菌紫质高密度偏振全息光数据存储实验研究

实验研究了基因改性菌紫质BR_D96N薄膜在不同偏振光记录下的全息存储特性，比较了不同 偏振态记录光和读出光对衍射像光强及信噪比的影响. 实验结果表明，与其他偏振全息记录 相比，正交圆偏振光记录可实现衍射光偏振状态与散射噪声偏振状态的分离，得到高信噪比 的衍射像，同时还具有高的衍射效率. 以 He_Ne 激光器（633nm，3mW）为记录和读出光源 ，用空间光调制器作为数据输入元件，CCD作为数据读出器件，采用傅里叶变换全息记录的 方法，在 BR_D96N 薄膜样品60μm×42μm的面积上进行了正交圆偏振全息数据存储，达到 了2×10⁸bit/cm²的存储面密度，并实现了编码数据的无误读出与 还原. 关键词： 菌紫质 偏振全息 光致变色 光致各向异性 高密度光存储     

利用菌紫质薄膜进行角度复用和偏振复用全息存储实验研究

全息光存储以其高密度、大容量、高速并行数据存取而成为光存储领域的一个重要研究方向。生物光致变色材料———菌紫质是一种新型可擦重写全息记录介质。实验证明了使用菌紫质薄膜进行角度复用和偏振复用全息存储的可行性。利用菌紫质的光致变色特性,采用90°角度复用全息存储光路,在BR-D96N薄膜样品同一位置上实现了6幅全息图存储,并分别读出了无串扰的再现像。利用菌紫质薄膜的光致各向异性进行了偏振复用全息存储,在BR-D96N薄膜样品的同一位置上存储了两幅正交偏振光记录的图像,用原参考光再现和偏振片选择,可分别读出这两幅图像。     

基于菌紫质薄膜的相移器及其应用

设计了一种基于菌紫质光致各向异性的相移器,并把它用于相移干涉计量。取向随机分布的极性菌紫质分子对线偏振诱导光的选择性吸收导致分子取向分布不均匀,使其呈现宏观的各向异性,这种各向异性与诱导光的偏振特性密切相关,圆偏振光经过各向异性的菌紫质薄膜后,出射光的偏振特性完全由偏振诱导光决定。基于上述原理设计了一种新型的相移器,用琼斯矩阵法推导了基于相移器的相移干涉原理。该相移器在工作过程中不需要移动Mach-Zender干涉仪内部的任何器件,仅需要改变外部控制光路中诱导光的偏振取向就可以控制参考光的相位,有助于提高设备的抗振能力。用最小二乘法对相移干涉结果进行重建,得到了和实际相位一致的结果,验证了相移器的可行性。     

菌紫质同线偏振全息记录时再现光偏振方向对衍射效率的调制

当用相同偏振方向的物光和参考光在菌紫质薄膜上记录光栅时,再现光的偏振方向会影响其衍射效率.采用琼斯矩阵方法对此进行了理论分析,结果显示,再现光的偏振方向对衍射光的光强产生余弦调制;当再现光的偏振方向平行或垂直于记录光的偏振方向时,衍射光仍为线偏振光,其他情况下衍射光均变成椭圆偏振光.再现光偏振方向对衍射效率峰值的调制为正向余弦调制,对衍射效率稳定值的调制为反向余弦调制(与前者在相位上相差π).加入辅助紫光可抑制光栅的饱和,从而使得再现光偏振对衍射效率稳定值的调制由反向余弦调制变为正向余弦调制,并且提高了衍 关键词： 菌紫质 光致各向异性 衍射效率 琼斯矩阵     

菌紫质光致各向异性动力学的理论和实验

对菌紫质(Bacteriorhodopsin,BR)薄膜的光致各向异性特性进行了理论模拟.由随机取向的极性BR分子构成的聚合物薄膜在宏观上是各向同性的,但在线偏振光的作用下,BR分子对激发光的选择性吸收,导致不同异构体分子取向的不均匀分布,从而使BR薄膜在宏观上呈现出各向异性.利用BR光循环的二能级模型,得到了B态分子取向分布随时间的变化关系,推导出了BR薄膜光致各向异性动力学的数学表达式,模拟了不同激发光强下BR薄膜的光致各向异性动力学曲线,得到了和实验结果一致的计算结果.     

