利用表面微结构提高波长上转换红外探测器效率

波长上转换红外探测器具有实现大面阵焦平面的优势, 但光提取效率是制约器件整体效率的关键因素之一. 本文主要研究利用表面微结构来提高波长上转换红外探测器的效率. 首先通过仿真计算研究了表面微结构参数对光提取效率的影响, 然后基于优化设计的参数, 采用聚苯乙烯纳米球掩膜刻蚀的方法制作了具有圆台型表面微结构的波长上转换红外探测器. 测试结果表明, 具有表面微结构的器件的光提取效率比无表面微结构的器件提高了130%. 本文制作表面微结构的方法可以实现波长上转换红外探测器件整体效率的提高.     

用于提高微波无线能量传输系统接收端能量转换效率的肖特基二极管

转换效率是微波无线能量传输系统的关键参数,为提高该参数指标,本文提出了一种GeOI折叠空间电荷区肖特基二极管,该器件结构可以显著降低肖特基二极管的零偏置电容,利于能量转换效率的提高.通过在ADS仿真软件中使用该器件SPICE模型进行整流电路仿真,在输入能量为24.5 dBm时,获得了75.4%的转换效率.     

单轴晶体Ⅰ类相位匹配时的转换效率分析

在考虑了二次谐波的吸收对转换效率影响的情况下,由光在介质中的波动方程,推导出负单轴晶体Ⅰ类相位匹配时平面二次谐波的耦合波方程和二次谐波转换效率的理论公式。在此基础上,再考虑走离效应的影响,给出了二次谐波转换效率的理论公式。根据这些公式,以负单轴晶体K2Al2B2O7（KABO）为例,对二次谐波的转换效率进行了数值计算。结果表明：考虑二次谐波的吸收时,存在倍频晶体长度的最佳值,当倍频晶体取该值时,二次谐波的转换效率最高;走离效应的存在使二次谐波的转换效率降低。     

W波段二次谐波突变复合腔回旋管数值模拟

通过对二次谐波低电压突变结构复合腔回旋管中谐振腔结构、模式竞争以及电子注-波互作用的研究,分析了高频结构特性、寄生模式的抑制和工作参数优化等问题。给出了3 mm 二次谐波低损耗TE02/TE03模式回旋管的模拟设计结果。计算采用了坡度磁场,互作用效率得到显著提高。PIC粒子模拟结果表明:在电子注电压25 kV、电流4 A、纵横速度比1.6、工作磁场1.72 T时,回旋管可获得37 kW 的输出功率,横向运动能量转换效率高达51%,器件效率为37%。     

单轴晶体Ⅰ类相位匹配时的转换效率分析

 在考虑了二次谐波的吸收对转换效率影响的情况下,由光在介质中的波动方程,推导出负单轴晶体Ⅰ类相位匹配时平面二次谐波的耦合波方程和二次谐波转换效率的理论公式。在此基础上,再考虑走离效应的影响,给出了二次谐波转换效率的理论公式。根据这些公式,以负单轴晶体K₂Al₂B₂O₇（KABO）为例,对二次谐波的转换效率进行了数值计算。结果表明：考虑二次谐波的吸收时,存在倍频晶体长度的最佳值,当倍频晶体取该值时,二次谐波的转换效率最高;走离效应的存在使二次谐波的转换效率降低。     

12 W高功率高可靠性915 nm半导体激光器设计与制作

本文设计并制作了一种高效率、高可靠性的915 nm半导体激光器。半导体激光器是光纤激光器的关键部件,为了最大限度地提高器件的电光转换效率,在设计上采用双非对称大光腔波导结构,同时对量子阱结构、波导结构、掺杂以及器件结构进行了系统优化。器件模拟表明,在25℃环境温度下,器件的最高电光转换效率达到67%。采用金属有机气相沉积(MOCVD)法进行材料生长,随后制备了发光区域宽度为95μm、腔长为4.8 mm的激光芯片。测试表明,封装后器件的效率以及其它参数指标达到国际先进水平,在室温下阈值电流为1 A,斜率效率为1.18 W/A,最高电光转换效率达66.5%,输出功率12 W时,电光转换效率达到64.3%,测试结果与器件理论模拟高度吻合。经过约6 000 h的寿命加速测试,器件功率没有出现衰减,表明制作的高功率915 nm激光芯片具有很高的可靠性。     

