Relevance of continuously self-imaging gratings for noise robust imagery

We have designed miniaturized, simple, and robust cameras composed of a single diffractive optical element (DOE) that generates a continuously self-imaging (CSI) beam. Two different DOEs are explored: the J₀ Bessel transmittance, characterized by a continuous optical transfer function (OTF) and the CSI grating (CSIG), characterized by a sparse OTF. In this Letter, we will analyze the properties of both DOEs in terms of radiometric performances. We will demonstrate that the noise robustness is enhanced for a CSIG, thanks to the sparsity of its OTF. A camera using this DOE has been made and experimental images are presented to illustrate the noise robustness.     

Nonuniform self-imaging of achromatic Talbot lithography

Achromatic Talbot lithography(ATL) with high resolution has been demonstrated to be an excellent technique for large area periodic nano-fabrication. In this work, the uniformity of pattern distribution in ATL was studied in detail. Two ATL transmission masks with ~50% duty cycle in a square lattice were illuminated by a spatial coherent broadband extreme ultraviolet beam with a relative bandwidth of 2.38%. Nonuniform dot size distribution was observed by experiments and finite-difference time-domain simulations. The sum of the two kinds of diffraction patterns, with different lattice directions(45° rotated) and different intensity distributions,results in the final nonuniform pattern distribution.     

Quadriwave lateral shearing interferometry in an achromatic and continuously self-imaging regime for future x-ray phase imaging

We present in this Letter a type of quadriwave lateral shearing interferometer for x-ray phase imaging. This device is based on a phase chessboard, and we take advantage of the large spectrum of the source to produce interferograms with a propagation-invariant contrast. Such a grating has been created for hard x-ray interferometry and experimentally tested on a synchrotron beamline at Soleil.     

Talbot experiment re-examined: demonstration of an achromatic and continuous self-imaging regime

In the original Talbot experiment, a grating made of thin slits was illuminated in polychromatic light. Reconstituting this simple experiment, we have observed that at a certain distance from the grating, achromatic lines are formed whose transverse-resolution remains unaffected over a wide propagation-distance range. To our knowledge, this phenomenon has never been reported before. A theoretical explanation of this achromatic and continuous self-imaging regime is given and experimental results are reported.     

Self-collimation and self-imaging effects in modulated waveguide arrays

Self-collimation and self-imaging are comparatively investigated for discretized light in engineered modulated arrays of optical waveguides. It is shown that self-imaging is a rather extraordinary effect related to a fortuitous band collapse and it is thus rather distinct from self-collimation.     

柱面镜对光栅自成像的旋转

本文运用傅里叶频谱分析方法，研究了柱面镜对光栅自成象的调制作用，发现光栅的自成象不仅周期和位置发生变化，而且产生了方向的旋转。文章分析了其旋转规律。     

Generation of the determined vectorial vortex beams by use of an achromatic axially symmetric waveplate

Optical Review - We review the generation of the determined vectorial vortex beams in the terahertz (THz) beams at frequencies of 0.16 and 0.36 THz, and intense middle infrared pulsed beam at...     

Generation of spirally polarized propagation-invariant beam using fiber microaxicon

We present here a fiber microaxicon (MA)based method to generate spirally polarized propagation-invariant optical beam. MA chemically etched in the tip of a two-mode fiber efficiently converts the generic cylindrically polarized vortex fiber mode into a spirally polarized propagation-invariant (Bessel-type) beam via radial dependence of polarization rotation angle. The combined roles of helico-conical phase and nonparaxial propagation in the generation and characteristics of the output beam from the fiber MA are discussed.     

Producing and testing binary amplitude gratings using a self-imaging and double-exposure technique

The influence of illuminating beam aberrations and master grating deviations on the performance of the technique of producing arbitrary opening ratio binary gratings using the self-imaging and double-exposure technique is studied analytically and experimentally. It is shown that due to the shear effect encountered in the direction perpendicular to the grating lines and due to the lateral displacement implemented between the two exposures the technique is sensitive to the first derivative of grating in-plane displacements and to the second derivative of the beam and grating out-of-plane errors.     

Generation of laser-polarized xenon using fiber-coupled laser-diode arrays narrowed with integrated volume holographic gratings

Volume holographic gratings (VHGs) can be exploited to narrow the spectral output of high-power laser-diode arrays (LDAs) by nearly an order of magnitude, permitting more efficient generation of laser-polarized noble gases for various applications. A 3-fold improvement in ¹²⁹Xe nuclear spin polarization, P_Xe, (compared to a conventional LDA) was achieved with the VHG-LDA’s center wavelength tuned to a wing of the Rb D₁ line. Additionally, an anomalous dependence of P_Xe on the xenon density within the OP cell is reported—including high P_Xe values (>10%) at high xenon partial pressures (1000 torr).     

The influence of the polarization effect in Talbot self-imaging of high-density gratings

The Talbot self-imaging of high-density gratings with different period at half Talbot distance for different polarization is analyzed with the finite-difference time-domain (FDTD) method. The numerical results indicate that the Talbot self-imaging of high-density gratings is obviously different for different polarization when the period d of the grating between 2λ and 3λ, which is verified through experimental results with the scanning near-field optical microscopy (SNOM) technique. Furthermore, the Fourier spectrum (far field) generated by the gratings is also given with the rigorous coupled-wave method, which is in agreement with the near field.     

