M. A. Davydov

High-resolution four-wave mixing spectroscopy of suspensions: the nonlinear mechanism of a Rayleigh-wing formation

Results of theoretical and experimental investigations of the nonlinear mechanism of Rayleigh-wing formation during the four-wave mixing process in suspensions are presented. The developed theory shows that simultaneous action of two laser radiations with different wavelengths on a spherical particle in a viscous liquid causes a nonlinear resonant response, whose width depends in a complex manner on the particle size, its mechanical properties and the bulk and shear viscosity of the surrounding liquid. The diffusion of particles in a liquid, which depends on several parameters including concentration, leads to concentration dependence of the resonance linewidth observed in the experiment. The four-wave mixing spectroscopy allows us to directly observe nonlinear Rayleigh scattering resonances in the suspensions of spherical nanoparticles whose bandwidth lies in the range from 20 MHz (7 × 10−4 cm−1) to 150 MHz (5 × 10−3 cm−1). These resonances are observed at a high enough level of the detected signal and the signal/noise ratio achieved in the individual measurements is of two orders of magnitude.

Four-wave mixing Rayleigh scattering spectroscopy: a new approach to studying binary solution dynamics

The Rayleigh resonance in binary solutions was studied by four-wave mixing light scattering spectroscopy for the first time. A hysteresis-like dependence of the resonance linewidth on the concentration was found.

Four-photon polarization spectroscopy of induced plasma oscillations in a skin layer of semiconductors

Probe-beam scattering spectra have been obtained for four-wave mixing of laser waves in the skin layer of intrinsic semiconductors. The spectra were recorded using the frequency dispersion of orthogonally polarized radiation, which arises as a result of nonlinear optical interaction with conduction-band electrons. The mixing of two counterpropagating light waves in a semiconductor, implemented under nonlinear excitation of longitudinal density oscillations in the plasma electron subsystem of the semiconductor, is theoretically considered. This mixing is shown to lead to the rotation of the probe-beam polarization vector. The results obtained are of interest, e.g., for studying optical metamaterials based on thin-film structures.

Low-frequency four-photon spectroscopy of surface waves in semiconductors: A new mechanism of optical nonlinearity

A new mechanism of optical nonlinearity of intrinsic semiconductors is proposed, which is based on bandgap modulation due to the four-wave mixing of interacting waves on the semiconductor surface. This phenomenon is theoretically considered within a one-dimensional model. The corresponding resonances are experimentally found in Ge and Si samples.

Four-Wave Mixing Rayleigh Scattering Spectroscopy of Binary Solutions

The concentration dynamics of the scattering spectral width in a number of binary solutions has been studied by four-wave mixing spectroscopy near the Rayleigh resonance. It is noted that, according to the classical concepts, a variation in the correlation length of fluctuations of the relative concentration of molecules in a solution plays a key role in the change in the spectral width. Some liquids exhibit nonmonotonic (hysteretic) concentration dependences of the Rayleigh linewidth.

High-Resolution Spectroscopy at Steady-State Lasing with Multiphoton Backscattering

A steady-state self-consistent lasing regime in a laser cavity is investigated with allowance for the back action of the output radiation at four-wave low-frequency scattering in the external sample. The scattering is by the photoelastic potential in the field of the additional opposing laser. General expressions for steady-state amplitudes of field oscillation in the cavity are obtained and employed for investigation of lasing features. Experiments were carried out with narrow-band (line width 1 MHz) continuously tunable diode lasers. The four-wave scattering occurred in solid and liquid dielectrics. It is shown that the fourwave scattering of the pumping laser radiation into the cavity of the signal laser substantially changes its lasing spectrum and can be used to measure dispersion of acousto-optic parameters.

High-resolution four-photon intracavity laser spectroscopy with the external phase conjugation mirror

The phase conjugation regime is experimentally implemented in a cell with a liquid (water, ethanol, carbon tetrachloride) at the four-wave mixing of counter-propagating beams of diode lasers. Intracavity enhancement of the conjugate wave and the wave of the coherent anti-Stokes Raman scattering (CARS) arising in the interaction of the conjugate wave and one of the pumping waves in CARS scheme is detected. The latter process occurs in a narrow spectral range when the geometry of the wave vectors of the interacting waves in CARS scheme ensures arrival of the CARS signal at the laser aperture. It is found out that the quality of the four-photon phase conjugate mirror in the given interaction scheme is very sensitive to any perturbations (mechanical, acoustic, thermal, etc.) of the induced grating in the sample, which manifests itself in the distortion of the signal spectrum.

Four-wave mixing spectroscopy of the photo-elastic scattering resonance in Nd:YVO4 crystal

A new method of non-linear laser spectroscopy based on four-wave scattering of pump laser radiation into the probe laser cavity is suggested and realized. As a result of intracavity amplification there is an opportunity to investigate weak narrow resonances of different types including the resonances of photo-elastic scattering in optical materials and laser crystals. A theory describing this phenomenon is suggested and experiments with narrowband (1 MHz linewidth) tunable continuous-wave diode laser were carried out. It is shown that the four-wave scattering of pump laser radiation into the cavity of the probe laser can be used for measurement of dispersion of photo-elastic constants in solid and liquid dielectrics.

Four-Wave Scattering of a Laser Beam by Induced Collective Oscillations of Solid Nanoparticles in Suspensions

Spectra of coherent scattering at four-wave mixing of two diode laser radiation in liquid suspensions of dielectric nanoparticles are obtained for the first time. Dependence of the scattering resonance width on the concentration of nanoparticles in the suspension is studied. It is shown that the experimentally observed dependences of the width of the scattered radiation spectrum on the concentration of nanoparticles in the suspension result from the collective excitation of acoustic phonons.

Low-Frequency Stimulated Raman Scattering on Acoustic Vibrations of Dielectric Nanospheres in Aqueous Suspension

A low-frequency SRS (LFSRS) signal is detected at a certain dielectric nanoparticle (latex spheres) concentration in an aqueous suspension. The SRS line shift is close to its estimate by the “transverse” hypersound speed in latex.