This work describes an efficient and simple method to determine the effective electrooptic coefficients of crystals, along with the continuous recording of their temperature dependence. A sample with plane and parallel optical end faces acts as a Fabry-Pe/spl acute/rot resonator, which is submitted to a linear ramp of temperature. The thermooptic effect generates a shift of interference fringes that are phase-modulated by applying an appropriate electric field. Residual absorption of the material is considered to achieve the best accuracy. The case of KTiOPO/sub 4/ is given as an example to illustrate the method; first results on the thermal behavior of its effective coefficients r/sub i3/ are presented.

The growth of paratellurite single crystals by the vertical-gradient freezing technique is reported for the first time. Boules of 120mm long and 25mm in diameter were obtained under a temperature gradient of 10°Ccm−1 and translation rates lower than 0.6mmh−1. The spatial distribution of defects along the growth axis reveals a continuous evolution of the free convective fluid-flow regime as growth proceeds. Gas bubbles and dark inclusions rejected to the periphery in the upper part of the crystal are observed to lay preferentially in (100), (001), (11¯0) and (112) crystallographic planes. Among them, SEM and microprobe analyses evidenced the presence of metallic platinum, while micro-Raman experiments allowed to assess oxygen as being actually the gas content of occluded bubbles, originated at the crucible wall through Pt-induced dissociation of Te–O bonds.

A proper implementation of electro-optic materials in laser systems requires an accurate knowledge of their electro-optic coefficients, along with their temperature dependence which could be of importance at high power level. A new technique has been developed for this purpose, which takes advantage of the thermodynamic equivalence of two intensive parameters, namely the temperature and applied electric field. A suitably oriented parallelepipedic shaped sample is exposed to a laser beam and acts as a Fabry-Perot interferometer which is submitted to a linear ramp of temperature. The interference pattern is observed by reflection and the shift of interference fringes generated by the thermo-optic effect is detected through amplitude modulation of the light beam and recorded as a function of temperature. We then switch from amplitude- to phase-modulation by applying a suitable electric field to the crystal: the signal features now the derivative of the thickness fringes generated by the electro-optic effect. The thermo- and electro-optic coefficients are obtained from the fringe shift recorded respectively through amplitude- and phase-modulated operating modes. The study of both KTiOPO4 and LiInS2 single crystals is given as an example to illustrate the so-called Fabry-Perot Thermal Scanning Interferometric (FPTSI) method.

Pyroelectric current measurements performed on a LiInS2 monodomain single crystal show a linear variation of the current between 120 and 260K. Near room temperature, a space charge relaxation screens pyroelectricity. The pyroelectric coefficient follows a linear thermal dependence leading to an extrapolated value of 6×10−10CK−1cm−2 at 300K. As for other oxide-type pyroelectric compounds, this value is shown to be proportional to the electro-optic coefficient r333 of LiInS2.

The resonant frequency in a piezoelectric crystal is strongly temperature dependent. This physical property may be exploited to measure small overheating of the material induced by a weak optical absorption. A sample of congruent LiNbO3 is exposed to a laser beam, with a wavelength lambda chosen inside the transparency window. One of the piezoelectric resonances is selected and used as an internal thermal probe to record both dynamical and steady state overheating induced by the residual absorption k of the material. A bolometer-type equation describing the time dependence of the sample temperature is used to determine k accurately, the capacitance-rather than frequency-being the temperature-sensitive electrical parameter of the resonance.

The optical properties of LiInS2 suggested it as a promising material for generation of coherent radiation in the mid-IR region. Before investigating such capabilities its optical and mechanical properties have to be characterized precisely, and especially their evolution with temperature. Sufficiently large and suitably oriented crystals of good optical quality were studied. We first deduced the transparency range of these samples, as well as the frequencies of the optical phonons. We observed a phase-matched second-harmonic generation, using a nanosecond-OPO in the range 2.4-2.6 microns as the pump source and estimated a first value of the type-II nonlinearity d(eff)(XY)=7.4pm/V. The thermal expansion, thermo-optic, piezoelectric and electro-optic coefficients were determined along the three principal directions of polarization from -20 degreesC up to +120 degreesC by means of original interferometric methods. A so-called Fabry-Perot Thermal Scanning (FPTS) interferometric method has been developed to measure accurately the electro-optic coefficients. For LiInS2 the values of r(i3) were found to be of the same order of magnitude as its piezoelectric coefficients, but around one order of magnitude smaller than the electro-optic coefficients of the well known KTiOPO4.

