Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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Mode suppression in a slanted grating
No full textIn this paper, we propose a novel method of mode suppression in a slanted grating; this can reveal the physical diffraction mechanism in the grating region. Analytical expressions are derived to illustrate the diffraction process based on the simplified modal method. Owing to the odd mode suppression, only two even grating modes determine the even symmetry field distribution at the output plane. In addition, a slanted grating is designed to make the oblique light mainly couple into the normal emission; this is notably different from a rectangular grating, which can never be used to realize this goal. Numerical simulation results verify the validity of the simplified modal method. We hope that this theoretical work can lay a solid foundation for potential applications of slanted gratings
Temporal speckle method for measuring three-dimensional surface of large-sized rough glass
No full textTo provide accurate three-dimensional (3-D) data for production and processing, 3-D surface measurement is always an essential step to the production of glass. Profilometry and Interferometry are traditional measurement apparatus, referring to different procedures. Although more precise, Interferometry cannot be used in milling procedure, owing to the scattering property of rough glass. While as a widely used Profilometry, Coordinate Measuring Machine (CMM) employs a probe for measuring by contacting surface directly. It should be noted that such a time-consuming machine is not practical for measuring large-sized rough glass, so a novel designed method called temporal speckle is introduced to a non-contact binocular 3-D measurement system for measuring. Specifically, N band-limited binary patterns are sequentially projected to rough glass from a pattern generation device, such patterns have been proved to depress scattering properties of rough surface. The whole binocular 3-D measurement system can finish a single measurement in one second with a standard deviation less than 73.44um. This system performs fast and accurate 3-D surface measurement for large-sized rough glass block
Study of a grating interferometer with high optical subdivision technique
No full textDisplacement laser interferometers and grating interferometers are two main apparatus for the micron-nanometer displacement measurement over a long range. However, the laser interferometers, whose measuring scale is based on the wavelength, are very sensitive to the environment. On the contrast, the grating interferometers change the measuring scale from wavelength to grating period, which is much stable for the measurement results. But the resolution of grating interferometer is usually lower than that of laser interferometer. Therefore, further investigation is needed to improve the performance of grating interferometer. As we known, the optical subdivision is a main factor that affects the measurement resolution. In this paper, a grating interferometer with high optical subdivision is presented based on the Littrow configuration. We mainly use right angle prisms accompanied with plane mirrors to make the measuring lights diffracted by the grating scale for many times. An optical subdivision factor of 1/24 can be obtained by this technique. A main difficulty of this technique is that the grating scale should be with high diffraction efficiency. Fortunately, the measuring light is incident on the grating scale at the Littrow angle, the grating scale can be designed with very high efficiency easily in this condition. Compared with traditional grating interferometers, this kind of grating interferometer can greatly increase the measuring resolution and accuracy, which could be widely used in nanometer-scale fabrications and measurements
Design and Analysis of Highly Efficient Reflective 1x3 Splitting Grating with Triangular Structure
No full textA highly efficient reflective 1x3 splitting grating with triangular structure operating in 1.064 mu m wavelength under normal incidence for TE polarization is designed. The schematic of the grating has four layers. The first layer with SiO2 is triangular structure. Rigorous coupled wave analysis (RCWA) and Simulated Annealing (SA) algorithm are adopted to design and analyze the properties. The theoretical efficiency is nearly about 99%. The bigger error tolerance is also analyzed by rigorous coupled wave analysis. These reflective gratings as splitters should be useful optical elements in the field of high-power laser as well as other reflective applications
Phase problems in optical imaging
No full textNational Natural Science Foundation of China [61377005, 61327902]; Chinese Academy of Sciences [QYZDB-SSW-JSC002]Because the phase contains more information about the field compared to the amplitude, measurement of the phase is encountered in many branches of modern science and engineering. Direct measurement of the phase is difficult in the visible regime of the electromagnetic wave. One must employ computational techniques to calculate the phase from the captured intensity. In this paper, we provide a review of our recent work on iterative phase retrieval techniques and their applications in optical imaging
Programmable uniformity correction by using plug-in finger arrays in advanced lithography system
