Efficient generation of high-power VUV ultrashort pulses by four-wave mixing

We report the generation of ultra-short pulses in the VUV (λ = 173.5 nm) using a four-wave mixing technique in magnesium vapour. Using a mode-locked ruby laser as the original source, conversion efficiencies of up to 0.2% and powers of 0.3 MW were obtained.     

Comment on “propagation of ultrashort light pulses in a resonant medium”

Previous conclusions on the propagation of ultrashort light pulses in a resonant medium are found to be in error. There is no physical basis for rejecting the nd u and dn u solutions.     

Coherent forward scattering of a single photon wave packet in a resonant medium

The propagation of a single photon wave packet in a thick resonant medium was studied theoretically and experimentally. The well-known acceleration of wave packet decay was observed upon wave packet exiting from a medium with single resonant absorption line. It was found that in a medium with two closely spaced absorption lines, the restoration of the photon wave packet is observed after the acceleration of decay.     

Level-splitting effects in resonant four-wave mixing

Resonant spectral structures of four-wave mixing (FWM) in molecular sodium are investigated. For a double- ? configuration with strong-weak-strong-weak fields, split components in FWM spectra induced by the strong pump fields are observed. It is shown that the split components merge into a single peak for a certain ratio of the strong field intensities. A correlation between the level-splitting effects and the saturation behavior of the FWM signal is experimentally demonstrated.     

Optical phase conjugation by resonant degenerate four-wave mixing in liquid phase medium

In this paper, frequency-doubled Nd:YAG laser's phase conjugation has been investigated experimentally using resonant degenerate four-wave mixing (DFWM). The iodine solution was used as resonant medium. In this way, the energy of the DFWM phase conjugation beam arrived at 43μJ/pulse while the total pump beam's energy reached 8mJ/pulse. The relation between the pulse energy of the DFWM phase conjugation beam and that of the pump beam was investigated. We also measured the optical field distributions of pump beam and DFWM phase conjugation beam, from which it can be noticed that the DFWM phase conjugation can improve the laser beam quality. At the same time, we observed the influence of the pump beam's disturbance on the DFWM signal.     

Two-photon resonant three-photon ionization with ultrashort pulses

The problem of two-photon resonant three-photon ionization is analysed for the case of ultrashort ionizing pulses. An analytic solution to the problem is obtained and discussed. A simple experiment is proposed which would demonstrate the effect of optical nutation on the photoelectron flux.     

Two-photon resonant four-wave mixing in atomic sodium vapour

Using the 4d- and 5s-states of sodium, two different types of two-photon resonance enhanced four-wave mixing have been observed. In the first type 2v _L =v _IR +v _pIR radiation near 2.34 μm and UV radiation near 320 nm has been detected. In the second typev _P −v _S =v _L +v _IR the UV radiation produced in the first parametric process acted as a pump for stimulated electronic Raman scattering via the 4p-state of sodium. Resonantly enhanced by the two-photon transition 3s–4s, radiation near 1.18 μm was produced in this scheme. The realisation of a tunable coherent IR source based on these four-wave mixing processes is discussed.     

Two-photon resonant four-wave mixing processes in atomic barium

By means of a N₂-laser pumped dye-laser (P _L ≈20kW, Δv _L < 10 GHZ) different two-photon resonant four-wave coupling processes in Ba vapour (n _Ba≈10¹⁶ cm⁻³) using the Ba states 6s8s ¹ S _o and 7s5d ¹ D ₂ were investigated. Coherent line radiation with conversion rates up to 10⁻³ was generated within the range of λ=190–200 nm by sumfrequency mixingv _UV=2v ₁+v ₂ of 3 laser photons and within the range of λ=250–380 nm by couplingv _UV=2v ₁±v _IR of 2 laser photons with one photonv _IR stimulated emitted in laser-induced Ba transitions. For the second coupling type the various nonlinear processes contributing to the formation of the coupling components are discussed. The power of the UV-component as function of inensity and resonance detuning of the laser as well as on the phase-mismatch was calculated on the basis of the small signal theory and compared to the experimental data.     

Propagation of the ultrashort laser pulses through the quantum nonlinear medium with resonant properties

The propagation of ultrashort few-cycle laser pulses through a quantum nonlinear medium with resonant properties is studied using the method of slowly varying amplitudes with allowance for dispersion effects. A self-consistent system of nonlinear wave equation for the evolution of laser field and the nonstationary Schrödinger equation that determines the material polarization response is numerically solved. Specific features of the propagation of laser pulse caused by a relatively large spectral width and the nonadiabatic character of the laser pulse are established. The rise of the slowly dumping polarization at the eigenfrequency of the medium and the consequent stretching of the laser pulse are observed. The role of the resonant absorption of the laser energy in the medium is analyzed. The nonlinear spectral broadening is demonstrated for the laser pulse propagating through the medium.     