The thermo-optic coefficient (delta) n divided by (delta) T of CaF2, ZnS and Ge single crystals have been measured in the infrared from 20 degrees C to 100 degrees C. The laser interferometric method employed allows a determination of (delta) n divided by (delta) T with an accuracy close to 10-6K-1 in the case of nonabsorbing materials. For Ge the uncertainty is increased by a factor of 3 and is mainly due to its increasing absorption coefficient with temperature. The behavior of ZnS was examined at 1.06 micrometers and 10.6 micrometers laser radiations; CaF2 and Ge were investigated respectively at 1.06 micrometers and 10.6 micrometers.

The pyroelectric effect exhibited by two nonlinear optical materials is used to measure the residual absorption in their transparency window. The polarization behavior of potassium titanyl phosphate KTiOPO4 and thallium arsenic selenide Tl3AlSe3 are first described to determine the value of their pyroelectric coefficient. The pyrospectroscopic technique is then applied for absorption coefficient measurements at discrete laser wavelengths with a relative uncertainty estimated around 10 percent.

An interferometric dilatometer has been designed for determination of thermo-optic coefficients of millimetric nonlinear optical (NLO) materials. The apparatus is a combination of a modified Mach-Zehnder arrangement for dilation measurements and a Fizeau technique for determination of changes in optical length. Its configuration allows measurements under known conditions of applied electric field. Analysis of the linear thermal expansion coefficient alpha b of a triglycine sulphate (TGS) single crystal around its second-order phase transition is used to evaluate the sensitivity of the interferometer, and measurements performed on a LiNbO3 single crystal exhibit step-like variations of changes in optical length from 20 degrees C to 122 degrees C. These experiments show that an accuracy better than 1*10-6 K-1 is achievable for both dilation and thermo-optic coefficients with this dilatometer, provided that they are not highly temperature-dependent and are under the condition of suitably controlled applied electric field.

The ENSH method (Epitaxial Nucleation in Submicroscopic Holes) is suitable to prepare a number of detachable oriented CdTe films of good crystalline quality with one bulk single crystal. It has been combined with the CSVD (Close-Spaced Vapour Deposition) to give detachable oriented films in a few minutes. The X-ray diffractograms given by reflection on such films are made of narrow peaks (i.e. Full Width at Half Maximum for the (111) peak ≊ 8' in 2θ scale).

Afin de pouvoir suivre d'une maniere continue l'evolution des frequences des modes de reseau de monocristaux en fonction de la temperature nous avons ete amenes a modifier un spectrometre pour l'infrarouge lointain. Tout en conservant les performances de l'appareil nous avons adapte un cryostat a temperature variable (1,6-270 K). Une cellule de mesure pour l'etude de la transmission et une cellule pour l'etude de la reflexion sont decrites. La sensibilite du recepteur a ete amelioree en remplacant le detecteur de Golay par un bolometre au germanium dope au gallium.

L'alternance des temps de pompage et des temps morts des pompes à vide mécaniques entraine une fluctuation de la pression au dessus du bain d'hélium liquide (par exemple 1.3 μtorr) qui est détectée avec un microphone à électret. Elle provoque une variation alternative de la température du bain superfluide (par exemple 55μK) qui est mesurée avec un bolomètre au germanium. Des écrans placés à l'intérieur du cryostat permettent de diviser par cent les fluctuations de la température du bain et par cinq le taux d'évaporation.

The pyroelectric probe technique which has been proven so valuable for observing domains in a ferroelectric plate cut perpendicular to the polar axis, can also be used to examine a plate parallel to the axis. Experimental problems peculiar to this display are considered in connection with calculations derived from Poisson's equation. Though the method is less sensitive, it is possible to look at nucleation, domain wall motion, reversible switching due to laser illumination etc… The longitudinal domain wall motion velocity in TGS is 24 times larger than the lateral one.

