离散效应对高强度激光三次谐波转换的影响

 使用分步傅里叶变换和四阶龙格库塔法(R-K) ，对高强度激光以Ⅰ/Ⅱ类角度失谐方式，在KDP晶体中的谐波转换进行了研究，详细讨论了离散效应对三次谐波转换的影响。结果表明，离散效应不但降低了三次谐波转换效率，而且使谐波光束质量显著降低；初始入射基频光束腰半径较小时，离散效应是二次谐波转换和三次谐波转换效率降低的主要因素，失谐角对三次谐波转换的影响较小；随着束腰半径的增加，离散效应的影响逐渐减小，失谐角对三次谐波转换的影响逐渐增加。     

Imaging theory of nonlinear second harmonic and third harmonic generations in confocal microscopy

ItisreportedrecentlythatnonlinearopticalphenomenonofSHGandTHGhasbeenobservedinmanybiologicaltissues[16].SHGandTHGhavebeenusedtoperformthethree-dimensionalimaginginlivingtissuesandhaveattractedmuchattentionrecently.TherearemanyadvantagesofusingSHGandTHGtoperformthethree-dimensionalimaginginlivingtissues,suchasnoninvasiveandnophotobleaching,inadditiontotheimagingpropertiesofmulti-photonfluorescenceimaging[7—9].Firstly,unlikeinthesingle-andmulti-photonfluorescenceprocesses,onlyvirtualstat…     

Multiple refocusing characterization and critical power measurement using third harmonic generation at interface

We have studied multiple refocusing in fused silica and measured the critical power for self-focusing using third harmonic generation at an air/glass interface. The third harmonic energy as a function of geometrical focal position obtained at different input energies provides much information, such as the critical power for self-focusing, intensity clamping during filamentation, and evolution of multiple refocusing filaments.     

Enhanced third harmonic generation in periodic structures

We consider third harmonic generation in a periodic layered medium with alternate nonlinear media. We show enhanced third harmonic generation when the fundamental frequency matches one of the mode frequencies of the distributed feedback structure. The observed feature is explained in terms of large local field enhancement for the fundamental wave.     

Phase-matched third harmonic generation in a plasma

Relativistic third-harmonic generation in a plasma is investigated. The growth of a third-harmonic wave is limited by the difference between the phase velocity of the pump and driven waves. This phase velocity mismatch results in a third-harmonic amplitude saturation and oscillation. In order to overcome this saturation, a phase-matching scheme based on a resonant density modulation is described. The limitations of this scheme are analyzed     

Nonresonant third harmonic generation in thallium vapour

Feasibility of nonresonant third harmonic generation in thallium is investigated. The third order susceptibility, for driving frequencies in the visible region, is calculated and the phase matching with Ar as buffer gas is investigated. Other related quantities like coherence length, minimum pulse lengths required to get phase matching and power input requirements to achieve 50% conversion are also calculated.     

Magnetization-induced third harmonic generation in magnetophotonic microcavities

Magnetization-induced third harmonic generation was experimentally observed in thin films of bismuth-dopedyttrium-iron garnet. The magnitude of magnetization-induced nonlinear optical response was enhanced through building-in a garnet film into a photonic-crystal microcavity. It was shown that the observed magnetization-induced variations in the third-harmonic intensity were caused by the internal homodyne of interfering weak magnetic and strong nonmagnetic polarization components of the cubic nonlinearity of the garnet.     

局域表面等离激元诱导的三次谐波增强效应

本文研究了二维金三角形纳米颗粒阵列的三次谐波非线性光学效应. 金三 角纳米颗粒阵列是基于微球刻印技术制成. 采用反射式光学系统, 观察到该纳米结构在光谱分辨的飞秒激光照射下产生明显的三次谐波. 研究表明, 当激光抽运频率接近金纳米颗粒的局域表面等离激元共振位置时, 三次谐波信号得到增强; 三次谐波辐射方向满足动量匹配条件. 关键词： 微球刻印 三次谐波产生 表面等离激元     

Theory of high efficiency third harmonic generation of high power Nd-glass laser radiation

Overall energy efficiencies on the order of 80% are predicted for the conversion of 1.054 μm laser radiation to the third harmonic. A new tripling configuration is used in which the fundamental beam is incident upon the first of two KDP Type II crystals linearly polarized at an angle of tan^?1 1/√2 to the ordinary direction. This configuration is compared with alternative tripling schemes.     

