准相位匹配PPLN、PPKTP、PPRTA光学参量振荡器及其应用(详细摘要)

线性光学频率变换技术主要用来产生传统激光光源所不能产生的相干辐射,这些激光光源或者限于离散的谱线或者仅能相对较窄的光谱范围。而实际上许多应用所需要的波长是直接激光光源所产生不了的,或者现存的激光器的效率低、太复杂,对许多应用来说是不切实际的。基于周期性极化的铌酸锂（PPLN）的准相位匹配光学参量振荡器（QPM-OPO）由于其具有很大的非线性系数、低的损耗,以及可以运转在宽的范围和制作工艺多样性等特点,已经得到广泛的重视及应用。准相位匹配的技术允许为了获得期望的相互作用而充分利用现存的已经发展成熟的非线性光学材料。由于近来周期性极化铌酸锂（PPLN）的发展,实现准相位匹配是可能的。近来利用这些材料已经成功地实现了高功率光学参量振荡器在技术上重要的中红外光谱范围1～5μm的宽调谐运转。这种技术在许多方面例如军事、科学、测量和光通讯均有应用。 本文将简要介绍PPLN（或PPMgLN、PPKTP、PPRTA）作为准相位匹配OPO的原理、主要的技术关键及可能的应用前景。     

近化学计量比铌酸锂晶体的研究进展

介绍了近化学计量比铌酸锂晶体的主要生长方法及其特点,总结了近化学计量比铌酸锂晶体的主要性能,通过与同成分铌酸锂晶体的比较,指出了近化学计量比铌酸锂晶体的主要应用优势,明确了该类晶体今后的研究重点.     

LiNbO3晶体点缺陷形成能的经验途径计算

基于通过经验参数化方法确定的铌酸锂晶体内离子间互作用势参数，计算了该晶体中点缺陷的形成能，由此判断锂Frenkel对是化学计量比铌酸锂晶体中的本征缺陷，锂空位模型为描述一致熔化组分铌酸锂晶体中点缺陷的主导类型。     

铌酸钾锂晶体的生长研究

首次使用坩埚下降法生长了蓝光掊频晶体铌酸钾锂K₃Li_2-xNb_5＋xO_15＋2_x（0＜x＜0．5）,探讨了该晶体的最佳生长条件,包括组份选择、原料处理、炉温控制、温场设计等,成功地生长出直径10mm、长度25mm的透明KLN晶体．     

掺镁铌酸锂晶体的光学均匀怀和抗光作性研究

研究了不同Ｌｉ／Ｎｂ克分子比，掺镁铌酸锂（ｍｇＯ：ＬｉＮｂＯ３）晶体的光学均匀性和我伤特性，以二地同成分配比为基础。掺入约５ｍｏｌ％ＭｇＯ的ＬｉＮｂＯ３晶体显示出高的抗光损伤特性，但光学均匀性较差，根据ＭｇＯ－Ｌｉ２Ｏ－Ｎｂ２Ｏ５三元相关系研究寻找到的三元同成分配比，生长出的ＭｇＯ：ＬｉＮｂＯ３晶体具有优良的光学均匀性。但其抗光伤能力低。     

铌酸锂光纤型行波调制器研究

以LiNbO3光纤作为通光部分,Si2N2O为衬底分别取代了传统波导电光调制器的中Ti:LiNbO3波导和铌酸锂衬底设计了带宽为95.49 GHz铌酸锂光纤型调制器.今利用有限元法分析SCPS电极结构下该铌酸锂光纤调制器的性能.研究结果表明,该新型调制器可以在很宽的频带内实现调制速度的匹配和阻抗匹配,半波驱动电压为2.56 V,特性阻抗为55.3Ω.     

莫斯科国立钢铁合金学院研制出新型振动传感器

正据俄罗斯科学网站2月24日报道,莫斯科国立研究型技术大学莫斯科国立钢铁合金学院研究人员研制了一种新型振动传感器,用于建筑物和桥梁状态诊断仪器以及航天器,传感器使用无铅铌酸锂(LiNbO3)晶体。铌酸锂自20世纪中叶以来就已为人所知,并广泛用于激光光学,但很少有人尝试在振动传感器中使用它,因为它的压电性能相当弱。但是,铌酸锂晶体比振动传感器制造商目前使     

光学倍频晶体的非共线相位匹配

根据相位匹配条件和波矢曲面特性，更简单地导出光学倍频晶体非共线匹配产生二次谐波的解析表达式，由此式易于求得与光轴共面、基波垂直光轴的非共线以及常用封共线等特殊情况下的相位匹配条件；并以实验验征了理论的正确性。     

