V.Ya. Molchanov

An acousto-optical imaging spectrophotometer for astrophysical observations

We present the results of our tests of an acousto-optical imaging spectrophotometer with a CCD detector for astronomical observations. The tunable acousto-optical filter, based on a paratellurite single crystal with a 13 Å pass band operates in the wavelength range 6300–11000 Å. We obtained image spectra for the planetary nebula NGC 7027 in the Hα line and for Saturn in the methane absorption band, as well as Hα and continuum images for the nuclear region of the Seyfert galaxy NGC 1068.

Acousto-optical adaptive correction of a chirped laser pulse spectral profile in a Nd-phosphate glass regenerative amplifier

We present results of experimental research carried out with the help of an acousto-optical light dispersive delay line (LDDL) on spectral correction of chirped laser pulses in a Nd-doped phosphate glass regenerative amplifier (RA) characterized by high gain (G 4 10 7 ). The spectral resolution of the LDDL was equal to 1:1 cm 1 at a diffraction efficiency greater than 80%. The use of the LDDL made it possible to implement operating conditions of the RA under which the duration of the output chirped pulse did not shorten in comparison with the duration of the input one, which meant that the width of the spectral emission could be preserved. (Some figures may appear in colour only in the online journal)

Influence of acoustic anisotropy in paratellurite on quasicollinear acousto-optic interaction.

The influence of paratellurite acoustic anisotropy on the quasicollinear acousto-optic diffraction characteristics was examined. In the presented case the quasicollinear geometry of acousto-optic diffraction is realized with the use of acoustic beam reflection from one of the crystal surfaces. The simulations were based on the solution of acoustic beams propagation problem for anisotropic media previously presented in Balakshy and Mantsevich (2012). It is shown that media inhomogeneity affects the distribution of the acoustic energy in the ultrasound beam and the shape of wave fronts. The acoustic beam structure influences the characteristics of quasicollinear acousto-optic diffraction causing transformation of acousto-optic device transmission function shape and reducing the diffraction efficiency.

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.

Generation of frequency-tunable pulsed terahertz radiation by a Cr : forsterite laser system with an acoustooptical control of the pulse temporal profile

We report the experimental results on generating pulsed terahertz (THz) radiation, frequency-tunable within the range . The THz pulse generation was implemented using the method of optical rectification of femtosecond laser pulses in the nonlinear organic crystal OH1. The frequency tuning of the THz radiation was provided by adaptive phase – amplitude modulation of the pump pulses from the Cr : forsterite laser system with a radiation wavelength of using the acoustooptical dispersion delay line.

Anisotropic light diffraction in crystals with a large acoustic-energy walk-off

The influence of energy walk-off in an acoustic beam on the characteristic of anisotropic Bragg diffraction of light has been investigated by the example of paratellurite crystal. The angular and frequency characteristics of acousto-optic diffraction have been calculated in wide ranges of ultrasound frequencies and Bragg angles using the modified Raman-Nath equations. It is shown that the walk-off of an acoustic beam may change (either widen or narrow) significantly the frequency and angular ranges. The calculation results have been experimentally checked on an acousto-optic cell made of 10.5°-cut paratellurite crystal.

An acousto-optical imaging spectrometer for astrophysical measurements

An optical scheme of an acousto-optical imaging spectrometer for observing extended astrophysical objects with line emission spectra is proposed. The use of an additional prism with a specified angular dispersion makes it possible to separate images of an extended object at different emission lines and images generated by minor maxima of the acousto-optical filter transmission function. A prototype of the imaging spectrometer has been designed.

Acoustic field structure simulation in quasi-collinear acousto-optic cells with ultrasound beam reflection.

HIGHLIGHTSThe bulk acoustic wave reflection from the crystal face influence on its structure.The TeO2 acoustic anisotropy influence before the ultrasound beam reflection is low.Low anisotropy before the reflection allows to form fairly homogeneous acoustic field. ABSTRACT Ultrasound wave reflection from one of the crystal faces is the convenient way to arouse the acoustic beam with a desired propagation direction in acousto‐optic cells with collinear and quasi‐collinear interaction geometries. The reflection process effects on the ultrasound field amplitude and phase structure. The method to simulate the reflected finite ultrasound beam structure in the case of acoustically anisotropic media is presented in this paper. The investigation is carried on the example of two quasi‐collinear acousto‐optic cells fabricated on the base of tellurium dioxide crystal. The cells have special geometry that allows to obtain extremely long acousto‐optic interaction length and to achieve unprecedented spectral resolution. The influence of reflection process in the acousto‐optic diffraction characteristics was also examined.

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.

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.