Frequency dependence of third harmonic generation in polyacetylene

The frequency dependence of the third harmonic generation in trans-polyacetylene is quantitatively interpreted by considering the bands of finite chain and the damping of excitation. Our theory shows that there are two distinct peaks in the spectrum of the third harmonic generation. The first one around 0.6 eV comes from the three-photon resonant transition between the edges of the valence band and conduction band; the second one around 0.9 eV is produced by the two-photon interband transition. The excitation-dependent damping is essential to determine the position of the second peak. The theoretical results agree well with the experimental data.     

Transverse and longitudinal phase-matching in third harmonic generation induced by the Bessel beams

Influence of transverse and longitudinal phase matching on the spectral and intensity properties of third harmonic generation induced by the Bessel pump beams has been investigated both theoretically and experimentally. Transverse phase matching, revealing itself as a ring pattern in the third harmonic intensity angular spectrum was demonstrated in both the normally and anomalously dispersive media. The conditions were found for the optimization of this conical third harmonic signal.     

Analysis of third and one-third harmonic generation in lossy waveguides

A comprehensive study on the requirements for the highly efficient third harmonic generation(THG) and its inverse process, one-third harmonic generation(OTHG), in lossy waveguides is proposed. The field intensity restrictions for both THG and OTHG caused by loss are demonstrated. The effective relative phase ranges, supporting the positive growth of signal fields of THG and OTHG are shrunken by the loss. Furthermore, it turns out that the effective relative phase ranges depend on the intensities of the interacting fields. At last, a modified definition of coherent length in loss situation, which evaluates the phase matching degree more precisely, is proposed by incorporating the shrunken relative phase range and the nonlinear phase mismatch. These theoretical analysis are valuable for guiding the experimental designs for highly efficient THG and OTHG.     

Sub-millimeter third harmonic generation in n-InSb waveguide

Resonant third harmonic generation of a sub-millimeter wave in n-InSb waveguide embedded with a density ripple is investigated. The non-linearity arises through the modulation of free electron mass while the ripple accounts for the phase mismatch. The efficiency of the third harmonic generation is large. However, as the plasma frequency increases the attenuation rate of the third harmonic increases and the third harmonic efficiency decreases as (ω_pb/c) is raised.     

Gradient enhanced third harmonic generation in a femtosecond filament

The third harmonic generated during femtosecond filamentation in air is studied. By establishing a gradient from atmospheric pressure to vacuum conditions, we truncate the filament abruptly at defined positions. The introduction of the pressure gradient leads to an enhancement of the generated third harmonic radiation by 3 orders of magnitude. This effect is attributed to an improved on-axis phase-matching condition. We investigate the spectral shape and the conversion efficiency of the third harmonic during the propagation in the filament.     

Two photon resonant third harmonic generation in calcium vapour

We have generated ultraviolet picosecond pulses by frequency tripling a mode locked dye laser in calcium vapour. Saturation of third harmonic generation is observed when the dye laser is turned to a two photon resonance. Peak powers of 100 kW, tunable around 200 nm are achieved at fundamental powers of 250 MW.     

Giant third optical harmonic generation in island silver films

Giant third optical harmonic (TH) generation has been experimentally observed in island silver films. The TH intensity in the island silver films studied is more than two orders of magnitude higher than the value observed for the smooth surface of a homogeneous silver film. The mechanism of enhancement of the nonlinear cubic response is associated with the resonance enhancement of the local optical field at the TH wavelength, which is caused by the excitation of local surface plasmons in the ensemble of metal nanoparticles.     

High power red laser generation by second harmonic generation with GTR-KTP crystal

In this Letter, a gray-tracking-resistant—potassium titanyl phosphate(GTR-KTP) crystal is used for intracavity frequency doubling red laser generation for the first time. Under the 808 nm LD pump power of 180 W, as high as 12.5 W of red laser output is obtained with the optimum repetition rate of 7 k Hz. Within the red laser power variation range between the maximum to 70%, a temperature tolerance is measured to be 35°C. The results prove that GTR-KTP should be a potential nonlinear crystal for red laser generation.