Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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Tunable compensation of GVD-induced FM-AM conversion in the front end of high-power lasers
No full textNational Natural Science Foundation of China (NSFC) [61405211]Group velocity dispersion (GVD) is one of the main factors leading to frequency modulation (FM) to amplitude modulation (AM) conversion in the front end of high-power lasers. In order to compensate the FM-AM modulation, the influence of GVD, which is mainly induced by the phase filter effect, is theoretically investigated. Based on the theoretical analysis, a high-precision, high-stability, tunable GVD compensatory using gratings is designed and experimentally demonstrated. The results indicate that the compensator can be implemented in high-power laser facilities to compensate the GVD of fiber with a length between 200-500 m when the bandwidth of a phase-modulated laser is 0.34 nm or 0.58 nm and the central wavelength is in the range of 1052.3217-1053.6008 nm. Due to the linear relationship between the dispersion and the spacing distance of the gratings, the compensator can easily achieve closed-loop feedback controlling. The proposed GVD compensator promises significant applications in large laser facilities, especially in the future polarizing fiber front end of high-power lasers. (C) 2017 Optical Society of Americ
A robust red-emitting phosphor-in-glass (PiG) for use in white lighting sources pumped by blue laser diodes
No full textKAKENHI [15K06448]; National Natural Science Foundation of China [61177050, 51572232, 61575182, 51272259]; China Postdoctoral Science Foundation [2016M601654]; Application Research Program of Commonweal Technology of Zhejiang Province [2015C31102]A red-emitting phosphor-in-glass (PiG) material was synthesized by dispersing CaAlSiN3:Eu2+ phosphor powders in a ZnO-B2O3-BaO-Al2O3 glass matrix. A fully densified translucent CaAlSiN3:Eu2+ PiG material was achieved at 650 degrees C for 40 min with an external quantum efficiency (QE) of 43%, transmittance of 30% at 640 nm and thermal conductivity of 1.12 Wm(-1)K(-1). The CaAlSiN3:Eu2+ particles were distributed in the glass matrix uniformly, and no serious interfacial reactions occurred between the glass matrix and the contained phosphor particles. Under the excitation of blue laser, the maximum luminous flux of CaAlSiN3:Eu2+ PiG sample is 39 lm at the laser flux density of 0.5 W/mm(2). Although luminous saturation was observed at high laser incident density, the PiG material would be a promising red color converter for use in white lighting sources pumped by blue laser diodes. (C) 2017 Elsevier B.V. All rights reserved
Modeling of ablation threshold dependence on pulse duration for dielectrics with ultrashort pulsed laser
No full textOpen Research Fund of State Key Laboratory of Pulsed Power Laser Technology, Electronic Engineering Institute [SKL2014KF05]; Fund of Key Laboratory of High Power Laser and Physics, Chinese Academy of Sciences [CXJJ-16S040]We present a numerical model of plasma formation in ultrafast laser ablation on the dielectrics surface. Ablation threshold dependence on pulse duration is predicted with the model and the numerical results for water agrees well with the experimental data for pulse duration from 140 fs to 10 ps. Influences of parameters and approximations of photo- and avalanche-ionization on the ablation threshold prediction are analyzed in detail for various pulse lengths. The calculated ablation threshold is strongly dependent on electron collision time for all the pulse durations. The complete photoionization model is preferred for pulses shorter than 1 ps rather than the multiphoton ionization approximations. The transition time of inverse bremsstrahlung absorption needs to be considered when pulses are shorter than 5 ps and it can also ensure the avalanche ionization (AI) coefficient consistent with that in multiple rate equations (MREs) for pulses shorter than 300 fs. The threshold electron density for AI is only crucial for longer pulses. It is reasonable to ignore the recombination loss for pulses shorter than 100 fs. In addition to thermal transport and hydrodynamics, neglecting the threshold density for AI and recombination could also contribute to the disagreements between the numerical and the experimental results for longer pulses. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE
Single-Shot Full-Field Characterization of Short Pulses by Using Temporal Annealing Modified Gerchberg-Saxton Algorithm
No full textNational Natural Science Foundation of China [61205103]The dispersive Fourier transform is suitable for characterizing short pulses. However, the traditional temporal Gerchberg-Saxton (GS) algorithm suffers from the timing error of measured dispersed waveforms, which limits the measurement performance of the temporal phase. An annealing modified GS algorithm that can simultaneously retrieve the temporal profile and phase is proposed. The inevitable timing error in the measurement can be accurately recovered by the algorithm, which significantly improves the retrieval performance. Based on the annealing modified GS algorithm, an experimental structure is proposed to achieve single-shot full-field measurement. The algorithm is analyzed numerically and the temporal waveform and phase of short pulses can be retrieved successfully in the experiment. The results indicate that this single-shot full-field measurement method is free from timing error, which is important for real applications. The simple single-shot method promises future applications to measure the temporal profile and temporal phase of short pulses with high accuracy simultaneously
Target Area Design of an Inertial Confinement Fusion Laser Driver Compatible with Multiple Irradiation Configurations of Targets
No full textCollaboration on Advancing Key Techniques for Inertial Fusion Energy in China [2012DFG62040]The target area of a 288-beam inertial confinement fusion laser driver was designed to allow lasers for direct-drive illumination, spherical hohlraum with six laser entrance holes (6LEHs), and baseline cylindrical hohlraums. The suggested radius of a target chamber was 6.0 m based on the ratio of the total port area to chamber area. Beam port distribution on the chamber was calculated if the direct propagation of laser beams into opposing beam ports was avoided, and this distribution was compatible with spherical hohlraums with 6LEHs without additional ports opened. According to the symmetry of the beam port distribution, an X-shaped beam-guiding system (BGS) in the switchyard was proposed and arranged within a baseline algorithm. The switch between direct-and indirect-drive modes was easy to operate using this BGS concept
Beam modulation due to thermal deformation of grating in a spectral beam combining system
No full textNational Natural Science Foundation of China (NSFC) [10704079, 11104295]As the power of a spectral beam combining (SBC) system increases, the temperature of the multilayer dielectric grating (MDG) inevitably rises under the influence of high-power continuous-wave (CW) laser irradiation. Hence, thermal deformation of the MDG occurs, along with degeneration of the combined beam properties. In this study, we experimentally and theoretically investigate the influence of the MDG thermal deformation on the combined beam properties. An experimental setup is first proposed, in which beam quality M-2, beam profile, and MDG wavefront deformation are investigated. The experimental results indicate that the beam quality clearly degrades and the MDG wavefront deformation becomes more significant with increasing pump-CW power density. On this basis, a calculation model for MDG thermal deformation in SBC systems is proposed. The results indicate that MDG wavefront deformation becomes more significant, combined beam profile becomes deformed, and beam quality of the combined beam degrades with increasing power density. Further, thermal expansion of the substrate is a crucial factor that induces MDG wavefront deformation and far-field intensity modulation.
