J.R. Birch

The optical constants of some common low-loss polymers between 4 and 40 cm−1

Abstract The results of the determination of both the refractive index and the power absorption coefficient of seven common polymers (low and high density polyethylene, polyamide, polymethyl methacrylate, polytetrafluorethylene, polystyrene and poly 4 methyl pentene-1) at a temperature of 290K in the spectral region between 4 and 40cm −1 by the techniques of dispersive Fourier transform spectrometry are presented.

The far-infrared optical constants of polypropylene, PTFE and polystyrene

Abstract The far-infrared optical constants of polypropylene, PTFE and polystyrene have been determined in the spectral region between 50 and 500 cm −1 at a temperature of 290 K by the method of dispersive Fourier transform spectroscopy.

The far infrared optical constants of polyethylene

Abstract The optical constants of high and low density polyethylene have been determined in the far infrared spectral region between 50 and 450 cm−1 at a temperature of 293 K.

An interferometer for the determination of the temperature variation of the complex refraction spectra of reasonably transparent solids at near-millimetre wavelengths

Abstract An interferometer for the determination of the temperature variation of the complex refraction spectra of reasonably transparent solids at near-millimetre wavelengths is described. Measurements are made by the technique of DFTS. The specimen is mounted in a variable-temperature cryostat, which allows any temperature between about 4.2 and 300K to be used. The performance of the instrument is illustrated with the results of such studies on high- and low-density polyethylene and on polystyrene.

The refractive index of water vapour: A comparison of measurement and theory

Abstract Calculations of the real refractive index of water vapour between 10 and 50 cm −1 using the Gross line shape have been compared with measurements made using dispersive Fourier transform spectrometry. The overall agreement between measurement and theory is good except near to line centre where the effects of the instrumental line shape have to be considered.

The FIR optical constants of the polymer TPX

Abstract The optical constants of the polymer TPX have been determined between 30 and 420 cm−1 at ambient temperature by the technique of dispersive Fourier transform spectroscopy. The results are compared with previous measurements.

A modular interferometer for dispersive reflectivity measurements on highly absorbing solids

Abstract A modular interferometer is described that has been used for dispersive Fourier transform determinations of the complex Fresnel reflectivities of absorbing solids from 5 to 450 cm −1 at ambient temperature. The interferometer is used in a mode of operation that eliminates the effects both of backlash in the moving mirror drive and of differential thermal expansion between the two arms of the interferometer. Typical results, on the lattice mode of cadmium telluride, are presented.

An improved experimental method for reflection dispersive Fourier transform spectrometry of very heavily absorbing liquids

Abstract An experimental method for the determination of the complex refractive index of a very heavily absorbing liquid at submillimetre wavelengths by dispersive Fourier transform reflection spectrometry is described. The method is superior to earlier dispersive reflection methods for liquids in that it avoids the collection of redundant data. This results in a halving of the experimental time, a reduced susceptibility to certain systematic errors and a small reduction in the random noise present in the derived values of the optical constants. The method is illustrated by the results of the determination of the optical constants of pure water and of a 5 M aqueous solution of NaCl in the spectral range between 50 and 400 cm−1.

The absolute determination of complex reflectivity

Abstract An absolute method for the determination of complex reflectivity has been applied to a specimen of high purity silicon between 5 and 120 cm −1 at 290 K, establishing its amplitude reflectivity with a precision of 10 −4 and its phase with a precision of 10 −4 rad. Using the specimen in a complex reflectivity comparison enabled the complex reflectivity of some thin aluminium films on glass substrates to be precisely measured.

DISPERSIVE FOURIER TRANSFORM MEASUREMENTS ON OPAQUE SOLIDS FROM 5 TO 350 cm 1

Abstract A two beam interferometer for use in ambient temperature dispersive Fourier transform measurements on opaque and highly reflecting solids is described. The spectral range between 5 and 350 cm −1 has been covered and the performance illustrated with the first reported direct measurements of the complex reflectivity and complex relative permittivity of potassium dihydrogen phosphate and ammonium dihydrogen phosphate.