Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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On-chip electro-optic tuning of a lithium niobate microresonator with integrated in-plane microelectrodes
No full textNational Basic Research Program of China (Program 973) [2014CB921300]; Natural National Science Foundation of China (NSFC) [61275205, 61590934, 61505231, 61405220]; Fundamental Research Funds for the Central Universities; Open Fund of the State Key Laboratory on Integrated Optoelectronics [IOSKL2015KF34]We demonstrate electro-optic tuning of an on-chip lithium niobate microresonator with integrated in-plane microelectrodes. First, the metallic microelectrodes were fabricated on the substrate using a femtosecond laser. Then high-Q lithium niobate microresonator located between the microelectrodes was further fabricated by femtosecond laser direct writing accompanied by focused ion beam milling. Thanks to the efficient design, a high electro-optical tuning coefficient of 3.41 pm/V has been obtained. (C) 2017 Optical Society of Americ
Range extension in laser-induced breakdown spectroscopy using femtosecond-nanosecond dual-beam laser system
No full textNational Basic Research Program of China [2014CB921300]; National Natural Science Foundation of China [11674340, 61575211, 11404357, 11604351]; Strategic Priority Research Program of the Chinese Academy of Sciences [XDB16030300]; Shanghai 'Yang Fan' program [14YF1406100]We extend the detection range of laser-induced breakdown spectroscopy by combining high-intensity femtosecond laser pulses with high-energy nanosecond - CO2 laser pulses. The femtosecond laser pulses ionize the molecules and generate filament in air. The free electrons generated in the self-confined plasma channel by the femtosecond laser serve as the seed electrons which cause efficient avalanche ionization in the nanosecond - CO2 laser field. We show that the detection distance has been extended by three times with the assistance of femtosecond laser filamentation
The controllable electron-heating by external magnetic fields at relativistic laser-solid interactions in the presence of large scale pre-plasmas
No full textNational Natural Science Foundation of China [11605269, 11674341, 11675245]; National Basic Research Program of China [2013CBA01504]; National Key Research and Development Program of China [2016YFA0401101]The two-stage electron acceleration/ heating model (Wu et al 2017 Nucl. Fusion 57 016007 and Wu et al 2016 Phys. Plasmas 23 123116) is extended to the study of laser magnetized-plasmas interactions at relativistic intensities and in the presence of large-scale preformed plasmas. It is shown that the electron-heating efficiency is a controllable value by the external magnetic fields. Detailed studies indicate that for a right-hand circularly polarized laser, the electron heating efficiency depends on both strength and directions of external magnetic fields. The electronheating is dramatically enhanced when the external magnetic field is of B equivalent to omega(c) /omega(0) > 1. When magnetic field is of negative direction, i.e. B < 0, it trends to suppress the electron heating. The underlining physics-the dependences of electron-heating on both the strength and directions of the external magnetic fields-is uncovered. With -infinity < B < 1, the electron-heating is explained by the synergetic effects by longitudinal charge separation electric field and the reflected 'envelop-modulated' CP laser. It is indicated that the 'modulation depth' of reflected CP laser is significantly determined by the external magnetic fields, which will in turn influence the efficiency of the electron-heating. While with B > 1, a laser front sharpening mechanism is identified at relativistic laser magnetized-plasmas interactions, which is responsible for the dramatical enhancement of electron-heating
The phosphorescence and excitation-wavelength dependent fluorescence kinetics of large-scale graphene oxide nanosheets
No full textNational Science Foundation of China [61108077, 61178085, 61008003, 61275147]; Key Project of Science and Technology of Shandong Province of China [2010GGX10127]; Shandong Province Natural Science Foundation of China [ZR2012AL11, ZR2013EML006]In this study, phosphorescence emission and a strong excitation-wavelength dependent fluorescence has been found in large-scale graphene oxide (GO) nanosheets. GO was covalently functionalized with triphenylamine (GO-CONH-TPA) in order to enhance the GO fluorescence quantum yield to 18%. The intersystem crossing (ISC) dynamics were studied using a femtosecond transient absorption technique, which appeared in the same timescale as the fluorescence dynamics of GO-CONH-TPA in both a polar solvent and solid film. Therefore, both, the solvation (several hundreds of picoseconds) and the intersystem crossing (ISC) gave rise to the strong excitation-wavelength dependent fluorescence. Moreover, the phosphorescence emission of the GO-CONH-TPA film at room temperature has been described for the first time in this report, and the lifetime of phosphorescence was found to be 6.95 ms. The fluorescence kinetics of GO-CONH-TPA were attributed to the aromatic hydrocarbon-carboxylic domain structure of GO
