A. I. Kolesnikov

Manifestation of Gyrotropy upon Light Scattering in Paratellurite

Upon scattering of laser radiation at different wavelengths, three optical effects—rotation of the plane of polarization of linearly polarized light, dependence of the specific rotation on the radiation wavelength, and the dependence of the scattered light intensity on the angle between the scattered and incident beams—are simultaneously observed. The intensity distributions of the scattered laser light at 0.488, 0.531 nm, and 0.633 μm along the optical axis of a thick sample of a TeO2 single crystal are visualized. Based on the patterns obtained, the values of the specific rotation are calculated, and the curve of the optical rotation for the visible range is obtained.

Optical properties of large germanium monocrystals

Optical characteristics of germanium monocrystals with a diameter of 150 and 200 mm grown by the Czochralski and directional crystallization methods were studied. We measured spectral transmittance of the monocrystals in the wavelength range of 2.3–25.0 μm, directional transmission and light scattering in the 2.4–3.0 μm range, and noninhomogeneity of the refractive index of monocrystals by the interference technique at 3.39 μm. The measurements were performed on antimony-doped germanium monocrystals with a diameter of 200 mm and thickness of 15 mm (grown by the directional crystallization method) and 18 mm thick (grown by the Czochralski method). Measurements were also performed on a germanium monocrystal with a diameter of 150 mm and thickness of 15 mm grown by the Czochralski method without adding a ligand. The measurement results revealed different optical quality of monocrystals, expressed in the nature and amount of refractive index inhomogeneity, which imposes restrictions on the use of blanks.

Surface structure of large germanium single crystals

The dependence between structural-defect generation and the growth kinetics of germanium single crystals pulled from melts is investigated via selective chemical etching and the optical, atomic-force and scanning electron microscopy techniques. It is ascertained that the surface microrelief of germanium crystals grown from melts by means of directional crystallization contains protrusions and cavities with spatial periodicities of 5 and 50 μm. The values of the kinetic coefficients are estimated. It is demonstrated that the main part of the crystals is formed according to the normal mechanism with the kinetic coefficients βk = 2 × 10−5 m s−1 K−1.

LASER CONOSCOPY OF LARGE-SIZED OPTICAL CRYSTALS

Conoscopic interferometry provides a simple method of non-destructive control of the quality of a number of ferro-piezoelectric and optical crystals. Standard optical microscopes, including some commercial instruments, are easily adapted for implementation of conoscopic studies, though limited to small handy samples with a thickness of the order of 0.5 mm. In the present work we show that the usage of wide convergent or divergent conical laser beams in a simple benchtop configuration makes it possible to examine large-sized optical crystals by the method of conoscopy, including samples elongated along the optical axis direction. As distinct from traditional optical microscopy the conoscopic figures obtained with the aid of the laser installment may contain tens and hundreds of isochrome fringes thus increasing the informative capabilities of the method. Large-sized crystals of LiNbO3 (5795 mm), TeO2 prisms (44×41×14mm) were examined experimentally at different angles between the optical axis and normal to the crystal surface. The experimental studies of different optical anomalies are confirmed by calculations based on the theoretical analysis given in a previous work of the authors.

Isochrome Shapes in the Conoscopic Patterns of Uniaxial Crystals

It is shown theoretically that in the method of conoscopy in the general case of arbitrary orientation of the optical axis (OA) and normal to the crystal surface, the isochromes should be described by the curves of the fourth order and higher. The existence of such type of isochromes is demonstrated experimentally. Examples of the computer calculation of the system of equations describing the isochrome shapes derived without commonly used approximations adopted in previous studies are presented.

Optical parameters of paratellurite crystals

Refractive indices and transmittances of paratellurite single crystals have been measured. The specific optical rotation is determined and the Verdet constants are calculated for a radiation wavelength of 355 nm.

Acousto-optic spectrometer for speckle imaging

We report on the acousto-optic spectral imaging system designed for speckle imaging observations and interferometry. The setup is based on a non-collinear paratellurite acousto-optic tunable filter (AOTF). Breadboard prototype of the system with an in-house fabricated AOTF has been designed and commissioned. The prototype spectral range covers the band from 3600 to 5800 Å. Arbitrary spectral transmission function synthesis of the AOTF was applied. The AOTF spectral transmission bandwidth is programmable in the range from 44 to 875 cm−1 (12.5–250Å at the wavelength of 5050Å). The AOTF is synchronized with the CCD readout and can be used as a global electronic shutter with on/off switching time of 12 μs. The exposure is adjusted as any integer multiple of 4.5 μs.

Wide-field acousto-optical imaging spectral polarimeter: design and commissioning

We report design of acousto-optic imaging spectrometer for spectral and polarimetric photometry and commis- sioning of the instrument at 0.6-m F/12.5 telescope at the Southern Astronomical Station of Lomonosov Moscow State University. The spectrometer was operating over the spectral range 3800–5800 Å with the passband of 10 Å at the wavelength of 5000 Å The imaging spectrometer could be used for observations of objects with the minimum brightness of 12.5 mag (for 0.6-m telescope, 120 s exposition, and SNR∼10). Spatial resolution of the spectrometer was estimated better than 1.2”, and the field of view was ∼250”.

Laser-ultrasonic imaging for evaluation of temperature fields in paratellurite optical crystal

The problem of internal temperature gradients is topical in design of high-performance acousto-optic devices. Current study is focused on the application of laser ultrasound method for evaluation of temperature fields in the paratellurite acousto-optic cell. An automatized laser ultrasonic structuroscope UDL-2M is used to scan the cell surface and to evaluate the temperature distribution from the time-of-fight measurements. The experimental results are presented and precision is discussed. The proposed method has the accuracy of 2–3 degrees Celsius.The problem of internal temperature gradients is topical in design of high-performance acousto-optic devices. Current study is focused on the application of laser ultrasound method for evaluation of temperature fields in the paratellurite acousto-optic cell. An automatized laser ultrasonic structuroscope UDL-2M is used to scan the cell surface and to evaluate the temperature distribution from the time-of-fight measurements. The experimental results are presented and precision is discussed. The proposed method has the accuracy of 2–3 degrees Celsius.

Thermal characteristics of paratellurite single crystals by the rectangular thermal wave method

The study of the thermal characteristics of bulk nonferroelectric materials with low heat conductivity coefficient by the pyroelectrical rectangular thermal wave is shown to need the solution of the problem of the thermal conductivity for a three-layer system. The thermal characteristics of a paratellurite crystal with various crystallographic directions were studied. The heat conductivity coefficient is found to depend on the crystallographic direction.