偶氮类有机材料光致双折射的测量

研究了2种偶氮聚合物薄膜的光致双折射效应,并探讨了泵浦光偏振态和光强对光致双折射的影响.采用远离共振区的He-Ne光(633nm)作为探测光,用Ar+激光(488nm)作为泵浦光,通过测量相关参量得到了样品的光致双折射值.实验结果表明:改变泵浦光的偏振态可以控制光致双折射值和探测光的透过信号强度,在0°～45°范围内,泵浦光光强存在最佳值,此时偶氮薄膜实验样品具有最大的双折射值.     

偏振全息光栅衍射光场的理论分析

利用介质的光致各向异性和可记录偏振全息光栅,从偏振全息的透射琼斯矩阵出发,运用傅里叶展开法,对记录光不同的偏振态组合情况下,衍射光场的可能出现的衍射级次及其偏振特性进行了理论分析.并以甲基橙掺杂聚乙烯醇膜为例,对各阶衍射光的衍射效率进行了理论计算.     

偏振全息光栅衍射光场的理论分析

利用介质的光致各向异性和可记录偏振全息光栅,从偏振全息的透射琼斯矩阵出发,运用傅里叶展开法,对记录光不同的偏振态组合情况下,衍射光场的可能出现的衍射级次及其偏振特性进行了理论分析.并以甲基橙掺杂聚乙烯醇膜为例,对各阶衍射光的衍射效率进行了理论计算.     

三光束飞秒激光干涉在GaP,ZnSe表面诱导二维复合纳米-微米周期结构

报道了三光束飞秒激光干涉在GaP和ZnSe晶体表面诱导二维复合纳米-微米周期结构.改变三束光的偏振组合方式,可以得到不同的纳米-微米复合结构.理论计算了相应偏振条件下光场强度分布、椭偏度分布和偏振方向分布.实验和理论计算结果表明,烧蚀斑上的微米长周期结构是由三光束干涉的强度花样决定,短周期纳米结构是由光场的偏振干涉花样决定.这些研究在纳米材料制备、超高密度光存储以及材料特性周期性调制等方面有很大的应用前景.     

紫光诱导菌紫质中同圆偏振光栅的衍射调制特性

基于琼斯矩阵和菌紫质分子光循环的简化光循环模型,建立了紫光诱导同圆偏振记录光栅的理论模型,采用四波耦合光路测量菌紫质光栅的衍射效率.理论模拟和实验结果表明:加入线偏振的辅助紫光,线偏振再现光与线偏振辅助紫光相互平行时,菌紫质光栅的衍射效率最大;线偏振再现光与线偏振辅助紫光相互垂直时,菌紫质光栅的衍射效率最小;菌紫质薄膜中同圆偏振记录光栅的稳态衍射效率随线偏振再现光偏振方向和线偏振辅助紫光偏振方向之间的夹角按余弦规律变化.线偏振紫光能诱导同圆偏振记录光栅由非偏振光栅转化为偏振光栅.     

Polarization multiplexed write-once-read-many optical data storage in bacteriorhodopsin films

In polymeric films of bacteriorhodopsin (BR) a photoconversion product, which was named the F620 state, was observed on excitation of the film with 532 nm nanosecond laser pulses. This photoproduct shows a strong nonlinear absorption. Such BR films can be used for write-once-read-many (WORM) optical data storage. We demonstrate that a photoproduct similar or even identical to that obtained with nanosecond pulses is generated on excitation with 532 nm femtosecond pulses. This photoproduct also shows strong anisotropic absorption, which facilitates polarization storage of data. The product is thermally stable and is irretrievable to the initial B state either by photochemical reaction or through a thermal pathway. The experimental results indicate that the product is formed by a two-photon absorption process. Optical WORM storage is demonstrated by use of two polarization states, but more polarization states may be used. The combination of polarization data multiplexing and extremely short recording time in the femtosecond range enables very high data volumes to be stored within a very short time.     

Rewritable polarization-encoded multilayer data storage in 2,5-dimethyl-4-(p-nitrophenylazo)anisole doped polymer

We report a rewritable polarization-encoded multilayer data storage method with a polymer film doped with the azo dye DMNPAA (2,5-dimethyl-4-(p-nitrophenylazo)anisole). It is found that under two-photon excitation by a linearly polarized femtosecond laser beam at wavelength 780 nm the optical axis of DMNPAA molecules can be oriented to the perpendicular direction of the beam via a trans-cis-trans isomerization process. As a result, multilayer polarization-encoded optical data storage is demonstrated by recording two letters of a bit spacing of 4 microm in the same region of a given layer. It is shown that erasing and rewriting a particular layer is possible.     

