A high efficiency polarizing interferometer for astronomical observations in the submillimetric region

We describe a high efficiency polarizing interferometer for astronomical observations in the submillimetric and millimetric region. The results obtained during tests at the focal plane of TIRGO (Gornergrat) lead to the conclusion that the instrument works with the expected efficiency and can be used for astronomical observations of faint sources.     

A circular reflector interferometer for the far infrared

The construction of a Fourier transform spectrometer to study magnetic resonances in solids is described. The spectrometer operates in the Far Infrared (maximum frequency of 500 cm^–1) and is based on a wavefront dividing interferometer with circular geometry. To illustrate the performance, a water vapour spectrum is given.     

Far infrared spectroscopy of praseodymium magnesium nitrate using a polarizing interferometer

A number of contradictions exist in the published far i.r. spectra of praseodymium magnesium nitrate. Spectra recorded with improved spectrophotometric accuracy with a polarizing interferometer have enabled these to be resolved. Transitions from the ground doublet to the first excited singlet state of the Pr³⁺ ion showed no evidence of the small ground state splitting. The Zeeman splitting of this absorption is as predicted from the ground stateg-value but the components are of unequal width. Other features of the spectrum are described.     

A far infrared scanning plane Fabry-Perot spectro interferometer

We describe a mounting fitted to select a narrow frequency band between 20 and 100 cm^–1 in the far infrared; it consists of a coupling of a grating monochromator with a plane scanning Fabry-Perot interferometer (F. P.).This apparatus is intended for the fine study of profiles, pure rotation line broadening and shifting of simple dipolar molecules perturbed under low pressure.     

A far infrared interferometer using a rotating polariser

A new type of polarising interferometer has been constructed for the study of anisotropic solids in the far infrared. The polariser is rotating to chop radiations, and the analyser is fixed to give a suitable polarisation.     

A vibrationally compensated far infrared laser interferometer for plasma density measurements

A modulated far-infrared laser interferometer which is presently operating on the PDX experiment at Princeton is described. The interferometer geometry permits the characterization of inside D, outside D as well as circular discharges. To achieve this versatility, a titanium corner cube reflector, mounted inside the PDX vacuum vessel is used in conjunction with a second visible wavelength interferometer for vibration corrections. In addition, the use of room temperature quasi-optical Schottky diodes in the far-infrared interferometer is reported. The minimum detectable line average density of the system is 5×10¹¹ cm^–3.     

A helium cooled Fabry-Perot interferometer for infrared astronomical spectroscopy

We have built a cooled, scanning Fabry-Perot interferometer for astronomical spectroscopy in the ten micron atmospheric window. The reasons for choosing this approach are discussed and details are given of the construction and performance of the prototype instrument.     

A two-beam interferometer for dispersive reflection spectroscopy of solids in the far infrared at temperatures between 4 and 300K

A Fourier spectrometer has been developed for determining the optical constants of highly absorbing solids in the far infrared at temperatures down to 4.2K from measurements of their amplitude and phase reflection spectra. The spectrometer has been constructed almost entirely from commercially available components, and its performance is illustrated with measurements of the optical constants of NaCl at 6K.     

Wide band measurement of power transmission coefficients and polarizing efficiency of free standing wire grids in the far infrared

In this paper we describe wide band measurements of power transmission coefficients and the degree of polarization of a set of free-standing wire grids in the far infrared. The measurements have been performed in two different spectral regions, with the grid parameter d/g ranging between 0.4 and 0.003. The results are compared with theoretical predictions and the accuracy of the experimental method is fully discussed.     

A high responsivity,low-noise germanium bolometer for the far infrared

A p-type compensated germanium bolometer operating at 0.1 K is found to have a responsivity of 2.8×10⁷ V/W and an estimated limiting NEP of 3x10^-16 W/(Hz)^{$\text{1}\text{2}$}.     

A polarizing Michelson interferometer for the far-infrared and millimetre regions

A polarizing Michelson interferometer for the far-infrared and millimetre regions is described. It uses a simple mechanical drive to attain high-resolution spectra with excellent frequency accuracy, as evidenced by measurements of the rotational parameters for N₂O, for which the D parameter is measured with an uncertainty of ± 190 Hz; comparable with the accuracy of microwave techniques.     

