X waves generated at the second harmonic

The process of optical frequency doubling in the undepleted regime can lead to the generation of an X-wave envelope with group velocity locked to the pump beam. Its parameters and its angular spectrum are directly related to the zeroth- and first-order dispersive features of the nonlinear process. This constitutes a novel mechanism for spatiotemporal localization of light.     

Generation of light of second harmonic frequency in a Gaussian light

The process of second harmonic frequency generation in a chaotic (Gaussian) light on the basis of a simple quantum-mechanical model is studied in this work. It is shown that the process of second harmonic frequency generation in the chaotic light is quicker than that in the coherent light with the Poisson distribution of photon number.     

Filtering of light fluctuations by multiple second harmonic generation

It is shown that the level of both quantum and classical light fluctuations can be considerably decreased by multiple second harmonic generation in thin nonlinear plates, when filtering out the generated second harmonic radiation behind each plate. As for the application, a second harmonic plate is proposed to be placed in the laser resonator in order to improve statistical and coherence properties of the lasing mode.     

Scaling law and polarization of second harmonic emission from laser generated plasma

Measurements are described of the intensity and polarization of the second harmonic emission from a plasma generated by 1.054 μm, 35 ps laser pulses at oblique incidence. It is shown that the measured scaling cannot be explained by a simple power law and that at high intensities the degree of polarization of the second harmonic radiation does not depend on the polarization of the incident laser light.     

Properties of the peaks of second harmonic light through Fibonacci-class ferroelectric domains

After establishing the method of constructing a class of one-dimensional (1D) Fibonacci-class quasiperiodic (FC(n)) ferroelectric domains system, we have studied the properties of the electric field of the second harmonic generation (SHG) by means of the small-signal approximation in the case of the vertically transmission. It was found that only the second harmonic light (SHL) peaks which were indexed by two special integers q and p would be the brightest and the spectra whose positions were decided by successive FC(n) integers and were perfect self-similar without considering the dispersive effect of the refractive index on SHL. The effect of the vacancies for some special spectral lines was also studied generally. The analytic results were confirmed by the numerical simulations. Received 26 October 1999 and Received in final form 6 January 2000     

Efficiency of second harmonic generation for partially coherent light in anisotropic crystals

This paper analyzes the second harmonic generation (SHG) efficiency of light with partial temporal coherence due to depolarization effects in birefringent media. It discusses relations between SHG efficiency fading, light source spectrum, crystal birefringence, and phase matching conditions. The efficiency of SHG pumped by the partially coherent light beam that may depolarize light in nonlinear birefringent crystal is also analyzed. The basic theory of SHG with its modification for partially coherent light with depolarization and some numerical calculations of the SHG process are described. Presented at 9-th International Workshop on Nonlinear Optics Applications, NOA 207, May 17–20, 2007, Świnoujście, Poland     

Nonlinear second harmonic generation by light wave-plasma interaction in oscillating magnetic field

The nonlinear generation of second harmonic electromagnetic waves in a thin inhomogeneous (dense and rarefied) plasma layer (of lengthd) by obliquely and normally incident light waves is analyzed. We consider the effect of an external time-dependent magnetic field on the generation and amplification of waves. Two cases are considered, when the magnetic field oscillates at a frequency (i) equal to and (ii) double that of the incident wave. For normal incidence, waves are not radiated in case (i), while in case (ii) the second harmonics are radiated equally from the plasma boundaries atx=0 andx=d. For a rarefied plasma, the second harmonics are radiated with equal amplitudes in both cases.     

Fluctuations in number of photons in region of unstable behavior in process of intracavity generation of second harmonic

Quantum fluctuations of the number of photons of the fundamental mode and of the second harmonic in the process of intracavity generation of the second harmonic in the unstable region of the system are studied. The distribution functions of the number of photons of interacting modes are calculated in the positive P-representation. The functions of the joint distribution of the number of photons of the fundamental mode and the number of photons in the second harmonic are also studied.     

