Fig. 1. Schematic of the experimental setup, which consists of an Yb-fiber-based CPA driving laser, an LMA fiber based pulse compressor, PDH locking electronics and a large-scale bow-tie enhancement cavity.

Fig. 2. (a) Optical spectra of FCPA output (blue) and compressed pulses (red). (b) Temporal pulse shapes as measured by FROG for original pulses from the FCPA (blue) and externally compressed pulses (red). (c) Output power (red) and total efficiency (blue) of the external pulse compression stage, including dispersion compensation. (d) Beam profile of the compressed laser pulses.

Fig. 3. Long-term measurement of average outcoupled power of 7th order of harmonic with Xe using driving laser and 3% IC.

Fig. 4. Outcoupled high harmonic spectra for post-compressed pulses (red) and original pulses (blue). The pulse durations of those pulses are estimated to be (red) and (blue). Xe gas was used. The first row of black dots indicates the position of different harmonic orders from 7th to 39th. For saving space, the numbers of 15th to 37th are now shown here. The second row of black dots indicates the contributions from higher order diffraction.

Table 1. The average power inside the enhancement cavity for short pulse duration at different conditions for 1% and 3% IC. IC: input coupler, IP: intra-cavity power, W/O gas: without gas loaded, With gas: with gas loaded.