Stability, beam profile, spectra and pulse duration of compressed pulse and dispersive wave

Temporal characterization of ultrafast pulse. Temporal characterization of pump pulses and pulses output from MPC and HCF compression stages was based on a home-built all-reflective split-mirror SHG-FROG set-up, based on a 10-μm-thick BBO crystal cut for type I phase-matching. Pulse characterization of dispersive-wave pulses at 250 nm and 400 nm was carried out using a home-built SD-FROG set-up. The optical path of SD-FROG is similar to SHG-FROG, with the main difference being 50-μm-thick fused silica replaced BBO crystal and used aluminum mirrors with high reflectivity for UV pulses. The raw traces were spectrally corrected using the frequency marginal and retrieved using a commercial software. The small FROG errors and excellent agreement between retrieved and measured spectra (Figs. 2, 3 and 6) confirm the reliability of the pulse measurement process.Measurement of laser beam profile. The beam profiles of the compressed pulses and the dispersive waves are both measured by a CCD camera (BGS-USB3-SP932U, Ophir-Spiricon). It should be pointed out that the measurements of dispersive-waves profiles are first filtered by the bandpass filters (Pelham Research Optical for 200-260 nm, Thorlabs for 260-400 nm, and LBTEK for >400 nm). The far-filed images are measured at the focus point of the lens with a focal length of 1 m.Measurements of laser spectrum. At a repetition rate of 25 kHz, we measure the pulse spectrum in the wavelength range of 200 nm to 300 nm using a UV spectrometer (Maya2000-Pro, 185–400 nm, Ocean Optics), in the wavelength range of 300 nm to 1000 nm using a ultraviolet-to-visible spectrometer (PG2000-Pro-Ex, 200–1100 nm, Ideaoptics), and in the wavelength range of 1000 nm to 1700 nm using a near-infrared spectrometer (NIR17S, 900–1700 nm, Ideaoptics). All three spectrometers have been calibrated and can be used to measure pulse spectra in a wide spectral range of 200-1700 nm. Splice the spectra measured by these three spectrometers, we finally obtained the full spectra of the HCF output pulses when the dispersive wave was generated at the wavelength of 250 nm, as shown in Figs. 5 and 6. Maya2000-Pro and HR4000CG (200–1100 nm, Ocean Optics) were used to measure the dispersive-wavs spectra at 100 kHz. It should be noted that some spectral measurements, dispersive waves with a wavelength range of >300 nm at 25 kHz and >230 nm at 100 kHz are first reflected by a fused silica to protect the spectrometer, and then the reflected light from the front surface is coupled to the fibre-coupled spectrometer connected with an integrating sphere.