Zemax软件在取样光栅对设计中的应用

 光束取样光栅(BSG)是一种重要的用于光束取样诊断的衍射光学元件。以2块取样光栅代替单块光栅作为初始光学结构,运用Zemax光学设计软件采用分步优化的方法设计了具有消像差功能的光栅对结构,此方法比采用Matlab语言编程计算的方法消像差更快捷、更灵活,同时可以验证程序计算结果的正确性。设计结果显示：再现的会聚光经2块光栅衍射后在像平面上点列图中的均方根半径仅为0.506μm,单块取样光栅的均方根半径则为7.284μm,说明2块光栅能够做到像差互相矫正,其像质明显好于单块取样光栅。另外,设计出的双光栅光学系统,可进行远场光斑质量检测,为激光束性能的在线诊断提供了行之有效的技术支持。     

Airy beam laser

A method to design lasers that emit an arbitrary beam profile is studied. In these lasers, output-coupling is performed by a diffraction grating that imposes a phase and amplitude distribution onto the diffracted light. A solid-state laser emitting beams with a two-dimensional Airy intensity profile is demonstrated both theoretically and experimentally. In this case, the diffraction grating adds a transverse cubic phase to the diffracted light. An Airy beam is obtained by performing optical Fourier transform of the out-coupled light. The laser beam profile and power characteristics are shown to agree with theory.     

Ultra-fast speed, low grating lobe optical beam steering using unequally spaced phased array technique

In this paper, we present a low grating lobe optical beam steering technique using an unequally spaced phased array, in which the required spacings among the phase elements are quantitatively analyzed so that the grating lobe can be minimized by destructive interference. A large grating lobe is one of the major drawbacks of optical phased array technology because it limits the light efficiency and the quality of the light beam. Thus, the low grating lobe technique presented in this paper could substantially improve the light efficiency and the quality of light beam, and could potentially be used in a variety of applications such as fast speed ladar beam steering, large size high resolution displays, and wide bandwidth free space optics communications.     

Interferometric grating method and its application in Fe-base shape memory alloy structure design

This paper presents an interferometric grating method used in measuring strain fields on a curved surface. This method can be used to determine the small and large strains with high sensitivity and has been applied successfully in Fe-base shape memory alloy (FSMA) structure design. In this study, five diffracted beam from the specimen surface produce the interferometric gratings through an optical system. Using image processing technique (fast Fourier transform with special interpolation and phase shifting technique), we have obtained the strain fields of outer surface of FSMA joint and contact pressure distribution on its inside surface which has mechanical deformation and transformation.     

Heterodyne detection scheme for light-induced transient grating experiment

A novel heterodyne detection scheme for light-induced transient grating technique is presented. The heterodyne detection is achieved coherently mixing the picosecond pulses of diffracted and scattered light. A phase difference between these pulses is controlled by moving a holographic beam splitter along its grating vector. This approach is employed to study a competition of coexisting electronic and thermal optical nonlinearities in CVD grown diamond films in sub-nanosecond time domain and to determine carrier parameters.     

Phase effects in the diffraction of light: beyond the grating equation

Diffraction gratings affect the absolute phase of light in a way that is not obvious from the usual derivation of optical paths using the grating equation. For example, consider light which encounters first one and then the second of two parallel gratings. If one grating is moved parallel to its surface, the phase of the light diffracted from the grating pair is shifted by 2pi each time the grating is moved by one grating constant, even though the geometric path length is not altered by the motion. This additional phase shift must be included when incorporating diffraction gratings in interferometers.     

Fourier optics analysis of grating sensors with tilt errors

Dynamic diffraction gratings can be microfabricated with precision and offer extremely sensitive displacement measurements and light intensity modulation. The effect of pure translation of the moving part of the grating on diffracted order intensities is well known. This study focuses on the parameters that limit the intensity and the contrast of the interference. The effects of grating duty cycle, mirror reflectivities, sensor tilt and detector size are investigated using Fourier optics theory and Gaussian beam optics. Analytical findings reveal that fringe visibility becomes <0.3 when the optical path variation exceeds half the wavelength within the grating interferometer. The fringe visibility can be compensated by monitoring the interfering portion of the diffracted order light only through detector size reduction in the expense of optical power. Experiments were conducted with a grating interferometer that resulted in an eightfold increase in fringe visibility with reduced detector size, which is in agreement with theory. Findings show that diffraction grating readout principle is not limited to translating sensors but also can be used for sensors with tilt or other deflection modes.     