Research on a grating interferometer with high optical subdivision based on quasi-Littrow configuration
No full textA grating interferometer is presented based on the quasi-Littrow configuration. We mainly use a plane mirror to make the measuring light reflect and diffract between the mirror and grating scale for several times. According to the grating Doppler shift, the more times that measuring light diffracted, the higher optical subdivision can be obtained. As an example, a grating interferometer with an optical subdivision factor of 1/12 is designed. This work provides a technique to increase the resolution of the grating interferometer, which should be interesting for high precision measurement
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
Diode laser array by spectral beam combing with a transmission grating
No full textThe 38.5 W spectral combined beam of a 19-element 940 nm diode laser bar has been demonstrated in the spectral beam combining experiment by using a Beam Transformation System (BTS). The outputs had a diffraction-limited beam quality in the fast axis and M-2=10.5 in the slow axis. Spectral beam combining was achieved by using an external cavity including a transmission diffraction grating
Depth-dependent dispersion compensation for full-depth OCT image
No full textInnovation Action Plan of Science and Technology Commission of Shanghai Municipality [15441905600]; Open Fund of Key Laboratory of Optoelectronic Information Processing of University in Guangxi [KFJJ2016-04]; National Natural Science Foundation of China [61405210]A depth-dependent dispersion compensation algorithm for enhancing the image quality of the Fourier-domain optical coherence tomography (OCT) is presented. The dispersion related with depth in the sample is considered. Using the iterative method, an analytical formula for compensating the depth-dependent dispersion in the sample is obtained. We apply depth-dependent dispersion compensation algorithm to process the phantom images and in vivo images. Using sharpness metric based on variation coefficient to compare the results processed with different dispersion compensation algorithms, we find that the depth-dependent dispersion compensation algorithm can improve image quality at full depth. (C) 2017 Optical Society of Americ
Simple phase shifting lateral shearing interferometer based on a thick birefringent plate
No full textNational Science and Technology Major Project of China [2011ZX02402]; International Science and Technology Center (ISTC) Cooperation Programs of China [2011DFR10010, 2012DFG51590]A simple phase shifting lateral shearing interferometer based on a thick birefringent plate is proposed. The interferometer is composed of a thick birefringent plate and a polarizer. The thick birefringent plate works as the shear generator as well as the phase shifter. The optical path difference and shearing amount between the two sub-beams emerging from the thick birefringent plate change depending on the incident angle. For incident angles in a certain range, the shearing amount stays almost constant while the optical path difference varies linearly. Thus phase shifting can be obtained by rotating the thick birefringent plate. It is a very simple structure for the testing of a small beam, and equidistant phase shifting can be obtained by equal incident angle variation. The validity of the interferometer is verified by both simulation and experiment
High transparency Cr,Nd:LuAG ceramics prepared with MgO additive
No full textNational Natural Science Foundation of China [61378069, 61405221, 61308021]; Youth Innovation Promotion Association of the CASCr (0.2 at.%) and Nd (0.8 at.%) co-doped Lu3Al5O12 ceramics were fabricated with MgO as the sintering additive. The addition of a small amount of MgO can affect the grain boundary mobility and influence the number and location of micropores in ceramics during the sintering process. The results show that when the MgO content is 0.02 wt.%, high-transparency Cr,Nd:LuAG ceramics can be obtained by vacuum sintering at 1670 degrees C for 5 h followed by hot isostatic pressing (HIP) post-sintering at 1750 degrees C in an argon atmosphere (P = 200 MPa) for 5 h. The optimum in-line transmittance of the HIPed Cr,Nd:LuAG ceramics (3 mm thick) is 83.5% at a wavelength of 840 nm and 84.0% at 710 nm. (C) 2017 Published by Elsevier Ltd