Jianyong Ma

Design and fabrication of a polarization-independent wideband transmission fused-silica grating

A fused-silica polarization-independent wideband transmission grating used in the -1st order (Littrow mounting) for chirped-pulse-amplification, high-power lasers is designed and manufactured. An approximate grating profile can be obtained by using the simplified modal method with consideration for the corresponding accumulated phase difference of two excited propagating grating modes. An exact grating profile is optimized by using the rigorous coupled-wave analysis. With the optimized profile parameters, the gratings can theoretically exhibit diffraction efficiencies of greater than 97% at a wavelength of 800 nm for both of TE- and TM-polarized waves. Diffraction efficiencies of greater than 92% can be obtained in a 100 nm bandwidth (from 750 to 850 nm) for both TE- and TM-polarized waves. Holographic recording technology and inductively coupled plasma etching are used to manufacture the fused-silica grating. Experimental results agree well with the theoretical values.

Three-dimensional Dammann array

We demonstrate a scheme that can produce a three-dimensional (3D) focus spot array in a 3D lattice structure, called a 3D Dammann array, in focal region of an objective. This 3D Dammann array is generated by using two separate micro-optical elements, a Dammann zone plate (DZP) that produces a series of coaxial focus spots and a conventional two-dimensional (2D) Dammann grating (DG). A simple, fast, and clear method is presented to design this binary pure-phase (0,π) DZP in vectorial Debye theory regime. Based on this kind of DZP, one can always obtain a 3D Dammann array both for low and high numerical aperture (NA) focusing objectives. For experimental demonstration, an arrangement combining a DZP, a 2D DG, and a pair of opposing lenses is proposed to generate a 5×5×5 Dammann array in focal region of an objective with NA=0.127 and another 6×6×7 Dammann array for an objective of NA=0.66. It is shown that this arrangement makes it possible to achieve 3D Dammann arrays with micrometer-sized focus spots and focus spacings of tens of micrometers for various practical applications, such as 3D parallel micro- and nanomachining, 3D simultaneous optical manipulation, 3D optical data storage, and multifocal fluorescence microscope, etc.

Design and analysis of broadband high-efficiency pulse compression gratings

We report on two effective methods, multiparameter optimization and local optimization combined with the diffraction bandwidth merit function, to design a broadband pulse compression grating (PCG), and we present broadband, high-efficiency PCGs based on both the multilayer dielectric grating (MDG) and metal-multilayer dielectric grating (MMDG) models. For MDG, the average diffraction efficiency is higher than 97.5% for TE polarization light over the 100 nm bandwidth centered at 800 nm. Moreover, a novel multilayer structure, which comprises higher index material in the high-reflectivity mirror and relatively lower index material on top, is first proposed to yield higher average efficiency, broader bandwidth, and excellent fabrication tolerance. For MMDG, it exhibits an ultrabroadband top-hat diffraction spectrum with average efficiency exceeding 97% over the 200 nm wavelength wide centered at 1053 nm. In addition, the MMDG structure, which has the best tolerance for grating fabrication, is determined by investigating characteristics of MMDGs with different thin-film structures.

Characteristics of high reflection mirror with an SiO2 top layer for multilayer dielectric grating

The high reflection (HR) mirror composed of dielectric stacks with excellent spectrum characteristics and high damage resistant ability is critical for fabricating multilayer dielectric (MLD) grating for pulse compressor. The selection of the SiO2 material as the top layer of the HR mirror for grating fabrication is beneficial for improving the laser-induced damage threshold of MLD grating as well as minimizing the standing-wave effect in the photoresist during the exposure process. Based on an (HLL)9H design comprising quarter-waves of HfO2 (H) and half-waves of SiO2 (L), we obtain an optimal design of the HR mirror for MLD grating, the SiO2 top layer of which is optimized with a merit function including both the diffraction efficiency of the MLD grating and the electric field enhancement in the grating. Dependence of the performance of the MLD grating on the fabrication error of the dielectric mirror is analysed in detail. The HR mirror is also fabricated by E-beam evaporation, which shows good spectral characteristics at the exposure wavelength of 413 nm and at the operation wavelength of 1053 nm and an average damage threshold of 10 J cm−2 for a 12 ns pulse.

