Fiber amplification of pulse bursts up to 20 μJ pulse energy at 1 kHz repetition rate

We demonstrate burst-mode operation of a polarization-maintaining Yb-doped fiber amplifier. Groups of pulses with a temporal spacing of 10?ns and 1?kHz overall repetition rate are amplified to an average pulse energy of ～20?μJ and total burst energy of 0.25?mJ. The pulses are externally compressed to ～400?fs. The amplifier is synchronously pulsed-pumped to minimize amplified spontaneous emission between the bursts. We characterize the influence of pump pulse duration, pump-to-signal delay, and signal burst length.     

Experimental and Theoretical Study of the Generation and Non-Linear Conversion of Picosecond Bursts from an Amplified Ytterbium-Doped Fiber Laser System

Abstract

This article presents an experimental and theoretical study of the generation of picosecond bursts by a non-polarization-maintaining ytterbium-doped fiber master oscillator fiber amplifier system. The peak power and pulse energy of the burst are higher than 45 kW and 350 nJ at 700 kHz, respectively. The master oscillator fiber amplifier was used to generate 3 W of green and 200 mW of UV light with conversion efficiencies of 16% and 8%, respectively. The enhancement of conversion efficiency by the pulse burst compared with regular pulses was analyzed and attributed to dynamically saturated gain of the pump-power-limited fiber amplifier.     

Doping management for high-power fiber lasers: 100 W, few-picosecond pulse generation from an all-fiber-integrated amplifier

Thermal effects, which limit the average power, can be minimized by using low-doped, longer gain fibers, whereas the presence of nonlinear effects requires use of high-doped, shorter fibers to maximize the peak power. We propose the use of varying doping levels along the gain fiber to circumvent these opposing requirements. By analogy to dispersion management and nonlinearity management, we refer to this scheme as doping management. As a practical first implementation, we report on the development of a fiber laser-amplifier system, the last stage of which has a hybrid gain fiber composed of high-doped and low-doped Yb fibers. The amplifier generates 100?W at 100?MHz with pulse energy of 1 μJ. The seed source is a passively mode-locked fiber oscillator operating in the all-normal-dispersion regime. The amplifier comprises three stages, which are all-fiber-integrated, delivering 13?ps pulses at full power. By optionally placing a grating compressor after the first stage amplifier, chirp of the seed pulses can be controlled, which allows an extra degree of freedom in the interplay between dispersion and self-phase modulation. This way, the laser delivers 4.5?ps pulses with ～200 kW peak power directly from fiber, without using external pulse compression.     

220 μJ monolithic single-frequency Q-switched fiber laser at 2 μm by using highly Tm-doped germanate fibers

We report a unique all fiber-based single-frequency Q-switched laser in a monolithic master oscillator power amplifier configuration at ~1920 nm by using highly Tm-doped germanate fibers for the first time. The actively Q-switched fiber laser seed was achieved by using a piezo to press the fiber in the fiber Bragg grating cavity and modulate the fiber birefringence, enabling Q-switching with pulse width and repetition rate tunability. A single-mode polarization maintaining large core 25 μm highly Tm-doped germanate fiber was used in the power amplifier stage. For 80 ns pulses with 20 kHz repetition rate, we achieved 220 μJ pulse energy, which corresponds to a peak power of 2.75 kW with transform-limited linewidth.     

Self-similar amplification in fiber Bragg gratings written in fiber amplifiers

We show, by using numerical simulations, that self-similar pulses with a duration on the order of few nanoseconds and an energy on the order of 10?μJ can be obtained at the output of a fiber Bragg grating (FBG) written in a fiber amplifier. The evolution of the amplified pulses is determined by the combined effect of Kerr nonlinearity, normal-dispersion, gain, and gain saturation, which limit the pulse energy. The output pulse mainly depends on the initial pulse energy rather than on the initial pulse profile. The reduced group velocity in FBGs can significantly increase the total gain for a given amplifier length. Hence we find that the proposed amplification scheme can be highly advantageous for amplification of nanosecond-scale pulses in fiber amplifiers.     

