Mutually pumped phase conjugator using a BaTiO3 crystal having two inclined faces

A pentagon-shaped undoped BaTiO₃ crystal was used to construct a high-quality mutually pumped phase conjugator. It yields two very stable phase-conjugate outputs (ǃ.7% fluctuation in intensity) with high reflectivity (the highest ᅝ%) when the two incident beams are of equal intensities. The response time of the conjugator is rather fast (ƻ s) and the tolerance of the acceptance angle is large too (걄°). Fine structures (35 7m) in an image, after passing through a phase aberrator, can be recovered by the conjugate waves yielded by this conjugator.     

Reduction of the specular reflectivity from Feinberg’s Cat conjugator operating in auto-oscillation mode

An incomplete correlation is discovered between the phase conjugate reflectivity in Feinberg’s Cat conjugator generating a train of regular pulses with the cw incident pump wave and inhibited specular reflectivity from the sample. The frequency chirp within every spike of conjugate wave is shown to affect the efficiency of the secondary phase conjugator generating auxiliary waves in the direction of Fresnel reflection of the incident wave. Received: 25 November 1998 / Revised version: 11 January 1999 / Published online: 31 March 1999     

BaTiO3晶体自抽运相位共轭特性研究

研究了多种Rh:BaTiO₃和Ce:BaTiO₃晶体样品的受激背向光折变散射自抽运相位共轭特性和响应时间特性.结果表明,入射光与晶体a面或b面法线的夹角较大时,自抽运相位共轭光有更高的反射率、更快响应时间.利用前向二波耦合特性和相向二波耦合特性对实验现象给予合理的解释.实验结果表明,多数Ce:BaTiO₃晶体比Rh:BaTiO₃晶体的共轭光反射率高. 关键词： 钛酸钡晶体 二波耦合 自抽运相位共轭 响应时间     

Properties of cat mutually pumped phase conjugation and two-wave mixing gain in doped KNSBN

Cat mutually pumped phase conjugation configuration is discovered and investigated by using two-wave mixing in (KyNa1-y)2z(SrxBa1-x)1-zNb2O6 (KNSBN) crystal. When only one signal or pumped beam does not give birth to phase conjugation, the maximum reflectivity of signal and pumped beam attain 140% and 30% due to two-wave mixing, respectively. The experimental results show that the two-wave mixing can reduce the threshold of incident beams power, extend the incident angle range, and shorten response rate in the process of self-pumped phase conjugator (SPPC) in KNSBN crystal.     

Nonlinear piezoelectricity in PZT ceramics for generating ultrasonic phase conjugate waves

We have succeeded in the generation of acoustic phase conjugate waves with nonlinear PZT piezoelectric ceramics and applied them to ultrasonic imaging systems. Our aim is to make a phase conjugator with 100% efficiency. For this purpose, it is important to clarify the mechanism of acoustic phase conjugation through nonlinear piezoelectricity. The process is explained by the parametric interaction via the third-order nonlinear piezoelectricity between the incident acoustic wave at angular frequency omega and the pump electric field at 2 omega. We solved the coupling equations including the third-ordered nonlinear piezoelectricity and theoretically derived the amplitude efficiency of the acoustic phase conjugation. We compared the efficiencies between the theoretical and experimental values for PZT ceramics with eight different compositions. Pb[(Zn1/3Nb2/3)(1 - x)Tix]O3 (X = 0.09, PZNT91/9) piezoelectric single crystals have been investigated for high-performance ultrasonic transducer application, because these have large piezoelectric constants, high electrical-mechanical coupling factors and high dielectric constants. We found that they have third-order nonlinear piezoelectric constants much larger than PZT and are hopeful that the material as a phase conjugator has over 100% efficiency.     

Temporal Behavior of Phase Conjugate Wave in Self-Pumped Phase Conjugator with Internal Total Reflection

Several temporal behaviors of the phase-conjugate output of a self-pumped phase conjugator with internal total reflection in BaTiO₃ crystal have been investigated as a function of the beam entrance position and incident angle on the crystal. Different sets of these conditions cause different behavior of phase conjugate wave which are unstable or pulsed output as well as temporally stable output. Classification of these temporal behaviors in phase conjugate wave by incident condition are shown.     

