D. A. Akimov

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.

ONE-DIMENSIONAL COHERENT FOUR-WAVE MIXING AS A WAY TO IMAGE THE SPATIAL DISTRIBUTION OF ATOMS IN A LASER-PRODUCED PLASMA

An experimental technique based on coherent one-dimensional hyper-Raman-resonant four-wave mixing in broad cylindrically focused light beams has been developed for line-by-line imaging of spatial distribution of excited atoms in a low-temperature plasma of optical breakdown. The technique was applied to map excited lead atoms in a low-temperature laser-produced plasma.

Optimizing Two-Photon Three-Dimensional Data Storage in Photochromic Materials Using the Principles of Nonlinear Optics

In the context of designing a three-dimensional optical-memory device, we investigate the cross section of two-photon absorption of a photochromic material as a function of the relative orientation of polarization vectors of light waves involved in two-photon data writing. It is demonstrated that, with an appropriate choice of polarization erectors of writing laser waves, one can considerably increase the efficiency of two-photon data writing.

Coherent anti-Stokes Raman scattering of slow light in a hollow planar periodically corrugated waveguide

Enhancement of coherent anti-Stokes Raman scattering (CARS) by molecular nitrogen in a hollow planar periodically corrugated waveguide is experimentally detected. The measured dependence of CARS efficiency on the thickness of the waveguide layer indicates that CARS enhancement under these conditions is at least partially due to the decrease in the group velocity of pump pulses around the photonic band gap.

Doubly phase-matched cascaded parametric wave mixing of ultrashort laser pulses

Doubly phase-matched cascaded parametric wave mixing of femtosecond laser pulses in tapered fibers is experimentally demonstrated. Fibers with an appropriately tailored dispersion profile allow simultaneous phase matching for two types of nonlinear-optical processes-third-harmonic generation and parametric four-wave mixing. Doubly phase-matched cascaded parametric interactions of ultrashort light pulses give rise to a manifold of new spectral components, expanding substantially the capabilities of the available laser sources of ultrashort pulses.

Cross-phase-modulation-controlled spectral transformations of ultrashort pulses in photonic-crystal fibres

Cross-phase modulation provides an efficient means to control spectral transformations of femtosecond laser pulses in photonic-crystal fibres with a specially designed dispersion profile. Femtosecond pulses of fundamental radiation of a Cr?:?forsterite laser are shown to induce an asymmetric spectral broadening of the anti-Stokes signal generated in a photonic-crystal fibre by the pulses of second-harmonic radiation of the same laser. Cross-phase-modulation-induced phase shifts control the efficiency of anti-Stokes generation in a photonic-crystal fibre, suggesting a method of switching the anti-Stokes signal on and off by varying the intensity of the control laser pulse.

Spectral superbroadening of subnanojoule Cr : Forsterite femtosecond laser pulses in a tapered fiber

Spectral superbroadening of subnanojoule femtosecond Cr:forsterite laser pulses is demonstrated for the first time in experiments with a tapered fiber. Coupling 40-fs 0.6-nJ pulses of 1.25-μm Cr:forsterite laser radiation into a tapered fiber with a taper waist diameter of about 2 μm and a taper waist length of 90 mm, we observed the spectra spanning more than two octaves at the output of the fiber. These experimental results open new horizons for the creation of compact femtosecond systems based on Cr:forsterite lasers and tapered fibers for optical metrology and biomedical applications.

Application of coherent four-wave mixing for two-dimensional mapping of the spatial distribution of excited atoms in a laser-produced plasma

Abstract An experimental technique for the two-dimensional mapping of the relative populations of excited states of atoms and ions in a low-temperature plasma of optical breakdown is developed on the basis of coherent four-wave mixing (FWM) with hyper-Raman resonances. The possibility to extract information concerning the spatial distribution of the populations of excited atomic and ionic states from two-dimensional maps of the FWM intensity allowing for phase mismatch and one-photon absorption is considered. Conditions when FWM in a plasma occurs in the phase-matched regime and is not subject to a considerable influence of one-photon absorption are experimentally determined.

Three-dimensional micro-imaging of inhomogeneities in transparent media using third-harmonic generation and four-wave mixing

Third-harmonic generation and four-wave mixing processes are shown to allow inhomogeneities in spatial distributions of absorption, refractive index, and nonlinear susceptibility to be imaged, thus offering a convenient method of 3D microimaging.

Tuning the frequency of ultrashort laser pulses by a cross-phase-modulation-induced shift in a photonic crystal fiber

Femtosecond pulses of fundamental Cr:forsterite laser radiation are used as a pump field to tune the frequency of copropagating second-harmonic pulses of the same laser through cross-phase modulation in a photonic crystal fiber. Sub-100-kW femtosecond pump pulses coupled into a photonic crystal fiber with an appropriate dispersion profile can shift the central frequency of the probe field by more than 100 nm, suggesting a convenient way to control propagation and spectral transformations of ultrashort laser pulses.