反常氧化碲声光偏转器控制理论研究

根据晶体的声光特性以及反常布喇格衍射的Dixon方程,得出了氧化碲声光偏转器在反常布拉格衍射条件下的参量矢量关系.分析了超声波方向、入射光角度、衍射光角度与声波频率之间的关系.针对卫星光通信中衍射角固定的应用情况,通过数值求解和参量拟合,建立了一个基于平面方程的简单控制模型.利用该模型可以很快得到超声控制频率,使衍射角固定不变.     

多频声光互作用的研究

本文推导出包括正常和反常声光互作用在内的多频声光耦合波方程的普适形式,并得出两个独立超声波信号时布拉格状态下方程的解.分析了多频声光互作用的各种线性和非线性效应,包括衍射效率、压缩、交叉调制和各级互调制强度等,并指出反常与正常多频声光衍射的差异.结论是反常多频声光互作用情况下,各级互调制模强度与主衍射模强度的比值小于正常多频声光互作用情况下的相应比值.实验结果与理论分析相符.     

基于声光效应的光束偏转控制理论研究

基于参量互作用观点及声光互作用原理,构建了入射光为高斯光并且存在声波吸收情况下的声光偏转器模型.基于此模型研究了超声波频率、声波功率和光束入射角对衍射光的影响.对比了有声波吸收和无声波吸收两种情况下上述三个参量对衍射光产生的不同影响.计算结果表明,同无声光吸收时相比,当存在声波吸收时,偏转器的衍射效率将减小,导致衍射波形畸变,光强峰值位置发生偏移.     

声光效应实验研究

介绍声光效应的最新理论进展。采用光栅假设，对各向同性介质中的声光效应作了简要讨论，导出了第m级衍射光的衍射效率公式。研究和介绍一种新的声光效应实验装置。在实验中，应用线阵CCD光强分布测量仪等，通过改变超声波的频率和功率，分别实现了对激光束方向的控制和强度的调制；定量给出了声光偏转量的关系曲线和声光调制测量的关系曲线。实验表明，在布喇格衍射下，通过固定超声波功率，测量衍射光相对于零级衍射光的相对光强与超声波频率的关系曲线，不仅可以计算声速，还可以确定声光器件的带宽和中心频率。     

声光技术的进展

一、声光效应和声光器件 当声波在介质中传播时,由于物质的光弹效应,使介质的折射率发生周期性变化,从而也像相位光栅那样使光衍射.当超声波频率较低,声光互作用区较短时,入射光常被衍射成多级衍射光,这就是喇曼-奈斯衍射.如果超声波频率很高,光沿着适当的角度射入介质并通过较多的超声波阵面,则高次衍射光消失,只剩下0级和1级光,这就是布喇格衍射,这时入射光与衍射光的角度应满足布喇格方程即     

氧化碲声光偏转器的布拉格带宽和扫描线性问题

按声光偏转器的实际使用情况在入射光方向?₁固定不变的条件下求解反常布拉格绕射的Dixon方程,得到起作用超声方向?_a和绕射光方向?₂随频率f的变化关系。由?_a-f关系可精确决定声光偏转器的布拉格带宽和换能器长度等重要设计参数。所解出的?₂-f关系具有良好的线性,因而以往所作关于矫正扫描线性的探讨显得多余。 关键词：     

相位、振幅调制两用声光调制器设计

针对实际应用中大多的光调制器只能实现单参数调制的情况,提出一种既可以调相又可以调幅的声光调制器的设计方案.运用矩阵级数解法求解正常声光相互作用Raman-Nath方程,通过计算机编程进行数值求解,得到衍射光的衍射光强和附加位相变化,从而指出以往解法的一些不合理性,并找到声波功率和衍射光的光强和位相的关系,为声光效应的位相调制和振幅调制设计提供了一种可行的方法.结合调制声波频率,可在同一个调制器上进行调幅、调相、调偏转方向.     

基于瑞利-索末菲积分的大衍射角衍射光学元件设计方法

针对现有的衍射光学元件设计方法只适用于小角度衍射的情况,本文提出了一种基于瑞利-索末菲衍射积分的设计方法,可以用来设计具有大衍射角的衍射光学元件。先对目标光场进行坐标变换和强度调整,再利用改进的Gerchberg-Saxton算法优化得到衍射光学元件的相位分布。分别采用本文方法和原有的基于夫琅禾费衍射积分的方法设计衍射光学元件实现线条结构光和不同角度方框图形的光场重构,结果表明:原有的设计方法只适用于衍射角全角小于25°的情况,当衍射角大于25°时,重构光场会出现显著的枕形畸变和不均匀的强度分布。而本文方法在小角度和大角度衍射下都能重构出准确的衍射角和较为均匀的强度分布.     

