SRS generation under phase matching conditions for four-wave interactions of SRS components in birefringent Raman-active crystals

The possibilities of efficient four-wave SRS generation in the schemes of cavity and cavity-amplifier SRS converters with the implementation of phase matching conditions for four-wave mixing of different SRS radiation components at an appropriate orientation of birefringent SRS crystals have been considered based on a numerical simulation. The threshold characteristics and achievable energetic parameters of the SRS generation of different frequency radiation components have been analyzed under the conditions of implementation of phase matching for four-wave mixing. Conditions have been found for a low-threshold SRS-four-wave mixing generation of an anti-Stokes wave with a conversion efficiency of up to 40%, as well as of the first, second, and third Stokes SRS components with conversion efficiencies of up to 90, 80, and 30%, respectively.     

Generation of tunable narrow-bandwidth VUV radiation by anti-Stokes SRS in H2

Thirteen tunable anti-Stokes components have been observed for the first time starting with a dye laser. Energies in the long-wavelength VUV region (around 190 nm) reach values of 50 μJ (～10 kW) corresponding to a conversion factor η～0.5×10^?3. The shortest wavelength observed is at 138 nm where up to 40 nJ (～8 W) are measured.     

Polarization of radiation under superradiance conditions

A theoretical study is made of the polarization properties of superradiance emitted by gases in a high-current longitudinal discharge. It is shown that the Zeeman effect in the discharge current makes the radiation at the periphery of a light beam totally polarized. Formulas are derived for relating the degree of polarization of a light beam with the dependences of the gain profile on the frequency and on the transverse coordinate. An analysis is made of the influence of diffraction on the polarization properties of a light beam and the anisotropic waveguide modes are found. A calculation is made of the distribution of the intensity of the optical field when radiation is generated between crossed Polaroids at the exit end of the discharge tube.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 51–56, May, 1980.The authors are grateful to A. I. Odintsov and V. P. Yakunin for frequent discussions.     

Duration of the excited state of complex molecules in the gas phase under anti-Stokes excitation

The dependence of the mean durations of fluorescence of rarefied complex molecule vapors is investigated by a fluorometric method according to the absorption spectrum under anti-Stokes excitation. Some phthalimide derivatives were used as subjects of the investigation. It has been established that the mean duration of fluorescence for the compounds studied remains constant in the whole range of anti-Stokes excitation investigated. This agrees with the results of investigating the dependence of the fluorescence quantum yield in the gas phase on the exciting light frequency according to data in the literature. The temperature dependence of the glow duration under anti-Stokes excitation is the same as in the contiguous Stokes domain. It is known that the true stores of vibrational molecule energy in the upper electron state characterizes the effective excitation energy E _ef ^* which differs considerably from the energy of an exciting quantum and is constant in the anti-Stokes domain for the compounds investigated, in the case of rarefied vapors. The independence of from established confirms the statement that molecules excited in the anti-Stokes domain do not differ in their properties from molecules excited in the adjacent long-wave Stokes domain, under conditions of constant vibrational energy.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 25–29, April, 1973.     

Coherent backscattering under conditions of pulsed radiation trapping

Coherent backscattering of pulsed radiation emitted by optically dense atomic ensembles is considered. The diagrammatic technique is used for deriving analytic expressions for correlation functions of scattered light, which make it possible to take into account all main factors affecting the dynamics of the process, including the hyperfine and Zeeman structure of the ground and first excited states of atoms, polarization of probe radiation, the actual shape and size of an atomic cloud, its spatial inhomogeneity, motion of atoms, and angular-momentum polarization of atoms. On the basis of these relations, the time dependence of the total intensity and the dependence of enhancement factor of backscattered light on the pulse duration, type of polarization of the polarization system of observation, optical thickness of the scattering medium, and the carrier frequency of the pulse are investigated. The calculations are performed for an ensemble of rubidium-85 atoms cooled in magnetooptical traps.     

Synchrotron radiation under conditions of violated lorentz invariance

We have obtained an exact solution to the Dirac equation for an electron in a constant uniform magnetic field by taking into account the anomalous magnetic moment and Lorentz invariance violation in minimal CPT-odd form. Based on the solution found, we have calculated synchrotron radiation characteristics and predicted possible observable effects attributable to the Lorentz invariance violation.     

Generation of tunable coherent VUV radiation by anti-Stokes Raman scattering of excimer-pumped dye laser radiation

A straightforward method of generating tunable coherent VUV radiation is described. Radiation down to 1362 Å was produced by Raman shifting the output of a commercially produced, excimer-pumped dye laser system. It is shown that generation of VUV radiation at 1640 Å is more efficient using the 8th anti-Stokes line from a UV dye than by using the 10th anti-Stokes line from a visible dye which had twice the output power.     

