N. V. Chigarev

Shot-noise-limited radio-frequency lock-in photodetection with a continuous wave mode-locked laser

We have developed quite a simple and original lock-in photodetection system that works at a fixed radio frequency. The system includes a photodetector, a frequency down converter and a standard low-frequency lock-in amplifier. The resonant implementation of the radio-frequency attachment provides high gain and high selectivity, which have enabled us to attain the shot-noise-limited sensitivity to relative optical power change δP/P≃4×10−8 Hz−1/2 at a detection frequency of 6.2 MHz in measurements with a cw mode-locked Nd:yttrium aluminum garnet laser. We have realized the precise position-sensitive photodetection for laser pointing noise measurements and picosecond photoacoustic spectroscopy of solids.

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.

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.

Wavelength dependence of ultrafast and large third-order non-linear optical response of polyacetylene nanoparticles

Abstract The third-order optical non-linearity was measured in nanopolyacetylene using femtosecond optical Kerr effect technique at wavelength from 790 to 860 nm. The ultrafast non-resonant effective second-order hyperpolarizibility for single polyacetylene nanoparticle was estimated to be as large as 1.0×10 −27 esu, which corresponding to the γ c of single carbon atom contribution equals to 5.0×10 −33 esu. We ascribed the observations to the highly ordered structure of nanopolyacetylene and delocalization of the π electrons along the conjugated chains was supposed to be responsible for such properties.

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.

Dynamic response of the 2Ag state in nanopolyacetylene on the time scale from femtoseconds to milliseconds

Summary form only given. Nanopolyacetylene (nano-(CH)/sub x/) is a /spl pi/ conjugated material in which 10-nm polyacetylene nanoparticles are dispersed in a polyvinylbutyral matrix. Each nanoparticle comprises of packed /spl pi/-conjugated chains of length about 30 double bond (C=C). The absorption spectrum of nano-(CH)/sub x/ has a well-resolved vibronic structure with the zero-phonon line at 1.7 eV. Nano-(CH)/sub x/ has a excellent long-term stability and reveals no symptoms of photooxidization. We present results obtained on nonoriented films of trans-cis blend of nano-(CH)/sub x/ at 300 K.