linear translation of a scanning mirror imposes stringent time-resolution limitations to these systems, which makes simultaneous high spectral and temporal resolution very difficult. Here, we demonstrate an FT spectrometer whose operational principle is based on continuous rotational motion of the scanning mirror, effectively decoupling the spectral resolution from the temporal one. Furthermore, we show that such rotational FT spectrometer can perform Mid-IR dual-comb spectroscopy with a single comb source, since the Doppler-shifted version of the comb serves as the second comb. In our realization, we combine the advantages of dual-comb and FT spectroscopy using a single quantum cascade laser frequency comb emitting at 8.2 μm as a light source. Our technique does not require any diffractive or dispersive optical elements and hence preserve the Jacquinot’s-, Fellgett’s-, and Connes’-advantages of FT spectrometers. By integrating mulitple broadband sources, such system could pave the way for applications where high speed, large optical bandwidth, and high spectral resolution are desired.
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Fourier transform spectroscopy
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Very Large Telescope
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Multiple-telescope interferometry for high-angular-resolution astronomical imaging in the optical-IR-far-IR bands is currently a topic of great scientific interest. The fundamentals that govern the sensitivity of direct-detection instruments and interferometers are reviewed, and the rigorous sensitivity limits imposed by the Cramér-Rao theorem are discussed. Numerical calculations of the Cramér-Rao limit are carried out for a simple example, and the results are used to support the argument that interferometers that have more compact instantaneous beam patterns are more sensitive, since they extract more spatial information from each detected photon. This argument favors arrays with a larger number of telescopes, and it favors all-on-one beam-combining methods as compared with pairwise combination.
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