Single-pulse time-resolved comparative study on the performance of a master-oscillator,power-amplifier copper-vapor-laser system with generalized diffraction-filtered and unstable resonators as master oscillators

We present results of comparative time-resolved coherence studies on a single pulse from amaster oscillator power amplifier (MOPA) copper vapor laser with generalized diffraction-filtered and unstable resonators as master oscillators. It is shown that, unlike the conventionally used unstable-resonator MOPA reported in literature, the coherence of a generalized diffraction-filtered resonator MOPA pulse is fairly independent of the delay between the oscillator and the amplifier. It also remains constant throughout the pulse, with the result that the flux is constant over a large range of the delay.     

High peak-power single-frequency pulses using multiple stage, large core phosphate fibers and preshaped pulses

We have developed a monolithic high power pulsed fiber laser in a master oscillator power amplifier (MOPA) configuration, which is capable of reaching 0.38 mJ pulse energy and 128 kW peak power for 3 ns pulses at ~1550 nm while maintaining transform-limited linewidth. The fiber laser pulse seed was achieved by directly modulating a CW single-frequency fiber laser using an electro-optic modulator. We used an arbitrary waveform generator to preshape the fiber laser pulses before amplification to avoid pulse steepening and dynamic gain saturation. Single-mode, polarization maintaining highly Er/Yb codoped large core phosphate fibers were used in the power amplifier stages to scale the transform-limited fiber laser pulses, avoiding any nonlinearities.     

150 W high-average-power, single-frequency nanosecond fiber laser in strictly all-fiber format

We demonstrate an all-fiber, single-frequency nanosecond laser with both high peak power and average power based on a master oscillator power amplifier (MOPA) configuration. The MOPA produced a single-frequency pulsed laser with pulse duration of ～8 ns. The average and peak power were as much as 139.3 W and 1.07 kW, respectively, when the repetition rate was 10 MHz, and 153.1 and 668 W, respectively, when the repetition rate was 20 MHz. Higher output power can be obtained by increasing pump power of the main amplifier.     

全光纤结构超短脉冲光纤放大器

本文利用掺Yb光纤的非线性偏振旋转效应搭建了光纤环形腔激光器,通过改变增益光纤的长度和耦合器输入输出的比例,对其进行优化,获得了稳定的自启动锁模脉冲,并以此作为种子源,采用主振荡功率放大MOPA全光纤结构,以双包层掺Yb光纤为增益介质实现了对种子源信号光的放大,获得了平均功率2.042W、中心波长1063.8 nm、重...     

500 Hz ultraviolet dye laser with pulse energy 1.7 mJ and potential for PLIF imaging

ABSTRACT

This paper describes a high-pulse-energy frequency-doubled ultraviolet dye laser operating at a repetition rate of 500?Hz. The pump source is a laser-diode side-pumped Q-switched Nd:YAG laser with a pulse energy of 29?mJ at 532?nm. A master oscillator power amplifier is employed to amplify the output pulse of the dye laser to 8.1?mJ at 566?nm, and by frequency doubling with BBO crystal a pulse energy of 1.7?mJ at 283?nm is achieved with a pulse width of 8?ns. This is more than four times the largest reported pulse energies generated by other fixed-frequency dye lasers when operating at repetition rates of more than 1?kHz. The conversion efficiency and stability of dye laser are discussed, which show the potential for high-speed laser diagnostics in the fields of combustion and turbulent flow detection.     

Scaling up of a high average power dye laser amplifier and its new pumping designs

Scaling up of a high average power dye laser amplifier is discussed. Differences in the characteristics between a high average power dye laser amplifier with transverse pumping and longitudinal pumping are presented by a simple theory and simulations. The simulation results for dye laser amplifiers of 10-kW average output power show that longitudinal pumping is as efficient as transverse pumping with the potential of orders of magnitude lower dye flow rate. New pumping designs are also proposed for a dye laser amplifier aimed to achieve high gain with high efficiency to reduce the number of amplifier stages. Simulation results suggest that the new designs, in comparison with a conventional amplifier, can produce several orders of magnitude higher gain without decreasing the conversion efficiency.     

Single-frequency pulsed laser source with hybrid MOPA configuration

A unique approach with a hybrid master oscillator power amplifier configuration to obtain single-frequency, high-energy laser pulses at 1064 nm is presented. The setup consists of a single-frequency seed laser, a multistage fiber amplifier, and a four-pass crystal rod amplifier. Pulse energy of 10 mJ is obtained at the repetition rate of 100 Hz. The pulse width is about 110 ns with a transform-limited linewidth of 3.2 MHz. The M(2) factor of the output beam is about 1.5. To our knowledge, this is the first report of using a hybrid amplifier to obtain 10 mJ pulses with long pulse width and transform-limited linewidth.     

