Paratellurite Crystal Research Articles

Converting IR radiation with broad-band pumping in nonlinear-optical crystals

This paper discusses the up-conversion spectra of broad-band thermal radiation in nonlinear optical crystals of lithium niobate and paratellurite with broad-band nonlaser pumping for various types of nonlinear interaction.

Piezogyration effect in paratellurite crystals

Piezogyration effect in paratellurite crystals

Diffraction of light by ultrasound in paratellurite crystals under Fresnel reflection conditions

We show that layers of acousto-optic gyrotropic paratellurite crystals perturbed by ultrasound can be used as efficient light modulators in transmission and reflection mode. We have established that the relative intensities of the diffracted waves are determined by the ratio of the refractive indices of the bounding media, the intensity of the ultrasound, and the thickness of the modulated layer. We show that for an asymmetric diffraction structure, efficient acousto-optic conversion is possible in reflection mode, and the weak effect of the gyrotropy is due to its suppression by Fresnel reflection at the boundaries of the layer.

Growth of the high quality and large size paratellurite single crystals

A new method was used to prepare the TeO 2 powders with high purity. Acousto-optic paratellurite (TeO 2) crystals were grown by the modified Bridgman method using the high purity TeO 2 powders. The highly perfect TeO 2 single crystal (bubble-free, twin-free, and crack-free) up to 52×52×80 mm 3 was obtained. The crack reason of the single crystal was discussed. The optimum conditions of growing high quality and large size TeO 2 single crystals were obtained, which included a growth rate of less than 0.6 mm/h, a temperature gradient in solid–liquid interface of about 45 K/cm and a growth direction of 〈1 1 0〉.

Bifrequency acousto-optic beam splitter

In this article, we present a bifrequency acousto-optic beam splitter used to select independently the two polarization states of an arbitrary polarized input beam with two acoustic carriers. We make use of a dual frequency anisotropic interaction in the crystal, two acoustic waves diffract the optical beam, each frequency being tuned for interaction with only one of the beam polarizations. We explain how this double interaction is made possible by a proper cut of the paratellurite crystal and for a chosen launching angle of the input beam. In the first part we derive the theory underlying the acousto-optic interaction and the design of the paratellurite device. Then we describe our experimental setup, show some experimental results, and discuss them.

Methods for measuring light scattering in germanium and paratellurite crystals

Methods for studying the scattered light in germanium and paratellurite (α-TeO2) crystals are considered. Investigations of the light scattering in Ge crystals were performed in the infrared wavelength range by the photometric-sphere method (in the range 2–3 μm) and by measuring the line-scattering functions (at 10.6 μm). In the visible range, the paratellurite single crystals were investigated by recording and analyzing images of laser beams transmitted through the samples. It is shown that small-angle Mie scattering is characteristic of both materials. Some conclusions about the sizes and the physical nature of scattering inhomogeneities are drawn. The effect of high-temperature annealing on the scattering intensity is studied.

Tunable acousto-optic filters with the multiple interaction of light and sound

Optical multipass schemes of the interaction of light and sound, which are promising for filtration of optical beams based on tunable acousto-optic filters, are studied. The features of operation of acousto-optic filters in the rejection and transmission regimes are considered. It is proved theoretically and confirmed experimentally that the use of multiple interaction improves the spectral and energy parameters of acousto-optic devices. The collinear and transverse geometry of acousto-optic interaction in cells based on a paratellurite crystal is studied in the double-pass, three-pass, and multipass diffraction regimes.

Measuring the light-attenuation coefficients of germanium and paratellurite crystals

This paper discusses the theoretical aspects of the optical properties currently used for determining the extinction coefficients, based on measurements of the transmittances of light. The measurement errors introduced by the spectrophotometric method and by versions of the directed transmittance method are estimated. Data obtained in wide spectral ranges concerning the transmission of light by single-crystal germanium and paratellurite are used to illustrate the points discussed here. © 2005 Optical Society of America

The relationship between mechanical stresses and optical anomalies in germanium and paratellurite

Optical interference and x-ray analysis methods are used to determine the mechanical stresses in single crystals of germanium and paratellurite, which cause local distortions of the wavefronts due to the photoelastic effect. The dislocation structure of the crystals close to optical anomalies is studied. The effect of high-temperature annealing on stress relaxation in germanium and paratellurite is investigated. © 2005 Optical Society of America

