Fig. 1. Experimental setup and beam spots. (a) Schematic of experimental setup for pulse post-compression in HCF; (b) output beam profile from fiber laser; (c) focal spot profile with diameter of 161 µm @ 1/e²; (d) output beam profile from HCF

Fig. 2. MPC pulse post-compression module. (a) Schematic of experimental path; (b) output beam profile from fiber laser; (c) output beam profile from MPC

Fig. 3. Comparison of pulse post-compression results. (a) HCF broadening spectrum (dashed line), MPC broadening spectrum (solid line), and original pulse spectrum (dotted line); (b) temporal curves for HCF compression (dashed line), MPC compression (solid line), and original (dotted line) pulses

Fig. 4. Experimental setup for gas-based HHG and detection and beam spots. (a) Schematic of experimental path ; (b) distribution of spot intensity at 2.4 mm before focus; (c) distribution of spot intensity at focus; (d) distribution of spot intensity at 2.4 mm after focus

Fig. 5. HHG spectra resulting from interaction of pulse with argon and krypton gas after recompression by HCF and MPC at driven light source with repetition rate of 200 kHz. (a)(d)(g) 6.5 bar backing pressure argon driven by 120 µJ, 27 fs pulse from HCF; (b)(e)(h) 4.0 bar backing pressure krypton driven by 120 µJ, 27 fs pulse from HCF; (c)(f)(i) 8.0 bar backing pressure krypton driven by 215 µJ, 55 fs pulse from MPC

Fig. 6. HHG simulation spectra using strong field approximation model with different driving pulse durations under krypton. (a) 27 fs; (b) 55 fs

Fig. 7. Optimized HHG signal from krypton under 500 kHz repetition rate. (a) Flat-field spectrum; (b) spatially integrated spectral lineout

Fig. 8. Impact of driving pulse energy on HHG signal. (a) Ar with 6.5 bar backing pressure; (b) Kr with 6.5 bar backing pressure

Fig. 9. 33rd harmonic signal intensity from krypton versus driving pulse energy

Fig. 10. Spectral comparison for HHG at 500 kHz repetition rate under different krypton gas backing pressures. (a) 6 bar; (b) 4 bar; (c) 2 bar

Fig. 11. Simulation with strong field approximation model for Kr-based HHG under different pressures. (a) 6.7 mbar; (b) 33.3 mbar; (c) 66.5 mbar

Fig. 12. HHG spectra at different Z positions from interaction between Ar with 6.5 bar backing pressure and driving pulse with 200 kHz repetition rate. (a) Z=-3.0 mm; (b) Z=-2.4 mm; (c) Z=-1.8 mm

Fig. 13. Simulation results of HHG from Ar at different Z positions. (a) Z=-3.0 mm; (b) Z=-2.0 mm