Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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High-precision active synchronization control of high-power, tiled-aperture coherent beam combining
No full textNational Natural Science Foundation of China (NSFC) [61378030, 61775223, 61521093]We propose and demonstrate a high-precision active control technique for tiled-aperture coherent beam combining suitable for high-power laser pulses. The method is a hybrid structure based on the near-field interference fringe technique and single-crystal balanced optical cross-correlation, which enables the active loop to exhibit high accuracy, wide dynamic range, and good capacity for resisting energy disturbance. In the proof-of-principle experiment, we realized an adjustable beam combining bandwidth of approximately 100 Hz (limited by the speed of the piezoelectric transducer) and root-mean-square deviation of approximately lambda/51 for two beam channels with a combining efficiency of 93%
Picosecond pulse compression by modulation of intensity envelope in a gas-filled hollow-core fiber
No full textNational Natural Science Foundation of China [61521093]; Strategic Priority Research Program of the Chinese Academy of Sciences [XDB1603]; International S&T Cooperation Program of China [2016YFE0119300]A method of temporally compressing picosecond pulses is proposed. To increase the spectral broadening, two picosecond pulses at different central wavelengths are overlapped spatiotemporally to induce a modulation on the intensity envelope, thus leading to a high temporal intensity gradient. The combined pulse is then coupled into a gas-filled hollow-core fiber (HCF) to broaden the spectrum through nonlinear propagation. After that the pulse can be compressed by chirp compensation. This method is demonstrated numerically with two 1-ps/5-mJ pulses centered at 1053- and 1064-nm, respectively, which are coupled into a 250-mu m-inner-diameter, 1-m-long HCF filled with 5-bar neon. After nonlinear propagation, the spectrum of the combined pulse is broadened significantly compared with the sum of the broadened spectra of a single 1-ps/10-mJ pulse centered at 1053- and 1064-nm. Under proper initial conditions, the pulse can be compressed down to similar to 16-fs. The influences of the energy ratio, time delay and wavelength gap between two input pulses, as well as the energy scaling are also discussed. These results show an alternative way to obtain ultrashort laser pulses from the picosecond laser technology, which can deliver both high peak power and high average power, and thus will benefit relevant researches in high-field laser physics
Self-Tuning Mode-Locked Fiber Lasers Based on Prior Collection of Polarization Settings
No full textNational Natural Science Foundation of China [11434005, 11404211]; National Instrumentation Program [2012YQ150092]; Shanghai Science and Technology Commission [14JC1401600]; China Postdoctoral Science Foundation [2015M581634]; Hujiang Foundation of China [D15014]We present a method to discriminate stable mode-locked states of an all fiber erbium-doped laser based on nonlinear polarization rotation mechanism. The method has a balance between the accuracy and rapidness of the pulses discrimination. Mode-locked states are distinguished and confirmed by an amplitude discriminator, which reflects the repetition rate information of the pulses. An electronic polarization controller is used to precisely adjust the intracavity polarization states. The driving voltages of the electronic polarization controller at those mode-locked states are recorded as populations, and it is benefit to reduce the build-up time for mode locking. The populations are also recorded at operation temperature covering from 20 degrees C to 50 degrees C, which exhibits the repeatability and stability of the mode-locked states. Rapid self-tuning mode-locked fiber lasers could be achieved by the repeatability of the polarization settings under the stable temperature environment
Spatiotemporal propagation dynamics of intense optical pulses in loosely confined gas-filled hollow-core fibers
No full textWe numerically study the propagation dynamics of intense optical pulses in gas-filled hollow-core fibers (HCFs). The spatiotemporal dynamics of the pulses show a transition from tightly confined to loosely confined characteristics as the fiber core is increased, which manifests as a deterioration in the spatiotemporal uniformity of the beam. It is found that using the gas pressure gradient does not enhance the beam quality in large-core HCFs, while inducing a positive chirp in the pulse to lower the peak power can improve the beam quality. This indicates that the self-focusing effect in the HCFs is the main driving force for the propagation dynamics. It also suggests that pulses at longer wavelengths are more suitable for HCFs with large cores because of the lower critical power of self-focusing, which is justified by the numerical simulations. These results will benefit the generation of energetic few-cycle pulses in large-core HCFs
Terahertz refractive anisotropy on femtosecond laser pulse ablated semi-insulating gallium arsenide surface