Light scattering by single crystals of paratellurite and germanium

The scattering of laser light with wavelengths of 0.53 and 0.63 µm has been studied in single crystals of paratellurite (alpha-TeO2) by recording and analyzing images of the cross sections of beams transmitted through the samples. The scattering of light with wavelengths 2-25 µm has been investigated in germanium crystals, using a method based on an integrating sphere and a spectrophotometric method. It is established that there is small-angle Mie scattering with the corresponding resonances in both materials. Based on data concerning the resonance frequencies, as well the form of the distributions, conclusions are drawn concerning the size, concentrations, and physical nature of the characteristic scattering inhomogeneities in the crystals. © 2005 Optical Society of America

Collinear Diffraction of a Divergent Light Beam by Ultrasound in a Paratellurite Crystal

The collinear acousto-optical interaction of a divergent light beam with ultrasound along the approximate [110] direction in a TeO2 paratellurite crystal is investigated theoretically and experimentally. The collinear diffraction is studied at an ultrasonic frequency f ≈ 149 MHz under exposure of the crystal to an uncollimated laser light beam at a wavelength λ = 633 nm and at an angle of divergence as large as 4°. It is shown that the collinear diffraction along the direction forbidden for acousto-optical interactions of plane waves occurs only under conditions where the light beam is uncollimated and the diffraction efficiency increases with an increase in the divergence of the light beam. It is proved that the attenuation of an acoustic wave brings about a decrease in the diffraction efficiency and an increase in the transmission bandwidth of the device used. A model of the collinear acousto-optical filter based on a paratellurite crystal with an interaction length l = 2.7 cm is analyzed. The collinear acousto-optical filter is characterized by a high resolving power (∼3000), a high diffraction efficiency (I1/I0 ≈ 0.8), and a large angular aperture (Δϕ ≈ 4°). This makes collinear diffraction promising for use in acousto-optical filters based on paratellurite crystals.

Two-Coordinate Diffusion of Optical Beams by an Acoustooptic Raman–Nath Modulator Based on a Paratellurite Crystal

Acoustooptic Raman-Nath diffraction by a standing acoustic wave in a paratellurite crystal is investigated. An acoustic line is made in the form of a polished cube and serves as a high-Q acoustic resonator. A slow shear wave is excited by a single piezoelectric transducer. Multiple lossless sound reflections lead to two-coordinate light diffusion. When the acoustic intensity introduced into the crystal is about 2 W/cm2 at a sound frequency of 7 MHz, there appears a diffraction pattern in the form of a homogeneous light spot with a solid angle of about 0.5 sr. An explanation for the features of the acoustooptic interaction is given. It is shown that this type of diffraction is helpful in designing acoustooptic two-coordinate diffusers of light beams.

Nearly Backward Reflection of Elastic Waves in an Acousto-Optic Crystal of Paratellurite

Some features of the propagation and reflection of acoustic waves in the XY plane of a paratellurite crystal have been studied. It is established that the acoustic waves exhibit an unusual backward reflection from the side crystal facet in the case of glancing incidence onto the crystal-vacuum interface. The experimental results are in good agreement with theoretical predictions.

Acoustooptic nonpolar light controlling devices and polarization modulators based on paratellurite crystals

A complex of investigations and projects aimed at solving problems of highly effective acoustooptic control of nonpolarized laser radiation is generalized on the basis of anisotropic Bragg’s diffraction in a TeO2 crystal from a slow acoustic wave, which is characterized by extraordinarily high acoustooptic quality. Modulators of the zeroth diffraction order, modulators of the first Bragg’s order, and a polarization-insensitive deflector are considered. The developed systems ensure the control of the polarization state of optical radiation. These systems are employed in setups and devices based on high-power solid-state and fiber lasers with a wavelength of 1.06 µm.

Defects of different sizes in large paratellurite single crystals

Paratellurite single crystals have good acoustooptical properties that are important for various devices, such as deflectors, modulators, and tunable noncollinear filters. Paratellurite single crystals of up to 80 mm in diameter and 100 mm in height were grown using the Czochralski method from ultrapure melts. Optical anomalies in the grown crystals—gas bubbles, striations, impurity inclusions with nearby stresses, and regions with high dislocation densities—were studied with chemical, X-ray, and optical methods.

