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Ultra-low power anti-crosstalk collision avoidance light detection and ranging using chaotic pulse position modulation approach

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Chinese Physics B 2016年第7期25卷 250-257页

作者：郝杰巩马理杜鹏飞卢宝杰张帆张海涛付星 center for photonics and electronics Department of Precision Instrument Tsinghua University

A novel concept of collision avoidance single-photon light detection and ranging（LIDAR） for vehicles has been demonstrated, in which chaotic pulse position modulation is applied on the transmitted laser pulses for robust anti-crosstalk purposes. Besides, single-photon detectors（SPD） and time correlated single photon counting techniques are adapted, to sense the ultra-low power used for the consideration of compact structure and eye safety. Parameters including pulse rate, discrimination threshold, and number of accumulated pulses have been thoroughly analyzed based on the detection requirements, resulting in specified receiver operating characteristics curves. Both simulation and indoor experiments were performed to verify the excellent anti-crosstalk capability of the presented collision avoidance LIDAR despite ultra-low transmitting power.

关键词： collision avoidance chaotic pulse position modulation time-correlated single photon counting anti-crosstalk

Wavefront sensing based on phase contrast theory and coherent optical processing

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Chinese Physics B 2016年第7期25卷 179-184页

作者：黄磊边琪周晨露李腾浩巩马理 center for photonics and electronics Department of Precision Instruments Tsinghua University

A novel wavefront sensing method based on phase contrast theory and coherent optical processing is proposed. The wavefront gradient field in the object plane is modulated into intensity distribution in a gang of patterns, making highdensity detection available. By applying the method, we have also designed a wavefront sensor. It consists of a classical coherent optical processing system, a CCD detector array, two pieces of orthogonal composite sinusoidal gratings, and a mechanical structure that can perform real-time linear positioning. The simulation results prove and demonstrate the validity of the method and the sensor in high-precision measurement of the wavefront gradient field.

关键词： wavefront gradients composite sinusoidal gratings phase contrast

Internal Features of Fiber Fuse in a Yb-Doped Double-Clad Fiber at 3 kW

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Chinese Physics Letters 2018年第5期35卷 29-33页

作者： Qi-Rong Xiao Jia-Ding Tian Yu-Sheng Huang Xue-Jiao Wang Ze-Hui Wang Dan Li Ping Yan Ma-Li Gong center for photonics and electronics Department of Precision Instrument Tsinghua University

We study internal features of fiber fuse in a Yb-doped double-clad fiber. The samples of fiber fuse are acquired at the power level of 3 kW in an all-fiber forward-pumped master oscillator power amplifier configuration fiber laser that is built specially for fiber fuse analyses. At this high power level, drastic refractive-index redistribution arises in an expended high refractive index area around the bullet-shaped voids of fiber fuse. Electron spin resonance analyses on post-fiber-fuse samples of the Yb-doped double-clad fiber indicate rising Frenkel defect concentration, meanwhile showing a new resonance center that is different from the ones of the Ge-doped fibers studied previously. This new resonance center probably suggests the generation of Al-oxygen hole center, a kind of defect formed during the catastrophic fuse process.

关键词： Fiber lasers

Efficient corner-pumped Nd:YAG/YAG composite slab laser

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Chinese Physics B 2010年第5期19卷 327-331页

作者：刘欢巩马理 center for photonics and electronics Department of Precision Instruments and MechanologyTsinghua University

A corner-pumped type is a new pumping type in the diode-pumped all-solid-state lasers, which has the advantages of high pump efficiency and favourable pump uniformity. A highly efficient corner-pumped Nd：YAG/YAG composite slab laser is demonstrated in this paper. The maximal continuous-wave output power of the 1064 nm laser is up to 18.57 W with a slope efficiency and an optical-to-optical conversion efficiency of 44.9% and 39.8%, respectively. Inserting an acousto-optic Q-switch in the cavity, the highest average output power of the quasi-continuous wave 1064 nm laser of 6.73W is obtained at a repetition rate of 9.26 kHz. The experimental results show that a corner-pumped type is a kind of feasible schedules in the design of diode-pumped all-solid-state lasers with low or medium output powers.