A quality of parametric wave phase conjugation of ultrasound

The criterion, known from optics, of wave phase conjugation quality is accommodated for acoustical experiment. An incident focused sound beam at 5 MHz is propagated towards a supercritical magnetoelastic conjugator through an introduced random phase layer, and the conjugate beam propagates backwards through the layer to the source. 1D and 2D distributions of wave field are measured for the conjugate beam of finite amplitude using a membrane hydrophone. The maximum sound intensity of 640 W/cm2 and acoustic power of 4 W are registered in the focal maximum of the conjugate wave. The quality of WPC is calculated from the ratio between the power in the central maximum and the total power of the conjugate beam. The method is applied to compare two operation modes of a supercritical parametric conjugator. It is shown that in the linear mode the conjugator provides higher quality than in the nonlinear (0.54 compared to 0.24).     

双光折变晶体半线性相位共轭器的自脉动

在由两块光折变BaTiO3晶体(其中一块晶体为全内反射式自抽运相位共轭镜工作方式,起外反射镜作用)构成的半线性自抽运相位共轭器中观察到了相位共轭光的自脉动现象。自脉动的平均频率f与入射光功率I0的关系为f∝I01.43;相位共轭光的平均维持时间ΔT与入射光功率I0近似成反比。观察到光折变BaTiO3晶体中扇形散射光具有动态的空间结构,扇形散射光的这种特性是引起上述半线性自抽运相位共轭器中相位共轭光脉动的原因     

Fast response self-pumped phase conjugator based on a +c-face incident configuration in a pentagon-shaped BaTiO3 crystal

We propose a novel geometry for a self-pumped phase conjugator that uses a +c-face incident configuration in a photorefractive pentagon-shaped 0°-cut BaTiO₃ crystal for obtaining fast response in phase conjugation. A steady phase-conjugate output with a fast response time 0.4 s is obtained when the incident beam has a 4 W/cm² intensity. The influences of position and angle on the temporal phase-conjugate response are also investigated. The advantage of this phase conjugator using this novel configuration is improved resolution of a phase-distorted image with a value as high as 128 lp/mm.     

晶轴与晶面成18°角的Ce:KNSBN晶体自泵浦位相共轭

分析了晶体的不同切割方式对形成自泵浦位相共轭输出的影响，报道了晶轴与晶面成１８°角的ＣｅＫＮＳＢＮ晶体自泵浦位相共轭输出特性，实验证实了共轭反射率与入射角和入射位置有关，并得到反射率为５７．１６％的共轭输出。共轭光的形成时间随入射光强的增大而缩短。     

北极水下声信号跨冰层变化分析

北极海冰阻碍了海水和空气两个空间的信息传输.为获得冰层对水下声信号跨冰层传输的影响,采用三维检波器在北冰洋中心区开展了水下声信号的跨冰层实验.利用水冰界面反射模型和自由冰层Lamb波模型,对水下声信号小角度(小于10°)入射冰层时测量数据进行分析,结果表明:(1)20 Hz～1 kHz声信号入射到光滑冰层时,某些频率声...     

Mutually Pumped Phase Conjugation of Three Incoherent Beams with a Novel Photorefractive Crystal

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熔石英棒-光纤构成的新型复合相位共轭镜的实验和理论研究

提出了一种新型的由熔石英棒和石英光纤组成的复合型相位共轭镜,其可运用于高重复频率激光输入系统中以改善光束质量.该复合相位共轭镜具有较高的受激布里渊散射反射率和受激布里渊散射损伤阈值以及较低的受激布里渊散射阈值等优点.实验中,在100 Hz重复频率下,最大获得了42.05%的受激布里渊散射反射率.根据实验条件,由耦合波方程及边界条件得到的物理模型,经数值求解后得到的结果和实验符合较好.且由理论结果提出了一种提高该复合型相位共轭镜工作状态的有效方法. 关键词： 复合型相位共轭镜 受激布里渊散射 熔石英 耦合波方程     

KNSBN晶体猫式互抽动相位共轭光特性

在KNSBN：Ce晶体中，利用二波耦合作用，在单一光束无法获得相位共轭光的条件下，实现了“猫”式互抽运相位共轭光输出，获得较高的共轭光发射率，实验结果表明，晶体的二波耦合作用可以使晶体的自抽运相位共轭光的阈值光强降低。入射光的入射角范围增大，响应时间缩短。     

