Armand Hadni

Far Infrared Study of the Copper Halides at Low Temperatures

The far infrared spectra of the copper halides CuCl, CuBr, and Cul have been measured in transmission and in reflection at various fixed temperatures from room temperature to liquid-helium temperature. Marked changes of such parameters as resonance frquency and damping as a function of temperature have been observed, also a line-splitting in the case of CuCl. In addition, a considerable increase in the asymmetry of the transmission curves with decreasing temperature has been observed.

Low temperature far infrared spectra of SiO2 polymorphs

Abstract Far-infrared transmission measurements of SiO 2 polymorphs (α-quartz, fused quartz, α-tridymite and α-cristobalite) have been extended into longer wavelengths (6–1000 μ) and to lower temperatures (the boiling points of liquid nitrogen, hydrogen and helium). The α-cristobalite sample was converted from fused quartz and the spectra taken before and after conversion. Differences were observed between the character of the low frequency resonance bands and that of the medium and high frequency bands. A possible explanation is put forward.

Sur le comportement différent des cristaux et des verres dans l’absorption de l’infrarouge lointain (40–1500μ) à la température de l’hélium liquide

Absorption spectra at liquid helium temperature in the far infrared are given for thick plates of CsI, CsBr, TlBr, TlCl, KI, NaCl, InSb, KBr, CuCl, Al2O3, SiO2, MgO, and LaCl3. For a thickness of about 3 mm all these crystals, completely opaque at room temperature, become quasitransparent at very low temperature. This supertransparency of crystals at low temperature gives several far infrared filters with remarkable cutoffs and a lot of available materials to the spectroscopist in a part of the spectrum where only quartz and polyethene were usable up to now. This is also evidence that the main part of the absorption at room temperature comes from the lattice phonons. It decreases with their number when the crystal is cooled (2 phonons difference process). The small absorption which remains in a few cases—KBr, —NaCl, KI—could arise from 2 phonons addition process nearly independent of temperature and much less efficient to give absorption. In the case of glasses the absorption coefficient is higher by 2 or 3 orders of magnitude and keeps constant when the glass is cooled. For quartz glass, the index of refraction also seemed invariant. An explanation is proposed in terms of one single phonon process, independent of temperature and allowed by the disorder characteristic of glassy states.

Laser scanning microscope for pyroelectric display in real time

The pyroelectric probe technique is now capable of inspecting a 100 x 100-microm TGS area in a few seconds with a 2-microm limit of resolution. The method is described in detail, and a calculation of the pyroelectric signal is presented. The longitudinal growth of a cylindrical domain is mathematically simulated and also the variation of pyroelectric signal at domain boundary. These calculations are in good accordance with experiment. With a 200-kHz chopping frequency only a thin layer of the crystal surface is inspected (thermal diffusion length l = 0.64 microm), while the lateral limit of resolution is given by the laser spot radius (R(1) = 1 microm). It is possible to decrease this limit by using a smaller laser spot, but the chopping frequency ought to be increased.

Spectres d'absorption dans l'infrarouge lointain de sept halogenures anhydrés et hydratés: BaCl2, BaBr2, SrBr2, SrCl2, PbCl2, PbBr2 et NaI

Abstract When anhydrous, crystals of nine inorganic chlorides, bromides and iodides exhibit three absorption bands in the far infra-red. When hydrated, it has been possible by deuteration to differentiate between: 1. (1) Several absorption bands mainly related to water molecules: -one perturbed valence vibration ◦ -two angular vibrations ◦ -three librations around the three principal molecular axis of inertia ◦ -six translational vibrations. 2. (2) Two low frequency absorption bands not sensitive to deuteration, which are related to motions involving mainly the heaviest atoms of the unit cell.

Instrumentation in the far infra-red-applications to molecular and solid state physics

Abstract We present here a brief progress report of some of our results in the far infra-red during the past two years. Only some of the problems considered have been resolved, we are still working on the others, the most promising being the study of lattice vibrations at very low temperatures.

Spectre d'absorption dans l'infrarouge lointain (15–250 cm−1) d'un cristal d'acide salicylique a temperature de l'azote liquide (80 K)

Abstract Comparison of absorption spectra of salicylic acid in the crystal state and in solution leads to a division of the spectrum into external frequencies lower than 92 cm−1 and internal frequencies higher than 125 cm−1 at 300 K. The external frequencies are ascribed to translational vibrations of the two dimers in the unit cell at 37.5, 47 and 54 cm−1, and to torsional vibrations of the dimers coupled either symmetrically or antisymmetrically. The determinations are made on consideration of the crystal trichroism in the far IR and on calculation of relative intensities of the torsional vibration absorption bands on the three observed directions.

Spectres de transmission et de reflexion de I’iodure de potassium, pur et dopé, aux basses températures

The far ir reflectivity of a pure single crystal of KI at liquid helium, liquid nitrogen, and room temperature has been measured from 10 micro to 700 micro. Kramers-Kronig analysis, and a two-oscillators Lorentz analysis lead to close results concerning the refractive index n, and the absorption index k in the whole ir spectrum, with maximum values of n and k ranging from 4 to 8. The strongest Lorentz oscillator has a frequency at 80 degrees K (nu(1))= 110 cm(-1))) close to the transverse optic frequency recently determined from neutron scattering at 95 degrees K (TO = 107 +/- 1.3 cm(-1)). The strength of the second Lorentz oscillator decreases rapidly when the temperature is lowered. Its frequency (nu(2) = 150 cm(-1) at 80 degrees K) is such that it can be considered as the TO + TA combination at point L of the first Brillouin zone, which is ir active, and expected at 152.7 +/- 3 cm(-1) from neutron scattering. Absorption bands,locaized in the gap determined by neutron scattering as extending from 104-143 micro (96-70 cm(-1)), are induced by sodium, cesium, and chlorine ions impurities. A peak of absorption in the acoustic phonons spectrum is induced by sodium ion impurities at 63 cm(-1)) close to a maximum in the frequency distribution function for the normal modes of vibration of KI computed recently by Cowley et al. Bromine ions, on the other hand, lead to a general background absorption.

Spectres d'absorption dans l'infrarouge lointain des clathrates de l'hydroquinone β avec H2S, H2Se; D2S et D2Se

Abstract The introduction of H 2 S, D 2 S, H 2 Se and D 2 Se in β quinol leads to three new absorption lines around the 65 cm −1 absorption band of pure hydroquinone β. They are located at 57, 75 and 79 cm −1 , and are explained as induced absorption by impurities revealing phonons at the Brillouin zone boundaries. Nevertheless the 57 cm −1 band is specially strong for H 2 S and D 2 S and most of its intensity shifts to 44 cm −1 with H 2 Se and D 2 Se. This could be explained as a resonance of the 57 cm −1 phonon peak with the rattling motion of the encaged molecule located at 57 cm −1 for H 2 S and D 2 S and decreasing down to 44 cm −1 for H 2 Se and D 2 Se. A broad band is observed at 20 cm −1 for H 2 S and D 2 S and shifts to 10 cm −1 for H 2 Se and D 2 Se at 10 K. It is a proof of nearly free rotation of the encaged molecule. A group theory analysis of the external vibrations leads to 4 infrared active vibrations. One is sufficiently strong to be observed at 65 cm −1 .

Electrical constants of triglycine sulphate, applications to pyroelectricity and the detection of far infrared radiations

Abstract Far infrared spectra of TGS from room temperature to liquid helium temperature in the spectral range extending from 3 to 400 cm−1, and description of a triglycine sulphate pyroelectric detector working at frequencies as high as 1 Megacycle per second.