Specially made bismuth blacks deposited on glass can lead to highly insulating absorbing layers for the visible and the near infrared up to 4μm (absorption A > 15%, R□ > 1012Ω) with a very small density per unit area (10 μg.cm−2). Better results are obtained with phthalocyanine but they are confined to a small wavelength range in the visible. With graphite sputtered in argon and gold evaporated in high vacuum very thin layers can also be made but the insulation is poorer. Deposition of either bismuth or graphite on ferroelectrics sometimes leads to difficulties which are discussed briefly.

The method of epitaxial nucleation in submicroscopic holes (ENSH) of an intermediate thin film closely applied to a bulk single crystal is extended to the growth of II-VI compounds (i.e. CdSe and CdTe) at high temperatures.

The growth of CdTe oriented thin films by the ENSH method - i.e. Epitaxial Nucleation in Sub-microscopic Holes of an intermediate layer closely applied on a bulk single crystal — has been recently described. The CdTe films are generally difficult to detach from the bulk crystal. However free films are needed to study the infrared transmission in the spectral region of high absorption. To get them, the vitreous or amorphous thin intermediate layers are substituted by quite soluble an oriented NaCl layer grown from phase vapour on a (111) CdTe bulk crystal surface. The X-ray diffraction and Laue patterns show that the CdTe thin film grown on the NaCl intermediate layer is (111) oriented, and also the NaCl layer which covers the (111) CdTe bulk crystal surface. The far infrared transmission spectra obtained through the oriented CdTe films give directly the TO phonon frequency for q = 0 with accuracy.

We have studied the far-infrared absorption of Ba${\mathrm{F}}_{2}$, Ca${\mathrm{F}}_{2}$, and Cd${\mathrm{F}}_{2}$ doped with Tb, Sm, Nd, Pr, Dy, Ho, Er from room temperature down to 1.4 K. The background absorption induced by the rare-earth ($R$) impurity is too high in the case of Cd${\mathrm{F}}_{2}$ for any electronic transition to be seen. It is low enough for Ca${\mathrm{F}}_{2}$- and Ba${\mathrm{F}}_{2}$- doped crystals. In the case of all Ba${\mathrm{F}}_{2}$:${R}^{3+}$ crystals considered, we have found a common absorption band at 131 ${\mathrm{cm}}^{\ensuremath{-}1}$. The structure is explained by localized vibrations of the compensation ${\mathrm{F}}^{\ensuremath{-}}$ ions, in three different sites: cubic, tetragonal, and trigonal, where the $R$ ions are distributed in different proportions: 4%, 46%, 50%, respectively. We have also found specific bands sensitive to magnetic fields in the case of ${\mathrm{Dy}}^{3+}$ (41.2 ${\mathrm{cm}}^{\ensuremath{-}1}$), ${\mathrm{Ho}}^{3+}$ (37 ${\mathrm{cm}}^{\ensuremath{-}1}$), and ${\mathrm{Er}}^{3+}$ (69.2 and 70.3 ${\mathrm{cm}}^{\ensuremath{-}1}$). The Zeeman effect gives information on the Land\'e $g$ factors ${g}_{1}$ and ${g}_{2}$ for ground and excited levels, respectively, and shows that for ${\mathrm{Er}}^{3+}$ the observed lines correspond to two different sites. It is shown that ${g}_{1}={g}_{2}=3.6$ for the trigonal one and ${g}_{1}={g}_{2}=0.98$ for the tetragonal site. For Ba${\mathrm{F}}_{2}$:${\mathrm{Dy}}^{3+}$, ${g}_{1}=3.2$, ${g}_{2}<{g}_{1}$; for Ba${\mathrm{F}}_{2}$:${\mathrm{Ho}}^{3+}$, ${g}_{2}\ensuremath{-}{g}_{1}=7.6$. In both these crystals only one site (trigonal) has led to far-ir electronic transitions.

Electronic transitions and localised vibrations of the compensation F − ion have been found in the case of rare earth ions, while resonant modes are observed in the case of several transition ions.