Shearograms of an optical phase singularity

Shearograms are known to represent phase gradients but when vortices are present in the optical field, these do not represent true phase gradients. Phase gradients of an optical phase singularity are presented. A lateral shear interferometer is used for obtaining shearograms of optical fields with vortices. A diffractive phase element is used to generate vortices. It is shown that shearograms can be used in the detection of optical vortices. Shearogram of speckle field is also presented.     

Displacements and deformations of a vortex light beam produced by the diffraction grating with embedded phase singularity

Properties of vortex light beams produced by a diffraction grating with groove bifurcation (“fork” structure) are studied in the case of small diffraction angles. Analytical expressions are derived for the amplitude distribution of a diffracted beam generated from an incident Gaussian beam with arbitrary radius and wavefront curvature, transversely shifted and inclined with respect to the nominal axis (normal to the grating crossing it at the bifurcation point). In such situations, the output beam becomes asymmetric; the optical vortex core and the intensity maximum displace orthogonally to the incident beam shift direction. The nearest vicinity of the vortex core preserves its circular symmetry and the optical vortex remains locally isotropic. The effects of misalignment depend on the incident beam characteristics, the diffraction order and the propagation distance behind the grating. Experimental measurements support the results of calculations.     

Single-slit diffraction of the arbitrary vector beams

We present the single-slit diffraction of the arbitrary vector fields with different parameters m, n, and φ0theoretically and experimentally. The single slit covers the polarization singularity in the center and therefore the influence of the polarization singularity on the diffraction fringes is analyzed. The experimental results which agree well with the simulation results show that the total intensity of the diffraction field is related only to the topological charge m, but the polarization distribution of the diffraction field is related to all the parameters m, n, and φ0. Therefore, the diffraction patterns allow to determine all the parameters of the arbitrary vector fields.     

Higher diffraction order photorefractive optical beam splitter

A higher diffraction order photorefractive (PR) optical beam splitter has been realized based on a PR higher diffraction order grating. In the experiments, the beam splitter was produced by two-wave coupling at a small incident angle in Fe:LiNbO₃ using the output from a He–Ne laser at 632.8 nm. An incident signal beam containing three different wavelengths (632.8, 532.0 and 488.0 nm) was split into multi-output beams by the beam splitter. The size of higher diffraction order is given and the influence of crystal thickness is discussed. Results show that the higher diffraction order PR optical beam splitter provides a practical method to split a multi-wavelength signal beam.     

Laser beam characteristic for laser resonators with diffraction optical elements

The matrix eigenvalue method is used to analyze a laser resonator composed of diffraction optical elements. The results show that this type of resonator can separate fundamental mode and high order modes effectively. The output beams can be designed for different requests.     

Generation of optical vortex light beams by volume holograms with embedded phase singularity

Special features of the optical-vortex (OV) beams generated by thick holographic elements (HE) with embedded phase singularity are considered theoretically. The volume HE structure is based on the 3D pattern of interference between an OV beam and a standard reference wave with regular wavefront. The incident beam diffraction is described within the framework of a linear single-scattering model in which the volume HE is represented by a set of parallel thin layers with the “fork” holographic structure. An explicit integral expression is derived for the complex amplitude distribution of the diffracted paraxial beam with OV. The numerical analysis demonstrates that the HE thickness may essentially influence not only selectivity and efficiency of the OV beam generation but also the amplitude and phase profile of the diffracted beam as well as regularities of its propagation. We have studied the generated OV morphology and laws of its evolution; in particular, the possibility of obtaining a circularly symmetric OV beam regardless of the diffraction angle is revealed.     

单级衍射量子点阵光栅的聚焦离子束直写法制备及光学性能检测

采用聚焦离子束直写技术,成功制作了面积为200μm×200μm,线密度500 mm 1,圆孔直径800 nm,金吸收体厚度为500 nm的单级衍射量子点阵光栅.研究了该光栅在波长442 nm激光下不同传输距离的衍射特性以及相对衍射效率.实验结果表明,量子点阵光栅不存在高级衍射,只保留了±1级和0级衍射,具有良好的单级衍射特性.1级衍射与0级衍射间距随传输距离的增大而增大,实测值与理论计算值相符.     

Effects of misalignments in the optical vortex transformation performed by holograms with embedded phase singularity

Spatial characteristics of diffracted beams produced by a “fork” hologram from an incident circular Laguerre-Gaussian beam whose axis differs from the hologram optical axis are studied theoretically. General analytical representations for the complex amplitude distribution of a diffracted beam are derived in terms of superposition of Kummer beams or hypergeometric-Gaussian beams. The diffracted beam structure is determined by combination of the “proper” topological charge m of the incident vortex beam and the topological charge l of the singularity “imparted” by the hologram. Evolution of the diffracted beam structure is studied in detail for several combinations of m and l and for various incident beam displacements with respect to the optical axis of the hologram. Variations of the intensity and phase distribution due to the incident beam misalignment are investigated and possible applications for the purposeful optical vortex beam generation and optical measurements are discussed.     

