基于菌紫质F态的永久光存储研究

在线偏振飞秒激光激发下, 菌紫质通过双光子光化学反应可以生成具有永久光致各向异性的蓝移产物F₅₄₀态. 基于F₅₄₀态的永久光致各向异性, 通过调控飞秒激光空间光场分布, 可以在菌紫质薄膜中实现永久光信息存储. 本文使用纯相位型空间光调制器调制飞秒激光光场, 在物镜焦平面上生成光学点阵图案, 可以将信息快速记录在菌紫质薄膜中. 同时, 通过改变入射激光偏振方向, 可以实现偏振复用光存储, 这在高密度光存储和数据加密领域具有潜在应用.     

Making an optical vortex and its copies using a single spatial light modulator

We demonstrate a technique for making copies of optical vortices with the same topological charge using a single spatial light modulator. It has been shown that by using suitable diffractive optical elements, several copies of optical vortices with the same topological charge could be created. We have devised diffractive optical elements using a single spatial light modulator which could be used to make a vortex and its copies without inverting the charge. The nature of the topological charge was investigated with the interferometric technique. The experimental results are verified with the theoretical analysis. We anticipate that our results may find applications ranging from optical manipulation to quantum information.     

Generation of optical vortices with arbitrary shape and array via helical phase spatial filtering

We report a method for generation of arbitrary shape and array of optical vortices by use of a superposition of coherent elementary vortices based on helical phase spatial filtering in spatial frequency domain. In this method, a helical phase spatial filter (HPSF) is placed in the spatial frequency plane of a 4-f imaging processing system. We demonstrated that the output field distribution represents the convolution between the input field and an elementary vortex field introduced by the HPSF, which results in a special shape or array of optical vortices determined by the “degenerate” properties of coherent elementary vortices and the distribution formats of the input field.     

Topological charge dependent propagation of optical vortices under quadratic phase transformation

We make optical vortices of different topological charge and diffract them through a quadratic phase mask using the same spatial light modulator. This phase mask shows the diffraction in which the positive diffracted order has different dynamics than the negative diffracted order. The diffraction pattern and its orientation depend on the charge of the vortex as well as its sign. The experimental results are verified with exact analytical results.     

Digital phase-shifting interferometer with an electrically addressed liquid-crystal spatial light modulator

A digital phase-shifting interferometer with a liquid-crystal-display coupled, parallel aligned, nematic liquid-crystal spatial light modulator is developed. The optical phase shift in the Michelson-type polarization interferometer is achieved by a digital phase shift of a grating displayed on the spatial light modulator. Accurate experimental results of using the heterodyne system for pi/2 phase steps were demonstrated. A phase-shifting interferometer with no moving parts and no requirement for calibration of the value of the phase shift was achieved.     

Bragg diffraction of light by a set of parallel phase gratings: Analysis and applications

Bragg diffraction of light by a set of parallel phase gratings is considered, utilizing two-dimensional coupled-wave theory. The diffraction characteristics of a Bragg-type spatial light modulator are presented. It is shown that the resolution limit and the accuracy of spatial light modulation are determined by the geometry parameter of the grating. The results obtained are used for the choice of the design parameters of various optical Bragg processors.     

Generation of optical vortex array based on the fractional Talbot effect

A phase-only diffractive optical element (DOE) for generating array of optical vortices with high compression ratio is presented. Since it is designed according to the fractional Talbot effect, we name the DOE optical vortex Talbot array illuminator (OVTAI). As an example, an OVTAI for generating a hexagonal array of optical vortices is designed, and demonstrated through displaying the OVTAI on a programmable liquid crystal spatial light modulator. The diffraction properties of the vortex array generated by the OVTAI are observed and analyzed, and an optimal distance for generating sharp ringed vortex arrays is given.     

