Ultrafast laser with high power and high energy is widely used in industry and scientific research. The femtosecond laser power output of the mode-locked oscillator stage is usually low, and it is difficult to meet the application requirements, power amplification is performed in the subsequent amplifier stage. Compared with fiber amplifiers, solid state amplifiers have low nonlinear effects and high damage thresholds, so they can support higher energy femtosecond laser output. However, at the same time of obtaining high energy laser output, due to the thermal effect introduced by high power pumping, the beam quality is significantly reduced, and in some applications, the pulse energy is not required to be extremely high, only the mJ magnitude can be reached, and ask it has the characteristics of high beam quality, high pulse quality and high stability. Therefore, it is significant to study a compact single-stage solid-state amplifier, which can output mJ energy while maintaining a high level of beam quality.Based on femtosecond mode-locked laser and all-fiber pre-amplifier stage, combined with chirped pulse amplification technology, a two-pass wave amplification system based on Yb:YAG is constructed. In order to reduce the influence of thermal effect on beam quality and improve pump efficiency, periodic signal modulation is applied to pump control current to realize synchronous pulse pumping with adjustable duty cycle. In order to control the size of the spot in the process of amplification, the self-reproducing optical path is designed and simulated according to the simulation results of thermal lens, and the numerical reference is provided for the selection of focal length parameters of the compensated lens (Fig.2). In order to obtain femtosecond laser output with high pulse quality, the pulse output near the transformation limit is obtained by optimizing the angle and distance of the grating and adjusting the second and third order dispersion values of CFBG. Based on the compressed femtosecond fundamental frequency light with high energy, high beam quality and high pulse quality, a third harmonic converter based on compensation plate is built. By optimizing the parameters of the fundamental frequency light beam size and crystal thickness, the third harmonic generation can be achieved with high conversion efficiency.The results of solid-state laser amplification with different repetition rates, different pumping modes and different pulse pumping widths are studied. When the signal laser repetition rate is low, the optimal pump width is narrower, and the corresponding optimal duty cycle at 1 kHz is 47% (Fig.3(a), Fig.3(b)). Compared with continuous pumping, pulsed pumping has a higher utilization of pump power and can effectively disperse the thermal effect of high pump power at the time scale, with a higher gain potential while maintaining a high beam quality pulse output (Fig.3(c)). A severe gain narrowing effect occurred during solid amplification, with the spectrum narrowing by a factor of 4 before and after solid amplification (Fig.3(d)). A femtosecond laser output with an energy of 1.65 mJ and pulse width of 623 fs was obtained by compressing the amplified laser at full power, with a compression efficiency of up to 93% (Fig.4(a)). The derived depolarization power in the dual-pass system is measured, and its power ratio is stable below 3%, which proves that pulse pumping can effectively alleviate the thermal depolarization effect and obtain better beam quality (Fig.4(b), Fig.4(c)). Due to the use of pulse pumping, its amplification gain is not supersaturated and therefore has a high pulse energy stability (Fig.4(d)). The conversion efficiency of second and third harmonics at different crystal thicknesses is measured. When the crystal length is too long, the nonlinear action is too strong, resulting in susaturation of the rotation efficiency. When the thickness of the double frequency crystal and the sum frequency crystal are both 2 mm, the highest third-harmonic conversion efficiency is 26.5% (Fig.5(a), Fig.5(b)). Due to the limitation of phase matching bandwidth, the spectrum from infrared to green to ultraviolet laser gradually narrows (Fig.5(c)). The beam quality of the third harmonic is reduced due to the effect of higher order nonlinear effect and two-photon absorption effect (Fig.5(d)). The 2-hour power stability of infrared, green, and ultraviolet beams are all measured, and the results show that the system has a high long-term stability (Fig.5(e)).A high energy solid femtosecond laser system was built, and the influence of pulse pumping on the output performance of solid amplification was studied. When the signal repetition rate was low, under the action of short pump pulse width, not only the pump power utilization could be improved, but also the influence of thermal effect was greatly reduced, and the gain potential was higher while maintaining high beam quality pulse output. The high energy and high beam quality femtosecond laser pulse output is obtained with repetition frequency of 1 kHz, energy of 1.65 mJ, pulse width of 623.4 fs, beam quality factor of 1.14, peak-to-peak power stability of 5.0% and energy stability of 1.11%(RMS). Moreover, the characteristics of high energy, high beam quality and high pulse quality lay a good foundation for efficient generation of third harmonic. The UV light with single pulse energy of 0.438 mJ and center wavelength of 344.35 nm was obtained, and the overall conversion efficiency was 26.5%. The third harmonic conversion efficiency reached the advanced level.