Wavelength stabilization and spectrum narrowing of high-power multimode laser diodes and arrays by use of volume Bragg gratings

Spectral line narrowing (by a factor of 8) and stabilization of the emission wavelength (by a factor of 30) of multimode high-power laser diodes and arrays is demonstrated by use of volume Bragg gratings fabricated in high-stability inorganic photorefractive glasses. Applications include stabilization of pump laser diodes and arrays for solid-state lasers and metal-vapor lasers, spin hyperpolarization of noble gases used in medical imaging, and others.     

Generation of multiple femtosecond pulses by step gratings

A simple method for generating multiple isolated femtosecond pulses by step gratings is presented, and a criterion for judging whether or not an incident pulse is just split into multiple independent pulses is obtained. The dependences of multiple pulses on the structural parameters of the step gratings are explored. The results show that an incident pulse can split into multiple isolated similar diffraction pulses for enough step height, and the pulse repetition interval increases with the increasing of the step height.     

Generation of flat-top pulse by means of step gratings

A simple method for generating flat-top pulse by means of step gratings is presented. Flat-top pulse specifications depend on the structural parameters of the step gratings. The results show that a short Gaussian-shaped femtosecond laser pulse can be shaped to be a long flat-top pulse by ensuring sufficient step level number and proper step height.     

Generation of dual-wavelength pulses by frequency doubling with quasi-phase-matching gratings

We demonstrate generation of two synchronized picosecond pulses at different wavelengths near 778 nm by frequency doubling of a femtosecond pulse. We use nonlinear frequency filtering with quasi-phase-matching gratings, which allow us to obtain second-harmonic spectral intensities that are higher than the spectral intensities of the pump.     

Generation of double pulses in-line by using reflective Dammann gratings

Doubled femtosecond laser pulses in-line are needed in the collinear pump-probe technique, collinear second harmonic generation frequency-resolved optical gating (SHG FROG) and the spectral phase interferometry for direct electric-field reconstruction (SPIDER), etc. Normally, it is generated by using a Michelson's structure. In this paper, we proposed a novel structure with two-layered reflective Dammann gratings and the reflective mirrors to generate doubled femtosecond laser pulses in line without transmission optical elements. Angular dispersion and spectral spatial walk-off are both compensated. In addition, this structure can also compress the positive chirped pulse, which cannot be realized with a Michelson's structure. By adopting triangular grating and blazed gratings, the efficiency of the system would in principle be increased as the Michelson's scheme. Experiments demonstrated that this method should be an alternative approach for generation of the double compressed pulses of femtosecond laser for practical applications.     

Generation of continuously tunable terahertz-wave radiation exploited by stimulated polariton scattering

The characteristics of a coherent tunable terahertz-wave source have been experimentally investigated in detail. By using a difference frequency generation as a result of stimulated Raman scattering by polaritons in MgO:LiNbO₃ crystals, the signal wave was continuously tuned in the range of 1.069–1.075 μm, which corresponded to a terahertz-wave in the wide range from 227 to 104 μm (1.3 to 2.9 THz). The highest output signal pulse energy at the pumping level of 44 mJ/pulse was 1.8 mJ/pulse with 20 mW seeder injection, and the terahertz peak power was 139 mW at the wavelength of 143 μm. This source has the advantages of simple alignment, simplicity of tuning, and compactness that makes the device more attractive.     

Temperature and flow-velocity measurements by use of laser-induced electrostrictive gratings

Light scattering from laser-induced electrostrictive gratings has been used for simultaneous, instantaneous, nonintrusive, and remote measurements of temperature and velocity in a submerged air jet. We accomplished phase-sensitive detection of scattered light by superimposing two signal beams whose frequencies were Doppler shifted by the movement of the grating. Temperatures in the range 295-600 K and flow velocities in the range 10-100 m/s were measured.     

用错位相位光栅产生的可调光学双阱

提出了用相位型错位光栅产生光学双阱的新方案.用平面光波(或TEM₀₀模式高斯光波)照射、正透镜聚焦,在透镜焦平面上产生的适用于冷原子或冷分子囚禁的多对可调光学双阱.计算和推导了双阱的光强分布、强度梯度以及光阱的几何参数与光学系统参数间的解析关系,研究了双阱到单阱三种不同的演化过程.同时还计算了光学双阱囚禁冷原子的光学偶极势和光子散射速率.研究发现,该方案不仅简单可行、操作方便,而且在原子物理、原子光学、分子光学和量子光学领域中有着广阔的应用前景. 关键词： 原子光学 相位光栅 光学双阱 冷原子囚禁     

Generation of surface soliton arrays

We discover that, at the edge of an optical lattice imprinted in a saturable nonlinear medium, one-dimensional surface solitons exist only within a band of light intensities and that they cease to exist when the lattice depth exceeds an upper threshold. We also reveal the generation of arrays of two-dimensional surface solitons mediated by the transverse modulational instability of one-dimensional solitons, a process that is found to exhibit specific features associated to properties of the optical lattice.