铌酸钾锂晶体的生长技术

铌酸钾锂被认为是目前综合性能指数最高的非线性光学晶体,在半导体二极管蓝激光倍频方面有广阔的应用前景。本文综述了用于蓝光倍频的铌酸钾锂晶体生长研究进展,比较了不同生长方法的优缺点,报道了我们在该晶体坩埚下降法生长研究方面的最新成果。     

利用新设计磨具对铌酸锂晶片的减薄及减薄后的测试

铌酸锂晶体具有较强的热释电效应,由铌酸锂制作的红外传感器敏感头受到科研人员的广泛关注。将晶片与硅衬底在200°C和压力100N的条件下键合,利用自行设计的磨具将铌酸锂减薄到40微米,磨料由水与刚玉以1∶1的比例制成。本文讨论了铌酸锂键合的过程,减薄的过程及厚度测试,通过拉曼光谱分析残余应力,通过原子力显微镜测试样品表面粗糙度。研究结果表明,通过自行设计的磨具研磨的晶片厚度最大差值7微米,较为均匀;研磨后晶片表面粗糙度为118纳米,较为粗糙;键合后存在一定的残余应力。制作好的铌酸锂晶片符合制作红外传感器敏感头的要求。     

Output power enhancement of a palmtop terahertz-wave parametric generator

Broadband terahertz (THz) waves were generated by optical parametric processes based on laser light scattering from the polariton mode of a nonlinear crystal. By using the parametric oscillation of a MgO-doped LiNbO3 crystal pumped by a nanosecond Q-switched Nd:YAG laser, we have realized a broadband, high-energy and compact THz-wave source. We report the development of a THz-wave parametric generator (TPG) using a small pump source with a short pulse width and a top-hat beam profile. These characteristics of the pump beam permit high-intensity pumping especially close to the output surface of the THz wave without thermal damage to the crystal surface. We also calculated the outcoupled THz wave for beams with two different intensity profiles: a top-hat beam (in this experiment) and a Gaussian beam (previously reported). The result shows the mechanism of the output energy and/or power enhancement.     

Investigation of multiconversion processes in periodically poled LiNbO3-based optical parametric oscillators

The multiconversion processes in optical parametric oscillators based on periodically poled LiNbO3 are investigated. Interpretations based on simultaneous quasi- and birefringent phase matching are presented. Three parametric and three harmonic generation processes in a multigrating periodically poled LiNbO3 crystal were observed. Two of the parametric processes and two of the harmonics were quasi-phase matched, and the other conversion processes were phase matched through birefringence in the crystal. The primary parametric process (omegap --> omegas + omegai) was obtained through first-order quasi-phase matching. The other quasi-phase-matched processes occurred within higher orders. The existence of even-order quasi-phase matching in the crystal is due to other than a 50% duty-cycle grating periods. The tuning range for each of the generated waves is obtained and compared with theoretical fittings.     

Difference Frequency Generation of 5-18 mum in a AgGaSe(2) Crystal

Mid-infrared radiation in the 5-18-mum range has been obtained by difference frequency generation in a AgGaSe(2) crystal by pumping with the output of a type I LiNbO(3) optical parametric oscillator (OPO). Here we suggest the use of a LiTaO(3) retarder to achieve an orthogonal state of polarization between OPO outputs that are necessary for efficient pumping of a AgGaSe(2) crystal. Several tens of kilowatts of peak power near 8 mum and continuously tunable operation in the above range have been obtained.     

Mid-infrared (5-12-microm) and limited (5.5-8.5-microm) single-knob tuning generated by difference-frequency mixing in single-crystal AgGaS2

We describe tunable 5-12-mum mid-infrared generation in single-crystal silver gallium sulfide (AgGaS(2)), from nonlinear optical difference-frequency generation. Signal and idler waves obtained from a Nd:YAG laser-pumped LiNbO(3) optical parametric oscillator (OPO) were mixed in AgGaS(2) crystal to yield difference-frequency waves. For the efficient generation of difference frequency, an unstable resonator was employed as the OPO to reduce output beam divergence. A maximum difference-frequency power of 95 muJ/pulse was obtained near 7.5 mum for a 1-cm-long AgGaS(2) crystal. Spectral noncritical phase matching within a specific tuning range was also investigated that permitted limited single-knob tuning (5.5-8.5 mum) of the difference-frequency generator.     