A tunable narrowband optical filter via phase conjugation by nondegenerate four-wave mixing in a doppler-broadened resonant medium

The formulation of phase conjugation via nondegenerate four-wave mixing in a Doppler-broadened resonant medium is generalized to include nondegenerate pump frequencies. This process is shown capable of yielding a tunable optical band-pass filter whose central frequency can be tuned over the entire Doppler profile with only a small degradation of the filter efficiency while still maintaining a bandwidth limited by the homogeneous linewidth.     

Coherent control of dressed images of four-wave mixing

In two-level as well as V-type three-level atomic systems, we study probe transmission, four-wave mixing (FWM) and fluorescence signals with dressing effect experimentally and theoretically. We find both the hyperfine structure (at the same energy level) and the transition dipole moment (at different energy levels) can affect the dressing effect. We also experimentally investigate that angle-control dynamics in the nonlinear propagation of the images of the probe and generated FWM in two-level atomic systems, and find that the focusing and defocusing of probe beam and FWM signals can be greatly affected by the angles between dressing fields.     

Dynamics of high-power ultrashort laser pulses in resonant media

Work supported by Russian Fund for Basic Research, Project 93-02-14271.     

Effects of two strong fields in resonant four-wave mixing

An explicit solution is obtained for the four-wave mixing ω₄=ω₁−ω ₂+ω₃ of two strong fields E ₁, E ₃ and two weak fields E ₂, E ₄ in a four-level system with large Doppler broadening. Resonance of the intensity dependence of the mixing coefficient is found around equal Rabi frequencies, E ₁·d ₁=E ₃·d ₃, where d _1,3 are the dipole moments of the corresponding transitions. The effect is interpreted as a crossing of quasi-energy levels. Up to 6 peaks appear in the dependence of the conversion coefficient on the detuning of the probe field E ₂. The unexpected additional pair of peaks is a consequence of averaging over velocities. The results permit interpretation of the saturation behavior found in recent experiments on mixing in sodium vapor. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 12, 777–782 (25 December 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Three-wave and four-wave forward mixing in photorefractive materials

An amplification mechanism relying mainly on the real part of the arising space charge field in the presence of two strong pump beams is described. The dependence of amplification on frequency detuning, applied electric field and pump beam ratio are investigated in the undepleted beam approximation.     

Mid-infrared efficient generation by resonant four-wave mixing in a three-coupled-quantum-well nanostructure

We present a cascade configuration for the realization of highly efficient four-wave mixing (FWM) process in an asymmetric semiconductor three-coupled-quantum-well (TCQW) structure based on intersubband transitions (ISBTs). In the proposed TCQW scheme, the efficiency of the generated FWM mid-infrared (MIR) signal is significantly enhanced and the obtained maximum efficiency is greater than 50%. The corresponding explicit analytical expressions for the input probe and generated FWM pulsed fields are derived by use of the coupled Schrödinger-Maxwell approach and the FWM efficiency versus several variables is also discussed in details. Such a semiconductor system is much more practical than its atomic counterpart because of its flexible design and the wide adjustable parameters. This nonlinear optical process in the TCQW solid-state material can be used for efficiently generating coherent short-wavelength radiation.     

Phase conjugation through two-photon resonant nondegenerate four-wave mixing

The theory of nondegenerate four-wave mixing is described for the case wherein the counter-propagating pump waves are in two-photon resonance with the nonlinear medium. In contrast to the one-photon case, the reflection bandpass is found to be mainly determined by the phase-matching requirement. The variation of the phase-conjugate reflectivity with the pump intensity and pump detuning is considered. The effect of the intensity-dependent Stark shift on the phase-conjugation efficiency is discussed in some detail.     

引入量子干涉的双光子共振非简并四波混频

研究了级联四能级系统中双光子共振非简并四波混频(NFWM)由于加入耦合光场而产生的量子干涉效应，发现在强耦合场作用下NFWM频谱呈现AT劈裂，它反映的是两个缀饰态的能级.量子干涉还使NFWM信号被抑制或增强.此方法牵涉到三光子共振，因此可以成为研究原子或分子高激发态的有效光谱学工具. 关键词： 四波混频 量子干涉     

Quantum interference and Manley-Rowe relations in resonant four-wave frequency mixing in an optically thick Doppler-broadened medium

It is shown that under resonant interaction conditions certain notions in nonlinear optics which are based on the Manley-Rowe relations no longer hold because of the interference of elementary quantum-mechanical processes. This conclusion is illustrated by numerical examples corresponding to the experiments performed. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 12, 862–866 (25 June 1999)     

汞蒸汽中双光子共振四波和频产生125nm的相干辐射

利用汞原子6~1S_0—7~1S_0双光子共振四波和频产生了125nm的相干辐射.对双光子共振增强效应、双光子共振克尔(Kerr)效应进行了研究.讨论了平面波和聚焦情况下最佳相位匹配的条件.实验中还观测到了四波参量振荡和四波差频的信号输出.