声光偏转效应在相干光检测的应用

为使现代电子侦察技术能适应信号密集、宽频谱、大动态的电磁环境, 提出了一种基于声光偏转器实现相关光信号处理的方法, 分析了射频信号频率变化与布拉格衍射角的关系, 讨论了声光偏转效应对信号频率的空间滤波特性; 在理论分析的基础上, 构建了在可见光范围内实现声光偏转的相干光信号探测的实验系统, 并通过计算机仿真对比, 验证了这种方法的可行性。实验表明, 采用波长为630 nm的单频激光, 带宽为200 MHz的声光偏转器, 其频率分辨率优于1 MHz, 频率信号的空间分离效果明显, 接收灵敏度和信噪比得到改善。     

多振源低频液体表面波声光效应研究

同时利用两个振源,在液体表面上产生两列低频表面波,实现了多振源条件下表面声光效应,观察到清晰、稳定、反衬度高的声光衍射条纹.当引起两列表面波的两个振源频率具有倍数关系时,声光衍射条纹的极大值位置与较小频率的振源单独存在时所产生表面波的极大值位置相同,与较大频率的振源单独存在时所产生表面波的极大值位置部分相同.当引起两列表面波的两个振源频率不具备倍数关系时,不仅观察到单振源的衍射条纹,而且也观察到了双振源的干涉条纹.理论上得到多振源衍射光场和表面波波长、振幅之间的解析表达式,理论规律与实验结果吻合较好.     

Collinear diffraction of a divergent light beam by ultrasound in a paratellurite crystal

The collinear acousto-optical interaction of a divergent light beam with ultrasound along the approximate [110] direction in a TeO₂ paratellurite crystal is investigated theoretically and experimentally. The collinear diffraction is studied at an ultrasonic frequency f ≈ 149 MHz under exposure of the crystal to an uncollimated laser light beam at a wavelength λ = 633 nm and at an angle of divergence as large as 4°. It is shown that the collinear diffraction along the direction forbidden for acousto-optical interactions of plane waves occurs only under conditions where the light beam is uncollimated and the diffraction efficiency increases with an increase in the divergence of the light beam. It is proved that the attenuation of an acoustic wave brings about a decrease in the diffraction efficiency and an increase in the transmission bandwidth of the device used. A model of the collinear acousto-optical filter based on a paratellurite crystal with an interaction length l = 2.7 cm is analyzed. The collinear acousto-optical filter is characterized by a high resolving power (～3000), a high diffraction efficiency (I₁/I₀ ≈ 0.8), and a large angular aperture (Δ? ≈ 4°). This makes collinear diffraction promising for use in acousto-optical filters based on paratellurite crystals.     

Filtration of partially coherent optical radiation by means of multiphonon Bragg diffraction

The filtering properties of three-phonon acousto-optical Bragg diffraction for increasing the degree of coherence of a partially coherent optical field are investigated by the example of multiphonon acousto-optical interaction in a TeO₂ single crystal. Two possible mechanisms of coherent scattering upon the formation of the highest orders are taken into account. It is shown that the three-phonon interaction is more efficient by at least a factor of two than any mode of one-phonon diffraction realized at the same frequency and the same acousto-optical interaction length. The experimental investigation, using partially coherent radiation of a He-Ne laser (λ = 0.63 μm) diffracted from a transverse acoustic wave propagating in a TeO₂ single crystal, on the whole confirmed the basic theoretical foundations.     

复杂流场的超声-激光测量原理研究

本文从复杂流场—旋涡场参量的超声—激光测试方法的需要出发,论述了超声波产生的声相位光栅对激光产生的偏转效应.并研制了适用于产生空气超声相位光栅的大功率高频超声换能器、位移灵敏接收器、数字相位差测定仪等设备,采用了超声发射的匹配技术等,从而获得了明显的空气超声-激光偏转效应,并且测定了两光束的偏转时间差.本文的结果为利用超声-激光的空气声光偏转效应测量空气旋涡流场参量提供了实验依据.     