Optimized stereo matching in binocular three-dimensional measurement system using structured light

In this paper, we develop an optimized stereo-matching method used in an active binocular three-dimensional measurement system. A traditional dense stereo-matching algorithm is time consuming due to a long search range and the high complexity of a similarity evaluation. We project a binary fringe pattern in combination with a series of N binary band limited patterns. In order to prune the search range, we execute an initial matching before exhaustive matching and evaluate a similarity measure using logical comparison instead of a complicated floating-point operation. Finally, an accurate point cloud can be obtained by triangulation methods and subpixel interpolation. The experiment results verify the computational efficiency and matching accuracy of the method.

Distorted Dammann grating

We introduce the Dammann phase-encoding method into original distorted gratings and propose a modified distorted grating, called a distorted Dammann grating (DDG), to realize multiplane imaging of several tens of layers within the object field onto a single image plane. This property implies that the DDG makes it possible to achieve simultaneously high axial resolving power and large axial imaging range without scanning. This DDG should be of high interest for its potential applications in real-time three-dimensional optical imaging and tracking. Multiplane imaging of 7×7 object layers onto a single camera plane is experimentally demonstrated using a 7×7 DDG for an objective of NA=0.127.

Electric field distribution in resonant reflection filters under normal incidence

Electric field distributions inside resonant reflection filters constructed using planar periodic waveguides are investigated in this paper. The electric fields may be intensified by resonance effects. Although the resonant reflection peaks can be quite narrow using weakly modulated planar periodic waveguides, the strong electric field enhancement limits their use in high-power laser systems. Strongly modulated waveguides may be used to reduce the electric field enhancement and a cover layer may be used to narrow the bandwidth at the same time. Desired results (i.e. almost no electric field enhancement together with narrow bandwidth) can be realized using this simple structure.

Laser-induced damage of TiO2∕SiO2 high reflector at 1064nm

A high laser-induced damage threshold (LIDT) TiO2/SiO2 high reflector (HR) at 1064 nm is deposited by e-beam evaporation. The HR is characterized by optical properties, surface, and cross section structure. LIDT is tested at 1064 nm with a 12 ns laser pulse in the one-on-one mode. Raman technique and scanning electron Microscope are used to analyze the laser-induced modification of HR. The possible damage mechanism is discussed. It is found that the LIDT of HR is influenced by the nanometer precursor in the surface, the intrinsic absorption of film material, the compactness of the cross section and surface structure, and the homogeneity of TiO2 layer. Three typical damage morphologies such as flat-bottom pit, delamination, and plasma scald determine well the nanometer defect initiation mechanism. The laser-induced crystallization consists well with the thermal damage nature of HR

Study of the surface plasma transmission properties of a Fabry?Perot resonator by numerical simulation

It is demonstrated with powerful evidence that the extraordinary transmission of a metallic grating is undoubtedly due to the excitation of standing surface plasma waves in the Fabry-Perot like resonator. This is the first time that the strong standing waves set up in the groove of a sub-wavelength double-layer grating (SWDG) for the surface plasma waves have been reported. Moreover, about 90% transmission is gained with an SWDG, more easily fabricated than ordinary metallic gratings, in the first peak of transmission spectrum.

Parallel laser writing system with scanning Dammann lithography

Scanning Dammann lithography (SDL) is proposed and implemented, which uses a Dammann grating to generate multiple beams with sharp step boundary for writing large-sized gratings efficiently. One of the most attractive advantages is that this technique can accelerate the writing speed, e.g. 1 × 32 Dammann grating can be 32 times faster than the single laser scanning system. More importantly, the uniformity of the multi-beams-written lines is much better than the single laser beam scanning system in consideration of the environmental effects such as air turbulence, thermal instability, etc. Using the SDL system, a three-port high-efficiency beam splitter at visible wavelengths is fabricated quickly, and the theoretical and experimental diffraction efficiencies are both higher than 90%. Therefore, SDL should be a useful tool for fabrication of large-sized gratings.