Vitaly V. Slabko

Negative group velocity and three-wave mixing in dielectric crystals

We investigate extraordinary features of optical parametric amplification of Stokes electromagnetic waves that originate from the three-wave mixing of a backward phonon wave with negative group velocity and two ordinary electromagnetic waves. Such properties were earlier shown to exist only in plasmonic negative-index metamaterials that are very challenging to fabricate. Nonlinear optical photonic devices with properties similar to those predicted for negative-index metamaterials are proposed.

Diagnostics of fs pulses by noncollinear random quasi-phase-matched frequency doubling

Noncollinear random quasi-phase-matched frequency doubling in nonlinear photonic crystal (NPC) of strontium tetraborate (SBO) can be used for background-free autocorrelation measurements of ultrashort pulses in wide spectral range without any angular tuning of nonlinear photonic crystal. Nonuniformity of reciprocal superlattice vectors spectrum of random structure does not affect the accuracy of measurement. Nonlinear photonic crystals of strontium tetraborate are attractive medium for cross-correlation measurements in deep and vacuum ultraviolet.

Čerenkov nonlinear diffraction in random nonlinear photonic crystal of strontium tetraborate

Cerenkov-type second harmonic generation of femtosecond pulses in random one-dimensional nonlinear photonic crystal of strontium tetraborate is investigated experimentally and theoretically. Sidebands in angular-spectral dependence of generated second harmonic were detected and found to be in perfect agreement with calculations. Spectral maximum of generated radiation experiences deviation from Cerenkov relation due to influence of nonlinear photonic crystal structure. Pulse duration and local spectrum of Cerenkov second harmonic are measured and found to be in fair agreement with each other.

Random quasi-phase-matched nonlinear optical conversion of supercontinuum to the ultraviolet

Conversion of fs supercontinuum to the ultraviolet (UV) range from 260 to 305 nm in nonlinear photonic crystal of strontium tetraborate is obtained. Spectral shape of generated UV radiation is governed by the shape of supercontinuum spectrum, focusing conditions and phase mismatch in the material of nonlinear photonic crystal. Maximum integral UV power of 2.6 μW was obtained in the case of weaker focusing, and peaks with the spectral width 1–3 nm dominate in the spectrum. Using tight focusing, broadband radiation in the range 265–300 nm was obtained.

Nonlinear optical frequency-mixing in dye vapors

Application of gas-phase molecular substances in nonlinear optics appears very promising. The paper reports on the experimental two-photon-resonant four-wave frequency-mixing of Nd: YAG laser radiation inp-terphenyl (PTP) vapors. The nonlinear susceptibility calculated from the experimental data made χ(3)≃10−31 ESU. This value is commensurable with the quasiresonant susceptibility of alkali atoms and is considerably higher than the resonant susceptibilities of simple molecules such as NO and CO. The paper seems to be the first devoted to the nonlinear frequency-mixing in dye vapors.

Nonlinear Raman–Nath diffraction of femtosecond laser pulses

We study the nonlinear Raman-Nath diffraction (NRND) of femtosecond laser pulses in a 1D periodic nonlinear photonic structure. The calculated second-harmonic spectra represent frequency combs for different orders of transverse phase matching. These frequency combs are in close analogy with the well-known spectral Maker fringes observed in single crystals. The spectral intensity of the second harmonic experiences a redshift with a propagation angle, which is opposite the case of Čerenkov nonlinear diffraction. We analyze how NRND is affected by the group-velocity mismatch between fundamental and second-harmonic pulses and by the parameters of the structure. Our experimental results prove the theoretical predictions.

Čerenkov nonlinear diffraction of femtosecond pulses

Cerenkov nonlinear diffraction of femtosecond pulses in one-dimensional nonlinear photonic crystal of strontium tetraborate was studied theoretically and experimentally in both frequency and time domains. Spectral features of second harmonic radiation were measured in the course of mapping the nonlinear photonic crystal structure. The local second harmonic spectrum demonstrates complex angular behavior within the beam cross section. The spectral width of the second harmonic radiation is found to be fundamental beam size-dependent, and optimal focusing should be used for exact conversion of the fundamental spectrum into the second harmonic one. Experimental results are in excellent agreement with calculations. Maximum second harmonic generation efficiency was up to 2.1% at pumping by a femtosecond oscillator.

Ninth-order nonlinear polarization and vuv generation in Hg vapor

Interference of resonant ninth-order and nonresonant seventh-order nonlinear polarizations in Hg atoms has been studied, and direct conversion of fundamental ir radiation into the vuv has been obtained. The interference has been observed in the form of a Fano-Boitler contour. The efficiency of generation by ninth-order processes appears to be higher than that by seventh-order.

Nonlinear Optics with Backward Waves: Extraordinary Features, Materials and Applications

Extraordinary properties of nonlinear-optical propagation processes are investigated that involve electromagnetic or elastic waves with negative group velocity. Nanostructured materials that support such waves and prospective unique photonic devices are described.

Unidirectional amplification and shaping of optical pulses by three-wave mixing with negative phonons

A possibility to greatly enhance frequency-conversion efficiency of stimulated Raman scattering is shown by making use of extraordinary properties of three-wave mixing of ordinary and backward waves. Such processes are commonly attributed to negative-index plasmonic metamaterials. This work demonstrates the possibility to replace such metamaterials that are very challenging to engineer by readily available crystals which support elastic waves with contra-directed phase and group velocities. The main goal of this work was to investigate specific properties of indicated nonlinear optical process in short-pulse regime and to show that it enables elimination of fundamental detrimental effect of fast damping of optical phonons on the process concerned. Among the applications is the possibility of creation of a family of unique photonic devices such as unidirectional Raman amplifiers and femtosecond pulse shapers with greatly improved operational properties.