光学晶体K2Al2B2O7用于全固态紫外激光器的理论研究

讨论了(KABO)晶体的折射率与群速指数随光波长参数的变化.基于非线性光学晶体的谐波理论,详细分析比较了KABO晶体倍频和三倍频的频率变换特性.得到了LD泵浦的调QNd:YAG激光器在Ⅰ类和Ⅱ类相位匹配下的倍频,三倍频、四倍频的相位匹配角、有效非线性系数、光波走离角等参量.     

腔内四倍频激光增强反射腔设计

腔内反射增强技术可有效提高紫外激光四倍频效率,但反射增强腔存在多次反射光斑不重合、光束发散角不一致的问题。为了获得更好的光束质量,设计了一种实现多次反射绿光光束可重现的反射腔结构,采用传输矩阵法计算了反射光束及四倍频转换等参量。结果表明,可重现的反射腔不仅能有效避免反射增强腔内光束半径不一致导致的光束质量差的问题,还可进一步提升四倍频效率。     

Optimum conditions for nonresonant third harmonic generation

A detailed theoretical analysis of nonresonant third harmonic generation (THG) is given which includes the intensity dependent refractive indices of the nonlinear medium as an integral part. According to the third-order analytic solution, the maximum attainable conversion efficiency is only limited by a nonlinear parameter β which is essentially the ratio of the Kerr-constants and the third harmonic coefficient. Only for|beta| < 1intensity (energy) conversion efficiencies in excess of 90 percent (40 percent) are possible. The influence of the intensity distribution of the input beam is discussed. Diagrams are given from which the optimum experimental conditions can be deduced in order to get the optimum harmonic output. Limiting processes, such as fifth-order effects or self-focusing, are analyzed. As an example, the optimum conditions for efficient frequency tripling of powerful Nd:glass laser radiation are evaluated.     

基于光子晶体光纤飞秒激光技术的高功率紫外激光源

实验研究了一种基于大模场面积光子晶体光纤飞秒激光技术的紫外飞秒激光源.分析了群速失配下的倍频光和基频光的走离长度,并实验比较了不同长度的BBO晶体的倍频功率和效率.分别采用5 mm和0.18 mm的两块BBO晶体,在Ⅰ类相位匹配条件下,对光子晶体光纤放大器输出的脉宽为110 fs,重复频率50 MHz的1040 nm飞秒激光进行腔外二倍频(SHG)和四倍频(FHG),获得了高功率紫外飞秒激光.在20 W的平均功率抽运下,获得了8.88 W的二倍频绿光输出,转换效率为44.4%.同时获得了656 mW的四倍频260 nm紫外激光,单脉冲能量13 nJ,最高功率时二次谐波(SH)到四次谐波(FH)的转换效率为7.39%.     

Cr:LiSAF激光器的双波长、双脉冲四次谐波的获得

利用一块BBO晶体高效倍频产生的两束具有特定时间间隔和波长差的Cr:LiSAF二次谐波激光束,经合束,获得了双波长、双脉冲的Cr:LiSAF四次谐波激光束。     

All-solid-state ultraviolet laser based on frequency doubling in an external ring cavity

An all-solid-state ultraviolet laser based on frequency doubling in an external ring cavity with low input pump power is reported. Both second harmonic generation (SHG) and fourth harmonic generation (FHG) occurred in an external three- mirrors ring cavity. The need for impedance matching of this cavity to the input radiation was eliminated and the cavity adaptation was simplified, because the mirrors were not highly reflecting at 1064 nm and the cavity resonates only at 532 nm. Experiment results demonstrate that the conversion efficiency of this external cavity is higher than that of the single- pass condition.     

Nonlinear wave propagation phenomena in left-handed transmission-line media

This paper introduces nonlinear transmission lines based on left-handed (LH) media and simulates harmonic generation and parametric generation in a material that, in two dimensions, could also focus microwaves. This paper discusses physical phenomena that lead to and affect self-supporting harmonic generation and parametric generation in LH nonlinear transmission-line media and outline advantages of these media for developing new types of compact and efficient frequency multipliers and "active lens" devices.     

Synthesis and Multiscale Evaluation of LiNbO3‐Containing Silicate Glass‐Ceramics with Efficient Isotropic SHG Response

A study of bulk second harmonic generation (SHG) response of lithium niobium silicate glass‐ceramics is presented. The observed macroscopic SHG signals have an isotropic 3D nature. To interpret this particular nonlinear optical response, a multiscale approach is used in which clear correlations between structure and optical response are characterized from the sub‐micrometer to the millimeter scale. In particular, it is inferred that the radial distribution of the LiNbO₃ crystallites in spherulite domains is at the origin of the isotropic bulk second order optical property. It is suggested that spherulitic crystallization in glass‐ceramic is a challenging method to elaborate isotropic nonlinear optical properties in inorganic materials.     