A Laser Source with High Spectral Purity for Simple Tunable Laser Raman Instrument

The authors present an external cavity diode laser with high spectral purity for tunable laser Raman spectroscopy. To achieve high spectral purity required for Raman spectroscopy, a laser cavity utilizing a volume phase holographic grating, which has very low stray light, is developed and the first-order diffracted beam from the grating is taken as the output. Raman signals can be obtained from common samples with only a commercial laser rejection filter, greatly simplifying a tunable Raman instrument.     

Aberrations in fractional-Talbot images of periodic binary gratings

We discuss the ray-optical aberrations which appear in the fractional-Talbot image of a periodic binary grating with coherent illumination. First we examine the complex amplitude of an aberration-free imaging field at a fractional-Talbot plane. We then trace the path of a diffracted ray of specific order which contributes to the fractional-Talbot imaging. Next we formulate the focus-shift and third-order aberrations which arise from a focusing error and a fourth-order approximation of the path length, respectively. We then evaluate the amplitude and phase of an aberrated imaging field that are represented in terms of aberration functions. When the grating period decreases to approach the optical wavelength, the aberrations of lower-order rays are shown to be more influential on the fractional-Talbot imaging field than those of higher-order rays. The theory of aberration discussed here could be very useful in evaluating the fractional-Talbot image of a periodic binary grating.     

一种新的光纤光栅温度传感器的设计

提出一种新的光纤温度传感器,在单模光纤的45°倾斜端面上制作光栅。沿光纤光轴传输到光纤倾斜端面上的光将被全反射,同时被光栅衍射。适当选择光栅常数,可以使衍射零级和衍射负1级在经过不同的传播路径后相遇,并产生干涉,干涉条纹的变化将体现传感器所处环境温度的变化。由理论计算知,当工作波长为1.55μm时,这种传感器可测的温度变化范围为1179℃。     

Theory of laser-induced amplitude and phase gratings including photoselection,orientational relaxation and population kinetics

The generation of amplitude and phase gratings in an absorbing medium is discussed, including the effects of light polarization, population kinetics and orientational relaxation. A theory is given which describes light diffraction by a combination of an amplitude and a phase grating. It is shown that the coherent coupling effect in transient absorption measurements is solely due to the amplitude grating. Weak absorption and a low triplet yield favour diffraction of the probing beam by the phase grating in triple-beam experiments. Phase grating experiments can be performed with highly soluble absorber dyes, the absorption maximum of which is far away from the laser wavelength. Due to photoselection, diffraction by an amplitude grating depends on the polarization of the probing beam while phase grating diffraction is insensitive to this. Perpendicular polarization of the two exciting pulses prevents the buildup of a phase grating and results in light diffracted by the amplitude grating that is proportional to the transient dichroism signal as known from the common absorption relaxation.     

An Iteratively-Designed Binary Phase Grating for Flattop Beam Generation

A binary phase grating capable of shaping an incident Gaussian beam to a flattop beam in a Fourier domain is designed iteratively. It is essential in grating design to consider the phases of diffracted waves by the grating, in addition to their amplitude uniformity and diffraction efficiency. The optimized grating phase produces the in-phase diffracted waves that interfere constructively to form a uniform amplitude and phase profile. The dependence of the shaped profile on the illuminating amplitude distribution, the grating misalignment, and the lens focusing error is investigated by computer simulation and optical experiment.     

Phase coherent photorefractivity in ZnSe single quantum wells

We observe an efficient phase coherent photorefractive effect in ZnSe single quantum wells for ultrashort light pulses resonant to the excitonic transition. The effect is attributed to the formation of an electron grating in the quantum well induced by the interference of coherent excitons that preserve phase and polarization of the incident light fields. All characteristic features of the diffracted signal are explained and reproduced by numerical calculations that are based on the optical Bloch equations for a three-level system.     

