偏振相移与相位共轭结合的散射光聚焦技术研究

散射介质对光的随机散射作用是制约其光学聚焦和成像的重要因素，光学相位共轭技术能够通过对散射光场共轭还原实现透过散射介质的光学聚焦和成像，其中散射光场相位的获取是共轭还原的核心。阐述了偏振相移的基本原理，将偏振相移与相位共轭技术相结合，设计了新的基于偏振相移的数字光学相位共轭系统。采用633 nm的HeNe激光器作为系统光源，毛玻璃作为散射介质开展散射光聚焦实验研究。实验结果表明:该装置能够成功实现透过散射介质的光学聚焦，其中聚焦点与背景光强的比值可达约400倍。     

The optical kerr effect in small metal particles and metal colloids: The case of gold

We first consider theoretically the various mechanisms contributing to the Kerr nonlinearity in small gold particles. The major ones are the conduction electron intraband contribution, the saturation of direct interband transitions and the change in dielectric constant due to hot photoexcited electrons. We present experimental results obtained using optical phase conjugation in gold-doped glasses. By varying several parameters, we were able to ascertain the origin of the nonlinear response: the main contributions are the hotelectron and the interband contributions. All experimental results, including saturation behaviour, are fully understood.     

Fundamental Studies of Stimulated Raman Scattering and Adaptive Optics on the Basis of Stimulated Light Scattering

Some results associated with the fundamental investigations of stimulated scattering of light in various media are reported. A number of problems of adaptive optics based on stimulated scattering is studied. Concrete results of experimental investigations of physically important characteristics of conventional (spontaneous) and stimulated Raman scattering are presented and discussed. Among them are the scattering indicatrix and the relations between the phases of laser radiation incident on a substance and stimulated scattering. These results were first obtained in the G. S. Landsberg Optical Department of the P. N. Lebedev Physical Institute of the Russian Academy of Sciences. Data on excitation sources and the radiation detection technique are systematized. The main characteristics of spontaneous Raman scattering and forward and backward stimulated Raman scattering (energy parameters, pulse duration, pulse shape, divergence, brightness, spectral width, far- and near-field intensity distributions) are presented. The results on dynamic holography, phase conjugation of light in stimulated scattering, and reconstruction and recording of information (images) with the help of amplifying dynamic holograms are presented. The physical mechanisms responsible for the interference field recording and the phase conjugation of pump radiation in stimulated light scattering are discussed. The data on phase conjugation for stimulated scattering excited by picosecond optical pulses and the results associated with the effect of excitation geometry on the optical phase conjugation in the case of stimulated scattering excited by nanosecond pulses are presented.     

Experimental Study of Four-Wave Mixing in Semiconductor Laser Amplifier and its Application to Dispersion Compensation in Mid-Span Spectral Inversion System

Properties of four-wave mixing (FWM) in the semiconductor laser amplifier are studied experimentally in this paper. The optical phase conjugation of the mixing wave is applied to compensate the chromatic dispersion of transmission fiber. It is presented experimental results of the transmission of short optical pulses with 12-ps width over 204 km standard single mode fiber. The results confirm that mid-span spectral inversion (MSSI) employing FWM in a semiconductor laser amplifier is one of potential dispersion compensation techniques for optical transmission over standard single mode fiber with bit rate beyond 40Gb/s.     

用于实现散射介质中时间反演的数字相位共轭的相干性

抑制散射介质对光的散射,调控光在散射介质中的传输,是光通信、生物光子学、光镊等领域的重要课题.设计并实现了基于宽谱光源和数字相位共轭的可调控光在散射介质中传输的时间反演实验系统.实验获取了不同相干长度下物光和参考光束之间的光程差与干涉图样、相位图及时间反演信号之间的关系,分析了光源相干性对调控光在散射介质中传输的影响.实验结果表明,基于宽谱光源的相干特性和数字相位共轭技术,通过调节光程差能选择性获取同一散射角度及相同传输路径的光束的相对相位,再利用空间光调制器对参考光束进行调控,实现光束的反向传播,从而选择性实现对同一散射角度及相同传输路径的光的时间反演.     