关键词： corner-pumped Nd:YAG crystal continuous wave acousto-optic Q-switch

Investigation on mode matching including thermal effects in LD end-pumped passively mode-locked Nd:YVO_4 laser

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Chinese Optics Letters 2010年第10期8卷 1004-1007页

作者：夏帕克提.吾守尔于海娟闫平巩马理 center for photonics and electronics Department of Precision Instruments and Mechanology Tsinghua University

We design a laser diode （LD） end-pumped passively mode-locked solid-state laser with a semiconductor saturable absorber mirror. Mode-matching efficiency in the active medium including the thermal effect is analyzed, and the optimum mode-matching coefficient is obtained by optimizing the pump mode. In the experiment, a total power of 4.2 W stable pulse sequences without multipulse at 1064 nm is obtained with a pulse repetition rate of 86 MHz and a pulse width of 13 ps, corresponding to a high optical to optical efficiency of 44%.

关键词： Lasers Mirrors Mode locked fiber lasers Neodymium lasers Pulse repetition rate Pumps Semiconductor lasers

Fiber core mode leakage induced by refractive index variation in high-power fiber laser

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Chinese Physics B 2017年第3期26卷 336-343页

作者：闫平王雪娇黄昱升付晨孙骏逸肖起榕李丹巩马理 center for photonics and electronics Department of Precision Instruments Tsinghua University Beijing 100084 China

This paper presents an investigation of specific optical fiber core mode leakage behavior that occurs in high-power double-clad fiber lasers as a result of thermally-induced refractive index variations. A model of the power transfer between the core modes and the cladding modes during thermally-induced refractive index variations is established based on the mode coupling theory. The results of numerical simulations based on actual laser parameters are presented. Experimental measurements were also carried out, the results showed good agreement with the corresponding simulation results.

关键词： double-clad fiber laser and amplifier Core loss cladding mode mode coupling theory

All-fiber linearly polarized laser oscillator by fiber coiling loss control

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Chinese Physics B 2018年第4期27卷 305-308页

作者： Yu-Sheng Huang Qi-Rong Xiao Dan Li Ze-Hui Wang Xue-Jiao Wang Ping Yan Ma-Li Gong center for photonics and electronics Department of Precision Instrument Tsinghua University Beijing 100084 China

In this paper,we demonstrate an all-fiber linearly polarized fiber laser *** single polarization of the oscillator is achieved through the careful designing of the active fiber *** relationship between fiber coiling diameter and polarization extinction ratio and optical efficiency is studied,whose results lead to an optimized *** thermal management of the oscillator is also refined,which allows the oscillator to reach a maximum output power of44.1 W with an optical-to-optical efficiency of 57.9%.A high average polarization extinction ratio of 21.6 d B is achieved during a 2-hour stability *** oscillator also owns a narrow 3-d B bandwidth of 0.1 nm,as well as near-diffraction-limit beam quality of M^2～ 1.14.

关键词： fiber laser oscillator linearly polarized all-fiber

Influence of mode competition on beam quality of fiber amplifier

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Chinese Physics B 2014年第10期23卷 235-241页

作者：肖起榕闫平孙骏逸陈霄任海翠巩马理 center for photonics and electronics State Key Laboratory of Tribology Department of Precision Instrument Tsinghua University

Theoretical and experimental studies of the influence of the mode competition on the output beam quality of fiber amplifiers are presented. Rate equations and modal decomposition method are used in the theoretical model. In the experiment, the output beam-quality factor of a fiber amplifier, which is based on a Yb-doped double-clad large mode area fiber as a function of the seed beam quality and the pump power of the amplifier, is measured. The experimental results are consistent with the theoretical analysis.

关键词： fiber laser and amplifier mode competition beam quality

A novel orthogonally linearly polarized Nd:YVO_4 laser

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Chinese Physics B 2010年第8期19卷 395-400页

作者：闫兴鹏柳强陈海龙付星巩马理王东生 State Key Laboratory of Tribology Center for Photonics and ElectronicsDepartment of Precision InstrumentsTsinghua University

We presented a novel orthogonally linearly polarized Nd：YVO4 laser. Two pieces of a-cut grown-together composite YVO4/Nd：YVO4 crystals were placed in the resonant cavity with the c-axis of the two crystals orthogonally. The polarization and power performance of the orthogonally polarized laser were investigated. A 26.2-W orthogonally linearly polarized laser was obtained. The power ratio between the two orthogonally polarized lasers was varied with the pump power caused by the polarized mode coupling. The longitudinal modes competition and the corresponding variable optical beats were also observed from the orthogonally polarized laser. We also adjusted the crystals with their c-axis parallele to each other, and a 40.7-W linearly polarized TEM00 laser was obtained, and the beam quality factors were Mx^2 = 1.37 and My^2 = 1.25.

关键词： orthogonally linearly polarized laser composite Nd:YVO4 optical beat frequency