Lasers and Their Application to Television Systems

This paper will first discuss characteristics of the different laser sources with particular emphasis on the display output power needs. There are a number of nonlinear optical effects that appear useful to display systems; of particular interest for displays are the effects related to the controllable change of the wavelength of coherent radiation incident on the nonlinear media. The nonlinear techniques to be discussed are those related to harmonic generation, Raman laser action, and optical parametric amplification and oscillation. Calculations on the parametric oscillation effect show that a one watt blue or UV laser can effectively provide the optical pumping which would result in a very appreciable tunable optical output over the visible spectrum.     

Subharmonic pumping of parametric amplifiers

The purpose of this paper is to present in some detail the operation of a parametric amplifier pumped subharmonically as compared to being directly pumped. As considered here, subharmonic pumping does not involve harmonic pump power generation (external to the varactor) but the utilization of higher-order time-dependent capacitances to yield parametric amplification by employing, basically, only a three-frequency system. The analysis given here is based on an evaluation of the Fourier series representation of the time-dependent capacitance resulting from large-signal ("hard") pumping of varactors. This evaluation indicates that significant values of higher-order time-dependent capacitances suitable for parametric amplification are obtained with relative pump swings in excess of about 90 per cent. Utilizing these higher-order time-dependent capacitances, the amplifier operation for various orders of subharmonic pumping is treated, including such factors as pump power requirements, gain, and noise figure. It is shown that, under certain conditions, less pump power is required to generate the same negative conductance than with direct fundamental pumping. Furthermore, for the same pump power and fundamental pump frequency, it is determined that significant improvements in amplifier noise figure are achieved by employing subharmonic pumping, provided varactor losses are small. From the results obtained by both analysis and experiment, it is concluded that subharmonic pumping, even without harmonic power generation, is not only feasible but can be very useful up to C-band signal frequencies with existing varactors.     

Wave propagation in nonlinear electromagnetic media

This brief tutorial review first discusses the physical origin of nonlinear electric and magnetic susceptibilities of electro-magnetic media, from the audio through the microwave to the visible range of the electromagnetic spectrum. Wave propagation in non-linear media can be described by a combination of Maxwell's equations and the nonlinear constitutive equations. The Manley-Rowe relationships are verified for anisotropic lossless dielectrica. Microwave harmonic generation in ferrites and other materials, microwave modulation of light, light harmonic generation, light mixing and parametric conversion are all discussed from a general common viewpoint. The boundary conditions at the surface of a nonlinear medium lead to generalizations of the laws of reflection and refraction of light.     

BaMgF4: An Ultra‐Transparent Two‐Dimensional Nonlinear Photonic Crystal with Strong χ(3) Response in the UV Spectral Region

Ferroelectric patterning is often used in advanced photonics and optoelectronic devices to increase their operational bandwidth and functionality, providing novel and unique performances. However, the extension of the ferroelectric structures to two‐dimensional geometries is currently limited to very few oxides and phosphates systems, which constrains its current and future applications. Here, careful processing based on e‐beam lithography and poling is employed to fabricate the first example of a two‐dimensional nonlinear photonic crystal in Barium Magnesium Fluoride, BaMgF₄, a ferroelectric fluoride crystal with an extraordinary transparency ranging from the deep ultraviolet (≈126 nm) to the mid infrared (≈13 μm). The optical characterization shows the possibility of obtaining simultaneously up to three different Cerenkov‐type second harmonic generation processes distributed in a conical geometry via χ⁽²⁾‐quasi‐phase‐matching technique. Additionally, the remarkably high χ⁽³⁾ nonlinear response of BaMgF₄ crystal in the UV spectral region is exploited to demonstrate what is believed to be the highest direct UV‐third harmonic generation conversion efficiency in a solid state system via pure χ⁽³⁾ nonlinear process. Together, the results highlight the outstanding opportunities offered by nonlinear photonic structures as innovative avenues to manipulate the light generation and control with reliable multifunctional optical character.     