Diode-end-pumped Ho, Pr:LiLuF4 bulk laser at 2.95 mu m
No full textNational Natural Science Foundation of China (NSFC) [61308042, 61675116, 61575110, 61405101, 51472257, 51321091]A diode-end-pumped continuous-wave (CW) and passively Q-switched Ho, Pr : LiLuF4 (Ho, Pr: LLF) laser operation at 2.95 mu m was demonstrated for the first time, to the best of our knowledge. The maximum CW output power was 172 mW. By using a monolayer graphene as the saturable absorber, the passively Q-switched operation was realized, in which regimes with the highest output power, the shortest pulse duration, and the maximum repetition rate were determined to be 88 mW, 937.5 ns, and 55.7 kHz, respectively. The laser beam quality factor M-2 at the maximum CW output power were measured to be M-x(2) = 1.48 and M-y(2) = 1.47. (C) 2017 Optical Society of Americ
Image lithography in telluride suboxide thin film through controlling "virtual" bandgap
No full textNational Natural Science Foundation of China (NSFC) [51672292, 61627826, 61137002]In this work, TeO0.7 thin films were prepared by the reactive magnetron-controlling sputtering method. Complex gray-scale patterns were successfully fabricated on TeO0.7 thin films through the laser direct writing method. The structural origin of TeO0.7 thin film was investigated for gray-scale pattern formation. It is found that multiple gray-scale levels are dependent on the "virtual" bandgap energy of TeO0.7 thin films. The bandgap energy changes lead to refractive index and reflectivity difference. Thus, gray-scale tones can be formed. By accurately controlling laser energy, various "virtual" bandgaps can be generated in TeO0.7 thin films, and colorful gray-scale levels can be formed. Experimental results indicate that TeO0.7 thin film can be used as micro/nano image writing material. (C) 2016 Chinese Laser Pres
Low-hydroxy Dy3+/Nd3+ co-doped fluoride glass for broadband 2.9 mu m luminescence properties
No full textChinese National Natural Science Foundation [61605192, 51472225, 51401197, 51502022]; Zhejiang Provincial Natural Science Foundation of China [LR14E020003]The novel Dy3+ singly doped and Dy3+/Nd3+ co-doped fluoride glasses have been synthesized, and their fluorescence properties have been monitored under 808 nm excitation. The addition of Nd3+ leads to a higher emission peak, and a longer lifetime of 270 mu s for Dy3+ 2.9 mu m emission, benefited by the low Off content (0.032 cm(-1)) host and effective energy transfer of Nd3+: F-4(5/2), H-2(9/2)-> Dy3+: F-6(5/2) with a energy transfer coefficient of 3.0 x 10(-46) cm(6)/s. Radiative and emission parameters were calculated based on the Judd-Ofelt theory, which shows that the Dy3+/Nd3+ co-doped sample possesses a high calculated spontaneous transition probability (38.3 s(-1)) together with a large emission cross section (5.22 x 10(-21) cm(2)). The FWHM is as wide as 260 nm, indicating it is suitable for tunable laser medium. These results prove the fluoride glass could be used as a potential candidate for compact and efficient eye safe mid-IR lasers
Optical spectroscopy of Dy3+-doped CaGdAlO4 single crystal for potential use in solid-state yellow lasers
No full textChina Postdoctoral Science Foundation [2016M592466]; National Natural Science Foundation of China [61621001]; National Key Research and Development Program of China [2016YFB0701002]The crystal growth, optical spectra and lifetime of Dy:CaGdAlO4 crystal were investigated for the first time to our best knowledge. Single Dy:CaGdAlO4 crystal with size of phi 4 x 40 mm(3) was grown by floating zone method. The peak absorption cross-sections were calculated to be 2.43 x 10(-21)cm(2) and 1.28 x 10(-21) cm(2) at 453 nm for sigma and pi polarizations. The Judd-Ofelt (JO) parameters of 02, 04 and 06 were calculated to be 1.8 x 10(-2)0cm(2), 1.0 x 10(-20)cm(2) and 0.5 x 10(-20)cm(2), respectively. The emission cross-sections were calculated to be 0.51 x 10(-20)cm(2) and 0.55 x 10(-20)cm(2) for a and pi polarizations. The fluorescence decay time is 222 mu s. The results indicate that the Dy:CaGdAlO4 crystal is a potential candidate for yellow laser operation. (C) 2017 Elsevier B.V. All rights reserved