Application of the inverse scattering problem method to stimulated Mandelstam-Brillouin backscattering of light

Stimulated Mandelstam-Brillouin backscattering of light is analyzed with the aid of the inverse scattering problem method. An asymptotic solution of this problem is obtained, as well as a solution for weak fields. It is shown that, just in the case of forward stimulated Mandelshtam-Brillouin scattering, the effective-interaction region, in which the intensity of the incident light wave is transferred to the scattered one, shifts towards the entrance face of the sample. It is also established that the asymptotic rate of decrease of the acoustic and scattered waves is independent of the rate of decrease of the initial distribution. The parameters characterizing the initial conditions are contained only in the pre-exponential terms.Translated from Preprint No. 173 of the Lebedev Physics Institute Academy of Sciences of the USSR, Moscow, 1988.     

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.     

Photonic-chip-based tunable slow and fast light via stimulated Brillouin scattering

We report the first (to our knowledge) demonstration of photonic chip based tunable slow and fast light via stimulated Brillouin scattering. Slow, fast, and negative group velocities were observed in a 7 cm long chalcogenide (As(2)S(3)) rib waveguide with a group index change ranging from ~-44 to +130, which results in a maximum delay of ~23 ns at a relatively low gain of ~23 dB. Demonstration of large tunable delays in a chip scale device opens up applications such as frequency sensing and true-time delay for a phased array antenna, where integration and delays ~10 ns are highly desirable.     

Multiwave stimulated raman scattering under quasi-phase-matching conditions

The effect of the generation of higher Stokes and anti-Stokes components of steady-state and transient stimulated Raman scattering (SRS) on the realization of quasi-phase-matching conditions in the course of generation of the first anti-Stokes SRS component is numerically analyzed by using a system of coupled equations derived with regard to diffraction effects. The calculations show that the application of a periodic layered structure in order to realize quasi-phase-matching conditions virtually does not reduce the anti-Stokes SRS efficiency and allows efficient conversion of pulses with a duration of 3 ns or longer. It is found that focusing of waves inside the medium allows partial compensation for diffraction spreading and provides for an increase in the efficiency of anti-Stokes SRS conversion, and, at a Fresnel number above three, the effect of diffraction on the realization of quasi-phase-matching conditions during SRS can be disregarded.     

Rayleigh and Mandelstam-Brillouin light scattering in chalcogenide glasses of the As-S system

The Rayleigh light scattering in chalcogenide glasslike alloys of the As-S system is investigated. The velocities of longitudinal hypersound, elasto-optical constants, extinction coefficients, and scattering losses have been determined. It is shown that an increase in the amount of sulfur in alloys leads to an increase in chemical differentiation and, as a result, to an increase in the intensity of Rayleigh scattering and in inherent optical losses.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, 823–826, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Investigation of stimulated Brillouin scattering under well-defined interaction conditions

Ruby-laser light scattering was used to gain spatially and temporally resolved information about plasma parameters for nanosecond CO₂ laser-plasma interaction studies. The results confirm a heating model, where heat conduction in dense model plasmas can be described classically. CO₂-laser excited stimulated Brillouin scattering could directly be shown to arise from near thermal level by simultaneous Thomson scattering with a ruby-laser, and turbulence enhanced density fluctuations could be excluded.     

Determination of the threshold intensity of a laser beam for exciting stimulated Mandelstam-Brillouin scattering in the atmosphere

Stimulated Mandelstam-Brillouin scattering at small angles is considered in the case of a powerful laser beam propagating in the static mode in an unbounded medium. In contrast to the pulse mode, a hypersonic wave can be formed not only in the backward direction, but also in the forward direction at small angles. In this work, the latter case is considered as having the smallest value of the threshold intensity. It is shown that finite dimensions of the beam significantly change the excitation conditions for a scattered radiation owing to the mismatch of the wave triplet due to diffraction effects. Determination of the threshold intensity is shown to be possible using the well-known expressions for a plane wave only if the Fresnel number of the beam on the path the length of which is equal to the distance of the optical wave decay due to absorption in the medium is much larger than unity. Moreover, a large number of decay distances of the hypersonic wave must fall on the beam radius. When these conditions are not satisfied, the threshold intensity increases as compared to the plane wave.     