Optimum conditions for the generation of the second harmonic of intense laser radiation

A generalized approximation of strong interactions of waves is suggested for the theoretical analysis of second-harmonic generation under conditions of self-action. On the basis of the method suggested, approximate solutions for the efficiency of second-harmonic generation are obtained with regard to the influence of higher nonlinearities, depletion of pumping radiation, and linear phase mismatch. The effects of the phase mismatch and the spatial distribution of the amplitude of the fundamental harmonic on the efficiency of second harmonic generation by intense laser radiation is analyzed. The results obtained with the approximate method developed are shown to be in good agreement with known experimental data and numerical calculations. Optimum conditions for second harmonic generation are determined in a wide range of laser radiation intensity and at different spatial distributions of the fundamental harmonic amplitude.     

Soliton generation via stimulated Brillouin self-scattering under slow light conditions

Acousto-optic soliton generation via stimulated Brillouin self-scattering is predicted for light propagating at the speed of sound under electromagnetically induced transparency conditions. As in stimulated Raman self-scattering, the frequency of the electromagnetic component is gradually Stokes shifted as its intensity increases; the acoustic component has no carrier frequency. This phenomenon is explained by the possibility of forward stimulated Brillouin scattering, which is forbidden in nondispersive media. In contrast to stimulated Raman self-scattering, the Stokes shift of the electromagnetic component approaches a constant limit after the pulse has propagated to a certain distance. It is shown that the predicted soliton generation does not involve any threshold condition and can occur at extremely low input pulse intensities.     

Investigation of ultrashort pulse parameters under SRS temporal compression

Based on numerical simulations, we analyze the compression of femtosecond pulses by forward stimulated Raman scattering (SRS). We have revealed the main patterns and determined the optimal conditions of this process to achieve the highest conversion efficiency. The influence of diffraction effects on the generation and compression of Gaussian beams is investigated.     

Efficient vacuum-ultraviolet generation by anti-Stokes Raman scattering using a cryogenic Raman cell

We have investigated the increase of efficiency for high-order anti-Stokes Raman scattering using a cryogenic Raman cell. By cooling the cell to liquid-nitrogen temperature, output energies of the 9th-order anti-Stokes wave at 133 nm in normal hydrogen were enhanced by a factor of 10, and the 11th-order anti-Stokes line at 141 nm in normal deuterium appeared, while no output was observed at room temperature. No output energy enhancement, however, was obtained using cooled para-hydrogen as a result of multiple rotational Raman scattering. For long-term operation, the output window surface of the Raman cell was kept at above 200 K in order to protect it from deposition, the absorption of which is detrimental to VUV transmission.     

Sound radiation accompanying perturbation generation in turbulent jets under aeroacoustic interactions

The shadow method is used to study the sound radiation that accompanies the action of finite-amplitude saw-tooth sound waves on supersonic jets.     

Self-action of laser radiation under the conditions of electromagnetically induced transparency

The laser-radiation self-action dynamics in the electromagnetically induced transparency band were studied analytically and numerically for an atomic gas with the Λ-type energy-level scheme. The self-consistent system of equations describing the spatiotemporal evolution of a finite-amplitude wave packet in the field of a uniform pump wave was derived. The self-action in the presence of competing diffraction, nonlinear dispersion, and radiation absorption in the system was qualitatively analyzed; in particular, the conditions for self-focusing of a probe beam were determined. The results were confirmed by the numerical simulation of wave-packet spatiotemporal evolution.     

Four-wave mixing under conditions of Doppler-free resonance induced by strong radiation

The possibilities of enhancing the nonlinear optical response of a gaseous medium and the radiation conversion efficiency in four-wave mixing processes through the use of atomic coherence effects and the induced elimination of the Doppler broadening of resonances are investigated. Numerical illustrations of the effects are given for experiments in progress. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 2, 98–103 (25 January 1999)     

Determination of parameters of phase element under conditions of multiray interference

The method of measuring the phase shift Γ and the relative amplitude transmission coefficient F of a phase element is developed and experimentally tested. The conditions minimizing an experimental error of measuring Γ and F are determined. The accuracy of the proposed method is shown to be comparable to that of the currently used one; however, the proposed method is simpler and allows automation.     

Efficient anti-Stokes generation through phase-matched four-wave mixing in higher-order modes of a microstructure fiber

Phase-matched four-wave mixing in higher-order modes of microstructure fibers allows unprecedentedly high efficiencies of anti-Stokes frequency conversion to be achieved for subnanojoule femtosecond laser pulses. 70-fs pulses of 790-nm radiation were used to generate an anti-Stokes component at 520-530 nm in a higher-order mode of a microstructure fiber with a 4.8-microm core. The maximum ratio of the anti-Stokes signal energy to the energy of the pump component in the output spectrum is estimated as 1.7.