An interaction of the stimulated spin-flip Raman scattering with the stimulated recombination radiation in InSb

We have observed an interaction of the stimulated spin-flip Raman scattering and stimulated recombination radiation in InSb. At magnetic fields, where these radiations have equal or nearly equal frequencies, we find an enhancement of the output power of stimulated spin-flip Raman radiation while the output power of recombination radiation decreases. This effect occurs with the first, the second and the third Stokes radiation.     

Nonstationary intracavity stimulated raman scattering by polaritons

Stimulated Raman scattering by polaritons when employing a nonlinear crystal inside the cavity of the laser with Q-switching and locked to fundamental frequency was theoretically studied. The equations were formulated describing the dynamics of the fundamental, Stokes and polariton waves under the assumption of instant Q-switching and uniformity of radiation except in the longitudinal direction. Numerical solutions of the equations were found and analysed. We demonstrate the influence, on generation characteristics, of the most important parameters, such as the effective nonlinearity, the initial level of population inversion, the feedback of the Stokes wave and the group mismatch between a Stokes and a pump wave. Optimum generation conditions are determined. Possibilities of the method are discussed for the generation of a) giant pulses which are controllable with regard to carrier frequency and duration but are unachievable with other methods, b) Stokes pulses of very small duration and high energy having sharp trailing edges, and c) analogous polariton pulses in the middle and far infrared range. The generation using a number of polariton branches in LiNbO₃ was considered as an example. Calculations are in qualitative agreement with experimental data.     

Optically-pumped stimulated recombination radiation inp-type InSb in high magnetic fields

In this paper measurements of the frequency, linewidth and polarization of stimulated recombination radiation (SRR) fromp-type InSb are reported. The samples had low excess-carrier concentrations between 10¹⁴ and 10¹⁵ per cm³ and different lengths between 0.4 and 9 mm. They were held in magnetic fields up to 6T at temperatures of pumped liquid helium. The excitation was done optically by the radiation of a Q-switched CO-laser. We could observe a number of different stimulated processes:

1. band-to-band recombination (tuning between 1875 and 1980 cm^?1),
2. band-to-acceptor recombination (tuning between 1840 and 1930 cm^?1),
3. stimulated spin-flip Raman scattering (SFR) of the SRR by excited electrons,
4. SFR of the laser by excited electrons and its interaction with the SRR.

From the observed shift of the band gap by exchange and correlation energy the number of created electron-hole pairs can be calculated to be up to 10¹⁶ per cm³. The observed acceptor binding energy varies from 66 cm^?1 atB=0 to 71 cm^?1 at 4.5T.     

A study of various intraband processes inn-InSb by means of stimulated spin-flip raman scattering

The spin-flip Raman (SFR) laser is shown to be an excellent tool to investigate different processes in the conduction band of the SFR laser crystal itself. For the case ofn-InSb, intracavity spectroscopy of inter-Landau transitions is demonstrated to be much more sensitive than conventional transmission spectroscopy. Data on cyclotron harmonic transitions, both free and LO-phonon assisted, are obtained from the output power characteristics of the SFR laser versus magnetic field. The spin-splitting energy and the effectiveg-factor up to 14 T are derived from the SFR laser frequency. The influence of temperature on SFR laser power, threshold and frequency is investigated. The relaxation following the SFR laser pulse is observed in the electrical conductivity. This yields in a direct way the spin-lattice relaxation time at high magnetic fields, which is of the order of 200 ns.     

Observation of stimulated raman scattering in CVD-diamond

We report the first experimental observation of a nonlinear laser effect, stimulated Raman scattering (SRS), in manmade diamond grown from the gaseous phase by the chemical vapor deposition (CVD) technique. Multiple Stokes and anti-Stokes generation in the visible and near-IR ranges was excited under nanosecond and picosecond pumping in a 350-μ-thick plate. All the registered Raman-induced lasing wavelengths were identified. We classify the CVD-diamond as a promising χ⁽³⁾-active material for Raman laser converters in a record wide spectral range.     

Molecular coherence effects in stimulated raman scattering

A semi-classical calculation of the three-level system consisting of the ground state, the vibrationally excited state and the electronic excited state under the laser and the Stokes perturbation is given. The induced molecular polarization produces gain modulation of the Stokes and loss modulation of the laser at a frequency that is dependent on the optical intensity. With the optical intensity in self-trapped filaments in nonlinear liquids such as CS₂, the period of modulation becomes of the order 10^?11 s and a large amplitude modulation of the laser and the Stokes waves will result. The amplitude modulation is not much reduced, if the molecular relaxation time of the order 10^?11 s is taken into account. Effects of non-uniform field distribution and the width and shape of the incident laser pulse are discussed. The frequency broadening caused by the three-level effect is shown to be larger than, or at least as large as, the broadening caused by the optical Kerr effect.     

Tunable UV-radiation by stimulated Raman scattering in hydrogen

We observed tunable UV radiation down to 175 nm by SRS of the output of a frequency-doubled dye laser in H₂. The high power output of the 4th anti-Stokes to 5th Stokes line generated by the frequency doubled dye laser and the 8th anti-Stokes to 3rd Stokes line generated by the undoubled dye laser represents a broadly tunable coherent radiation source between 189 nm and 2064 nm.     