No full textInternational Science & Technology Cooperation Programs of China [2011DER10010, 2012DFG51590]; Science and Technology Commission of Shanghai Municipality [14YF1406300]; National Science and Technology Major Project of China [2011ZX02402]Illumination integrated non-uniformity (IINU) is one of the key factors to determine the resolution and Critical Dimension Uniformity (CDU) which are important performance parameters in advanced lithography system. To further reduce the IINU, uniformity correction technology has been adopted. In this paper, an approach of programmable uniformity correction with higher flexibility and better correction capability is proposed. The method is composed of variable attenuation correction element arrays which are inserted into the edge of an illumination field to shield the energy through programming. Based on the proposed method, a programmable uniformity correction unit is applied to an illumination optical system. The simulation results show that the value of the corrected IINU reaches less than 0.25%, which satisfies the requirements of IINU hi advanced lithography system, and the energy loss is less than 1.1%. It verifies the higher flexibility and better correction capability of the proposed method
200 J high efficiency Ti:sapphire chirped pulse amplifier pumped by temporal dual-pulse
No full textNational Natural Science Foundation of China [61521093, 61378030]We report on an experimental and theoretical study of a large-aperture Ti: Sapphire (Ti: S) amplifier pumped with a novel temporal dual-pulse scheme to suppress the parasitic lasing (PL) and transverse amplified spontaneous emission (TASE) for high-energy chirped-pulse amplification (CPA). The pump energy distribution was optimized and the time delay between each pump pulse was controlled precisely. Both the numerical and experimental results confirm that the temporal dual-pulse pump technique can effectively suppress PL and TASE. The maximum output energy of 202.8 J was obtained from the final 150-mm-diameter Ti: S booster amplifier with a pump energy of 320.0 J, corresponding to a conversion efficiency of 49.3%. The compressed pulse duration of 24.0 fs was measured with a throughput efficiency of 64%, leading to a peak power of 5.4 PW. This novel temporal dualpulse pump technique has potential applications in a 10 PW CPA laser system. (C) 2017 Optical Society of Americ
Collisionless Shock Acceleration of High-Flux Quasimonoenergetic Proton Beams Driven by Circularly Polarized Laser Pulses
No full textMinistry of Science and Technology of the People's Republic of China [2016YFA0401102]; National Natural Science Foundation of China [11705260]; Shanghai Natural Science Foundation [17ZR1434300]; Strategic Priority Research Program of the Chinese Academy of Sciences [XDB16]We present experimental studies on ion acceleration using an 800-nm circularly polarized laser pulse with a peak intensity of 6.9 x 10(19) W/cm(2) interacting with an overdense plasma that is produced by a laser prepulse ionizing an initially ultrathin plastic foil. The proton spectra exhibit spectral peaks at energies up to 9 MeV with energy spreads of 30% and fluxes as high as 3 x 10(12) protons/MeV/sr. Two-dimensional particle-in-cell simulations reveal that collisionless shocks are efficiently launched by circularly polarized lasers in exploded plasmas, resulting in the acceleration of quasimonoenergetic proton beams. Furthermore, this scheme predicts the generation of quasimonoenergetic proton beams with peak energies of approximately 150 MeV using current laser technology, representing a significant step toward applications such as proton therapy
Fabrication of "petal effect" surfaces by femtosecond laser-induced forward transfer
No full textNational Key Research and Development Program of China [2016YFB1102400]; National Natural Science Foundation of China [11374316, 61178024]Superhydrophobic adhesive glass surfaces with polystyrene has been obtained via femtosecond laser induced forward transfer (LIFT). Using this facile method, we obtained composite structures on the glass surface, achieving the transformation from hydrophilicity to superhydrophobicity with contact angle from 36.22 degrees on the glass surface to 159.19 degrees on the LIFT modified glass surface. Analogous to the "petal effect", the obtained superhydrophobic surface also shows high adhesion. Furthermore, the wettability of LIFT modified glass surface can be tuned by changing the interval width of laser scanning, which can be explained by the Cassie impregnating wetting model. (C) 2016 Elsevier B.V. All rights reserved
Femtosecond-laser-driven wire-guided helical undulator for intense terahertz radiation
No full textNational Natural Science Foundation of China [11425418, 11127901, 61521093, 11405244]; Shanghai Natural Science Funds [14ZR1444800]; Strategic Priority Research Program [XDB16]; State Key Laboratory Program of Chinese Ministry of Science and Technology; Key Laboratory for Laser Plasmas (Ministry of Education); Shanghai Jiao Tong University; National Basic Research Program of China [2014CB339802]The capability of synchrotron radiation to produce ultrabright emission has attracted considerable interest over the last half a century. To date, magnetic undulators with a period of several centimetres are commonly used for wiggling relativistic electrons in a modulated field. Here, we propose a novel compact undulator with a period down to the submillimetre level based on a spontaneous electric field that is driven by a femtosecond laser. Both the guided energetic electrons and the gyrotron-like undulator are spontaneously produced by irradiating a thin metallic wire with an intense laser pulse. An intense radial electric field instantaneously created on the wire can guide the electrons' helical motion along the wire and induce periodic THz emission. We have demonstrated that this scheme can produce intense THz sources with a conversion efficiency of 1% that are frequency-tunable by adjusting the diameter of the wire. Amplified emission of THz radiation by more than tenfold has been observed