Dynamic generation of plasmonic Moiré fringes using phase-engineered optical vortex beam

Dynamic generation of plasmonic Moiré fringes using a phase engineered optical vortex (OV) beam is experimentally demonstrated. Owing to the unique helical phase carried by an OV beam, the initial phase of surface plasmon polaritons (SPPs) emanating from a metallic grating can be adjusted dynamically by changing the phase hologram displayed on a spatial light modulator. Plasmonic Moiré fringes are readily achieved by overlapping two SPP standing waves with certain angular misalignment, excited by the positive and negative topological charge components, respectively, of a cogwheel-like OV beam. The near-field scanning optical microscopy measurement result of SPP distributions has shown a good agreement with the numerical predictions.     

Partially incoherent optical vortices in self-focusing nonlinear media

We observe stable propagation of spatially localized single- and double-charge optical vortices in a self-focusing nonlinear medium. The vortices are created by self-trapping of partially incoherent light carrying a phase dislocation, and they are stabilized when the spatial incoherence of light exceeds a certain threshold. We confirm the vortex stabilization effect by numerical simulations and also show that the similar mechanism of stabilization applies to higher-order vortices.     

Modulated optical vortices

Single-beam optical gradient force traps created by focusing helical modes of light are known as optical vortices. Modulating the helical pitch of such a mode's wave front yields a new class of optical traps whose dynamically reconfigurable intensity distributions provide new opportunities for controlling motion in mesoscopic systems. An implementation of modulated optical vortices based on the dynamic holographic optical tweezer technique is described.     

基于液晶纯相位光调制器的4f系统去噪方法

分析了4f系统的噪声来源,提出使用液晶空间光调制器实时去除系统噪声.通过使用Zemike多项式拟合透镜等光学器件引入的像差,根据液晶纯相位光调制器利用位相共轭波进行静态波面校正的工作原理,提出了一种新的相位校正算法,模拟仿真美国BNS公司反射式256×256纯相位液晶空间光调制器,通过重构并逼近畸变波面,产生相位共轭波...     

相位板偏振偏转角对径向偏振光的梯度力分布的影响

 研究了同心分区偏振偏转相位板对径向偏振光梯度力的调制效应。给出了相位板各部分偏振偏转角不同时,光学梯度力的分布情况。模拟结果表明:随着同心分区相位板各部分的半径和偏振旋转角的改变,光学梯度力方向及大小明显变化,且会产生许多可控的梯度力分布模式,可应用于微粒的收集、分离和合并。结果显示同心分区相位板对径向偏振光的调制可以用来生成可调光镊。     

螺旋光束经过振幅型衍射光学元件的传输特性及其拓扑电荷数的测量

本文提出了一种利用空间光调制器生成杨氏双缝和三角孔等振幅型衍射光学元件的方法. 利用平面波角谱衍射公式和柯林斯公式研究了螺旋光束经过这两种衍射元件后的传输特性, 并利用杨氏双缝和三角孔实现了螺旋光束拓扑电荷数的测量. 由于空间光调制器可以方便和高精度地改变光学器件的几何尺寸和所在的空间位置, 因此可便捷地实现螺旋光束拓扑电荷数的测量.     

Entangled double-helix phase

We present a novel phase with an entangled double-helix structure. Beams with this phase have the same transverse patterns as those of interference between two doughnut beams. This proposed method allows a complete set of the superpositions of the doughnut modes or the orbital angular momentum states with different topological orders to be obtained. Furthermore, it introduces a simple continuous and controlled rotation of the transverse patterns by use of a spatial light modulator. It can be used to form a three-dimensional structure by three-dimensional trapping in an optical tweezers setup or to study the quantum characteristics of an optical vortex.     

液晶相息图用于光学检测

根据液晶的动态响应和位相调制特性,研究了一种利用液晶显示器进行光学检测的检测方法.实验中,把液晶显示器改造为纯位相的空间光调制器,并测定了它的位相调制特性.实验测得：改造后的液晶显示器可实现1 λ(λ=632.8 nm)的调制量.通过引入相息图的方法,实现了液晶空间光调制器的大位相调制量.并产生了调制量为3.4 λ的球面波.最后,利用液晶显示器检测了凸透镜的前表面.检测结果发现,干涉条纹为平行直条纹且PV值为0.32λ.     