Anisotropic acoustooptic modulator of nonpolarized light based on diffraction by a slow acoustic wave in a paratellurite crystal

The problem of anisotropic Bragg diffraction of nonpolarized light by a slow acoustic wave in a TeO2 crystal is solved. Two independent acoustic waves are excited in the crystal. Nonpolarized light splits in the crystal into two orthogonally polarized eigenmodes, either diffracting by its associated acoustic beam. Conditions under which the angles of incidence and diffraction are the same for both diffraction processes are found. Depending on the acoustic frequency, the diffracted light at the exit from the crystal may be represented either by a single nonpolarized beam or by two orthogonally polarized beams with different directions and orthogonal polarizations. This may provide a high diffraction efficiency (up to 100%) for nonpolarized light in a TeO2 crystal. Theoretical calculations are supported by experiments. Modulators capable of controlling a high-power laser operating at a wavelength of 1.06 µm are fabricated.

Partial Ferroelastics

As it follows from the symmetry consideration of nonmagnetic crystals there are only 11 possible nonferroelectric species for partial ferroelastics, which are characterized by the absence of full primary ferroic properties. It has been suggested that these partial ferroelastics should be full secondary ferroics (ferroelastoelectrics or/and ferrobielastics). To prove this statement the crystallophysical method was considered. It has been shown that partial ferroelastics may be (i) full ferrobielastic and full ferroelastoelectric (one species); (ii) full ferrobielastic only (two species); (iii) full ferroelastoelectric and partial ferrobielastic (the rest 8 species). Primary and secondary ferroic properties of cristobalite (SiO2) and paratellurite (TeO2) crystals are discussed.

Prise en charge des lombalgiques

The quasicollinear geometry of acousto-optic (AO) diffraction is notable as makes it possible to achieve an extremely high AO interaction length and, consequently, an anomalously high spectral resolution for AO devices. This geometry is especially convenient for the implementation of multifrequency AO diffraction, which has found wide application for solving the problems related to the laser pulse shaping. Since acoustic beams propagate over long distances in quasicollinear AO devices, and optical radiation spectral components diffract in the acoustic field in different parts of the AO crystal, accurate calculation of the characteristics of such devices requires knowing the distribution of the acoustic field amplitude inside the AO cell. The acoustic beam structure is affected by several factors in quasicollinear AO cells: the dimensions of the piezoelectric transducer, the geometry of acoustic wave propagation in the AO cell, acoustic anisotropy and the acoustic energy absorption along the chosen direction in the crystalline material used. In this paper, we propose a generic method to measure the acoustic beam power distribution along the direction of its propagation in the quasicollinear AO cell in the presence of ultrasound power absorption and media acoustic absorption. The measurements were carried out for the ultrasound frequency range from 72 to 176 MHz, for the case when the wave vector of the acoustic beam is directed at an angle of 1.58∘ to the [110] axis in the (11¯0) plane of the paratellurite crystal. The ultrasound attenuation coefficients were obtained for frequency interval between 87 and 176 MHz and their linear dependence on ultrasound frequency was confirmed.

Angular aperture characteristic of the optical activity for the paratellurite crystal

Angular aperture characteristic of the optical activity for the paratellurite crystal

P‐98: Acousto‐Optic Separator for Stereoscopic Laser Videoprojection

AbstractIn this paper, we present an original acousto‐optic device which allows to separate an arbitrary polarised incident light beam into two orthogonally polarised diffracted beams. This device operates with a single frequency ultrasonic wave and the two diffracted orders are frequency up and down shifted, respectively. A birefringent crystal of Paratellurite has been chosen for experimental validation due to its very high acousto‐optic figure of merit for the slow acoustic shear wave. This device has been conceived in order to be implemented in a optical modulation line of a stereoscopic laser videoprojector based on the simultaneous projection of the two left and right images orthogonally polarised. Special polarising glasses select the two images for each eye. The projection is based on a X‐Y scanning of a laser beam which is both intensity and polarisation modulated. The “on‐line” separator allows to dynamically control and minimize the “ghost” phenomenon of a such a stereoscopic system.