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In this paper, we report a 3.7 kW all fiber narrow linewidth single mode fiber laser. The full width at half-maximum is about 0.30 nm, and the beam quality is Mx2=1.358, My2=1.202 at maximum output power. The laser is achieved by simultaneously suppressing nonlinear effects and mode instability (MI). Different seeds are injected into the main amplifier to study stimulated Raman scattering (SRS) effect. The results show that the phase modulated single frequency seed is benefit to suppress the SRS effect. For the phase modulated single frequency seed, inserting a filter in preamplifier will suppress amplified spontaneous emission (ASE) and decrease the backward power. By optimizing the coiling of active fiber, the MI effect is suppressed.

A new method of generating periodic linear chirped pulse is proposed, and a 0.52 nm bandwidth periodic chirped pulse is generated. Numerical simulation shows that the gain saturation, group velocity dispersion and synchronization jitter have great influences on chirped pulse; and self-phase modulation has little influence since the peak power stays at a low level. The experimental results indicate that the polarization mode dispersion will lead to a great intensity modulation, and the amplified spontaneous emission will break the light stability, which leads to the fewer round-trips of light. Research shows that the direct phase modulation is a novel method of generating periodic linear chirped pulse, which could be used for smoothing the spectral dispersion.

To improve laser irradiation uniformity, experimental research on smoothing by spectral dispersion (SSD) and continuous phase plate (CPP) is carried out on the technical integration line (TIL). A bulk phase modulator with 9.2 GHz modulation frequency is adopted. The output spectrum of the phase modulator is stable and the residual amplitude modulation is quite small. The experimental results indicate that when the number of color cycles (Nc) is adopted to be 1, imposing of SSD in this divergence does not lead to pinhole closure in the spatial filters of the preamplifier and main amplifier. The contrast of the focal spot with 95% energy included with SSD and CPP drops to 0.47 compared with 1.71 without SSD and CPP. When the pulse width of the third harmonic wave is 1 ns and its energy is 1115 J, no damage is found in CPP and other final optics. The experiment solves some key techniques by using SSD and CPP on high-power laser facilities, and provides sound basis for the upcoming physics experiment.

Using comb laser pulses synchronized with the main pulse output by large laser facility as time fiducial to scale the reaction process between high power laser pulse and target is very important for the realization of precise measurement and simulation in the intense field experiment. We demonstrate a fiber multiharmonic time fiducial laser pulse generation system using optic-electric modulation and optical pulse stacking. A unit optical pulse with a width of 150 ps generated by modulation was stacked in a fiber stacker to form a 1053 nm comb pulse. The pulse was then amplified and frequency-converted to generate green (527 nm) and UV (351 nm) fiducials. The system can stably provide Shenguang-Ⅲ prototype facility with multi-frequency laser time fiducials which is essential for the precise physical experiment. In addition, the system is highly adaptive since it can generate fiducial signals with variable pulse intervals and amplitudes flexibly according to the requirements of different physical experiments.

The conversion of frequency modulation to amplitude modulation (FM-to-AM) effect is harmful to the high power laser facility based on the phase modulation technique. The FM-to-AM effect of phase modulation pulse induced by the weak etalon effect in wave plates was investigated theoretically and experimentally. A bulk phase modulator with a modulation frequency of 9.2GHz was employed. The numerical simulation results show that the FM-to-AM effect with a temporal modulation depth of 2.5% and 29.7% on the top of the pulse shape was induced by the weak etalon effect in half-wave plate with thickness of 1mm and residual reflectance ratio of 0.5% for 1 pass and 12 passes respectively. On the same condition, the temporal modulation depth is 3.0% and 23.4% respectively in the experiment. The results are in good agreement with numerical simulation results. To our knowledge, it is the first time to introduce the weak etalon effect in wave plates for a complex phase modulation laser system.

We demonstrate an all fiber multi-laser pulse generation system that can output broadband chirped pulse, nano-second shaped pulse and narrowband pump pulse for optical parametric chirped pulsed amplifiers system with precise synchronization. Yb3+-doped fiber mode-locked laser and single longitudinal oscillator are used as the optical source for the fiber system. The ultra-short pulse train generated from the mode locked fiber laser was split into two beam-lines and both were chirp-stretched to 0.9 ns. One of them was directly amplified to a magnitude of 10 μJ to provide the high-energy petawatt laser facility with seed pulse. The other was tailored by a 1.2 nm bandwidth filter to form a 140 ps unit pulse. It was then stacked in a fiber stacker and formed a 2.3 ns arbitrarily shaped pulse. The shaped pulse was amplified to 10 μJ to provide seed pulse for the pellet compression. Simultaneously, we sampled part of the ultra-short pulse train from the mode locked laser. The sampled pulse train was converted to electrical signal and phase-locked to generate trigger pulse that precisely synchronized with the mode locked pulse for an amplitude modulator. The continuous-wave laser generated from the fiber single longitudinal oscillator was tailed by the amplitude modulator and then amplified to provide seed pulse for the OPCPA system. The output of the fiber system can switch between different kinds of pulses with flexibility according to the physical experimental requirement.