Experimental Study of Four Wave Mixing in Semiconductor Laser Amplifier and its Application to Dispersion Compensation in Mid Span Spectral Inversion System

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Simultaneous dispersion and non-linearity compensation with mid-span optical phase conjugation and distributed Raman amplifier for a sub-carrier multiplexed optical transmission link

Optical phase conjugation (OPC) and distributed Raman amplifier (DRA) combination (OPC-DRA) is demonstrated as a potential enabling solution for simultaneous reduction of fiber non-linearities and dispersion compensation of a sub-carrier multiplexed (SCM) optical transmission link. The present work is focused on the use of OPC-DRA combination for system performance improvement in terms of composite second order distortion (CSO) and carrier to noise ratio (CNR) of the SCM link. The analysis further shows that, introduction of DRA with proper pumping scheme significantly reduce fiber non-linearity resulting in improvement of the system performance in terms of CNR, compared to the situation where only mid-way optical phase conjugation is used.     

熔石英棒-光纤组合型相位共轭镜的研究

提出了一种由大口径的熔石英棒和较大芯径的光纤组成的相位共轭镜.在光纤中产生的斯托克斯(Stokes)种子光经由熔石英棒放大后输出.该相位共轭镜可以用于高重复频率激光系统中以改善激光光束质量.实验中,在重复频率100 Hz的情况下,最大获得了42.05%的受激布里渊散射反射率,光束质量从3降低到1.6;在重复频率400 Hz的情况下,光束质量从4降到了1.7.根据实验条件建立的理论模型经数值求解后与实验结果拟合较好,并由理论推导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.     

Pulsed solid-state laser system with fiber phase conjugation and 315 W average output power

Solid-state laser sources with high average output power and high beam quality are required for numerous applications in industry and science. To improve the beam quality, stimulated Brillouin scattering (SBS) mirrors based on optical phase conjugation are used to compensate for phase distortions in master oscillator power amplifier (MOPA) systems. SBS phase conjugation in commercially available silica optical fibers facilitates the construction of high-power solid-state laser systems with high beam quality. Here we present a flash lamp-pumped, passively Q-switched Nd:YAP system which delivers an average output power of 315 W with M²=2.6 at a wavelength of 1.08 μm. Received: 11 July 2001 / Revised version: 28 September 2001 / Published online: 23 November 2001     

大尺度光学列阵的成像特性

本文由光线光学理论出发,分析了无单元像差的光学元件大尺度列阵的成像特性,得到了较傍轴近似更普适的成像特性变换矩阵,其结果包含了列阵的傍轴近似成像理论.并进一步证明了大尺度平面列阵的成像特性只具有近似的准相位共轭特性,且只有在傍轴近似下才是较完善的准相位共轭成像.该结论与以往理论相比更接近实际,且能更好地解释迄今为止所观察到的实验结果及本文的实验结果.     

Nonlinear optical interactions in dye-doped solids

We present a brief review of non-linear optical investigations on dye-doped solids using low-power CW lasers. After a brief introduction to the photophysics of the dye molecules, we discuss specific nonlinear processes such as self-diffraction, optical phase conjugation, two-beam coupling and polarization gratings in these systems. The application potential of dye-doped solid devices is discussed.     

Study of second harmonic generation by non-linear crystals with phase conjugation

We present the correction of the phase distortion which occurs during the second harmonic generation by non-linear crystals, such as KDP and KTP at high average power laser. This is due to the optical quality and thicknesses of the crystals which in turn influence the quality of the incident laser beam. This phase distortion is corrected by reflecting back the laser beam into the crystal using a phase conjugate mirror. It is found that the conversion efficiency of second harmonic generation without phase conjugation is more than that with phase conjugation. Far field pattern shows that the distortion of the laser beam can be corrected by using the phase conjugate mirror. Fidelity of the beam profile increases significantly with phase conjugation in the case of KDP crystal.     