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。     

负折射率材料中强基频光条件下二次谐波转换效率的研究

研究了二次谐波(SHW)是负折射率而基频光是正折射率的材料中,影响二次谐波转换效率的因素。根据考虑了走离效应、相位失配和振幅缓变近似情况下的二次谐波的耦合波方程,推导出了二次谐波转换效率的严格解析表达式。采用数值计算的方法分别研究了相位失配量Δk、走离角ρ和基频光强对转换效率的影响。结果表明,当基频光强较小时,二次谐波的转换效率随着基频光强的增加而增大;随着走离角和相位失配量的增大而减小。基频光强较大时,随着负折射率材料的长度或基频光强的增加,二次谐波的转换效率呈现明显的周期性变化。负折射率材料长度对转换效率的影响与基频光强一样。     

超短强激光作用下空气的三次谐波辐射

进行了飞秒强激光与自由空气和充气毛细管相互作用产生三次谐波的实验研究，成功地获得了功率达0.17GW、重复频率为10Hz的紫外三次谐波信号，谐波的转换效率达到0.04%。对自由空气和充气毛细管中的谐波转换效率和谐波空间分布特性进行了比较。实验表明微毛细管虽然使谐波转换效率略有降低，但能有效地改善谐波的空间分布，使其更好地满足实际应用的需要。     

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。     

准晶非线性光子晶体中二次谐波波长和温度调谐的研究

在八重准周期极化的铌酸锂非线性光子晶体中,通过调节基频光波长实现了多个波长的同时共线准相位匹配倍频,最高转换效率达36%.同时,测量了准晶非线性光子晶体中二次谐波转换效率随晶体温度以及入射波长的变化,结果表明二次谐波在长波处具有更宽的温度以及波长调谐带宽.该项研究对于准周期非线性光子晶体在实际工作中的运用具有重要的指导意义. 关键词： 准周期 非线性光子晶体 温度调谐 波长调谐     

Frequency-doubled vortex beam emitter based on nonlinear Cherenkov radiation

In this work, we propose a new scheme to generate frequency-doubled vortex beams from a radially poled Li Nb O3 micro-ring resonator based on nonlinear Cherenkov radiation. The near-infrared fundamental wave is resonant in the micro-ring, while the second harmonic is emitted from the resonator along the Cherenkov phase-matching direction. The topological charge of the emitted second-harmonic vortex beam is determined by both the azimuthal order of the whispering galley modes and the number of nonlinear grating elements. The field distribution and the conversion efficiency of the emitted vortex beam are investigated.     

Efficient collinear frequency tripling of femtosecond laser with compensation of group velocity delay

This paper demonstrates an approach that negative uniaxial crystal has a relative anomalous dispersion effect which can compensate group velocity delay, and applies this approach to nonlinear frequency conversion of an ultrafast laser field. High efficiency of the third harmonic generation is experimentally fulfilled by adopting a collinear configuration of doubing-compensation-tripling system. Through finely adjusting the incident angle and optical axis direction of the compensation plate, it obtains ultraviolet (UV) output energy of 0.32~mJ centered at 270~nm with spectral bandwidth of 2~nm when input beam at 800~nm was 70~fs pulse duration and 6~mJ pulse energy which was extracted from Ti:sapphire laser system by a diaphragm, corresponding to an 800-to-270~nm conversion efficiency of 5.3% and a factor-of-1.6 improvement in the third harmonic generation of UV band in comparison with a general conventional configuration. Furthermore, when the full energy of 18~mJ from a Ti:sapphire laser system was used and optimized, the UV emission could reach 0.83~mJ.     

透射共振对二次谐波产生的增强

为了提高二次谐波产生转换效率,本文提出将一维周期光学超晶格两端贴上未被极化的厚度可以改变的非线性介质层,通过调整附加介质层的厚度来调制基频波的场,从而观察二次谐波产生转换效率的变化情况.结果表明:基频渡场可以很大程度地调制二次谐波产生;随着能量的增加,二次谐波产生转换效率增加,随着能量的减小,二次谐波产生转换效率减小;...     