Application of optical diffraction method in designing phase plates

Continuous phase plate(CPP),which has a function of beam shaping in laser systems,is one kind of important diffractive optics.Based on the Fourier transform of the Gerchberg-Saxton(G-S) algorithm for designing CPP,we proposed an optical diffraction method according to the real system conditions.A thin lens can complete the Fourier transform of the input signal and the inverse propagation of light can be implemented in a program.Using both of the two functions can realize the iteration process to calculate the near-field distribution of light and the far-field repeatedly,which is similar to the G-S algorithm.The results show that using the optical diffraction method can design a CPP for a complicated laser system,and make the CPP have abilities of beam shaping and phase compensation for the phase aberration of the system.The method can improve the adaptation of the phase plate in systems with phase aberrations.     

Single-slit split-ring resonators at optical frequencies: limits of size scaling

We present magnetic metamaterials composed of 35 nm minimum feature-size gold split-ring resonators with a fundamental magnetic resonance at a wavelength of 900 nm. Corresponding calculations reveal excellent agreement with the experiments and show that the limits of size scaling have been reached.     

Design of refractive/diffractive hybrid optical elements for beam shaping with large diffraction pattern

Diffractive optics is an important technique for beam shaping with high light efficiency and strong diffraction pattern flexibility. Since the diffraction angle is limited by the unit size of the diffractive optical element(DOE),the size of the required diffraction pattern is always rather small. In this Letter, refractive/diffractive hybrid optical elements(RDHOEs) consisting of a DOE and a lens are used to realize beam shaping for a large diffraction pattern. The lens, as the component of the RDHOEs, can not only be concave but also convex,and the double sampling Fresnel diffraction algorithm is developed for the design of these two types of RDHOEs.The simulation and experimental results provide solid evidence to demonstrate the proposed method with the pure phase spatial light modulator.     

菲涅耳区衍射光学束匀滑器件的设计

 采用精细化设计方法，进行了菲涅耳区衍射光学束匀滑器件的设计，利用爬山-模拟退火混合优化算法，获得了真实的束匀滑分布，不仅控制了算法采样点上的光强分布，还控制了其他非采样点上的光强分布。优化得到的束匀滑器件的位相深度小于π，易于后续加工。     

菲涅耳区衍射光学束匀滑器件的设计

采用精细化设计方法,进行了菲涅耳区衍射光学束匀滑器件的设计,利用爬山-模拟退火混合优化算法,获得了真实的束匀滑分布,不仅控制了算法采样点上的光强分布,还控制了其他非采样点上的光强分布。优化得到的束匀滑器件的位相深度小于π,易于后续加工。     

相位片角向衍射产生拉盖尔-高斯光束的实验研究

设计了一种角向分布的相位片,利用离子束刻蚀技术加工成0和π二级的相位片.利用角向衍射理论对相位片的衍射场分析表明,衍射场为拓扑指数相反的两束拉盖尔-高斯光束的叠加场.用直径为4 mm的近平行光照射相位片,获得径向指数为零,拓扑荷相反的叠加拉盖尔-高斯光场.采用较大孔径的光束入射时,仍为拓扑荷相反的两束光的叠加,但径向指数会发生变化. 关键词： 信息光学 拉盖尔-高斯光束 相位片 离子束刻蚀     

Binary diffraction optical element focusing a Gaussian beam to a longitudinal segment

A phase binary ring diffraction optical element (DOE) with a radius of 3.5 mm and microrelief height of 1.06 μm was calculated and fabricated. The element focuses a Gaussian beam of a He-Ne laser with radius of 1.5 mm to a 1.7 mm long axial segment, which ranges from 51.9 to 53.6 mm, with a focal spot diameter of about 30 μm.     

衍射光学元件设计参数对束匀滑衍射效率的影响

经过理论推导,分析了320 mm口径衍射光学元件在束匀滑实验中光强分布出现高级次衍射斑和元件实际衍射效率变低的原因,模拟计算得到了接近实验的光强分布。模拟分析发现:通过调整设计参数,如适当增加抽样点数,使设计时焦斑主瓣占输出计算窗口的比例减小至0.2以下,可以大大降低由于高级次衍射斑造成的衍射效率损失,控制在2%以内,使台阶分布式相位片实际衍射效率得到提高,在对口径为70及320 mm的台阶分布式相位片样品测试中得到了验证。     

衍射光学元件设计参数对束匀滑衍射效率的影响

经过理论推导,分析了320 mm口径衍射光学元件在束匀滑实验中光强分布出现高级次衍射斑和元件实际衍射效率变低的原因,模拟计算得到了接近实验的光强分布。模拟分析发现:通过调整设计参数,如适当增加抽样点数,使设计时焦斑主瓣占输出计算窗口的比例减小至0.2以下,可以大大降低由于高级次衍射斑造成的衍射效率损失,控制在2%以内,使台阶分布式相位片实际衍射效率得到提高,在对口径为70及320 mm的台阶分布式相位片样品测试中得到了验证。