Dmitri Yu. Paraschuk

Highly sensitive polarimetry

We present a highly sensitive method of pump-probe polarimetry for measurements of small pump-induced polarization rotation and ellipticity. The sensitivity of the method is analyzed for technical and shot-noise probe power fluctuations. The optimal polarimeter configuration is found. We show that it is possible to enhance the sensitivity to the pump-induced ellipticity by setting a small probe ellipticity inside the polarimeter with the help of a small shift wave plate. We applied the method in cw and ps measurements of photoinduced polarization parameters in a nanopolyacetylene film. The typical measured angles of polarization rotation were approximately 10-5 and approximately 10-8 rad in the cw and ps experiments, respectively.

Laser hypersound spectroscopy in Si and GaAs

We apply a transient pump-probe photo deflection technique to measure the profiles of subnanosecond sound photoexcitation. We show that the photoexcited electron-hole plasma expands with a supersonic velocity in GaAs and a subsonic velocity in Si.

Faraday effect in nanopolyacetylene

We measured small Faraday polarization rotation in nanopolyacetylene in a magnetic field approximately 150 Oe. We found that approximately 1% polyacetylene nanoparticles increase up to 50% the polarization rotation angle of the transparent matrix containing them when probed near and at the NPA absorption band. The rotation angles were in the range 1 - 15 (mu) rad.

Photothermal probing Ag states of trans-nanopolyacetylene in its transparency range

Dipole-forbidden states of trans-nanopolyacetylene in the near infra-red are probed by a photothermal method at room temperature. We found that light absorption at approximately 1 micrometers is four orders weaker than that corresponding to the main dipole-allowed transition.

Highly sensitive cw and transient polarization spectroscopy of photoexcited states in nanopolyacetylene

A highly sensitive photoinduced polarimetry method was applied to probe optical anisotropy of the photoexcited states in non-oriented films of nano-polyacetylene. The photoinduced absorption anisotropy was observed in both cw and transient polarization experiments. The photoinduced dichroism parameter of the nano-polyacetylene films, (mu) equals (forula available in paper) was measured on the sub-nanosecond time scale ((mu) approximately equals 1) and on the millisecond time scale ((mu) approximately equals (formula available in paper) are the absorption indexes of the linear polarized probe polarized along and across the linear polarized pump, correspondingly. We discuss delocalization of (pi) electrons in the photoexcited states of trans-nano-polyacetylene chains.

Precise photodetection with shot-noise-limit sensitivity for picosecond laser measurements: detection of small surface gradients with photodeflection technique

We present the simple and very effective radio frequency lock-in technique for precise measurements with cw-pumped mode-locked lasers. The technique is applied for the photodeflection transient spectroscopy that allowed to reach the sensitivity to surface displacement about one femtometer. We use the method for probing hypersound generation and propagation in a semiconductor plate.

Depolarization degree of diode-pumped single-frequency monolithic ring Nd3+:YAG laser

For the first time depolarization degree of the diode-pumped monolithic ring Nd3+:YAG laser has been measured. The obtained value of depolarization degree equals 3 (DOT) 10-3. It has been shown that the dominant mechanism of the intracavity losses and the output light depolarization is diffraction on random inhomogeneities of birefringence in the laser media.

Nonlinear frequency converters as sources and detectors of polarized light with linear polarization degree of 10-9

High degrees of linear polarization of laser radiation and sensitivity to its variation are achieved by applying frequency converters using nonlinear crystals as polarizers and analyzers. The factors leading to distortion of linear polarization of light in such devices are identified. A KD*P polarimeter with extinction ratio of 5 (DOT) 10-9 is developed on the basis of a quasi-CW picosecond YAG laser.

Photoinduced and electroabsorption spectroscopy studies of a highly stable form of transpolyacetylene

We present the results of steady-state photoinduced and electroabsorption spectroscopy studies in nonoriented films of highly stable soluble trans-polyacetylene. Using Kramers- Kronig analysis of the electroabsorption spectra the nonlinear third-order non-resonant susceptibility (chi) (3) ((omega) ;(omega) ,0,0) of trans-polyacetylene was estimated to be in the range of 10-9-8 esu.

Physical mechanisms of light-induced polarization effects "on reflection" in GaAs

Non-steady-state polarization response of photoexcited GaAs has been investigated with the specular micropolarimetry particularly in crystals with laser induced damages of near surface layer. Physical models of the polarization response in the excited GaAs due to electron-hole plasma photogeneration are discussed: the nonlocal electron-hole plasma model the optically induced piezogyrotropy the electrooptic effect in the Dember field. 1.