Sinusoidal phase modulated pulse could provide broad bandwidth and high modulation frequency for spectral dispersion method in high power laser driver system. Phase modulation could be converted to intensity modulation due to dispersion during the pulse propagation in the fiber,and the intensity modulation enhances the nonlinear effect in the large-mode-area double-clad fiber amplifier and make the spectral controlling more difficult. 2 GHz and 1425 GHz phase modulation pulses propagated in fibers with different lengths were measured, and based on the dispersion model in the fiber, theoretical analysis shows good similarity between simulation and experimental results for the 2 GHz phase modulation pulse.

By time division multiplexing (TDM) technique, an all-solid-state all-fiber multibeam optical pulse generation system used for an inertial confinement fusion driver is developed. The continuous wave signal is provided by a single longitudinal mode oscillator. The TDM technique and he high speed electro-optic modulation technique are utilized to realize the train pulse and arbitrary pulse-shaping. The polarization independent acoustooptic modulation technique is adopted to independently output the multibeam. Eight sub-pulses which may be shaped arbitrarily are included in each train pulse, and the time delay between adjacent sub-pulses is 120 ns. A single pulse selection module is used so that each beam turns into an independent output beam and then each beam is amplified and transmitted to output. Finally, it is successfully verified that the train pulse can be produced by the TDM technique, and its sub-pulse can be shaped arbitrarily and independently. The each beam energy is 1.275 μJ.

We numerically simulated the dymamics of mode locking in pure positive dipersion lasers by NLS. Different from soliton lasers operating in net negative dispersion regime or dispersion mananged soliton and similariton lasers operationg in net positive dispersion regime with disperion compensation components, gain saturation and narrowing plays an important role in pulse formation in lasers composed of pure positive dispersion medium, in which the pulses evolve to gain-guided solitons. Stable gain-guided soliton was obtain in two kinds of mode locked fiber lasers operating in the positive dipersion regime, and experimental results confirmed the numerical simulation.

We demonstrate an integrated all fiber optical pulse generation system for laser fusion driver. CW laser signal generated from a single longitudinal fiber oscillator was modulated by phase modulator and amplitude modulator to form an optical pulse with shaped waveform and bandwidth of 0.1 nm. The pulse was amplified and split by fiber multiplexer to four pulses. Time delay of each pulse was controlled by synchronization unit and power of each pulse was adjusted by programmable variable optical attenuator. The four pulses were amplified and then transmitted through a 150 m fiber to the pre-amplify system. The fiber system can generate almost arbitrarily shaped optical pulse with duration of 0.2—20 ns, bandwidth of 0.1 nm and power of several nJ. As the front-end of the SG-Ⅲ prototype facility, it has successfully lunched about 2.6 million shots of pulses. The fiber system is compact and highly stable and reliable.

A new coupling method is put forward for high power LDA end-pumped large-aperture amplifiers. The LDA is inscribed on a sphere and then a duct is added adjacent to it. Three-dimensional ray-tracing program is used to simulate the features of the new coupling method. Simulation results show that when the area contraction coefficient is about 30, deposition efficiency in the gain media as high as 93.7% can be achieved; When the emitting area is not less than the aperture of the duct, uniform and top-hat distribution is obtained. When several stacks are spliced to make an inscribing area, amplifiers with larger aperture can be end pumped. When stacks in LDA is placed as m×n(m≠n) arrays, uniform and top-hat distribution is also obtained. In the LDA coupling experiment, the output is top-hat distributed at the end of the duct and the coupling efficiency is 85.4%.

Theory of the self-starting passive mode-locked Yb3+-doped fiber ring laser generating short pulses is presented. The ultrashort pulse Yb3+-doped fiber ring laser with all-fiber structure has been designed and turned out. Two 976nm LD pumped lasers are used as the pump sources and high concentration Yb3+-doped fiber is adopted as gain medium. Using the nonlinear polarization rotation (NPR) effect of the fiber, self-starting stable mode-locked pulse is obtained. The mode-locked threshold power of the laser is 260mW and the output power is 25mW. The center wavelength of the mode-locked pulse is 1056nm with 3dB bandwidth of 11.7nm at repetition rate of 20MHz. Comparing with the other structures of the fiber lasers, the structure we adopted is more efficient and has better stability.