Generation of a forward-traveling phase-conjugate wave in germanium

In this communication, we report the generation of a picosecond forward-traveling phase-conjugate wave at 1.06 μm in thin germanium samples by degenerate four-wave mixing. At this wavelength, the conjugate wave is produced by diffraction of the pump from an absorption grating produced by direct absorption of pump and signal pulses. We measure and discuss the transient effects caused by the finite duration of the nonlinear material response.     

Deflection of a phase-conjugate wave in nondegenerate four-wave mixing

The boundary problem for signal phase conjugation at nondegenerated four-wave mixing (FWM) is considered. In contrast to the statements of some authors it is shown that noncollinearity of the incident and the phase-conjugate waves occur. Expressions have been obtained for the deflection angle for a number of configurations of practical importance. Useful analogy between linear and nonlinear reflection at the FWM is noted.     

Focusing of a nonlinear phase-conjugate ultrasonic wave transmitted through a phase-inhomogeneous layer

The propagation of a nonlinear phase-conjugate ultrasonic wave through a layer introducing random phase aberrations is studied experimentally. The wave is generated by an overthreshold parametric phase-conjugating ultrasonic amplifier. It is shown that, with the extent of nonlinearity achieved for the conjugate wave, the phase locking of harmonics is retained and, as a consequence, a compensation of the distortions introduced by the layer takes place. The possibility of an automatic focusing of a nonlinear phase-conjugate wave propagating in an inhomogeneous medium is demonstrated, which is important for practical applications.     

The signal synchronization transmission of a spatiotemporal chaos network constituted by a laser phase-conjugate wave

The signal synchronization transmission of a spatiotemporal chaos network is investigated.The structure of the coupling function between connected nodes of the complex network and the value range of the linear term coefficient of the separated configuration in state equation of the node are obtained through constructing an appropriate Lyapunov function.Each node of the complex network is a laser spatiotemporal chaos model in which the phase-conjugate wave and the unilateral coupled map lattice are taken as a local function and a spatially extended system,respectively.The simulation results show the effectiveness of the signal synchronization transmission principle of the network.     

Probe fluctuations in a phase-conjugate resonator

Analytical expression are derived for the conjugated and specular reflections from a phase-conjugate resonator probed by a fluctuating beam. Phase fluctuations are described by a diffusion model. The results, demonstrating a strong dependence on the coherence time, are shown to coincide with expressions based on abrupt phase changes. Amplitude fluctuations, represented by a sudden-jump model, are shown to play almost no role in the behaviour of the resonator.     

Temporal contrast enhancement of picosecond pulses based on phase-conjugate wave generation

A practical technique based on the phase-conjugate wave (PCW) generation is proposed to improve the temporal contrast of the picosecond pulses. Our theory predicts the temporal contrast of the picosecond pulses can be enhanced to about the cube of the temporal contrast of the input pulse via the PCW generation, in which the conversion efficiency from the incident pulse to the PCW is about 25%. In a proof-of-principle experiment, the temporal contrast of picosecond pulses was enhanced from 1.7×10³ to 8.6×10⁸ with the conversion efficiency of 10%. This technique is promising to effectively eliminate the background of the ultrashort and ultraintense laser pulses in the future.     

泵浦光强对激光相位共轭波非线性效应的影响

分析了泵浦光强对激光相位共轭谐振腔中探测光场的作用。基于稳定性定理,通过确定系统的Lyapunov指数,数值计算了在不同泵浦光强下的激光相位共轭波的非线性效应。结果显示,泵浦光强是系统的控制参量。调节泵浦光强的数值,系统的动力学性质发生了改变,可以呈现一周期、二周期、四周期以及倍周期分岔、周期并缩和混沌现象。     

Chaos in phase-conjugate resonators as a multimodal mapping

An optical phase-conjugate resonator, realized by a Kerr-like phase conjugator, and represented by a two-dimensional slowly varying envelope plane-wave model is driven to chaos using two laser pumps in standard four-wave mixing geometry. The relevant slowly varying envelope wave equations are reduced to a one-dimensional map for intracavity intensity and a quasi-periodic hop for its phase. One-dimensional multimodal Bessel mappings arising in this analysis are considered using elementary symbolic dynamic methods.     

Laser wiggler beat wave in a plasma

It is shown that by combining a laser wave and an electron beam propagating through a plasma inside a wiggler: (i) Electrons can be accelerated to high energies. For usual laser frequencies and wiggler wavelengths, plasma densities are in the range 10¹⁵–10¹⁶ cm^-3. The plasma density fluctuation in the longitudinal wave suffices to obtain electron energies of several hundred MeV over short distances. (ii) High frequency radiation can be amplified.     

Nonlinear theory of self-oscillations in a phase-conjugate resonator

We present an exact, nonlinear analysis of self-oscillations in a phase-conjugate resonator. Optical bi- and multistability, as well as period doubling to chaos are predicted.     

Non-linear jump of wave polarization in a plasma

The hysteresis is pointed out of a non-linear dependence of electromagnetic waves polarization near plasma resonance in magnetoactive plasma due to the wave energy. Stable “low-temperature” and “high-temperature” conditions are found of polarization and critical fields corresponding to transitions between them.     

Large-amplitude plasma wave generation with a high-intensity short-pulse beat wave

A short-pulse laser beat wave scheme for advanced particle accelerator applications is examined. A short, intense (3-ps, >10(18)-W cm(-2)) two-frequency laser pulse is produced by use of a modified chirped-pulse amplification scheme and is shown to produce relativistic plasma waves during interactions with low-density plasmas. The generation of plasma waves was observed by measurement of forward Raman scattering. Resonance was found to occur at an electron density many times that expected, owing to ponderomotive displacement of plasma within the focal region.     

Oscillating two-stream instability of a plasma wave in a plasmachannel

A long wavelength Langmuir wave (ω₀, k₀), propagating through a parabolic plasma density channel, can decay into a low-frequency mode (ω,k&oarr;) and two short wavelength Langmuir wave sidebands (ν_1,2,k&oarr;_1,2 ), via two-stream instability where ω_1,2=ω∓ω₀ and k&oarr;_1,2=k&oarr;∓k&oarr;₀. Depending on the mode number n, the growth rate maximizes in the range γ_max≃0.1ω_pi-0.4ω_pi for the range of k from 0.1(ω_pi/c_s) to 0.2(ω_pi/c_x) for ν₀~ν_th where ν₀ and ν_th are the oscillatory and thermal velocities of electrons, ω_pi is the ion plasma frequency on the axis, and c_s is the sound speed. The growth rate increases with the width a of the plasma density channel. It decreases with the mode number. The instability may be relevant to laser based charged particle accelerators