Typesetting of terahertz waveforms

We demonstrate programmable generation of temporally shaped terahertz waveforms in LiNbO3 by spatially shaping the beam profile of femtosecond excitation laser pulses with a spatial light modulator. The generated terahertz waveforms have amplitudes that are approximately proportional to the first spatial derivative of the excitation beam profile.     

Spectral dependence of the excitation of the “forbidden” second optical harmonic in an aqueous suspension of purple membranes by femtosecond laser pulses under electronic resonance conditions

The spectral dependence of the efficiency of generation of the forbidden (in the electric-dipole approximation) second harmonic (FSH) and its energy on the energy of the excitation pulses is investigated experimentally in a highly disperse suspension of purple membranes containing bacteriorhodopsin (BR) under excitation by femtosecond laser pulses into the single-photon absorption band of BR. The experimental data for the case of resonance excitation attest to an interference character of the interaction of optical nonlinearities of different orders in the process leading to the formation of the FSH signal. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 4, 251–255 (25 February 1998)     

Compact and self-aligned all-optical image correlator based on third-harmonic generation

We demonstrate a compact optical correlator using a diffractive optical element (DOE) beam splitter for 2D optical image processing. Image frequency conversion and correlation are demonstrated using third-harmonic generation (THG) in an organic film with a 1550 nm femtosecond laser. Spatial and temporal alignment of the femtosecond pulses are obtained by imaging the DOE onto the organic film.     

用于宽带啁啾脉冲光参量放大系统精确同步的新方法

基于非共线光参量放大,以波长800 nm飞秒激光的倍频光为抽运光,以激光二极管640 nm连续波激光为信号光,产生了与800 nm飞秒激光精确同步的无直流本底的1064 nm脉冲光。实验结果显示该1064 nm的光脉冲在脉冲能量和空间光束质量上均可作为1064 nm波长脉冲放大器的种子光。仅通过一级简单紧凑的非共线参量放大就可实现光周期量级的光参量啁啾脉冲放大系统的抽运激光和种子光的精确同步。     

Femtosecond pulse laser scanning using Acousto-Optic Deflector

Acousto-optic modulation of the femtosecond laser beam has wide potential in various fields such as microscopic imaging, micromachining and optical storage because of its rapidity, high accuracy and good repeatability. This paper reviews the latest research on acousto-optic modulation of femtosecond laser, describes the effects of spatial and temporal dispersion of such lasers after acousto-optic modulation, introduces the theoretical outcomes on pulse width evolution of the Gaussian laser pulses after acousto-optic modulation, discusses the characteristics of contemporary dispersion-compensating techniques for the acousto-optic modulation of femtosecond laser, and finally refers to the challenges of this technique. Supported by the National Natural Science Foundation of China (Grant Nos. 60278017, 30328014, and 30370463) and the National Basic Research Program of China (Grant No. 2004CB520804)     

Invertible dark-center diffraction of the metal film induced by femtosecond laser

We found reversible dark-center diffraction of the transmitted probe beam passing through the chromium film, which is induced by the pump femtosecond laser. The dark-center diffraction of the transmitted probe beam appears and disappears with and without the pump beam. A view of diffractive optics with binary phase plate is put forward, which explains the reversible dark-center diffractive optical phenomenon. The pre-ablated hole on the metal film can be regarded as a uniform light filed without phase modulation, the surrounding circular part around the pre-ablated hole can be regarded as “phase modulated”. Therefore, this diffraction optic view might be helpful for us to understand the phase change of the metal film introduced by the femtosecond laser pulse.     

基于DVD光头的双光子光致漂白三维光存储

基于现有的DVD光头物镜与音圈电机，根据光致漂白的双光子吸收气维光信息存储原理，以钛蓝宝石飞秒脉冲激光进行双光子光信息写入和读出，利用音圈电机进行选层，在新型光致漂白材料二苯乙烯衍生物中进行光致漂白二进制编码信息的存储和读出实验研究；实现了三层光信息存储，信息点间距和信息层间距分别为4μm和15μm；用Matlab软件读出信息的信号强度并对其进行了识别，识别结果与写入的二进制编码信息完全一致。实验证明了用DVD光头进行双光子三维光数据存储的可行性，表明双光子吸收光致漂白技术可以与现有CD／DVD兼容，为实现多层高密度和超高密度光信息存储打下基础。