Dispersive shock waves in nonlinear arrays

We experimentally study dispersive shock waves in nonlinear waveguide arrays. In contrast with gap solitons, the nonlinearity here pushes the propagation constant further into the transmission bands, facilitating Bloch mode coupling and energy transport. We directly observe this coupling, both within and between bands, by recording intensity in position space and power spectra in momentum space.     

Dispersive shock waves with nonlocal nonlinearity

We consider dispersive optical shock waves in nonlocal nonlinear media. Experiments are performed using spatial beams in a thermal liquid cell, and results agree with a hydrodynamic theory of propagation.     

Spatiotemporal toroidal waves from the transverse second-harmonic generation

We study the second-harmonic generation via transversely matched interaction of two counterpropagating ultrashort pulses in chi(2) photonic structures. We show that the emitted second-harmonic wave attains the form of spatially expanding toroid with the initial thickness given by the cross correlation of the pulses. We demonstrate the formation of such toroidal waves in crystals with random ferroelectric domains as well as in annularly poled nonlinear photonic structures.     

Spatial solitary waves and patterns in type II second-harmonic generation

The existence of Turing patterns and of spatial solitary waves that arise from a polarization instability of the fundamental field is predicted in type II second-harmonic generation in a quadratically nonlinear optical cavity. The analogy between these dissipative structures and those studied in absorptive optical bistability is pointed out.     

固体板中SH型板波的\

从理论上研究了固体板内SH型板波的\     

Cumulative second-harmonic generation of Lamb waves propagating in a two-layered solid plate

The physical process of cumulative second-harmonic generation of Lamb waves propagating in a two-layered solid plate is presented by using the second-order perturbation and the technique of nonlinear reflection of acoustic waves at an interface. In general, the cumulative second-harmonic generation of a dispersive guided wave propagation does not occur. However, the present paper shows that the second-harmonic of Lamb wave propagation arising from the nonlinear interaction of the partial bulk acoustic waves and the restriction of the three boundaries of the solid plates does have a cumulative growth effect if some conditions are satisfied. Through boundary condition and initial condition of excitation, the analytical expression of cumulative second-harmonic of Lamb waves propagation is determined. Numerical results show the cumulative effect of Lamb waves on second-harmonic field patterns.     

Polarization-vortex-driven second-harmonic generation

Polarization vortices exist in the focus of a class of vector beams, the lowest order of which possess full vector symmetry about the axis of propagation of the beam. At high numerical apertures these beams are known to exhibit large, local, longitudinal fields in the focal region. At an interface these fields can be many times stronger than the largest available transverse component and are therefore candidates for a variety of different experiments in surface physics. The observation of vortex-driven surface second-harmonic generation at smooth metal and semiconductor surfaces and thin films is reported. By comparing the response to that of a purely transverse field, we show that the smooth surface responds primarily to the longitudinal field component.     

分层结构中兰姆波二次谐波发生的模式展开分析

采用二阶微扰近似和模式展开方法,对分层结构中兰姆波的二次谐波发生问题进行了深入研究,得到了二次谐波声场的一般表达式。兰姆波在分层结构中传播时,固体板材的体弹性非线性效应导致在各固体层的内部及表面出现二倍频的体驱动力及面驱动应力,其作用是在分层结构中激发出一系列二倍频兰姆波的简正模式,这些简正模式的叠加即构成分层结构中兰姆波的二次谐波声场。当构成二次谐波声场的某一二倍频兰姆波简正模式的相速度等于基频兰姆波的相速度时,该二倍频兰姆波简正模式分量表现出随传播距离积累增长的性质。本文还就铝板-环氧粘接层-铝板结构中兰姆波的二次谐波声场进行了数值分析,结果显示,软粘接层性质对二次谐波声场的影响很大。     

IR-poled second-harmonic generation in glass

Infrared (IR)-induced second-harmonic generation in the chalcogenide glasses is observed. A phenomenological approach of IR picosecond non-linear optical (NLO) response in glass is developed for the middle IR spectral range (5–15 μm). The observed effect is explained within the framework of fifth-order NLO susceptibilities. A model that reproduces the basic characteristics of the experimental data, in which the optical non-linearities caused by photoinduced electron–phonon anharmonic interactions, is proposed. The role of the IR-induced phase matching conditions in the observed phenomenon is discussed.     

Surfing and generation of cosmic rays in relativistic shock waves

We consider the problem of cosmic-ray generation through the surfing acceleration of charged particles in relativistic magnetosonic shock waves (the branch of fast magnetic sound) propagating in magnetized space plasmas. The dependence of the particle surfing acceleration efficiency on the angle θ _Bn between the normal to the shock front plane and the magnetic field vector in the plasma upstream of the shock is analyzed in detail. We show that for angles satisfying the condition χ = βΓ tan θ _Bn ⩾ 1, where β = U/c, Γ = (1 − β)^{2 −1/2}, U is the shock velocity, and c is the speed of light, the particles can theoretically be accelerated through surfing for an unlimited time and can gain an unlimited energy. For angles satisfying the condition χ < 1, the kinetic energy ℰ of the particles is limited by ℰ = 2mc ²χ²/(1 − χ²) (m is the particle rest mass). Our main conclusion is that the generation of cosmic rays through the surfing acceleration of particles in the front of a relativistic shock wave for Γ ≫ 1 is also efficient when the angle θ _Bn is very small, i.e., it differs significantly from a right angle. Estimates for the energies of particles accelerated through surfing in relativistic jets are provided.     

