Fig. 1. Conceptual design of the kilohertz ultra-intense ultra-short Yb:KGW-based CPA system.

Fig. 2. Laser system design. HW: half-wave plate; QW: quarter-wave plate; FR: Faraday rotator; TFP: thin-film polarizer; PC: Pockels cell; M1, M2, M6 and M7: cavity mirrors; M3 and M4: dichroic mirrors.

Fig. 3. (a) Illustration of gain-narrowing effect compensation under the dual-crystal configuration; (b) spectrum of Q-switched laser output under the two crystal placement configurations. The black line denotes the configuration with the crystals placed in the same orientation, while the red line is under the configuration of crystals placed in orthogonal orientation.

Fig. 4. Beam radius variation on the two crystals while changing the focal length of the thermal lensing effect.

Fig. 5. Output characteristic of the cavity working under QCW pumping (1/3 duty cycle at 1 kHz) with a pump peak power up to 80 W. PC: Pockels cell.

Fig. 6. Ray-tracing model of our stretcher and compressor. TG: transmission grating; P1, P2: periscope; M1: broadband high reflection mirror at 0°; M2–M6: broadband high reflection mirrors at 45°; L1, L2: lenses; S1: translation stage where M2 and M3 were fixed.

Fig. 7. Calculated compressed pulse output (blue solid line) with 150 fs pulse input (dark dashed line) by our compact stretcher and compressor.

Fig. 8. Intra-cavity pulse amplification process monitored by an oscilloscope. The pulse underwent an unsaturated amplification because of the mirror damage limitation.

Fig. 9. (a) Input seed spectrum (black line) and output pulse spectrum (red line) delivered by the regenerative amplifier. (b) Compressed pulse duration (black line) and its Gaussian fit (red line) showing a pulse duration of approximately 227 fs. (c) M² factor of the output laser beam (inset: near-field and far-field beam profiles).