Diode grids for electronic beam steering and frequency multiplication

Loading a grid with diodes offers the possibility of two-dimensional control of millimeter waves that is analogous to holography and nonlinear optics. These grids are attractive because they are suitable for monolithic integration with gallium-arsenide Schottky diodes and for high-power operation. Here we present grid designs for electronic beam-steering and harmonic generation. The beam-steering grid is a programmable reflector, where the diode bias controls the phase shift of the reflection. The variation of the phase across the grating sets the direction of the reflected beam. The reflection loss in computer simulations is 3dB at 90GHz. The harmonic-generating grid acts as a nonlinear reactive surface, where the nonlinear capacitance of the diodes produces the harmonic frequencies. Quasioptical filters select the desired harmonic. Computer simulations predict that a 65GHz-to-130GHz doubler would have an output power of 0.56W/cm² and a conversion efficiency of 35%.     

Walk-off and phase-compensated resonantly enhanced frequency-doubling of picosecond pulses using type II nonlinear crystal

We propose enhanced frequency-doubling inside an external ring-cavity using type II nonlinear crystal. A KTP type II twin-crystal device is implemented for compensation of both walk-off and phase-shift between ordinary and extraordinary fundamental waves. Starting from an 850 mW diode-pumped actively mode-locked Nd:YAG laser at 1.064 μm with 100 MHz repetition rate and 25 ps pulse duration, we performed 54% harmonic conversion efficiency in the green. Received: 31 August 1998 / Revised version: 10 February 1999 / Published online: 19 May 1999     

Enhancement of the second harmonic generation from monolayer WS2 coupled with a silica microsphere

Monolayer transition metal dichalcogenides (TMDs) are widely used for integrated optical and photoelectric devices. Owing to their broken inversion symmetry, monolayer TMDs have a large second-order optical nonlinearity. However, the optical second-order nonlinear conversion efficiency of monolayer TMDs is still limited by the interaction length. In this work, we theoretically study the second harmonic generation (SHG) from monolayer tungsten sulfide (WS₂) enhanced by a silica microsphere cavity. By tuning the position, size, and crystal orientation of the material, second-order nonlinear coupling can occur between the fundamental pump mode and different second harmonic cavity modes, and we obtain an optimal SHG conversion efficiency with orders of magnitude enhancement. Our work demonstrates that the microsphere cavity can significantly enhance SHG from monolayer 2D materials under flexible conditions.     

Generation of femtosecond laser pulses at 396 nm in K_3B_6O_(10)Cl crystal

K_3B_6O_(10)Cl(KBOC), a new nonlinear optical crystal, shows potential advantages for the generation of deep ultraviolet(UV) light compared with other borate crystals. In this paper we study for the first time the second harmonic generation(SHG) of a femtosecond Ti:sapphire amplifier with this crystal. Laser power is obtained to be as high as 220 m W at the central wavelength of 396 nm with a 1-mm-long crystal, and the maximum SHG conversion efficiency reaches 39.3%. The typical pulse duration is 83 fs. The results show that second harmonic(SH) conversion efficiency has the room to be further improved and that the new nonlinear crystal is very suited to generate the high efficiency deep ultraviolet laser radiation below 266 nm.     

高功率高效率三次谐波二维数值模拟研究

对大口径、高功率情况下的三次谐波转换,选择KDP晶体TypeⅠ/TypeⅡ匹配角度失谐的三倍频方案,并从非线性三波耦合方程组出发,采用离散傅立叶变换和四阶龙格库塔(R-K)积分方法,编制了二维模拟三次谐波转换的计算程序。计算了各种晶体厚度和不同失谐角条件下,二、三次谐波的转换特性和效率。并对入射基频光为六阶超高斯分布时的三倍频器进行了优化,三倍频转换效率达80%,此时具有较大的动态范围和较高的三倍频转换效率。     

Nonlinear computer-generated holograms

We propose a novel technique for arbitrary wavefront shaping in quadratic nonlinear crystals by introducing the concept of computer-generated holograms (CGHs) into the nonlinear optical regime. We demonstrate the method experimentally showing a conversion of a fundamental Gaussian beam pump light into the first three Hermite-Gaussian beams at the second harmonic in a stoichiometric lithium tantalate nonlinear crystal, and we characterize its efficiency dependence on the fundamental power and the crystal temperature. Nonlinear CGHs open new possibilities in the fields of nonlinear beam shaping, mode conversion, and beam steering.