P. A. Apanasevich

All-solid-state stimulated Raman scattering-based source of pulsed radiation tunable in 345-625 and 690-1250 nm ranges for spectroscopic applications

The generation characteristics of a barium nitrate Raman laser with pumping by a narrowband tunable nanosecond (tp 9 ns) Ti : Sapphire laser were studied for the first time. The generation of the first three Stokes components of stimulated Raman scattering (SRS) and their second harmonics was obtained with a spectral linewidth of <0.4 cm 1 and tuning ranges 930‐1250 and 465‐625 nm. The efficiencies of energy conversion obtained for the first, second and third SRS components were h1s = 60%, h2s = 49% and h3s = 33%, respectively. On the basis of the investigated barium nitrate Raman laser, an all-solid-state laser system was built for various spectroscopic applications, which provides powerful narrowband pulsed radiation tunable in the spectral ranges 345‐625 and 690‐1250 nm. The applicability of the constructed laser system in Raman spectroscopy was successfully tested by performing a saturation resonance Raman experiment on nickel porphyrin in water solution. Copyright ” 2000 John Wiley & Sons, Ltd.

Barium-nitrate-based Raman lasers excited with LiF:F2-laser and its second harmonic

Raman lasers on barium nitrate crystal pumped with the radiation of nanosecond LiF:F2 laser and its second harmonic have been developed and optimized. As a result, using simple and cheap all-solid-state laser technique the continuously tunable radiation of the first, second, and third Stokes components of stimulated Raman scattering of LiF laser radiation with maximum conversion efficiencies of about 35, 28, and 10%, respectively, was obtained in the spectral range between 1240 and 1800 nm. Using the second harmonic radiation for pumping barium nitrate allowed us to generate the continuously tunable radiation of its first and second Stokes components in 594-682 nm range with maximum conversion efficiencies of approximately 40-45 and 10-15%, respectively.

Thermal lensing in barium nitrate due to stimulated Raman scattering of nanosecond laser pulses

Barium nitrate crystal are studied using one- and two-beam Z-scan techniques by excitation with the second harmonic radiation of nanosecond Nd:YAG laser and probing with the cw He:Ne laser. For the first time, a thermal lens due to the dissipation of energy of the SRS-excited Ag vibrational mode to the heat is observed and measured.

Nonlinear refraction and absorption in vanadate crystals at 532 nm

The nonlinear optical properties of a number of vanadate crystals were studied using a single-beam Z-scan at 532 nm (with a picosecond Nd:YAG laser (YAG: yttrium aluminum garnet)). Both nonlinear refraction indices and nonlinear absorption coefficients were measured for the crystals. A substantial dependence of the nonlinear optical properties of the vanadates on the cuts of the crystals, the orientation of their axes relative to the polarization vector of the laser radiation, and the ligation with active ions was observed.

Spectral shift of Raman generation band in a Bessel pump beam

A spectral shift in the first Stokes generation band has been observed at stimulated Raman scattering in a Bessel light beam. Under nanosecond pulse excitation in barium nitrate crystal, the Stokes emission propagating along the Bessel beam axis has been found to be frequency shifted toward the blue side by 3.7 GHz with respect to the Stokes emission propagating along the surface of a cone. Numerical data have shown that the observed frequency shift is directly related to the contribution of the real part of the Raman susceptibility to the refractive index. This contribution causes an increase in the Stokes gain out of exact Raman resonance owing to induced focusing, which inhibits diffraction spread of generated light and thus provides its better spatial overlap with the pump beam.

Time-resolved cross-correlation spectroscopy with incoherent light for studying inter- and intramolecular processes

The application of two-color incoherent cross-correlation spectroscopy to study ultrafast processes in organic liquids and solutions is discussed. This kind of time-resolved spectroscopy is based on using two broadband correlated pulses of long duration with different central frequencies. Its time resolution is determined by the cross-correlation time of the intensities of used radiations. The statistical properties of the radiations have been investigated. The developed technique allowed us to perform kinetic measurements with femtosecond resolution on the ordinary nanosecond laser spectrometer modifying it in a comparatively simple way. The present technique was demonstrated and tested by studying subpicosecond Kerr dynamics in a number of organic liquids and their mixtures. An approach is also proposed to study the population relaxation of electronic and vibronic states of organic molecules including non-luminescent ones.

Eye-safe solid-state quasi-CW Raman laser with millisecond pulse duration

We demonstrate the first quasi-CW (ms-long pulses, pump duty cycle of 10%) end-diode pumped solid state laser generating eye-safe radiation via intracavity Raman conversion. The output power at the first Stokes wavelength (1524 nm) was 250 mW. A theoretical model was applied to analyze the laser system and provide routes for optimization. The possibility of true CW operation was discussed.

Generation of eye-safe radiation in passively Q-switched laser with three Stokes intracavity Raman conversion

Raman conversion is one of the methods for obtaining pulsed laser radiation into the eye-safe (near 1.5 µm) spectral region. Well developed lasers on Nd doped crystals generate radiation around the 1.06 and 1.3 µm wavelengths. Both passive and active Q-switchings are widely used for pulse generation at 1.06 µm wavelength. For generation at 1.3 µm wavelength an active Q-switch is primary applied, because of low efficiency of passive absorbers in this spectral range. Starting at 1.06, or 1.3 µm wavelengths Raman conversion in crystal media with Raman shifts from 900 to 1000 cm−1 allows to reach the eye-safe region by three, or one Raman shifts. Such possibilities were demonstrated at the flash lamp pumping for milliJoule level of laser pulses. For laser systems with longitudinal diode pumping when pulse energy is in the microJoule range the one shift Raman conversion of the 1.3 µm laser radiation is usually used with active Q-switch laser operation. Meanwhile, a possibility to obtain the eye-safe radiation from a passively Q-switched all solid-state laser system with Raman conversion and longitudinal pumping is highly attractive due to constitutive simplicity, compactness and good beam quality.

Multi-wavelength quasi-continuous wave all-solid-state system based on Raman lasers

High-repetition-pulse-rate nanosecond laser system is developed. It is based on Raman lasers with barium nitrate and KGW crystals. The minimum Raman threshold of laser generation corresponds to only 0.2-0.4 kW of peak pumping power. The laser system generates the radiation at 22 wavelengths in the 280-1600 nm spectral range with average powers from several mW to 1.4 W. The maximum Raman conversion efficiency reaches 40 %. The minimum spectral width of the generated radiation is equal to 0.1 cm-1. This laser system can be used for spectroscopy studies, medicine, and for other applications.

Dynamics of light-induced anisotropy in Cu-porphyrin solutions studied with correlation incoherent-light technique

Transient spectroscopy technique based on correlation properties of the second harmonic of nanosecond Nd:YAG-laser and its first Stokes component from stimulated-Raman- scattering generator was applied for studying orientational diffusion of Cu-octaethylporphyrin and Cu-tetraphenylporphyrin dissolved in tetrahydrofuran and toluene.