Near-diffraction-limited, high-energy, high-power, diode-pumped laser using thermal aberration correction with aspheric diamond-turned optics

We achieved a 1.3× diffraction-limited output beam with a pulse energy of 0.76 J at 60 Hz (average power of 46 W) at 1.064 μm from a diode-pumped Nd:YAG master oscillator power amplifier rod laser using a diamond-turned aspheric optic to compensate thermally induced phase distortion of the gain medium. The output was frequency doubled in KTP to 30 W (0.5-J pulse energy) and 2.4× diffraction-limited at 532 nm.     

Compact 50-Hz terawatt Ti:sapphire laser for x-ray and nonlinear optical spectroscopy

We report a high-repetition-rate, compact terawatt Ti:sapphire laser system. The oscillator produces an 82-MHz pulse train consisting of broad-bandwidth pulses of 0.5-nJ/pulse energy and of 9-fs pulse duration. The spectrally shaped, lambda/4 regenerative amplifier supports an 80-nm bandwidth. A single 50-Hz repetition-rate pump laser pumps both the regenerative amplifier and a multiple-pass amplifier. The final output from this laser is a 50-Hz pulse train made from pulses of 53 mJ/pulse energy and of 24-fs pulse duration. For generating ultrafast x-ray pulses, 90% of the energy from the final output of a 28-mm-diameter (1/e2) beam is focused onto an ultrafast x-ray wire target. The energy conversion efficiency from optical (800-nm central wavelength) to x-ray (characteristic lines of K(alpha) from Cu at 8 keV) pulses is estimated to be 7 x 10(-5). This laser system can also generate a lower-peak-power, dual-pulse output that can excite, simultaneously and coherently, Raman modes within an adjustable bandwidth (up to 700 cm(-1)) and at a tunable central vibrational frequency. Preliminary results for the generation of dual-pulse output and ultrafast x rays are presented.     

Generalized formula for continuous-wave end-pumped Yb-doped material amplifier gain and laser output power in various pumping configurations

We present a general formula fitted for computing the amplification and laser output power in a Yb-doped material under various quasi-end-pumping configurations. These configurations include single pass pumping, backreflection pumping in which the pump is reflected by a mirror set on the rear face of the amplifier medium, contrapropagation pumping where two pump beams are launched on both sides of the amplifier and, for every configuration, regenerative pumping in which the transmitted or reflected pump beam is recycled using the proper apparatus. We show that, with regenerative pumping, the efficiency is drastically improved and the optimum amplifier length leading to the maximum laser output power is shorter compared with the one obtained with conventional pumping. In this model, we do not take temperature effect into account.     

Pulse shaping fiber laser at 1.5 μm

In this paper we present, for the first time to our knowledge, a new pulse shaping technology (modulation schemes for seed laser) used to mitigate pulse narrowing effect and SBS effect in a high energy Er:Yb codoped fiber master oscillator power amplifier system at 1.5 μm to obtain longer pulse duration and higher energy. An average power of over 1.3 W and a pulse energy of over 0.13 mJ were obtained at 10 kHz repetition rate with a pulse duration of 200 ns and near-diffraction-limited beam quality (M(2)<1.2).     

Diode-pumped Nd:YAG master oscillator power amplifier with high pulse energy, excellent beam quality, and frequency-stabilized master oscillator as a basis for a next-generation lidar system

A pulsed, diode-laser-pumped Nd:YAG master oscillator power amplifier (MOPA) in rod geometry, frequency stabilized with a modified Pound-Drever-Hall scheme is presented. The apparatus delivers 33-ns pulses with a maximum pulse energy of 0.5 J at 1064 nm. The system was set up in two different configurations for repetition rates of 100 or 250 Hz. The beam quality was measured to be 1.5 times the diffraction limit at a pulse energy of 405 mJ and a repetition rate of 100 Hz. At 250 Hz with the same pulse energy, the M2 was better than 2.1. The radiation is frequency converted with an efficiency of 50% to 532 nm. This MOPA system will be the pump laser of transmitters for a variety of high-end, scanning lidar systems.     

Characterization of a high-brilliance soft x-ray laser at 13.9 nm by use of an oscillator-amplifier configuration

We have improved a highly coherent x-ray laser at 13.9 nm using an oscillator-amplifier configuration. To improve a high-brilliance x-ray laser, we adopted traveling wave pumping for the amplifier target and rotated the amplifier target 3-4 mrad in the counterclockwise direction. Thereby, a seed x-ray laser can be amplified by medium plasma of the amplifier target with a high gain coefficient. The amplified x-ray laser has the output energy of approximately 1.3 microJ, corresponding to a large photon flux of 6.5 x 10(10) photons/pulse and a high peak brilliance of 5 x 10(26) photons/(s x mm(2) x mrad(2) x 0.01% bandwidth).     

