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The infra-red absorption spectrum of terbium iron garnet, (TbIG), has been recorded at liquid helium temperature. The energy level scheme was reduced and simulated within the frame of crystal field (cf) theory. The cf parameters of TbIG are not significantly different from those of terbium aluminum garnet, (TbAlG).

Recent progress in thin film deposition techniques has motivated a renewed interest in artifically prepared layered microstructures. These multilayers can be used as Bragg reflectors for X-ray-UV optics in the range 100–1000 eV. Ideal multilayers require optimized thicknesses of low and high absorbing materials with perfect interfaces. The main problems are the control of the layer thicknesses to a high accuracy and the attainment of good quality interfaces between the layers. We have used a low energy (300–500 V) d.c. triode sputtering system which gives very sharp interfaces. We describe a new method of thickness monitoring which is based on the dependence of the deposition rate on the target current. The sequence and timing of the deposition of each layer is controlled using a microprocessor which also regulates the sputtering parameters (pressures, target voltage etc.). Thicknesses can be controlled with an accuracy to better than 0.1 A and a reproducibility of better than 0.1%.

The crystal field splitting of the energy levels of Fe3+ ions in octahedral and tetrahedral sites of Y3Fe5O12 have been computed between 10000 and 32000 cm−1. The calculation is performed using, first, the cubic field approximation, then the effect of a trigonal distortion, and finally the spin-orbit interaction in the two magnetic sites. It is shown that the contributionof thetrigonal distortion to the absorption spectrum can be neglected. Thespin-orbit coupling does not disturb the value of the calculated level energies but induces a coupling between some multiplets. With the use of the spin-orbit coupling a very good fit between the computed and theexperimental spectra is obtained leading to an assignment of the observed absorption lines which is slightly different from that obtained without the spin-orbit coupling effects.

The following features of Pt-Al2O3 cernet coatings deposited by r.f. cosputtering on metallic substrates are reported in this paper. 1. (1) An appropriate choice of cermet composition and coating thickness results in very good optical selectivity. 2. (2) This selectivity is increased if the cermet film has a molybdenum underlayer and an Al2O3 overlayer of adequate thickness. An absorptivity a of 0.92 and an emissivity e of 0.14 (at 300°C) have been obtained. 3. (3) These selective absorbers are stable at temperatures of up to 400°C when cermet coatings are deposited on stainless steel substrates and of over 600°C when superalloy substrates are used.

A first observation of modulation of light induced by second-order magnetooptical interactions is reported in ferrimagnetic rare-earth garnets (Y 3 Fe 5 O 12 and Tb 3 Fe 5 O 12 ) and discussed on the basis of the anisotropy of the linear magnetic birefringence.

L'analyse en seconde quantification des interactions magneto-optiques dans un cristal ferromagnetique montre que les effets statiques (effets Faraday et Cotton-Mouton) et dynamiques (Raman a 1 et 2 magnons) apparaissent comme des diffusions spin-photon elastiques et inelastiques respectivement. Les relations physiques et analytiques entre ces differents effets dispersifs induits par les transitions dipolaires electriques et magnetiques sont precisees. On montre que les susceptibilites Raman a 1 et 2 magnons sont proportionnelles au carre des birefringences magnetiques specifiques circulaire et lineaire respectivement. Enfin les anomalies importantes de diffusion Raman a 1 magnon que nous avons observees recemment sont interpretees a partir de l'influence des interactions magneto-optiques du second ordre sur les diffusions inelastiques du premier ordre.

A jump like magnetic transition is observed at relatively weak field in Tb3Fe5O12 when the magnetic field is applied along the hard axis and no transition is observed with the field applied along the easy axis. We believe that this evolution is related to the ”Umbrella” type magnetic structure known to exist in Tb3Fe5O12 at low temperatures.

PtAl 2 O 3 cermet films (Pt volume fraction 0.18–0.53) have been deposited on optically polished glass substrates by co-sputtering using composite targets. The optical transmittance and reflectance in the range 300–3000 nm and the electrical conductivity have been measured. The electrical percolation and the optical cross over occur around 0.43 Pt volume fraction. Cermet films with a composition close to this percolation threshold show a good solar spectral selectivity which can be improved when they are overcoated by an Al 2 O 3 film. Solar absorptances greater than 0.95 and emittances of about 0.14 have been obtained. These selective absorbers deposited on stainless steel show a good stability up to 400°C in air. Between 400 and 600°C, the diffusion of certain elements of the substrate into the coating and their oxidization contribute to the degradation of the optical properties. Coatings deposited on iron, nickel, cobalt base superalloy substrates are stable over 600°C and appear to be attractive for collector applications operating at high temperatures and under a high concentration of solar flux.

A linear modulation of light intensity by second‐order magnetooptical interaction (linear magnetic birefringence (L.M.B.) is reported. Theoretical predictions and experimental curves are given for two cubic crystals: YIG and TbiG and for rhombohedral crystal: α−Fe2O3 (Hematite).

The specific circular φF and linear φCM magnetic birefringences of Tb3 Fe5 O12 single‐crystal are reported as a function of the d.c. field Ha and from liquid helium temperature to room temperature. The sign, amplitude and slope of the Cotton‐Mouton effect are strongly dependent on T, Ha and on the direction of this field with respect to the crystal axis. Well defined maxima of % % the slope ΔφF/ΔHa and ΔφCM/ΔHa, observed near T=45 °K, are discussed both from the paramagnetic evolution of the Tb3+ ions in the anisotropic exchange and crystal fields which induce a noncolinear magnetic structure.

In a previous paper on Si-SiO2 multilayered mirrors (1), we have shown that metal-oxyde systems can be an interesting alternative to metal-metal multilayered coatings for XUV optics in the range from 10 nm to 60 nm. In this paper, we report experimental results of studies made on : a) an Si-Si02 Fabry-Perot etalon b) an Al-Si02 multilayered mirror c) an Al-A1203 multilayered mirror

Field and temperature dependence of the magnetization of some anisotropic garnets at low temperature and under dc fields up to 150 kOe are studied. An anisotropy energy taking into account the RE sites local symmetry (orthorhombic) allows: 1) a good fit with experimental results, 2) the description of the magnetic structure (cone type) evolution with applied field.

Rare‐earth iron garnets (RIG) are well known for their numerous interesting magnetic properties, but few works have been done on their optical behavior, especially at low temperatures. This paper studies the optical properties of TbIG, one of the most anisotropic RIG at low temperatures, showing large magnetic and magneto‐optical effects, in relation with its magnetic properties. For this purpose, polarized and unpolarized spectra of oriented single crystal of TbIG have been recorded at low temperatures (77, 4.2, and 2 °K) and in external magnetic fields up to 5 T, applied along the principal axis of a (110) plane. Transitions were observed from the ground level 7F6 to other states of the 7FJ multiplets of Tb3+ ions (between 2000 and 5500 cm−1). From the derived energy‐level scheme, a set of crystal‐field parameters was derived, within the D2 point symmetry. These parameters as well as the energy levels show no noticeable difference with those of Tb3+ ions in paramagnetic TbAlG. Correlations between polar...