Interactive length of fundamental wave and second harmonic generated on the surface of anomalous dispersion medium

In this Letter, a new method is presented to calculate the interactive length between the fundamental wave and second harmonic generation(SHG) for the configuration of total internal reflection on the inner surface of a nonlinear crystal. Three independent experiments are designed to measure the bandwidths of this second harmonic wave. The theoretical expression of the intensity of SHG is obtained through a nonlinear coupled wave equation. The interactive length of this phase-matched SHG can be calculated mathematically by utilizing the measured bandwidths and the intensity equation. There is no existing method to obtain the interactive length either from theoretical calculations or by experimental measurement. This method can be applied to estimate the extremely short interactive volume in nonlinear processes.     

Observation of the second harmonic generation pumped by microscopic to extraterrestrial incoherent light sources

I report on the experimental demonstration of the second harmonic generation in bulk nonlinear crystals excited by light emitting diode, halogen lamp and the Sun. Practical application for measurement of autocorrelation functions of incoherent non-laser driven sources via second order nonlinearity is demonstrated for the first time.     

Generation of green light in a thermally poled silica fiber by quasi-phase-matched second harmonic generation

Thermal poling is an attractive method to induce a nonlinear coefficient in silica materials. We have investigated potential silica materials with respect to their suitability for thermal poling and analyzed the achievable depletion thickness in the poling process. Based on this investigation, a fiber was designed and prepared for second harmonic generation. The generation of light in the visible range at a wavelength of 532 nm was successfully demonstrated with a poled fiber and with quasi-phase matching using a pump wavelength of 1064 nm.     

CW blue light generation at 429 nm by utilizing second harmonic process with KNbO_3

Continuous-wave blue light at 429 nm from a second harmonic process has been investigated at room temperature with Potassium Niobate (KNbO3) crystal. Optimum parameters for nonlinear conversion in our designing single-resonant, external ring cavity pumped by the Ti:sapphire laser are established. 39% of maximum overall conversion efficiency is obtained and factors that limit the conversion efficiency is discussed.     

Spatio-temporal characterization of self-formed hollow light pulses in the pump depletion regime of second harmonic generation

Depletion of the pump pulse in second harmonic generation (SHG) and its back-regeneration from the second harmonic pulse is a well known process in nonlinear optics. Nevertheless how the pump pulse reshapes as a three-dimensional object in space and time has never been investigated. In this work we apply a three-dimensional mapping technique to record this transformation and we experimentally show the formation of a hollow as well as more complex layered spatio-temporal structures of the fundamental pump pulse in different regimes. The results are compared with numerical simulations.     

非线性光波导中基波和二次谐波的模场分布研究

非线性波导是一种重要的光量子器件。采用马卡梯里近似,可以近似描述波导的模场分布特征。针对ee-e准相位匹配的周期极化铌酸锂波导,分析波长为1 064 nm的基波和532 nm的二次谐波的基模模场分布。结果表明:如果波导为嵌入型正方形波导,基波和二次谐波的光斑基本为圆形,基波场分布范围较大;在截面正方形边长为5 μm并且芯区比包层折射率略高0.02时,波导就能将两种光波场基本约束在芯区中,但是这种波导边长为0.5 μm时约束能力就变得很差;如果采用芯区与包层折射率差别较大的波导,芯区边长为0.5 μm就可以将两种场分布基本约束在芯区中。结果对分析其他类型的非线性波导的模场分布具有指导意义。     

Fluctuations in doubly scattered laser light

Fluctuations in laser light, doubly scattered by brownian particles, were analysed by measuring the spectral noise power of the photodetector current. Scattering took place at two spatially separated systems of spherical particles. Analytic expressions for the field and intensity correlations are derived. The analytic expressions for the spectrum of the intensity fluctuations of the doubly scattered laser light demonstrate that the frequency dependence of the spectrum depends strongly of the geometry of the experimental arrangement. This is not the case for singly scattered light where in good approximation the spatial and temporal correlations can be separated analytically.Our measurements show that the noise spectrum of the doubly scattered radiation may have the same frequency dependence as the spectrum of the singly scattered light. However, there are conditions where the frequency dependence of the noise of the doubly scattered light diverges markedly from that of the singly scattered light.     

Determination of spectral width and chirp of ultrashort light pulses by analysis of second harmonic beam divergence

It is shown that in the noncollinear second harmonic generation scheme used for ultrashort light pulse duration measurements the divergence of the second harmonic beam is determined by the spectral width and chirp of the pulse. This enables one to measure simultaneously the spectral width, pulse duration, spectral-time product, chirp and its sign for a single pulse in the same device.