Acousto-optical spectrum analysis of ultra-high-frequency radio-wave analogue signals with an improved resolution exploiting the collinear acoustic wave heterodyning

This article is devoted to the problem of improving the frequency resolution inherent in a parallel acousto-optical spectrum analysis via involving an additional nonlinear phenomenon into the data processing. In so doing, we examine possible application of the wave heterodyning to the real-time scale acousto-optical analysis of the frequency spectrum belonging to ultra-high-frequency radio-wave signals peculiar, for example, for radio-astronomy. The nonlinear process of wave heterodyning is realized through providing a co-directional collinear interaction of the longitudinal acoustic waves of finite amplitudes. This process, which is beforehand studied theoretically and investigated experimentally via the acousto-optical technique as well, allows us either to improve the frequency resolution of spectrum analysis at a given frequency range or to increase by a few times the current frequencies of radio-wave signals under processing. The first step along this way is connected with the experimental modeling of the acoustic wave heterodyning in solids via exploitation of the specific acousto-optical cell based on a liquid, which allows the simplest realization of a cell with the needed properties. Then, these theoretical and practical findings are used in our experimental studies aimed at creating a new type of acousto-optical cells, which are able to improve the resolution inherent in acousto-optical spectrum analyzer operating over ultra-high-frequency radio-wave signals. In particular, the possibility of upgrading the frequency resolution through the acoustic wave heterodyning is experimentally demonstrated using the cell made of lead molybdate crystal. The obtained results demonstrate practical efficiency of the novel approach presented.     

Wide-bandwidth phase lock between a CW laser and a frequency comb based on a feed-forward configuration

Wide-bandwidth phase lock between the tooth of a frequency comb and a CW extended-cavity diode laser at 1.55 μm is achieved by the use of an acousto-optical frequency shifter in a feed-forward configuration. The coherence properties of the comb are efficiently transferred to the CW laser, whose linewidth is narrowed down to the ～10 KHz comb level. A maximum control bandwidth of ～0.6 MHz has been experimentally achieved, limited by the transit time of the acoustic wave inside the frequency shifter.     

水下低频声信号的激光探测及波的衰减

为了探测几十赫兹的低频水下声信号,建立了水下低频声信号的光学探测系统,得到了稳定、清晰的衍射图样.得到了衍射图样的宽度与声源距离的变化关系,声源距离越小,衍射图样越宽.当水下声波传至水表面后,实验上得到了表面声波的衰减特性,理论上得到了衍射图样的角宽度和液体表面波振幅的解析关系式.发现表面波振幅的衰减随距离是指数型衰减.并研究了衰减系数随频率的变化,频率不同衰减系数也不同,而且频率越大,衰减系数越小.     

Image aberrations in an acousto-optical tunable filter

The problem of deformation of images due to diffraction from 3D diffraction gratings (in particular, the grating formed by an acoustic wave in an acousto-optical filter) is considered. For the first time, the exact solution is obtained without using the small birefringence approximation. The form of aberrations induced by main types of acousto-optical filters is analyzed and illustrated by calculations.     

La_3Ga_5SiO_(14)声光可调谐滤波器设计

分析了La3Ga5SiO14(简称LGS)既可以做成同向声光可调谐滤波器,又可以做成大孔径非同向声光可调谐滤波器。推导出超声波频率f和光波波长λo的调谐关系;计算出滤波器的光谱分辨率R和集光能力δiθ;光入射角iθ与衍射角θd、声入射角θa之间的关系。为LGS声光可调滤波器的实用化设计提供了充分可靠的理论依据。把LGS与TeO2声光可调滤波器的光谱分辨率和集光能力做了比较,认为LGS设计成同向声光可调谐滤波器既简便又实用。     

Prolonged acousto-optic interaction with Lamb waves in crystalline plates

The propagation and acousto-optic interaction of Lamb modes in an anisotropic plate of tellurium dioxide (TeO2) are studied numerically and analytically. In the case of a Y-cut X-propagating TeO2 plate, the very high elastic anisotropy of the crystal greatly modifies the dispersion curves, giving rise to their multiple oscillations. The existence ranges of backward Lamb modes increase with the mode order contrary to the case of isotropic plates. The quasi-collinear light scattering by Lamb waves is considered. Owing to the structure of Lamb wave field, a simultaneous light diffraction at two different optical frequencies can take place while Lamb waves are excited only at the single frequency. It is demonstrated with the Z-cut (110)-propagating plate that a small change in the acoustic frequency can result in a significant shift in the frequency of the scattered light.