载波-包络相位稳定的周期量级近红外超短脉冲激光系统

利用光参量放大过程输出的闲置光载波-包络相位(CEP)被动稳定的特点,搭建了三级光参量放大(OPA)系统,获得了CEP稳定的近红外高能量超短激光脉冲(1.4 mJ/40 fs/1 kHz @ 1.8 μm),其CEP抖动为516 mrad(rms).经空心光纤展宽光谱和块体材料补偿色散,激光脉宽最终可被压缩至小于两个光学周期(<12 fs),脉冲能量达到0.54 mJ.该系统为单个阿秒脉冲的产生和其他高次谐波实验提供了优质的光源. 关键词： 光参量放大 周期量级近红外激光脉冲 载波-包络相位稳定     

Low-repetition-rate,all-polarization-maintaining Yb-doped fiber laser mode-locked by a semiconductor saturable absorber

A low-repetition-rate, all-polarization-maintaining(PM)-fiber sub-nanosecond oscillator is presented, which is simple and low-cost, composed of standard components. The ring cavity is elongated by 114-m-long standard PM fiber, and passively mode-locked by a fiber pigtailed semiconductor saturable absorber. Linearly polarized pulses with 1.66 MHz repetition rate and 22 dB polarization extinction ratio are generated at a wavelength of 1030 nm, which is determined by an intracavity filter. In addition, to demonstrate that the oscillator is a good seed for high energy pulse generation, an all-fiber master oscillator power amplifier is built and amplified pulses with energy about 2 μJ are obtained.     

1 MHz repetition rate hollow fiber pulse compression to sub-100-fs duration at 100 W average power

We report on nonlinear pulse compression at very high average power. A high-power fiber chirped pulse amplification system based on a novel large pitch photonic crystal fiber delivers 700 fs pulses with 200 μJ pulse energy at a 1 MHz repetition rate, resulting in 200 W of average power. Subsequent spectral broadening in a xenon-filled hollow-core fiber and pulse compression with chirped mirrors is employed for pulse shortening and peak power enhancement. For the first time, to our knowledge, more than 100 W of average power are transmitted through a noble-gas-filled hollow fiber. After pulse compression of 81 fs, 93 μJ pulses are obtained at a 1 MHz repetition rate.     

Generation of broadly tunable sub-30-fs infrared pulses by four-wave optical parametric amplification

We report on the generation of sub-30-fs near-IR light pulses by means of broadband four-wave parametric amplification in fused silica. This is achieved by frequency downconversion of visible broadband pulses provided by a commercial blue-pumped beta-barium borate crystal-based noncollinear optical parametric amplifier. The proposed method produces the IR idler pulses with energy up to ～20 μJ and tunable in wavelength from 1 to 1.5 μm. The shortest pulse duration is 17.6 fs, measured at 1.2 μm.     

飞秒光脉冲光纤放大增益特性的实验研究

报道了掺Ｅｒ＾３＋光纤激光器输出１．５３１μｍ波长飞秒激光脉冲增益放大的实验研究结果,将自起振相加脉冲摹参Ｅｒ＾３＋光纤激光器输出的飞秒激光脉冲注入掺Ｅｒ＾３＋光纤放大器中进行放大,分别采用正向和逆向抽地这的方式,得到了最高放大倍数５５倍（１７．４ｄＢ）和６４倍（１８．１ｄＢ）的增益,对应的最大单脉冲能量（峰值功率）分别为０．３８４ｎＪ（７５２Ｗ）０．４５２ｎＪ（１２９５Ｗ）,脉冲重复率为２０．８     

Eye-safe, high-energy, single-mode all-fiber laser with widely tunable repetition rate

We present a novel high-energy, single-mode, all-fiber-based master-oscillator-power-amplifier （MOPA） laser system operating in the C-band with 3.3-ns pulses and a very widely tunable repetition rate, ranging from 30 kHz to 50 MHz. The laser with a maximum pulse energy of 25 μJ and a repetition rate of 30 kHz is obtained at a wavelength of 1548 nm by using a double-clad, single-mode, Er：Yb co-doped fiber power amolifier.     