Improved algorithm for image encryption based on stochastic geometric moiré and its application

A technique based on optical operations on moiré patterns for image encryption and decryption is developed. In this method, an image is encrypted by a stochastic geometric moiré pattern deformed according to the image reflectance map. The decryption is performed using pixel correlation algorithm in the encrypted image and the stochastic geometrical moiré pattern. The proposed technique has a number of advantages over existing encryption techniques based on moiré gratings. No original moiré grating can be reconstructed only from the encrypted image. Stochastic moiré grating can be deformed in any direction what is an important factor of encryption security. Finally, the quality of the decrypted image is much better compared to decryption methods based on the superposition of the regular and deformed moiré gratings. The proposed technique has a great potential, because the process is performed using computational algorithms based on optical operations and optical components are avoided.     

基于相移的彩色结构光编码三维扫描技术

在物体三维轮廓扫描中,被动式双目立体视觉方法对表面特征不明显的物体难以获取足够的三维信息,针对这一问题,基于双目立体视觉原理,结合主动视觉中结构光投射方法,提出了基于相移的彩色结构光编码方法。该方法将四种颜色按照全排列的相关性质编码产生彩色光栅投射在被测物体表面,依据光栅相位移动增大光栅密度,结合极线约束实现立体匹配,最终获取物体三维数据。结果表明使用该三维扫描技术得到的三维曲面符合原物特征,特别适用于物体三维轮廓的致密测量。     

用傅里叶变换法测试平面衍射光栅的分辨特性

本文提出了测试平面衍射光栅的分辨特性的新方法,用干涉法测量光栅衍射的波阵面的相位,得出衍射波阵面的三维波面图,并用所取得的相位数据作傅里叶变换求得其在谱面上的光谱衍射斑——光谱线像的强度分布,并可据此确定半宽度值和分辨极限.文中叙述了这一新方法的优点、基本原理和实验方法,并给出应用这方法测量一批光栅所得结果中的两个例子,结果表明,与通常所用直接扫描光谱线法所测结果相符合.     

Orientation-enhanced nonlinear optical properties and phase-conjugate reflective system of a novel Azobenzene doped polymer film

This paper reports that the nonlinear refractive index of a novel organic optical storage film doped azo-diphenylamine polymer is measured by using the $Z$-scan technique. The nonlinear refractive index up to $3.7\times 10 ^{ - 6 }$~cm$^{2}$/W induced by thermo-optical effect is obtained. It indicates that the sample has excellent optical nonlinear properties. The physical mechanism of the great nonlinear optical effect is analysed and the optical conjugate characteristic is also discussed with degenerate four-wave-mixing. The phase conjugate wave diffracted from the formative refractive index grating in the sample is acquired and its equivalent reflectivity reaches about 22{\%}. On this basis, the reflective wave phase-conjugated mirror system was designed, and the image aberration experienced in propagation in the storage experiment is corrected by using the system.     

Moiré displacement measurement technique for a linear encoder

The light intensity diffracted from superimposed dual transmission gratings is sensitive to their relative lateral displacement but is also affected by changes in the air gap between them. Averaging the diffracted light intensities obtained in the gap range of a Fourier image distance, the resultant intensity was almost independent of the gap between the two gratings and had a period of half the pitch of the grating for the lateral displacement. This method can be used for a linear encoder in precision machining.     

利用光电检测技术分析光栅衍射

本文利用光电检测技术对光盘光栅的衍射特性进行研究.实现了对分光范围、衍射光强分布、衍射叠级、自由光谱范围、衍射角与衍射光波长的线性度、角分辨率和光栅常数等光栅参数的观测和计算.该实验结果与衍射理论结果一致.该方法在一定程度上弥补传统光栅实验的不足,有利于增进本科生对大学光学中衍射光栅的认识.     

Self-diffraction and Z-scan studies in organic dye doped thin films

Self-diffraction in Acid Red 87 (eosin Y) dye doped thin films is studied using argon ion laser (514.5 nm). Growth of self-diffraction grating is monitored by measuring intensities of various diffraction orders. This study has resulted in the observation of phase variation between the contributing beams in any diffracted order. This change of phase is measured at various stages of grating formation. Due to self-phase modulation, circular concentric rings pattern is obtained in the far field. The observed fluctuation in this pattern may be due to the phase variation between the contributing beams in any diffracted order. Z-scan technique is used to study the optical non-linearity of the sample.