Coherent Four-wave Mixing Research Articles

Electron-phonon quantum kinetics in the strong-coupling regime

Summary form only given. While ultrafast semiconductor spectroscopy has investigated scattering times, i.e. the time between different scattering events, for many years, quantum kinetics asks for the duration of one scattering process, i.e. for the memory time. For the electron-LO-phonon quantum kinetics in the weak coupling regime (GaAs), quantum kinetics shows up as an oscillation in the coherent four-wave mixing (FWM) signal. This observation was interpreted as an oscillation of a band electron back and forth between its initial and a final state it scatters into (for long times) due to the emission of n=1 phonon. We discuss the strong electron-phonon coupling regime, in which n>1 phonon scattering processes are expected to become important as well. Bulk ZnSe is used as a model system, in which the Frohlich-constant is about one order of magnitude larger than in GaAs. In our experiments, the band edge of an antireflection-coated, 100 nm thin film of ZnSe at low temperatures is excited with blue, transform-limited 13 fs pulses. Two-pulse, three-pulse FWM-experiments and coherent control experiments are performed and discussed.

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.

Four-wave mixing with matter waves

The advent of the laser as an intense source of coherent light gave rise to nonlinear optics, which now plays an important role in many areas of science and technology. One of the first applications of nonlinear optics was the multi-wave mixing1,2 of several optical fields in a nonlinear medium (one in which the refractive index depends on the intensity of the field) to produce coherent light of a new frequency. The recent experimental realization of the matter-wave ‘laser’3,4—based on the extraction of coherent atoms from a Bose–Einstein condensate5—opens the way for analogous experiments with intense sources of matter waves: nonlinear atom optics6. Here we report coherent four-wave mixing in which three sodium matter waves of differing momenta mix to produce, by means of nonlinear atom–atom interactions, a fourth wave with new momentum. We find a clear signature of a four-wave mixing process in the dependence of the generated matter wave on the densities of the input waves. Our results may ultimately facilitate the production and investigation of quantum correlations between matter waves.

Measurement of electric fields in a plasma with the aid of the coherent four-wave mixing polarisation technique

A method for the measurement of a homogeneous static electric field in an isotropic homogeneous plasma by the coherent four-wave mixing (FWM) techniques is proposed and theoretically substantiated. The influence of plasma microfields on the intensity and polarisation of the FWM signal is investigated.

Kogerentnye chet'rekhvolnovye protsessy v vozbuzhdennykh i ionizovannykh gazovykh sredakh: chetyrekhfotonnaya spektrokhronografiya, ellipsometriya i vizualizatsiya prostranstvennogo raspredeleniya atomov i ionov

Когерентные четьрехволновые процессы в возбужденных и ионизованных газовых средах: четырехфотонная спектрохронография, эллипсометрия и визуализация пространственного распределения атомов и ионов, Желтиков А.М., Коротеев Н.И.

Imaging of the spatial distribution of atoms in an optical-breakdown plasma with one-dimensional coherent hyper-Raman scattering

A technique based on coherent four-wave mixing with a hyper-Raman resonance in wide beams was developed for line-by-line reconstruction of the spatial distribution of excited atoms in a laser-produced plasma. This method was used to study the spatial distribution of excited lead atoms in an optical-breakdown plasma formed on a metal target. A comparison was made of the technique of constructing plasma images line-by-line with a four-photon technique of point-by-point measurements. Estimates were obtained of the spatial resolution of the proposed technique. Potential applications of this approach in plasma diagnostics were analysed.

Excitonic optical nonlinearities and dynamics in II–VI heterostructures and laser diodes

The extremely strong Coulomb correlation in wide-gap II–VI semiconductors results in considerable excitonic contributions to optical nonlinearities still at excitation densities sufficient for stimulated emission and lasing. In pure ZnSe and ZnCdSe QWs, even more complex exciton systems like biexcitons may dominate the emission spectra at moderately high densities. In ternary wells of compositions typical for laser diodes, the exciton-biexciton kinetics is still described without the assumption of strong localization. In highest-quality ZnSe wells with excitonic line widths as small as 0.75 meV and large biexciton binding energies, the nontrivial polarization and intensity dependence of exciton and biexciton contributions to coherent four-wave mixing is for the first time systematically investigated and explained by a microscopic density-matrix model taking into accounthigher-order correlations. Whereas biexcitons have also been proved to give rise to stimulated emission at temperatures ⩽ about 150 K in undoped QW structures, they play no role for stimulated emission in favor of a strongly Coulomb-correlated electron-hole plasma in operational, injection laser diodes. Its dynamical behavior after ps-pulse excitation reveals novel features of kinetic and spectral hole burning and a coupling of the longitudinal ground and higher lateral modes in resonator structures. Eventually, an overall understanding of the lasing properties of II–VI diode structures is nowadays possible.

