Mode-coupling phenomena in intracavity second harmonic generation

The dependence of intracavity second harmonic generation efficiency on the linear phase detunings in crystal and air is studied both theoretically and experimentally. It is shown that in the presence of feedback at the second harmonic frequency an optimum conversion efficiency can be achieved by a mutually correlated choice of phase mismatch in a nonlinear crystal and the position of the latter inside the cavity.     

Correlation of fluctuations of the quadrature amplitudes of interacting modes in the instability region of intracavity third-harmonic generation

Correlation of fluctuations of quadrature amplitudes of interacting modes is studied for the process of intracavity third-harmonic generation in the region of instability. It is shown that this correlation strongly depends on the value of the nonlinear mode coupling coefficient. For small values of the coupling coefficient, correlation of fluctuations of quadrature amplitudes is small. With increasing coupling coefficient, the correlation increases (states of the subsystems become entangled). Then, starting from a certain value of the coupling coefficient, it starts decreasing gradually, tending to zero (entanglement of states of the subsystems decreases). Correlation of fluctuations of quadrature amplitudes decreases also when the amplitude of the fundamental mode perturbing field is decreased.     

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.     

Effect of pump fluctuations on second harmonic generation and parametric amplifications

The effect of phase and amplitude fluctuations of the pump wave on second harmonic generation and parametric amplification has been considered. Expressions for the intensity and linewidth have been obtained. In the incoherent regime, the second harmonic intensity is directly proportional to the interaction length (L) and its linewidth ₂1/L. A noise pump is more effective in parametric amplification. The linewidth of the generated signal and idler waves decrease with increasing interaction length.     

Use of nonlinear properties of intracavity type II second harmonic generation for image processing

We discuss the use of intracavity type-II second harmonic generation for all-optical processing of images. Injecting an image in a pump beam linearly polarized and a homogeneous field in the orthogonally polarized pump, it is possible to magnify the contrast and to recognize the contour of any part of the image whose intensity is above a tunable reference level. This can be done using ideal planar cavities where all the fields are resonant as well as in the more realistic situation where only the fundamental fields are resonant and using cavities with spherical mirrors. PACS 42.30.-d; 42.65.Ky; 42.65.Pc     

光抽运垂直扩展腔面发射激光器腔内倍频理论研究

建立了计入光波在非线性晶体中走离和相位失配情况下的光泵面发射激光器腔内倍频的速率方程理论模型,采用循环数值逼近的方法对该速率方程进行求解.以BBO,LBO,PPLN等非线性晶体为例,研究了晶体长度以及抽运功率等因素对倍频输出功率的影响,模拟结果与实验结果符合得较好. 关键词： 光抽运 垂直扩展腔面发射激光器 腔内倍频 数值模拟     

Calculation of the stationary generation power of a solid-state raman laser with intracavity second harmonic generation and sum frequency mixing

Analytical equations for the power of second-harmonic stationary generation or sum frequency mixing in a Raman laser with an intracavity nonlinear medium are developed and analyzed as functions of pumping mode and other parameters of the laser system. Parameter relationships providing the maximum output power and conditions for suppression of both stimulated Raman scattering by sum frequency mixing and; consequently, of sum frequency mixing itself are found.     

Distribution of numbers of photons in the region of unstable behavior in the process of intracavity second harmonic generation

For the process of intracavity second harmonic generation we investigate in positive P-representation with simulation of Langevin noise sources the distribution functions of numbers of photons in fundamental and second harmonic modes in the region of unstable behavior of the system. It is shown that in the unstable region, as distinct from the stable, the functions of distribution have two-peak structure. We also study the joint function of distribution of photon numbers in interacting modes.     

On the theory of second harmonic generation

It is shown how the theory of non-linear interaction between the modes of the open resonator, developed previously [1] and used to study resonant second harmonic generation [2], can be applied to second harmonic generation in the absence of a resonator. The conditions under which the second harmonic output, in the small conversion approximation, can be approximated by a Gaussian beam are derived.The optimum value of the focusing parameter I/z₀ (hereI is the length of the crystal, andz ₀ is one-half the confocal parameter of the fundamental beam) for the total output is shown to be 5.68 agreeing precisely with the value given by Boyd and Kleinman [3].     

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.     

Self pulsing in second harmonic generation

We consider nonlinear optical processes in a cavity maintained far from thermal equilibrium by external pumping. In second harmonic generation we predict a hard mode instability at a critical pump strength indicating the existence of undamped spiking similar to that in strongly pumped lasers. In subharmonic generation above the soft mode transition noted by Graham we predict the appearance of sidebands in the subharmonic spectrum.     

Noncollinear second harmonic generation in KDP

This paper reports experimental and analytical results on optical second harmonic generation when a noncollinear arrangement is employed. The dependence of second harmonic power on crystal length, absorption, beam radius and the angle between the two fundamental waves is obtained. Double refraction of the crystal is taken into account, but the divergence and depletion of the fundamental waves are neglected. The results of the calculations are confirmed by experiments carried out with a KDP crystal in the near field of two intersecting TEM₀₀ ruby laser beams.An extension of the theory to nonlinear interactions other than second harmonic generation - e.g. four-wave interaction - is possible.     

Efficient second harmonic generation in CDA

Efficient second harmonic generation at 0.532 μ has been achieved in a temperature tuned CDA crystal when a narrow beam divergence Nd:YAG laser was used. At a crystal temperature of 40.3°C, a peak second harmonic power of 7.5 MW was obtained with a peak power conversion efficiency of 33%. The temperature variation of the refractive indices in CDA has been determined to be d(n^e_2ω?n⁰_ω)/dT = 7.2 × 10^?5°C^?1.     

Optimization of quadrature frequency conversion with type-Ⅱ KDP for second harmonic generation of the nanosecond chirp pulse at 1053 nm

A second harmonic generation system with two type Ⅱ KDP crystals in quadrature is optimized for the nanosecond chirp pulse.The acceptance bandwidth of this optimizing scheme is close to 10 nm by using two crystals with slightly opposite angular detuning from phase matching and the conversion efficiency can reach 70%for top-hat chirp pulse at ～2 GW/cm2in theory.The preliminary experimental results are obtained on the 9th beam of Shen Guang Ⅱ SGⅡ laser system,and the performance of optimization is partially verified.     

二次谐波产生过程中准相位匹配条件的研究

从耦合波基本方程出发,在实空间严格推导出二次谐波产生(SHG)过程中的准相位匹配(QPM)条件.讨论了满足QPM条件时,SHG的转换效率以及相位失配角随波传播距离的变化.着重研究了非线性极化率的周期性调制对提高SHG转换效率的贡献.     

Optical second harmonic generation in ammonium tartrate

Second harmonic generation was observed in ammonium tartrate single crystals by a phase matching technique at the fundamental wavelength 1.153 μm. The nonlinear coefficients were found to be comparable in magnitude to those of KDP. The optical transmission and the refractive indices were also measured.     

DC-induced generation of the reflected second harmonic in silicon

DC-induced generation of the reflected second harmonic is experimentally observed on the surface of a centrosymmetric silicon single crystal. A direct current with a surface density of j _max ～ 10³ A/cm² violates the symmetry of the electron distribution function and induces the optical second harmonic with an intensity corresponding to the dipole quadratic susceptibility χ^(2)d (j _max) ～ 3 × 10^?15 m/V.