Optical second-harmonic generation by electrically polarized isotropic media

In relation to recent experiments, a quantitative discussion of the microscopic mechanisms accounting for second-harmonic generation (SHG) and harmonic mixing in isotropic media immersed in a dc electric field is given, comprising the temperature-independent effect of nonlinear electronic polarizability and the temperature-dependent effect of reorientation of permanent electric dipoles. It is shown that in the case of a very strong dc electric field, when all the microsystems undergo complete alignment in the direction of the field vector, these two mechanisms attain saturation, raising considerably the intensity of SHG in the case of prolate microsystems and lowering it in the case of oblate ones. Electric saturation effects can take place in strongly dipolar molecular substances but are especially intense in solutions of macromolecules and colloid particles. The discussion covers, moreover, the symmetry relations between the nonzero elements of the nonlinear susceptibility tensor of the medium in weak as well as in strong electric fields, and the application of these relations in determining the values of elements of the tensors of second- and third-order polarizabilities of the individual microsystems. A preliminary interpretation of the available experimental data is proposed, and new procedures of SHG measurements are suggested.     

Light waves mixing in nonlinear anisotropic media

A recent method for the solution of problems at the boundary of nonlinear electromagnetic media is extended to the anisotropic case for the purpose of studying the mixing between two strong electromagnetic waves in crystals. The general solution for the wave at the beat frequency is first derived for an unbounded medium on the hypothesis of weak harmonic generation. The boundary conditions at the plane surface of a nonlinear dielectric are then considered and the polarization characteristics of the fundamental waves are examined with the aim of obtaining a more efficient mixing.     

Hybrid mode phase matching and effective nonlinear coefficient forsecond harmonic generation in biaxial waveguides

Phase matching between fundamental and second harmonic hybrid guided modes in nonlinear biaxial planar waveguides is determined for the first time based on principal axes orientations of the film, substrate, and cover. We have derived an expression for the effective nonlinear coefficient D_eff of hybrid modes in a biaxial waveguide and have calculated this coefficient numerically along the effective index phase match loci for these modes supported by a POM waveguide surrounded by isotropic media. The optimum phase matching orientations are determined for a fixed waveguide thickness. Dispersion of the principal indexes is considered     

Strontium Barium Niobate as a Multifunctional Two‐Dimensional Nonlinear “Photonic Glass”

The ability of Strontium Barium Niobate crystal as a two‐dimensional nonlinear optical multiple‐wavelength‐and‐direction converter is demonstrated, showing how harmonic generation can be obtained in an extremely large spectral range. The whole visible spectral region can be continuously generated without any angle or temperature tuning by using different nonlinear schemes involving SHG and THG in different configurations. The dominant frequency conversion mechanisms acting in each case are experimentally determined. The system can act as a nonlinear prism since the SHG conical radiation from 430 to 680 nm can be dispersed into an external angle range of 36°. Conical nonlinear processes are also demonstrated under intracavity conditions from a diode pumped Nd³⁺:SBN laser crystal. Different harmonic generated rings appear simultaneously inside the cavity, while the crystal is lasing at 1063 nm. The system constitutes the first experimental example of a two‐dimensional generalized nonlinear photonic glass on a tunable solid state laser and can be useful for novel optical multifunctional devices such as nonlinear prism self‐frequency converted solid state lasers.     

超短光脉冲感应级联五阶非线性相移分析

由于群速度失配的影响,飞秒光脉冲在感应到FONPS（级联五阶非线性相移）的同时,将不可避免地发生脉冲畸变.通过理论分析及数值模拟,提出了使级联五阶非线性过程运行在较大相位失配条件下的解决方案,成功地消除了脉冲畸变.并且借助于该过程中倍频效率的提高,有效地补偿由于相位失配量的增大所造成的FONPS的下降,实现飞秒基频光脉冲在感应到大的FONPS的同时无脉冲畸变发生.     

A Fast and Reliable Method for Computer Analysis of Microwave Mixers

In this paper, a numerical method is presented for analyzing microwave mixers. Particular consideration is given to the solution of the nonlinear pumping problem of real Schottky-barrier diodes. The new technique has a significantly improved convergence rate, which is demonstrated by means of direct comparisons with other methods. A convergence test procedure is proposed and applied which uses randomly generated harmonic impedances. The proposed numerical technique for solving the nonlinear and linear problem is extended to the analysis of balanced mixers. Fabricated planar balanced mixers are analyzed, both theoretically and experimentally, in a separate paper.     

双端抽运腔内和频紫外激光器的实验研究

为了获得高功率全固态355nm紫外激光器,采用平平腔结构,通过LD双端抽运Nd:YVO4晶体,在声光Q开关调制作用下产生1064nm脉冲基频光,利用两块LBO晶体分别进行腔内倍频、和频产生355nm紫外激光。在LD抽运功率54W、调制频率40kHz的条件下,获得紫外的最高输出功率为6.67W,脉冲宽度为20ns, M2=1.1。结果表明,腔内和频可得到高效率、高光束质量的紫外激光输出。