Panoramic two-dimensional visualisation of the spatial distribution of the atomic and ionic components of a laser plasma by the method of coherent four-photon spectroscopy

An experimental method is proposed for two-dimensional mapping of the relative populations of excited states of atoms and ions in a low-temperature optical-breakdown plasma. The method is based on a technique of coherent four-wave mixing combined with a hyper-Raman resonance. A study is reported of the possibility of obtaining information on the spatial distribution of the excited-state populations of atoms and ions from two-dimensional maps of the four-wave mixing signal taking account of the phase mismatch and of one-photon absorption. Conditions were found experimentally for the four-wave mixing in a plasma in a phase-matched regime without a significant influence of the one-photon absorption.

Coherent Four-Wave Mixing in a Laser-Preproduced Plasma: Optical Frequency Conversion and Two-Dimensional Mapping of Atoms And Ions

We discuss applications of coherent four-wave mixing in the plasma of optical breakdown produced by an additional laser pulse (laser-preproduced plasma) for the generation of short-wavelength radiation and the investigation of spatial distribution of atoms and ions. The use of an additional laser for the generation of laser-produced plasma on the surface of a metal target makes it possible to optimize the efficiency of frequency conversion and to implement plasma diagnostics at various stages of plasma expansion. An experimental technique based on hyper-Raman-resonant four-wave mixing is developed for two-dimensional mapping of relative populations of excited atomic and ionic states in laser-produced plasma.

Four-wave polariton scattering of light in LiNbO3

Four-wave Stokes k-spectra for light scattering on polaritons in lithium niobate crystals with an Mg impurity are studied experimentally. The mechanisms for direct, cascade, coherent, and incoherent four-wave mixing of light are discussed in the course of interpreting the angular dependences of the scattered light intensity. It is shown that the dispersion of the real part of the polariton wave vector and the refractive index of the crystals at the polariton frequencies can be measured with an order of magnitude greater accuracy than by spontaneous three-wave polariton light scattering. A significant discrepancy is found between determinations of the polariton absorption coefficient from the angular spectra of three-wave scattering and four-wave scattering in terms of the model employed here.

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

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.

Measuring the ultrafast dynamics of Coulomb correlation effects: Dephasing in nonequilibrium Fermi seas

We measure the dynamics of the quantum phase coherence of the wave function describing interacting electrons and holes optically excited into the continuum of a GaAs/AlGaAs quantum well. We achieve this by spectrally resolving both the transient four-wave mixing signal and the differential transmission signal arising from such interacting carriers. We observe a dynamical blue shift of the coherent four-wave mixing emission spectrum with respect to the excitation laser pulse and interpret this as a direct manifestation of the dynamic Coulomb correlation effects in this many-body system.

Degree and state of polarization of the time-integrated coherent four-wave mixing signal from semiconductor multiple quantum wells.

All four of the Stokes parameters of the time-integrated degenerate four-wave mixing signal from a GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As multiple quantum well are measured as a function of the relative angle between the linear polarizations of the pump and the probe and of the incident fluence, thus completely characterizing the polarization state of the signal. The degree to which the signal is polarized, the ellipticity, and the orientation of the polarization ellipse are found to be strongly dependent on the orientation of the incident polarizations and on fluence. The principal features can be qualitatively understood in terms of a simple model that includes density-dependent dephasing and local-field corrections.

Bridging THz-frequency gaps in the near ir by coherent four-wave mixing in GaAlAs laser diodes

Coherent non-degenerate four-wave mixing in multiple quantum well GaAlAs laser diodes is investigated by injecting two narrow-band signals into a third laser, acting as optical mixing element, and heterodyne-detecting the mixing product. Promising S/N-ratios of the mixing product are found for detunings between the two injection signals up to 3 THz. The coherent nature of the process is verified by phase locking an independent LD to the mixing product.

Molecular, multiresonant coherent four-wave mixing spectroscopy

Abstract Recent research has expanded the capabilities of four-wave mixing by providing it with component selectivity, site selectivity, and mode selectivity. The selectivity is achieved by taking advantage of the three resonance enhancements that occur in a four-wave mixing process. New spectral scanning strategies allow one to scan a single resonance while maintaining the other two resonances at constant values. The constant resonances can be used to select a specific component, a specific site within an inhomogeneously broadened envelope of a component, and/or a specific vibrational or vibronic mode of that site. The scanned resonance will then contain enhanced features corresponding to the particular component, site, and/or mode that was chosen by the constant resonances. These component and site selective capabilities of the four-wave mixing complement the single vibronic level fluorescence methods. The relative transition intensities from a specific component or site reflect the mode coupling betwee...

