High refrequency extreme ultraviolet light source

Post-compression techniques combined with two-color fields produce a high-flux extreme ultraviolet light source
For Tr-ARPES applications, reducing the wavelength of driving light and increasing the probability of gas ionization are effective means to obtain high flux and high order harmonics. In the process of generating high-order harmonics with single-pass high-repetition frequency, the frequency doubling or triple doubling method is basically adopted to increase the production efficiency of high-order harmonics. With the help of post-pulse compression, it is easier to achieve the peak power density required for high order harmonic generation by using a shorter pulse drive light, so higher production efficiency can be obtained than that of a longer pulse drive.

Double grating monochromator achieves pulse forward tilt compensation
The use of a single diffractive element in a monochromator introduces a change in optical path radially in the beam of an ultra-short pulse, also known as a pulse forward tilt, resulting in a time stretching. The total time difference for a diffraction spot with a diffraction wavelength λ at the diffraction order m is Nmλ, where N is the total number of illuminated grating lines. By adding a second diffractive element, the tilted pulse front can be restored, and a monochromator with time delay compensation can be obtained. And by adjusting the optical path between the two monochromator components, the grating pulse shaper can be customized to precisely compensate the inherent dispersion of high order harmonic radiation. Using a time-delay compensation design, Lucchini et al. demonstrated the possibility of generating and characterizing ultra-short monochromatic extreme ultraviolet pulses with a pulse width of 5 fs.

The Csizmadia research team at the ELE-Alps Facility in the European Extreme Light Facility achieved the spectrum and pulse modulation of extreme ultraviolet light using a double grating time-delay compensation monochromator in a high-repetition frequency, high-order harmonic beam line. They produced higher order harmonics using a drive laser with a repetition rate of 100 kHz and achieved an extreme ultraviolet pulse width of 4 fs. This work opens up new possibilities for time-resolved experiments in situ detection in the ELI-ALPS facility.

High repetition frequency extreme ultraviolet light source has been widely used in the study of electron dynamics, and has shown broad application prospects in the field of attosecond spectroscopy and microscopic imaging. With the continuous progress and innovation of science and technology, the high repetition frequency extreme ultraviolet light source is progressing in the direction of higher repetition frequency, higher photon flux, higher photon energy and shorter pulse width. In the future, continued research on high repetition frequency extreme ultraviolet light sources will further promote their application in electronic dynamics and other research fields. At the same time, the optimization and control technology of high repetition frequency extreme ultraviolet light source and its application in experimental techniques such as angular resolution photoelectron spectroscopy will also be the focus of future research. In addition, the time-resolved attosecond transient absorption spectroscopy technology and real-time microscopic imaging technology based on high repetition frequency extreme ultraviolet light source are also expected to be further studied, developed and applied in order to achieve high-precision attosecond time-resolved and nanospace-resolved imaging in the future.