A polarizing device for laser spectroscopy

A low-loss polarization prism is described which is highly resistant to the radiation of high-power pulse lasers. The transmission of the ordinary and the extraordinary waves and the angle of deflection have been calculated for KDP, ADP and LilO₃ as a function of the angle of incidence, the prism angle, the direction of the optical axis and the wavelength. The numerical results have been compared with the experimental ones and are shown to be in good agreement. Some examples of the application of the new polarization device are presented.     

A new quasi-optical filter: the reflective polarizing interferometer

Conclusions A new type of optical filter element has been described and tested, offering an alternative frequency response to that of a Fabry-Perot or Michelson interferometer. It is quite compact, mechanically stable, and suitable for cryogenic operation. Use of this device is planned as a sideband filter in a 15 element imaging array receiver for 90–115 GHz.     

A new version of a Michelson interferometer for Fourier transform infrared spectroscopy1

A new version of a Michelson interferometer is described which is suitable for double-beam differencing Fourier spectroscopy due to its easy optical access to the two inputs and two outputs. The instrument uses only one source and one detector, but an input and an output beam-splitter allows combination of the two normal and two antiphase interferograms in various ways to achieve compensation of the a.c. and d.c. parts. For use in single-beam operation, the interferometer can easily be changed, yielding doubling of the path difference and tilt-compensation. The possibilities for amplitude-phase Fourier spectroscopy are discussed.     

Atmospheric spectroscopy at very high resolution in the middle infrared with a rapid-scan Michelson interferometer

A high resolution Michelson interferometer (λ/Δλ/ ∼ 10⁴) has been built for use on the NASA C141 i.r. airborne telescope to study far i.r. emission lines from HII regions. In preparation for the first airborne measurements, the instrument has recently been used on the 1 m telescope at the Observatoire du Pic du Midi. Atmospheric emission spectra were obtained between 17.5 and 20 μm at a spectral resolution of 0.02cm⁻¹; line identifications tabulate numerous H₂O rotation lines throughout the “18 μm window”. Limits were put to the integrated water vapour above the site and upper limits to the intensities of two ionic emission lines of Sulphur in the Orion nebula.     

A high-resolution Fourier transform spectrometer for far infrared magneto-optic spectroscopy of magnetic materials

We describe a high-resolution (0.015 cm⁻¹) Fourier transform spectrometer which has been developed to investigate bulk and surface magnetic polaritons in magnetic media by far infrared magneto-optic spectroscopy. The spectrometer uses a novel combination of laser-controlled sampling of the interferogram and phase modulation of the infrared beam to combine very accurate sampling and low signal-to-noise ratio. The spectrometer is coupled to a liquid helium cryostat with a 7 T superconducting magnet, and a liquid helium-cooled silicon bolometer is used as the detector. Samples can be mounted in the cryostat for polarised oblique incidence reflection measurements in the Voigt geometry with the applied magnetic field vertical. Measurements on surface polaritons are made by using attenuated total reflection (ATR) spectroscopy with silicon prisms to obtain the necessary wave vector enhancement. The resolution of the instrument is demonstrated with measurements on the rotational lines of water vapour, and a selection of measurements on a bulk single crystal of FeF₂, a uniaxial antiferromagnet, is presented to illustrate the performance of the instrument as a probe of magnetic excitations.     

A method of determining the flatness of metal mesh elements of a far infrared Fabry-Perot interferometer

A simple and inexpensive method is described for determining the flatness of metal mesh elements of a far infrared Fabry-Perot interferometer.     

Analysis of the mode of operation of a polarizing interferometer in dispersive Fourier transform spectroscopy

An analysis is given of the mode of operation of a polarizing interferometer constructed in a configuration which has been widely used to measure the refractive indices of solids and liquids in the far-infrared by dispersive Fourier transform spectroscopy. It is shown how the instrument produces an inverted interferogram and that the efficiency, which is essentially constant below the cut-off region, is approximately half the peak efficiency of a conventional Michelson interferometer at the centre of the beam-splitter pass band. It is also shown how the appropriate amplitude and phase spectra of the specimen are obtained in the usual way by taking the ratio of the complex Fourier transforms of double sided specimen and background interferograms.     

The use of the Fabry-Perot interferometer for high resolution microwave spectroscopy

A simple Fabry-Perot interferometer was used for measurements of microwave spectra. Both basic experimental arrangements, absorption and emission, were tested on the rotational spectra of acetonitrile. The interferometric results obtained were compared with the spectra measured using a standard high resolution microwave spectrometer.