Model of transient amplification by stimulated raman scattering

A semiclassical model for light amplification by stimulated Raman scattering is presented. The phases of the Stokes, anti-Stokes, and laser waves are assumed to be perfectly matched. Depletion of the laser pump is neglected. The corresponding system of equations for input pulses of arbitrary shape is solved analytically by the Riemann-Volterra method. Gain is suppressed for close Raman polarizations.     

Excimer ArF/XeF lasers providing high-power stimulated radiation in Ar/Xe and F lines

Lasing in atomic lines of noble gases and fluorine, prior to excimer radiation, was observed in an electric discharge ArF/XeF excimer laser. Some Ar/Xe lines end at metastable levels, which are very important for the formation of ArF/XeF excimer molecules. Five new lasing lines of atomic fluorine have been obtained. Consideration is given to the use of lasing in atomic and molecular lines, that occurs in one burst, in investigations of the excitation kinetics of excimer states under the conditions of a high-pressure electric discharge.     

Theory of spin-flip Raman amplification in InSb

The advantages of a magneto-Raman amplifier technique for accurate study of the spin-flip Raman gain and line shape are discussed. Spin-saturation is accounted for in the theory, and found to cause anomalous line-broadening, as well as gain reduction. Related applications of the technique are outlined.     

Capture of the stokes wave under coherent stimulated raman scattering

Interaction of coherent light pulses with a three-level medium of the “lambda” configuration is studied analytically and numerically. It is shown that in the course of Raman scattering the Stokes wave can be captured in the region of inversion. Conditions are found for complete energy transfer from the pump 2π-pulse to the Stokes wave.     

N2 laser frequency conversion by stimulated Raman scattering in H2

High-efficiency frequency conversion in H₂ of a nitrogen laser oscillator-amplifier system is described. The laser system provides about 1 MW output power with a very low intrinsic divergence. Up to 3 Stokes lines at 392, 468, and 581 nm and 3 Anti-Stokes at 296, 263, and 237 nm, respectively, have been observed at the output of the 60 cm long H₂ Raman cell. Peak power values of 500, 300, and 70 kW have been measured for the first 3 Stokes, respectively, corresponding to a 56% pump energy conversion efficiency.A comparison between free and guided propagation (in a hollow dielectric waveguide) is also reported, for various values of the pump intrinsic divergence.     

Enhanced adsorbate raman scattering and surface plasmon radiation

We present the first experimental results which demonstrate a quadratic relationship between the enhanced Raman scattering from molecules on Ag surfaces and roughness-coupled surface-plasmon radiation. These results are interpreted by a model which includes both roughness assisted surface-plasmon scattering and radiative coupling.     

A Vlasov code for the numerical simulation of stimulated raman scattering

Numerical simulations of the stimulated Raman scattering are presented using an Eulerian relativistic Vlasov code. Such a code allows a finer resolution in phase space than a particle code and provides a better understanding of the acceleration process for the particles at relativistically high energy. Forward Raman scattering as well as backward Raman scattering are considered to illustrate the possibilities of the Eulerian Vlasov code.     

Threshold and conversion experiments on seeded stimulated Raman scattering

High energy-conversion efficiencies in Stimulated Raman Scattering (SRS) are demonstrated both in experiments and by simulations for pump powers below SRS threshold. The scattering is induced by a short seed pulse at the Stokes frequency, the pulse width of which is much shorter than the pump pulse width and which is comparable with the medium's dephasing time.     

Spontaneous spin-flip Raman linewidth and nonlinear processes in InSb

A small-signal gain technique has been used to measure the lineshape of spontaneous spin-flip Raman scattering as a function of magnetic field (H = 0.5–10 kG) for an electron concentration n = 10¹⁵ cm^-3 at T = 2°K with both photons propagating normal to H. Four-wave mixing processes have been observed for varying carrier concentrations together with an interference between the resonant spin-flip nonlinearity and the nonresonant nonlinearity resulting from conduction electron nonparabolicity.     

Quantum beats in stimulated electronic raman scattering of ultrashort laser pulses

A theory of quantum beats in a Stokes signal observed in pump-probe experiments upon excitation of four-level atoms with two close upper lying levels by femtosecond laser pulses is developed. Quantum beats arise in the intensity of the Stokes field due to the interference of two atomic wave packets generated by ultrashort pump and probe pulses. An analytical solution of the non-steady-state Maxwell-Bloch equations is obtained, and the dependence of the Stokes radiation intensity on the delay time between two laser pulses is investigated. The theoretical results describe qualitatively well the observed features of quantum beats.     

Structure in the Stokes output of the InSb spin-flip Raman laser

Stokes output and threshold pump intensity of the InSb spin-flip Raman laser have been measured as a function of magnetic for various pump wavelenghts and crystal orientations. The observed structure is shown to arise from intraband absorptions of the pump and Stokes radiation and not from electron spin-phonon interactions.