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This article discusses the development of a cryogenically cooled rod Yb:YAG regenerative amplifier that produces high-energy, ultrashort laser pulses. The amplifier delivers 12-mJ, 90-ps pulses at a 1-kHz repetition rate with an efficiency of 31.7%. The design compensates for thermal lensing effects and achieves a beam quality of 1.1 in both horizontal and vertical directions. The Yb:YAG material used has high thermal conductivity and emission cross-section, but its narrow emission spectrum bandwidth limits pulse durations. The article presents experimental results and discusses the potential for further increasing pulse energies. The authors provide their raw data and funding sources, stating no conflicts of interest. [Extracted from the article]

We report on a continuous-wave (CW) pumped cryogenically cooled rod Yb:YAG regenerative amplifier delivering uncompressed 12-mJ, 90-ps, 1030-nm pulses at a 1-kHz repetition rate. The amplifier demonstrates an efficiency of 31.7%. A symmetric cavity design was utilized to compensate for the substantial thermal lensing effect, yielding a final measured beam quality of 1.1 in both horizontal and vertical directions. After significant gain narrowing, the measured spectra exhibit a bandwidth of 0.3 nm corresponding to an approximately 5 ps transform-limited pulse.

The photoinjector laser system of Shenzhen Superconducting Soft X-Ray Free Electron Laser (S3FEL) is reported in this paper. This laser system operates at up to 1 MHz and produces more than 50 μJ infrared (IR) laser pulses. With a customized fourth harmonic generation (FHG) module, more than 2 μJ ultraviolet (UV) laser pulses were obtained. The power standard deviations of the IR laser and the UV laser are 0.093% and 0.395% respectively. While the pulse energy standard deviations are 1.087% and 1.746% correspondingly. We implemented the pulse stacking scheme to generate flat-top pulses. With four birefringent uniaxial crystals, the Gaussian pulses were converted to flat-top shape, featuring 10 ps pulse width and 0.5 ps rising and falling edges. A cut-Gaussian transverse profile with very sharp rising and falling edges can be produced after the spatial pulse shaper.