No full textNational Natural Science Foundation of China [61307130, 11374316]; Shanghai Municipal Education Commission [14YZ077]; Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education MinistryWe present an artificial variation of THz refractive index ellipse from isotropy to anisotropy at the surface of < 100 >-oriented semi-insulating gallium arsenide (SIGaAs) via femtosecond pulse laser ablation. The refractive index ellipse is determined by the frequency and the polarization of incident THz radiation. The THz wave is localized in the gap of columns of micro-ripples when the polarization of THz is parallel to the micro-ripples, while no electric energy localization occurs when the polarization of THz is perpendicular to the micro-ripples. We found that the laser ablation process can induce a periodic distribution of n- type GaAs at the surface of SI-GaAs. These n- type GaAs micro-ripples work as plasmonic resonators, which are proposed to be the origin of the induced refractive index anisotropy
Optical properties of Cr-doped Sb2Te thin films during ultrafast crystallization processes
No full textNational Natural Science Foundation of China [51472258, 61178059, 61137002]; National Basic Research Program of China [2013CBA01900]The crystallization process of Cr-doped Sb2Te thin films induced by repeated femtosecond laser pulses was studied systematically. The threshold effects and corresponding mechanism were comprehensively analyzed by real-time reflectivity measurements, optical microscopic imaging, and Raman scattering spectra. It was found that by doping the appropriate content of Cr into Sb2Te thin films, improved optical-thermal properties could be obtained, even in ultrafast crystallization processes
Temperature dependent thermal conductivity and transition mechanism in amorphous and crystalline Sb2Te3 thin films
No full textNational Natural Science Foundation of China [51672292, 61627826]Sb2Te3 thin films are widely used in high density optical and electronic storage, high-resolution greyscale image recording, and laser thermal lithography. Thermal conductivity and its temperature dependence are critical factors that affect the application performance of thin films. This work aims to evaluate the temperature dependence of thermal conductivity of crystalline and amorphous Sb2Te3 thin films experimentally and theoretically, and explores into the corresponding mechanism of heat transport. For crystalline Sb2Te3 thin films, the thermal conductivity was found to be 0.35 +/- 0.035 W m(-1) K-1 and showed weak temperature dependence. The thermal conductivity of amorphous Sb2Te3 thin films at temperatures below similar to 450 K is about 0.23 +/- 0.023 W m(-1)K(-1), mainly arising from the lattice as the electronic contribution is negligible; at temperatures above 450 K, the thermal conductivity experiences an abrupt increase owing to the structural change from amorphous to crystalline state. The work can provide an important guide and reference to the real applications of Sb2Te3 thin films
Effects of CaO/Al2O3 ratio on structure and spectroscopic properties of Nd3+-doped CaO-Al2O3-BaO aluminate glass
No full textNd3+-doped CaO-Al2O3-BaO glasses with varying CaO/Al2O3 ratios were synthesized, and their thermal, structural, absorption, and emission properties were characterized as functions of the CaO/A1203 ratio. The thermal stability of the glasses was analyzed by differential scanning calorimetry. The Raman spectra indicated that the amount of A1-0-Al bridging oxygen bonds decreased and the amount of the Al-non-bridging oxygen (NBO) bonds increased with an increase of the CaO/Al2O3 ratio. A broadband emission was observed in the fluorescence spectra, and the full width at half maximum bandwidth was found to increase from 38.6 nm to 41.2 nm with the increase of CaO/Al2O3 ratio. Meanwhile, the fluorescence peak shifted from 1064 rim to 1068 nm. Based on the Judd-Ofelt parameters, the transition probabilities, emission cross-sections and gain parameters of the glasses were calculated to evaluate the optical amplification performances; the stimulated emission cross-section decreased from 2.11 x 10(-20) to 1.35 x 10(-2) cm(2) with the increase in the CaO/A1203 ratio. These results indicate that Nd3+-doped CaO-Al2O3-BaO aluminate glasses with a broadband fluorescence bandwidth and suitable gain property have potential for the application in high-energy ultrashort-pulse lasers
Modelling and characteristics of actively Q-switched Er-doped fibre laser with Tm-doped fibre saturable absorber
No full textHundred-Talent Program of the Chinese Academy of Sciences; State Key Laboratory [SKLLIM1409, SKLLIM1503]A theoretical model concerning FSA-based active Q-switching is developed. And, characteristics of the active Q-switching operation are investigated and compared with the traditional passive Q-switching operation. Numerical results demonstrate that the active control of the repetition rate of FSA-based Q-switching is attainable. And, stable active Q-switching could be obtained from both no lasing state and stable passive Q-switching state
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