Transient Stimulated Raman Scattering Research Articles

Multiwave quasi-phase-matched anti-Stokes stimulated Raman scattering

In our method of anti-Stokes generation at stimulated Raman scattering (SRS) with quasi-phase-matched conditions we took into account the generation of high-order Stokes and anti-Stokes components. The dependence of Raman gain dispersion on SRS generation was studied using numerical simulation. The possibility of an effective periodical structure for hydrogen was determined. For a multiwave media model we found that the efficiency of first anti-Stokes generation reached ~40%. We determined that for transient SRS the maximum efficiency of quasi-phase-matching anti-Stokes generation does not depend on pulse duration while the medium length greatly increases as transience increases. Our calculations showed that for hydrogen and barium nitrate if the duration of interacted pulses is 3 ns and more then we can neglect the influence of transitivity on quasi-phase-matching conditions. The results of our research can be used for the creation of new effective nonlinear optical frequency converters and Raman amplifiers.

Nonlinear vibrational spectroscopy of water structures utilizing laser-induced phase transition phenomena in liquid water

Anomalous enhancement of the stimulated Raman scattering (SRS) of water molecules in the OH stretching vibrational region is observed when a laser-induced phase transition from liquid to plasma takes place in liquid water. The SRS is emitted before the phase transition and has a duration of several tens of picoseconds full width at half maximum. From the spectroscopic analysis of the SRS, it is suggested that the excess electrons, which are generated in a few picoseconds before the phase transition, play an important role in the transient SRS enhancement through the change of the nonlinear polarizability induced around the electrons in liquid water. Several applications of the enhanced vibrational spectra in the OH stretching vibrational region to the spectroscopic analyses of local water structures in various environments are also described.

Extending the Tuning Range of Short-Pulse Lasers by Transient Stimulated Raman Scattering in Gases

Transient stimulated Raman scattering (SRS) is a convenient method to extend the tuning range of short-pulse lasers. In this paper we present results obtained by using 400 nm pump pulses of 2.5 ps duration. After briefly reviewing earlier work on transient SRS in pure hydrogen and in H

Comparative spontaneous Raman spectroscopy of crystals for Raman lasers

A comparison of the spectroscopic parameters of Raman-active vibronic modes in various crystalline materials with a view to the use of these crystals for stimulated Raman scattering (SRS) is presented. It includes data on the Raman frequency shift, linewidth, integral, and peak Raman scattering cross sections. For steady-state SRS the highest Raman gain coefficient has been proved to be in barium nitrate and sodium nitrate crystals; for transient SRS it is expected to be in lithium niobate and tungstate crystals. Barium tungstate and strontium tungstate are proposed as new highly efficient Raman materials for both SRS cases.

Integrability and Self-Similarity in Transient Stimulated Raman Scattering

The phenomenon of stimulated Raman scattering (SRS) can be described by three coupled PDEs which define the pump electric field, the Stokes electric field, and the material excitation as functions of distance and time. In the transient limit these equations are integrable, i.e., they admit a Lax pair formulation. Here we study this transient limit. The relevant physical problem can be formulated as an initial-boundary value (IBV) problem where both independent variables are on a finite domain. A general method for solving IBV problems for integrable equations has been introduced recently. Using this method we show that the solution of the equations describing the transient SRS can be obtained by solving a certain linear integral equation. It is interesting that this equation is identical to the linear integral equation characterizing the solution of an IBV problem of the sine-Gordon equation in light-cone coordinates. This integral equation can be solved uniquely in terms of the values of the pump and Stokes fields at the entry of the Raman cell. The asymptotic analysis of this solution reveals that the long-distance behavior of the system is dominated by the underlying self-similar solution which satisfies a particular case of the third Painleve transcendent. This result is consistent with both numerical simulations and experimental observations. We also discuss briefly the effect of frequency mismatch between the pump and the Stokes electric fields.

Stimulated Raman scattering of picosecond pulses in barium nitrate crystals

Stimulated Raman Scattering (SRS) of picosecond pulses was investigated in Ba(NO 3) 2 crystals. The results are in good agreement with transient SRS theory. First and second Stokes conversion efficiencies were measured to be 25% and 5%, respectively.

Transient Stimulated Raman Scattering

The system: $u_\xi = - zv$, $v_\xi = \bar zu$, $z_\tau = u\bar v - \gamma z$ with $z \to 0$ at $\tau \to - \infty $ and initial data for ${\bf u} = (u,v)$ at $\xi = 0$ are considered. Well posedness results are obtained for this and also for a version discretized in $\tau $. Stability is considered as $\xi \to \infty $.

Beam-pointing fluctuations in a gain-guided Raman amplifier.