掺镁近化学计量比LiNbO3晶体的生长

利用提拉法，从掺入11mol％K2O和1mol％MgO的化学配比LiNbO3熔体中生长了高质量的掺镁近化学计量比LiNbO3晶体．与同成分LiNbO3晶体相比，紫外吸收边发生明显蓝移，OH^-红外吸收峰的位置和波形也发生了显著的变化，初步断定晶体中Mg^2 的掺杂浓度已达到抗光伤阈值浓度．酸腐蚀结果表明，晶体具有区域性单畴结构。     

Multiple-wavelength quasi-phase-matching for efficient idler generation in MgO:LiNbO3 based nanosecond optical parametric oscillator

We present numerical results for optimization of the overall idler conversion efficiency of a nanosecond optical parametric oscillator (OPO), wherein the signal generated in the OPO process is also used as the pump for a difference frequency generation (DFG) process in a quasi-periodic MgO:LiNbO(3) crystal. The phase-matching conditions are considered such that the generated idler frequencies in both the processes (i.e., OPO and DFG) coincide. Optimization for the idler generation has been performed with respect to the different parameters, such as input pump power, pump pulse duration, and the output coupler reflectivity, for quasi-phase-matched interaction in MgO:LiNbO(3). Wavelength of the pump, signal, and idler waves considered in the optimization are 1.064 μm, 1.456 μm, and 3.95 μm, respectively. A maximum overall idler generation efficiency of ≈33% could be obtained in the simultaneous OPO+DFG process for a pump pulse duration of 72 ns and output coupler reflectivity (R(s)) of 90%, whereas for the stand-alone OPO process, the maximum idler generation efficiency was found to be ≈15%. The optimization has been illustrated for an average pump power of 8 W at a pulse repetition frequency (PRF) of 10 kHz. This approach of simultaneous OPO+DFG process can be employed to significantly enhance the idler generation efficiency of nanosecond OPOs.     

High-power narrow-band pulses with wavelengths tunable about 1.053 µm from a synchronously pumped optical parametric oscillator

We have constructed an optical parametric oscillator to generate 75-ps near-transform-limited pulses with wavelengths tunable about 1.053 μm for use in pump-probe studies of self-focusing. The singly resonant oscillator uses a Brewster-cut LiB(3)O(5) crystal that is oriented for type-II phase matching and synchronously pumped by the amplified and frequency-tripled pulse trains from a mode-locked and Q-switched Nd:YLP laser. An intracavity Pockels cell is used to switch out single 0.5-MW pulses at rates of 1 to 10 Hz. The design, construction, and performance of the oscillator are discussed. Measured performance is compared with design predictions and with detailed numerical simulations.     

Long-pulse, amplitude-modulated optical parametric oscillator

A singly resonant optical parametric oscillator (OPO) based on periodically poled LiNbO(3) is pumped by a Nd:YAG-based oscillator-modulator-amplifier source. This pump source, operating at 1.064 μm, provides the ability to control the temporal characteristics of the OPO waveform. We illustrate pulse tailoring by demonstrating three pulse formats: a pulse with a sharply rising edge, a square pulse, and an amplitude-modulated square pulse. The OPO output is tuned over 1.45-1.67-μm (signal) and 2.9-4.0-μm (idler). We demonstrate a 7-μJ, 2-μs square pulse with 5-MHz sinusoidal amplitude modulation.     

Thermal lensing in silver gallium selenide parametric oscillator crystals

We performed an experimental investigation of thermal lensing in silver gallium selenide (AgGaSe(2)) optical parametric oscillator crystals pumped by a 2-μm laser at ambient temperature. We determined an empirical expression for the effective thermal focusing power in terms of the pump power, beam diameter, crystal length, and absorption coefficient. This relation may be used to estimate average power limitations in designing AgGaSe(2) optical parametric oscillators. We also demonstrated an 18% slope efficiency from a 2-μm pumped AgGaSe(2) optical parametric oscillator operated at 77 K, at which temperature thermal lensing is substantially reduced because of an increase in the thermal conductivity and a decrease in the thermal index gradient dn/dT. Cryogenic cooling may provide an additional option for scaling up the average power capability of a 2-μm pumped AgGaSe(2) optical parametric oscillator.     

Film-loaded SAW waveguides for integrated acousto-optical polarization converters

We report on a detailed theoretical and experimental investigation of film-loaded surface acoustic wave (SAW) waveguides in lithium niobate (LiNbO3) for integrated acousto-optical (AO) polarization converters. The numerical analysis is based on both a scalar and a full-vectorial model. Dispersion plots and figures of merit for several structures are given, which lead to design parameters for optimized polarization converters. It is pointed out that very attractive structures are metal/dielectric/LiNbO3 strip waveguides and dielectric/LiNbO3 slot waveguides, in which metal is either gold (Au) or aluminum (Al), and the dielectric film is an optical transparent material such as silicon oxide (SiO2), magnesium oxide (MgO), or aluminium oxide (Al2O3). Polarization converters with the designed acoustical waveguides have been realized and characterized by optical conversion and laser probing measurements.