Measurement of intrinsic Brillouin linewidth of fibers based on stimulated Brillouin scattering slow light

Intrinsic Brillouin linewidth is one of the essential parameters to optimize the gain spectrum of stimulated Brillouin scattering (SBS). A novel method for the measurement of the intrinsic Brillouin line-width based on SBS slow light is proposed and demonstrated. In this method, an implicit model based on the transient SBS theory is developed, and a data processing method is designed to obtain the value of the intrinsic Brillouin linewidth from the model. The measured results show that the method is effective for studying SBS slow light.     

Energy characteristics of photothermal vibrational instability at stimulated Raman and Mandelstam-Brillouin scattering in aerosol droplets

The threshold intensity and the combination frequencies for photothermal vibrational instability in high-Q aqueous aerosol droplets in the two-mode regime have been calculated. The selection rules for coupling electromagnetic and temperature modes in a droplet are obtained. A comparative analysis of the threshold excitation intensities of photothermal vibrational instability, stimulated Mandelstam-Brillouin scattering, and stimulated Raman scattering in droplets is performed. It is shown that photothermal vibrational instability in the two-mode regime can be developed at a pump intensity of about 10⁴ W/cm² for droplets with radii of 2–20 μm for a pump wavelength of 0.532 μm. A method of remote measurement of the microphysical droplet parameters from the additional periodic temperature shift of droplet eigenfrequencies in the spectrum of stimulated Raman scattering and lasing is proposed.     

Transient effects in stimulated light scattering

Transient stimulated scattering of light is treated numerically for situations with arbitrarily high conversion of laser into scattered light. New, transient effects are predicted and will be dicussed for scattering in the backward and in the forward directions. The computations are found to be in good agreement with time-resolved, experimental studies of stimulated Brillouin scattering in several liquids.     

Collective processes during stimulated light scattering

An approach to the analysis of the phase conjugation by stimulated light scattering that is alternative to the mode theory of 3D hologram, which is usually applied for these purposes, has been studied. As is known, the use of the mode theory is based on the phenomenological gain factor of the Stokes wave, which is induced by a pump wave in a nonlinear medium. The approach developed in this work directly considers the interaction between plane components of the pump and Stokes waves via hypersonic gratings of the dielectric permittivity, which the pump and Stokes waves induce in the medium. It has been shown that, as a result of the phase conjugation, two hypersonic gratings participate equally efficiently in the interaction between any pair of plane components of the pump and Stokes waves, with one of these gratings being excited by the interacting waves themselves. The other grating in each such pair is unambiguously identified with a simplest vector diagram. Conditions have been analyzed under which numerous other gratings, which could also participate in the interaction of each pair of plane components of the pump and Stokes waves without violating the Bragg conditions and the joining conditions of the transverse components of the wave vectors at the interface between the two media, contribute negligibly to stimulated light scattering. It has been shown that, if the pump is spatially coherent, the considered approach yields the same results as the standard mode theory does. In October 2011, I reported the results of this work at the Vavilov State Optical Institute at the Memorial Meeting “Half a Century of New Optics in Russia: Lasers, Nonlinear Optics, and Optical Holography” and at the International Conference “Laser Optics—2012” (June 2012).     

Nonlinear phase shifts of modulated light waves with slow and superluminal group delay in stimulated Brillouin scattering

Brillouin amplification with counterpropagating modulated pump and Stokes light leads to nonlinear modulation-phase shifts of the interacting intensity waves. This is due to a partial transformation of the nonmodulated light component at the input into modulated light at the output as a result of a mixing process with the counterpropagating modulated component of the pump and results in an advance or delay of the input modulation. This occurs for interactions over less than half of a modulation wavelength. Milliwatts of power in a kilometer of standard single-mode fiber give significant tunability of the modulation phase.     

The scattering of slow atoms by light

A kinetic equation has been obtained describing the motion of atoms in a resonant field of standing light wave. This equation is used to describe the scattering of atoms for conditions close to experimental ones [1]. It is shown that the dependence of atomic scattering has a dip at the resonance frequency of the field.