晶体几何结构及入射角度对自抽运相位共轭特性影响的研究

基于两块不同尺寸的Cu∶KNSBN晶体自抽运相位共轭实验,研究了光折变晶体的几何结构及入射角度对自抽运相位共轭特性的影响,得到在入射位置不变化的情况下,随着入射角度的变化相位共轭光输出有最大值,几何结构不同对应的最大值不同。并从理论上分析了晶体结构及入射角度在双作用区自抽运相位共轭机理中的作用,指出几何结构、入射角度与自抽运光通道、耦合系数的关系,及在自抽运相位共轭效应中存在一个最佳入射角度,这时相位共轭光输出最大。最后,对理论上的相位共轭反射率公式进行了修正。对自抽运相位共轭实际应用中,选择最佳入射角度提供了理论和实验依据。     

Visualization of phase conjugate ultrasound waves passed through inhomogeneous layer

Compensation of phase distortions of ultrasound beams by means of parametric phase conjugation is visualized. Quasi-plane and focused primary beams were distorted by a polymer aberration layer introduced between the primary wave source and the wave phase conjugator. It is demonstrated acousto-optically that, while the acoustic field is strongly irregular in the area between aberration layer and conjugator, the phase conjugate wave visibly reproduces the primary beams in the area between the layer and the primary wave source. The phenomenon is observed in supercritical mode of parametric amplification when intensity of phase conjugate wave is high enough for manifestations of acoustic nonlinearities in water.     

KNSBN：Co晶体自泵浦位相共轭特性的研究

本文报道在两块不同尺寸的KNSBN:Co晶体中实现了自泵浦位相共轭输出,通过实验验证了位相共轭反射率与入射角、入射位置以及波长有关,并给出各自的实验曲线.保持激光器工作波长为514.5nm不变,在大块晶体中可得到高达73.0%的位相共轭反射率.文章还给出共轭光的形成时间随系统光强变化关系的实验曲线,并指出自泵浦形成时透射光强和晶体表面反射光强的时间变化特性,解释了自泵浦形成的阈值特性.     

激光辐照光学镜头猫眼效应反射率测试

 为了验证普通光学镜头猫眼效应的存在性和应用可行性,利用532 nm激光辐照调焦范围为12～72 mm的普通摄像镜头,测试了猫眼效应绝对反射率及其与镜头焦距、F数、入射角等参数的关系。采用双光路同时测量法,解决了猫眼效应反射光与入射光相互干扰不易测试的问题。结果表明,该镜头的猫眼效应绝对反射率最高可达35.87 ％,并且与焦距正比,与F数和入射角成反比;近场时的几何发散角与焦距和F数成反比。     

楔角参量对角度调谐滤光片反射特性影响的光谱学研究

三端口可调谐滤波器是全光智能交换网络和密集波分复用系统中的核心器件。其反射端口的光谱特性,尤其是反射率和信道隔离度对于滤波器的性能至关重要。角度调谐滤光片因其良好的矩形度和温度稳定性被广泛应用于三端口可调谐滤波器的制备,其反射端口的光谱特性不仅与倾斜入射角度的大小有关,而且与其非平行端面间的楔角参量有关。文章详细分析了楔角参量对非平行角度调谐滤光片的反射率及半宽的影响,仿真计算了楔角参量在不同极性和大小条件下角度调谐滤光片的反射光谱特性,揭示了保持适当的楔角参量和方向性可以改善倾斜入射状态下滤光片的反射光谱特性。设计并制备了楔角为0.8°的楔形角度调谐滤光片,实验证明了当保持楔角方向与倾斜入射方向相同时会严重的劣化透反射光谱的半宽和隔离度,方向相反时则可以改善反射光谱的反射率和半宽指标。通过负楔角参量的引入使得角度调谐滤光片较之高平行度的同类器件具有更高的反射率和信道隔离度。     

The effect of a high external electric field on a photorefractive ring phase conjugator

It is shown that a high external electric field often used to enhance the efficiency of photorefractive beam coupling and to decrease the photorefractive response time, may cause mode switching in photorefractive ring phase conjugator leading to a significant drop in the phase conjugate reflectivity.