Multiple image encryption using an aperture-modulated optical system

A multiple image cryptosystem based on different apertures in an optical set-up under a holographic arrangement is proposed. The system is a security architecture that uses different pupil aperture mask in the encoding lens to encrypt different images. Based on this approach multiple encryption is achieved by changing the pupil aperture arrangement of the optical system among exposures. In addition to the classical speckle phase mask, the geometrical parameters characterizing the apertures are introduced to increase the system security. Even when an illegal user steals the speckle phase mask, the system cannot be broken into without the correct pupil geometrical parameters. The experimental set-up is based on a volume photorefractive BSO crystal as storing device. Information retrieval is done via a phase conjugation operation. We also have to stress that the multiple storage under this scheme, is only possible with the help of the aperture mask. Simulation and experimental results are further introduced to verify the proposed method.     

Distortion correction by phase conjugation of nonparaxial vectorial beams: a general proof

We present a general proof of the distortion-correction theorem, that is, of the possibility of correcting wave distortion by the technique of optical phase conjugation. The proof is valid for fully vectorial nonparaxial propagation in the presence of a tensorial refractive-index perturbation and backscattering of the incident field.     

Experimental verification of optical image encryption based on interference

We present experimental results to verify the optical image encryption based on interference. The optical experiment is performed by using a reflective phase-only spatial light modulator (SLM) to generate the desired phase retardations. A hologram plate is employed to record the modulated wavefronts in a double-step-holographic-exposure process. The experiment results are in good agreement with the numerical simulations of the encryption algorithm, which demonstrates the feasibility of the optical image encryption in actual optical systems.     

Narrow band optical filter in fluorescein doped boric acid glass saturable absorber thin films

We demonstrate narrow band optical filter like frequency response with full width half maximum (FWHM) of nearly (1.75 ± 0.25) Hz in fluorescein doped boric acid glass films [10⁻⁴ M], using modulated optical phase conjugation and a nearly non-degenerate four wave mixing technique. Modulated optical phase conjugation signals are described in the limit of a weak probe and relatively strong pump beams. Both pump beams are of nearly equal intensity at a wavelength of 514.5 nm from a continuous-wave Ar⁺ laser. The probe beam frequency has been detuned with a ramp signal using a piezo electric mirror.     

Development of high-repetition-rate LD pumped Nd:YAG laser and its application

High-average-power and high-energy lasers with good beam quality are fundamental tools for pumping high-peak and high-average-power ultrafast Ti:sapphire laser systems. Laser-diode (LD) pumped solid slate lasers with phase conjugation offer a unique combination of efficiency, reliability, and compactness. We present the design details and performance characteristics of a 360-W 1-kHz LD pumped Nd:YAG phase-conjugated laser. We also discuss the basic design aspects and present our preliminary experimental investigations on ultrashort-pulse laser systems.     

向列相液晶中光学相位共轭技术的研究进展

对向列相液晶中光学相位共轭技术的研究进展进行了介绍,分析总结了向列相液晶中光学相位共轭过程的机理与实验方法,并对向列相液晶中的光学相位共轭技术的应用前景进行了展望。     

相位共轭皮秒光脉冲的直接观察和记录

利用条纹照相机直接观察和记录了由全息相位共轭技术产生的相位共轭的皮秒光脉冲。实验结果与理论相符合。 关键词：     

A semiclassical approach for electro-optic effect

In this article, we present a semiclassical approach for modeling of electro-optic (EO) effect. We calculate phase retardation between x and y polarizations of optical electric field when a transverse external electric field is applied. Our results are well agreed with experimental measurements. Moreover, we show when wavelength of optical signal decreases, the phase retardation increases.