Electric-field-induced second-harmonic generation in GaN devices

Electric-field-induced second-harmonic generation is used to detect electric fields in a GaN UV Schottky photodiode and in a GaN light-emitting diode. The second-harmonic signal is measured as a function of bias voltage and incident laser power. This technique is sensitive to small applied voltages and can be used to track electronic waveforms. The photocurrent generated by this technique is found to be less than 100 pA when the fundamental and second-harmonic frequencies are both below the device bandgap.     

Enhancement effect of cumulative second-harmonic generation by closed propagation feature of circumferential guided waves

On the basis of second-order perturbation approximate and modal expansion approach,we investigate the enhancement effect of cumulative second-harmonic generation(SHG) of circumferential guided waves(CGWs) in a circular tube,which is inherently induced by the closed propagation feature of CGWs.An appropriate mode pair of primary-and doublefrequency CGWs satisfying the phase velocity matching and nonzero energy flux is selected to ensure that the second harmonic generated by primary CGW propagation can accumulate along the circumference.Using a coherent superposition of multi-waves,a model of unidirectional CGW propagation is established for analyzing the enhancement effect of cumulative SHG of primary CGW mode selected.The theoretical analyses and numerical simulations performed directly demonstrate that the second harmonic generated does have a cumulative effect along the circumferential direction and the closed propagation feature of CGWs does enhance the magnitude of cumulative second harmonic generated.Potential applications of the enhancement effect of cumulative SHG of CGWs are considered and discussed.The theoretical analysis and numerical simulation perspective presented here yield an insight previously unavailable into the physical mechanism of the enhancement effect of cumulative SHG by closed propagation feature of CGWs in a circular tube.     

Quantum fluctuations in second-harmonic light generation

Second-harmonic light generation (SHLG) is analyzed from the viewpoint of the photon statistics of the fundamental and generated beams versus the path traversed by the two waves in the medium. The calculations lead to an anti-bunching effect for coherent incident light.     

Optical second-harmonic generation in ferroelectric nanowires

Optical second-harmonic generation in ferroelectric nanowires of potassium dihydrogen phosphate (KDP) and sodium nitrite embedded into chrysotile-asbestos nanotubes from a melt or solution has been studied. The second-harmonic radiation appears to be polarized, and its intensity is unexpectedly high in comparison with bulk materials. Analysis of the polarization characteristics of the observed signal reveals the possibility of the formation of ferroelectric nanocrystals having the same orientation along the matrix nanotubes and randomly orientated in the plane perpendicular to this direction.     

Magnetic-field-induced second-harmonic generation in semiconductor GaAs

We show that application of a magnetic field induces optical second-harmonic generation (SHG) in GaAs. This phenomenon arises from field-induced symmetry breaking causing new optical nonlinearities. A series of narrow SHG lines is observed in the spectral range from 1.52 to 1.77 eV that we attribute to Landau-level quantization of the band energy spectrum. The rotational anisotropy of the SHG signal distinctly differs from that of the electric-dipole approximation. Model calculations reveal that nonlinear magneto-optical spatial dispersion that comes together with the electric-dipole term is the dominant mechanism for this nonlinearity.     

Optimization of second-harmonic generation microscopy

We describe the principles and characteristics of second-harmonic generation imaging (SHGI) and explore various methods for optimization of the technique. Second-harmonic imaging is optimized for ultrashort laser pulses, high numerical aperture microscope objectives, a highly sensitive non-descanned large area detector, pseudo-phase-matching, and specimens with large second-order non linearity or which exhibit surface plasmon enhanced phenomena. We also compare and contrast the techniques of SHGI and two-photon excited fluorescence imaging.     

Photoinduced stable second-harmonic generation in chalcogenide glasses

We report on photoinduced second-harmonic generation (SHG) in chalcogenide glasses. Fundamental and second-harmonic waves from a nanosecond pulsed Nd:YAG laser were used to induce second-order nonlinearity in chalcogenide glasses. The magnitude of SHG in 20G?20A?60S glass was 10(4) larger than that of tellurite glass with a composition of 15Nb(2)O (5) 85TeO(2) (mol.%). Moreover, no apparent decay of photoinduced SHG in 20G?20A?60S glass was observed after optical poling at room temperature. We suggest that the large and stable value of chi((2)) is due to the induced defect structures and large chi((3)) of the chalcogenide glasses.