Super-Resolution Two-Photon Fluorescence Tomography Through the Phase-Shifted Optical Beatings of Bessel Beams for High-Resolution Deeper Tissue 3D Imaging

A novel z-scanning-free epi-detected super-resolution two-photon fluorescence tomography (TPFT) technique enabling super-resolution deeper tissue 3D imaging is reported. To accomplish this, a unique method is conceived by generating the phase-shifted optical beatings of Bessel beams (PS-OB³) with a spatial light modulator (SLM) to break the diffraction limit for enhancing both the lateral and axial resolutions as well as improving the penetration depth in TPFT for super-resolution deeper tissue imaging. By electronically varying the optical beating frequency and the phase shifts of the beating patterns through SLM, the depth-resolved TPF signals about the volumetric tissue are encoded in the spatial frequency domain and hence, a series of depth-resolved TPF images can be retrieved by implementing inverse fast Fourier transform without a need of mechanical depth-scanning. PS-OB³ TPFT provides ≈1.3- and 2-fold improvements in lateral and axial resolutions in comparison with conventional point-scan TPF imaging. It is also illustrated that the epi-detected PS-OB³ TPFT imaging with inherent scattering-resilient properties of the Bessel beams employed gives over 2-fold improvement in imaging depth in porcine brain tissue compared to conventional point-scan Gaussian beam TPF imaging. The z-scanning-free optical sectioning ability of PS-OB³ method developed in TPFT is universal, which can be readily extended to practically any other nonlinear optical imaging modalities for super-resolution deeper 3D imaging in biological and biomedical tissues.     

Phase singularities and coherence vortices in linear optical systems

It is demonstrated for a time-invariant linear optical system that there exists a definite connection between the optical vortices (phase singularities of the field amplitude) which appear when it is illuminated by spatially coherent light and the coherence vortices (phase singularities of the field correlation function) which appear when it is illuminated by partially coherent light. Optical vortices are shown to evolve into coherence vortices when the state of coherence of the field is decreased. Examples of the connection are given. Furthermore, the generic behavior of coherence vortices in linear optical systems is described.     

Generation of hollow beams by using a binary spatial light modulator

We demonstrate the generation of hollow laser beams by using a binary spatial light modulator and compare the results with those for a continuous modulator. The binary phase modulator produces beams that have continuous, azimuthally varying phase profiles and can be dynamically changed with kilohertz refresh rates. The intensity and phase profiles are recorded through the focus of an imaging lens and are compared with scalar diffraction theory. We highlight properties of the beams relevant to optical dipole traps.     

Multi-beam second-harmonic generation in beta barium borate with a spatial light modulator and application to internal structuring in poly(methyl methacrylate)

Parallel beam frequency doubling of 170 fs, NIR pulses is demonstrated by placing a thin beta barium borate (BBO) nonlinear crystal after a spatial light modulator. Computer-generated holograms applied to the spatial light modulator create 18 parallel diffracted beams at the fundamental wavelength λ=775 nm, then frequency doubled to λ=387 nm and focussed inside the poly(methyl methacrylate) (PMMA) substrate for refractive index structuring. This procedure, demonstrated for the first time in PMMA, requires careful attention to phase matching of multiple beams and opens up dynamic parallel processing at UV wavelengths where nematic liquid crystal devices are more sensitive to optical damage. By overlapping filamentary modifications, an efficient, stable volume phase grating with dimensions 5×5×2.0 mm³ and pitch Λ=15 μm was fabricated in 18 minutes and reached a first-order diffraction efficiency of 70 % at the Bragg angle.     

Experimental generation and characterization of Devil’s vortex-lenses

We propose the first experimental approach for both generation and characterization of high quality Devil’s vortex-lenses. These new type of lenses, able to produce a sequence of optical vortices, are addressed onto a programmable spatial light modulator (SLM) operating in phase-only modulation. The static aberrations arising by the lack of flatness of the SLM display are characterized and mostly compensated by using a Shack–Hartmann wavefront sensor. The analysis of the residual aberrations and their effect on the vortex-lens performance are studied.