Amplification Of Solid-State And Fiber Ultra-Short Pulse Lasers

With the development of the ultrafast lasers, reliable and stable performance high power high energy ultrashort pulsed lasers with repetition rates from 100 kHz to 1 MHz have facilitated extensive applications in micro-fabrication, clinical medicine, spectroscopy and national defense fields and they have been concerned as a topic of research in recent years. Consequently, to meet the requirements of the development of the high average power ultrafast lasers in various areas of reaearch and application, this dissertation is focused on the investigation of the high repetition rate high energy 100 kHz,21 W all-solid-state picosecond laser amplifier based on the hybrid amplification technology consisting of an electro-optic modulated regenerative amplifier and three-stage single pass power amplifiers and 1 MHz,10.5 μJ all-fiber femtosecond laser amplifier based on the acousto-optic modulated all fiber chirped pulse amplification (CPA) scheme.Together to cater for the requirements of the development of the high repetition rate hundreds of Watts laser amplifier systems for the femtosecond seed sources with compactness in structure and low cost and easy operation, further combining polarization maintaining (PM) large mode area (LMA) rod-type photonic crystal fiber (PCF) with nonlinear polarization evolution mode-locked technique, we conduct an experimental study on high power environmentally stable rod-type femtosecond mode-locked all-normal-dispersion (ANDi) fiber laser, which has an important significance for the development of the hundreds of watts laser systems toward the direction of the facilitation and compactness.1. An efficient amplification of the picosecond Nd:YVO4 laser system at a repetition rate of 100 kHz based on highly stable all-solid-state picosecond laser oscillator as seed source and high power 808 nm diode lasers as pump sources is presented. This amplifier system consists of a regenerative amplifier and three-stage single pass power amplifiers. In order to improve the amplification efficiency of the regenerative amplifier, the Nd:YVO4 gain crystal in the regenerative cavity is put close to the pump mirror with a spatial distance of 8 mm to allow for four passes of the seed laser pulse through the gain crystal for each cavity round-trip period rather than two passes. As a front end, the regenerative amplifier emits average power of 2.6 W at 100 kHz repetition rates seeded with a 10 ps,1064 nm mode-locked vanadate oscillator. Adopting the end-pumping scheme with 808 nm fiber coupled laser diodes as pump sources, the following three-stage booster amplifiers further amplify the average power to 21 W. The corresponding extraction efficiencies are 31%,26% and 36%, respectively. The final pulse duration is approximately 30 ps and the beam quality factors M2 are 2.0 in the horizontal and 1.9 in the perpendicular direction, respectively. This laser may enable wide applications for micro-fabrication and laser matter interaction.2. Tunable high peak signal-to-noise ratio (SNR) harmonically mode-locked ANDi femtosecond fiber laser has been developed based on highly doped Yb gain fiber and NPE technique and the corresponding theoretical explanation has also been provided. The external compressed pulse duration is 627 fs assuming a sech2 distribution with 600 lines/mm grating pair at the 4th harmonic of 88 MHz with 73 dB SNR. In addition, it is also experimentally found that multipulse soliton bunches with controllable pulse spacing and number could been realized in the formation process of the harmonic mode-locking, which promotes the further understanding of the ANDi dissipative soliton mode-locked operation. Furthermore, high energy low repetition rate ytterbium fiber triple-wavelength mode-locked laser has also been realized at 1.7 MHz repetition rate based on birefringent filter as spectral shaper. To our best knowledge, the widest tuning range (19 nm) and the highest output power (161.4 mW) in mode-locked operation have been obtained in this presented fiber laser and the corresponding mechanism has been explained based on four-wave mixing (FWM).3. In view of the dissipative mechanism related mode-locked operation in ANDi ultrafast fiber lasers, which provides a possibility for the generation of the high power high energy laser pulses in theoretical, therefore adopting PM rod-type PCF with 85 μm core diameter, a 16 W,182 fs environmentally stable high power rod-type mode-locked fiber laser oscillator has been firstly developed domestically at 58 MHz repetition rate based on ANDi scheme. Further, by optimization of the cavity structure and adopting more powerful wavelength-stabilization 976 nm laser diode as pump source, the highest 31 W mode-locked output power has been obtained with 124 fs compressible pulse width at a repetition rate of 57.93 MHz, and the measured short-term power fluctuations is 0.3% (RMS) over two hours. The newly developed high power high energy rod-type mode-locked fiber laser will find wide applications such as in high power fiber laser pumped femtosecond optical parametric oscillator and as a front-end seed source in hundreds of watts femtosecond laser amplifier system. In addition, aiming at realizing high power laser amplifier with high peak power without external compression, a MW peak power PM all rod-type fiber amplifier has been proposed, which consists of a home-made 30 MHz femtosecond mode-locked seed source, a core-pumped single mode preamplifier, a pre-chirper and two-stage rod-type fiber amplifiers. The seed pulse is firstly amplified to 321 mW in core-pumped preamplifier and then pre-chirped to 7.23 ps. After polarization through a Glan laser polarizer, the pulse train is injected into the first-stage rod-type fiber amplifier to be amplified to 32.6 W with 6.5 ps pulse duration. The pre-amplified pulse train is finally amplified to 53.4 W in the second-stage rod-type fiber amplifier. The adopted rod-type gain fibers have 85 μm core diameter and 260 μm pump cladding. However, due to the mismatch of the wavelengths from the pump diode with the absorption peak of the rod-type gain fiber in the second-stage amplifier, the amplification efficiency is low and further optimization is going on.4. An all-fiber amplifier at 1 MHz repetition rate has been successfully developed based on self-made dispersion-management 32.7 MHz ytterbium fiber femtosecond mode-locked seed source and CPA scheme. By temporally stretching the pulses to hundreds of picoseconds in single mode fibers and reducing the repetition rate to 1 MHz with acousto-optic modulator, up to 10.5 μJ pulse energy could been obtained with 804 fs compressible pulse duration. The shortest pulse duration achieved is 424 fs corresponding to the uncompressed pulse energy of 6.75 μJ. The developed high energy all-fiber femtosecond laser amplifier will find wide applications in practice.