We present a measurement of the beam-pointing fluctuations of a transient Raman-amplifier output using an interferometric method and a theoretical treatment of the three-dimensional, spatial propagation of transient stimulated Raman scattering (SRS) including the fluctuations of the Stokes field giving rise to the beam-pointing fluctuations. The theory is based on an effective steady-state model for the transient SRS process. By using nonorthogonal transverse modes to expand the field, we incorporate the effects of excess spontaneous-emission noise associated with gain-guided amplifiers. The agreement of the measurements with the theoretical treatment demonstrates that the beam-pointing jitter is caused by quantum noise. The beam-pointing fluctuations increase as the Fresnel number of the interaction volume increases because more spatial modes are excited.

Transient stimulated Raman scattering in lead vapor

An investigation of stimulated Raman scattering (SRS) of short-pulse (6-ns) XeCl-laser radiation in Pb vapor is reported. Conversion efficiencies, based on peak power, up to 15% have been obtained for Pb-oven temperatures of 1260 degrees C. The functional dependence of conversion efficiency, in the short-pulse regime, upon buffer-gas pressure and species differs significantly from that observed for long-pulse (>20-ns) pumping, corresponding to steady state behavior. Analysis of the data and comparison with transient SRS in H/sub 2/ yield an estimate of T/sub 2/ approximately=1ns for the transient response time T/sub 2/ of Pb vapor. The observed pressure effects are explained in terms of a reduction in T/sub 2/, and hence Raman gain, by collisions with buffer-gas atoms.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Investigation of transient electronic SRS by the excitation and probing technique using a double train of picosecond pump pulses

The accumulation effect (i.e. the atomic-memory effect) in the transient electronic Stimulated Raman Scattering (SERS) in barium vapor under the influence of a picosecond pump pulse train has been observed for the first time. We used either a single (in the case of relative large T 2, T 2 > T) or a double pump pulse train with variable intertrain interval T' (in the case of small T 2, T 2 < T. Energy ratios of three pump and three Stokes pulses are sufficient to obtain the T 2 value at a single laser shot. There w a reasonable agreement between theory and experimental results.

Macroscopic Manifestation of Quantum Fluctuations in Transient Stimulated Raman Scattering

Macroscopic Manifestation of Quantum Fluctuations in Transient Stimulated Raman Scattering

Transient stimulated raman scattering in high laser depletion and its effects on vibrational dynamics experiments

The progress of laser depletion and Stokes growth in transient stimulated Raman scattering (TSRS) is investigated using a Rayleigh-scattering technique. High laser depletion is found to dominate the behavior of TSRS under conditions relevant to excite-and-probe vibrational dynamics experiments. The results are used to explain differences between recent vibrational dephasing experiments. Implications of the results on both energy relaxation ( T 1) and phase relaxation ( T 2) experiments utilizing TSRS excitation are discussed.

Tunable picosecond transient stimulated Raman scattering in ethanol

Transient stimulated Raman scattering (TSRS) of picosecond dye laser pulses in ethanol has been investigated experimentally. In particular some temporal features of TSRS from the C-H stretching mode (2928 cm -1) in ethanol have been studied with a Photochron II streak camera with subpicosecond time resolution. It is shown that the use of TSRS provides a simple method for producing picosecond pulses tunable over the spectral region ≈492–532 nm and 691–772 nm by tuning a passively mode-locked Rhodamine 6G dye laser from 575–630 nm.

Experimental Investigation of Transient Stimulated Raman Scattering in a Linearly Dispersionless Medium

The results of numerical calculations of the transient stimulated Raman scattering reported previously have been verified experimentally under conditions where both linear dispersion and self-focusing effects were negligible. The existence of a delay between maxima of the laser and Stokes pulses is experimentally demonstrated for the first time, while the pulse shortening in time via Raman scattering is established more firmly than in previous work. The incident-laser-pulse duration, generated-Stokes-pulse duration, and delay between intensity maxima for the laser and Stokes pulses were measured with the two-photon absorption-fluorescence technique. The effective phonon-dephasing time is determined via spontaneous Raman scattering. By using these measured quantities, inferences are made as to the magnitude of the transient gain and the shape of the exciting picosecond laser pulse.

Theory of Stokes Pulse Shapes in Transient Stimulated Raman Scattering

The theory of transient stimulated Raman scattering has been extended to include an arbitrary shape of the laser pump pulse. It is shown that the maximum Stokes gain depends on the total energy content per unit area of the pump pulse, and not on the instanteous intensity for an exciting pulse of short duration. The Stokes pulse has a leading edge which rises sharply to a maximum, where the maximum occurs with some delay with respect to the maximum of the pump pulse. The trailing edge follows the decay of the pump. In a nondispersive medium, the gain is not reduced by frequency broadening of the laser output, while in a dispersive medium, considerable gain reduction is expected. Numerical results for various laser-pulse shapes and spectral distributions are presented.

Forward Picosecond Stokes-Pulse Generation in Transient Stimulated Raman Scattering

The transient excitation of molecular vibrations by a picosecond laser-pulse train depends critically on the detailed shape of the exciting pulses. Stokes pulses shorter than or equal to the generating laser pulses have been observed in C${\mathrm{Cl}}_{4}$. Other aspects of the transient nature include the stimulation of two Stokes lines in methanol and the absence of backward Stokes radiation.