高功率双包层Er3+/Yb3+共掺光纤放大器的动态响应

基于速率方程的离散算法,分析了双包层Er3 /Yb3 共掺光纤放大器的动态响应,显示了输出功率和增益的动态特征。当单个脉冲注入放大器时,输出脉冲的峰值功率不仅依赖于输入脉冲的峰值功率,而且依赖于泵浦功率;当脉冲序列注入时,输出脉冲的功率和增益最终将收敛于它们的稳态值。在双信道情况下,输入脉冲重叠时的输出功率和增益变得更陡峭。在连续波泵浦下,反向自发辐射输出功率(ASE-)首先快速地增加到峰值功率,然后单调下降到稳态值;在脉冲波泵浦下,反向自发辐射输出功率(ASE )与光纤长度成反比,而ASE-与光纤长度成正比。     

Semiconductor saturable absorber mirror passively Q-switched fiber laser near 2 μm

A passively Q-switched fiber laser near 2?μm is achieved with a semiconductor saturable absorber mirror (SESAM) as a saturable absorber. Stable Q-switched pulses are generated from an extremely compact setup with a central wavelength of 1958.2?nm. Under the bidirectional pump configuration, the repetition rate of the fiber laser can be widely tuned from 20 to 80?kHz by increasing the pump power at the same time the pulse width decreases from 1?μs to 490?ns. When the incident pump power is 1.3?W, the average output power, the pulse repetition rate, the pulse width, and the highest single pulse energy are 91?mW, 80?kHz, 490?ns, and 1.14?μJ, respectively. To further optimize the system configuration, the pulse width can be reduced to 362?ns when the cavity length is reduced.     

Operational stabilization of a high-power ultrashort dye oscillator-amplifiers laser chain

Stable operation of a high-power ultrashort dye laser chain is achieved with an inexpensive heating technique. The femtosecond oscillator and its pumping laser are separately covered with boxes to isolate them from external temperature fluctuations. Both laser-isolating boxes are lined with a heating pellicle that permanently and uniformly warms the lasers to preset operating temperatures. The power, spectrum, and duration of the laser-chain output pulse remain constant from day to day. This technique could be applied to other ultrafast laser devices that require long-term performance stability.     

High-power widely tunable thulium fiber lasers

Applications requiring long-range atmospheric propagation are driving the development of high-power thulium fiber lasers. We report on the performance of two different laser configurations for high-power tunable thulium fiber lasers: one is a single oscillator utilizing a volume Bragg grating for wavelength stabilization; the other is a master oscillator power amplifier system with the oscillator stabilized and made tunable by a diffraction grating. Each configuration provides >150 W of average power, >50% slope efficiency, narrow output linewidth, and >100 nm tunability in the wavelength range around 2 μm.     

Laser-induced predissociative fluorescence: dynamics and polarization and the effect of lower-state rotational energy transfer on quantitative diagnostics

Laser-induced predissociative fluorescence is often used for diagnostics because its short-lived upper states are minimally disturbed by collisions. We discuss the effects of lower-state collisions with parameters relevant to our atmospheric H(2)-O(2) flame. A pulse of tunable KrF excimer-laser light induces the A ? X, Q(1)(11), 3 ? 0 transition in OH. We measure the intensity and the polarization of the resulting A ? X, Q(1)(11), 3 ? 2 fluorescence as a function of laser brightness. A simple model that uses no adjustable parameters produces a reasonable fit to the data. It predicts that, even at very modest laser energies, the fluorescence intensity is almost directly proportional to the rate constant for rotational energy transfer (RET) within the lower vibrational state. That rate constant can be a strong function of local conditions. Furthermore, under typical operating conditions the excimer will pump an amount of OH out of the lower state that is many times as large as that originally present. This occurs because RET within the X-state continuously replenishes the lower state during the laser pulse. Even when this occurs, the signal may still vary linearly with laser intensity, and the polarization may be nearly that expected for weak pumping. At the higher laser intensities, a significant fraction of the measured OH arises from two-photon photodissociation of the water from the flame reaction.     

Output Energy Fluctuations of the Nd:YAG Amplifier Chain of a Photoinjector Drive Laser System

In the Etude d'un LaSer Accordable, electron bunches consist of trains of picosecond pulses extracted from a photocathode by a drive laser system: This system consists of a mode-locked Nd:YAG oscillator followed by a pulse compressor, an amplifier chain, and a second-harmonic-generation stage. The performance of the linac critically depends on the energy stability of this system. It is demonstrated theoretically and experimentally that the energy fluctuations of the Nd:YAG oscillator are significantly reduced by the amplifier chain, that the remaining energy fluctuations of the whole system are mainly due to amplifier pump fluctuations, and that the amplifier chain can be optimized to reduce the global energy fluctuations from 1.5% rms to <1% rms.     

High-power tunable narrow-linewidth Ti:sapphire laser at repetition rate of 1 kHz

We report a high-power tunable narrow-bandwidth Ti:sapphire laser at a repetition rate of 1?kHz. The spectral linewidth of 0.4?pm with wavelength tuning range from 780?nm to 820?nm is obtained by a spectrum-compressing technique that consists of one grating and four fused silica prisms in the oscillator cavity. This narrow-bandwidth seed from the oscillator is further amplified to 6.5?W with pulse duration of 16?ns under the pumper power of 22?W. This high-power laser with narrow linewidth is candidate for isotope separation and accuracy spectrum analysis.