ChemInform Abstract: Analysis of Vibrational Correlations and Couplings in the Lowest Two Singlet States of Pentacene by High Resolution, Fully Resonant, Coherent Four‐Wave Mixing Spectroscopy

ChemInformVolume 21, Issue 38 Physical Organic Chemistry ChemInform Abstract: Analysis of Vibrational Correlations and Couplings in the Lowest Two Singlet States of Pentacene by High Resolution, Fully Resonant, Coherent Four-Wave Mixing Spectroscopy R. J. CARLSON, R. J. CARLSON Dep. Chem., Univ. Wis., Madison, WI 53706, USASearch for more papers by this authorJ. C. WRIGHT, J. C. WRIGHT Dep. Chem., Univ. Wis., Madison, WI 53706, USASearch for more papers by this author R. J. CARLSON, R. J. CARLSON Dep. Chem., Univ. Wis., Madison, WI 53706, USASearch for more papers by this authorJ. C. WRIGHT, J. C. WRIGHT Dep. Chem., Univ. Wis., Madison, WI 53706, USASearch for more papers by this author First published: September 18, 1990 https://doi.org/10.1002/chin.199038040Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume21, Issue38September 18, 1990 RelatedInformation

Analysis of vibrational correlations and couplings in the lowest two singlet states of pentacene by high resolution, fully resonant, coherent four-wave mixing spectroscopy

Coherent, fully resonant four-wave mixing (FRFWM) spectroscopy is used to probe the vibrational and vibronic state of the pentacene S0 and S1 electronic states. High resolution is obtained using mixed molecular crystals at cryogenic temperatures. The FRFWM spectra combined with conventional absorption and fluorescence spectra allow correlation of the S1 fundamentals to the corresponding ground state normal coordinates. Couplings between modes are indicated and may be related to Fermi resonance of the pentacene vibrations by means of host librational phonons.

Analysis of vibronic mode coupling in pentacene by fully resonant coherent four-wave mixing

This paper develops the theoretical framework for the analysis of relative peak intensities in fully resonant, three laser, coherent four-wave mixing spectra of molecular vibrational and vibronic levels. For a Franck–Condon system, the relative vibronic peak intensities are shown to scale as the square of the absorption spectrum for all resonances not associated with the normal mode selected by the fixed vibrational resonance. A large enhancement of vibronic resonances involving the selected mode is predicted for typical potential well offsets. Higher order mode coupling causes deviations from these predictions by allowing other coupled resonances to be enhanced as well. Vibrational peak intensities are similarly related to the emission spectrum. Pentacene in benzoic acid mixed crystals at 2 K are used to experimentally study the mode mixing effects. It is shown that important coupling occurs between the 747.7 and 790.8 cm−1 vibronic modes of the pentacene S1 electronic state. Two possible mechanisms for this coupling are suggested. This work shows that the relative intensities of vibrational and vibronic resonances in fully resonant four-wave mixing spectra can serve as a useful probe of mode coupling.

Two-photon resonance spectroscopy of vibrational transitions in molecules under four-wave frequency mixing conditions

Generation of the sum and difference frequencies ωvis + 2ωir as a result of coherent four-wave frequency mixing of quasiresonance (relative to vibrationai transitions) CO2 laser radiation and of visible radiation in the form of the second harmonic of a YAG:Nd laser was studied in media consisting of various molecules (SF6, BCl3, CF3Br, CF3I). The signal was very sensitive to tuning of the infrared radiation frequency relative to the Q branch of a two-photon vibrational transition. A theoretical model was developed which ensured a good agreement with the experimental dependence of the intensity of the signal on the infrared radiation frequency in the case of gaseous CF3Br. It was predicted theoretically that the investigated process should cause a considerable narrowing of the Q branch of a two-photon transition compared with the usual thermal width.

Coherent forward four-wave mixing of ultrashort radiation pulses in a resonant medium

Forward four-wave mixing (FFWM) of ultrashort light pulses is considered theoretically under their coherent propagation in a resonant-absorbing medium. Nonlinear equations describing FFWM are obtained and studied and it is shown that the energy exchange between pulses of exact resonance may lead to the enhancement of weak radiation. The influence of input radiation parameters and interaction geometry on the FFWM characteristics has been studied.