一种基于增益调制技术的全光纤化脉冲Yb光纤激光器

以波长为975 nm的半导体激光器作为泵浦源,周期性地脉冲泵浦一个包含Yb掺杂光纤和光纤光栅对的Yb光纤激光器,实现了基于增益调制技术的全光纤化高功率Yb光纤激光器的稳定脉冲输出.在50 kHz重频下,采用20 W的泵浦功率和2.4 μs的泵浦脉冲宽度,获得了1 060 nm波长脉冲宽度仅100 ns的稳定脉冲激光输出,单脉冲激光能量约为20 μJ.以此作为脉冲激光种子进行功率放大,获得了性能稳定的全光纤结构高功率脉冲激光输出,放大后单脉冲能量超过200 μJ,激光放大器斜率效率达到60%.     

Transparent laser damage resistant nematic liquid crystal cell “LCNP3”

There exists the problem in diagnostics of dense plasma (so-called Thomson diagnostics). For this purpose the plasma is illuminated by series of high energy laser pulses. The energy of each separate pulse is as large as 3 J, so it is impossible to generate a burst of such pulses by a single laser. In this situation, the pulses are generated by several independent lasers operating sequentially, and these pulses are to be directed along the same optical path. To form an optical path with λ = 1.064 μm and absolute value of the laser pulse energy of 3 J, a special refractive index matched twisted Nematic Liquid Crystal Cell of type LCNP3, with switching on time τ_ON smaller than 3 μs was applied.     

皮秒光纤激光脉冲两个关键问题的研究

窄带耗散孤子锁模光纤激光器可以产生接近变换限制的皮秒脉冲,但受非线性相移的限制,输出脉冲重复频率不能通过增加腔长来降低,脉冲能量仅在0.1 nJ以下,严重制约着这类皮秒脉冲的实际应用。提出一种通过耦合器抽取腔内脉冲能量、抑制腔内非线性相移积累,进而允许增加腔长来降低窄带耗散孤子皮秒光纤激光脉冲重复频率的方法。运用该方法,成功地将激光器重复频率由35.2 MHz降低到了1.77 MHz,且脉冲时频特性保持不变。提出了一种基于级间FBG陷波滤波的抑制皮秒脉冲光纤放大中光谱展宽的方法。通过简单地使用级间陷波滤波器,既可窄化第一级光纤放大器后的输出脉冲谱宽,允许采用第二级光纤放大器进一步提升脉冲能量,而且,还可将脉冲重塑为近高斯形,利用高斯脉冲光谱展宽斜率小的特点,允许第二级光纤放大器将脉冲能量提升得更高。利用该方法,在RMS（均方值）谱宽保持0.4 nm以内的前提下,10 ps脉冲经标准单模光纤放大器后,能量可由0.2 nJ可提升到10 nJ以上。     

High-repetition-rate sub-5-fs pulses with 12 GW peak power from fiber-amplifier-pumped optical parametric chirped-pulse amplification

An optical parametric chirped-pulse amplification system delivering pulses with more than 12 GW peak power is presented. Compression to sub-5 fs, 87 μJ and 5.4 fs, 100 μJ is realized at the 30 kHz repetition rate. A high-energy fiber chirped-pulse amplification system operating at 1 mJ pulse energy and nearly transform-limited pulses is used to achieve ultrabroadband amplification in two 2mm beta-barium borate crystals. Precise pulse shaping is used to compress the pulses to a few percentages of their transform limit. Assuming diffraction limited focusing (d<2 μm), peak intensities as high as 10(18) W/cm(2) can be reached.     

Generation of high-energy, sub-20-fs pulses in the deep ultraviolet by using spectral broadening during filamentation in argon

Generation of sub-20-fs UV pulses with more than 300 μJ energy at 268 nm is reported. First, the UV pulses are produced by successive second-harmonic and third-harmonic (TH) generation of 805 nm pulses of a 1 kHz Ti:sapphire laser amplifier. The spectral broadening of TH pulses is realized in a filament, generated in argon. The produced pulses are compressed in a simple double-pass prism-pair compressor. Starting from 100 fs pulses, we achieve a fivefold pulse shortening.     

4 μJ, 3 ns phase-modulated laser pulse from ytterbium-doped polarization-maintaining large-mode-area fiber amplifier

In the current inertial confinement fusion laser drivers, integrated fiber front-end is widely applied to generate the phase-modulated, linearly polarized laser pulses with an output energy of several nano-joules. In this contribution, we design an amplifier with polarization-maintaining optical components. The amplification of the phase-modulated 3 ns, 0.24 nm pulse is experimentally demonstrated in the ytterbium-doped large-mode-area (11 ??m-diameter) fiber amplifier. The pulse energy is amplified to around 4 ??J which is free of pulse distortion and stimulated Brillouin scattering. The modulation degree after optimal compensation of waveplates is less than 6%. The output mode field is diffraction-limited.     

Single mode MOPA structured all-fiber Yb pulse fiber amplifier at low repetition

We describe a mopa structured all-fiber 15 μm fiber amplifier cascade. A single-mode diode laser generating 1064 nm wavelength, several nanosecond pulses at 100 Hz repetition was adopted to seed a corepumping amplifier featuring a 6 μm core Yb-doped fiber. Multi-stage pulse-pumping technology was applied to eliminate ASE as much as possible and ease the heat load of the system that leads to the freedom of temperature control of the laser diode. The master oscillator-power amplifier (MOPA) generated 1064 nm, 18 ns pulse-width, 100 Hz repetition of 220 μJ single pulse energy, peak power >12 kW with single transverse output. The pulse energy of 220 μJ is the largest to date in the all-fiber MOPA amplifier with core diameter around 15 μm to our knowledge.     

6.1 MW, 10 kHz Side-Pumped Burst-Mode Nd:YAG Laser

We present a compact high-peak-power, high-repetition-rate burst-mode laser from a master-oscillator power amplifier (MOPA) at 1064 nm for laser-based measurement applications. The oscillator is an 808 nm pulsed laser diode side-pumped acousto-optical (A-O) Q-switched Nd:YAG laser at repetition rates ranging from 10–100 kHz, producing a pulse train with a pulse number of 2–25. The maximum output energy of the oscillator is 15.6 mJ at 10 kHz, whereas it is 1.7 mJ at 100 kHz. After twostage amplifiers, a single-pulse energy of 85.2 mJ with a pulse-width of 14.5 ns is achieved at 10 kHz, which produces a peak power of 6.1 MW. At 100 kHz, the total burst energy reaches 220 mJ with a single-pulse energy of 8.8 mJ in the pulse burst laser system.     

The 266-nm ultraviolet-beam generation of all-fiberized super-large-mode-area narrow-linewidth nanosecond amplifier with tunable pulse width and repetition rate

We report on a compact, stable, all-fiberized narrow-linewidth (0.045 nm) pulsed laser source emitting laser beam with a wavelength of 266 nm, and tunable pulse width and repetition rate. The system is based on all-fiberized nanosecond amplifier architecture, which consists of Yb-doped fiber preamplifiers and a super-large-mode-area Yb-doped fiber power amplifier. The fiber amplifier with a core of 50 μ is used to raise the threshold of the stimulated Brillouin scattering (SBS) effect and to obtain high output power and single pulse energy. Using lithium triborate (LBO) crystal and beta-barium borate (BBO) crystal for realizing the second-harmonic generation (SHG) and fourth-harmonic generation (FHG), we achieve 17 μJ (1.73 W) and 0.66 μJ (66 mW), respectively, at wavelengths of 532 nm and 266 nm and a repetition rate of 100 kHz with pulse width of 4 ns. This source has great potential applications in fluorescence research and solar-blind ultraviolet optical communication.