With the development of ultrafast laser technology, especially the generation of high power few-cycle femtosecond laser pulses with their carrier-envelope phase (CEP) locking, attosecond laser pulses based on high-order harmonic generation (HHG) via interaction between high power femtosecond lasers and noble gas have become a leading direction in ultrafast sciences. In 2001, the attosecond pulse train and isolated attosecond pulse (IAP) were realized successively by Pierre Agostini’s team and Ferenc Krausz’s team respectively, and the generation and measurement of attosecond pulses made scientists master a powerful tool to look into ultrafast processes inside materials at unprecedented precision, thus giving birth to a new field and research direction: attosecond science. Characterized by unique specifications such as very short pulse duration with high photon energy and sound coherence, the attosecond light beam provides unprecedented new tools that can go deep into the interior of atoms to measure their electronic dynamic behavior, thus triggering a revolution in basic research. Therefore, the 2023 Nobel Prize in Physics was awarded to three physicists, Pierre Agostini, Ferenc Krausz, and Anne L’Huillier, for their pioneering contributions to the experimental method of generating attosecond light pulses to study the electron dynamics in matter. Many countries have invested a lot of funding to carry out relevant studies. In particular, Europe soon established the attosecond alliance. Meanwhile, Ferenc Krausz led the establishment of the Max Plank center for attosecond science including scientists from China, Japan, the Republic of Korea, Australia, and other countries. Meanwhile, it is worth mentioning that under the proposal of G. Mourou and other scientists, the European Union started to conduct a research program on the extreme light infrastructure (ELI) early in 2006. This program included the ELI-attosecond light physical science (ELI-ALPS) facility located in Hungary with attosecond light sources as the main beams, in which attosecond beams with different specifications, high harmonics, terahertz, and ion electron beams were contained. In 2019, partial beams were completed and open to users. In China, theoretical and experimental studies on attosecond pulse generation and application are also significant. The first IAPs were demonstrated by the Institute of Physics, Chinese Academy of Sciences (CAS) in 2013. Subsequently, Xi’an Institute of Optics and Precision Mechanics of the CAS, the National University of Defense Technology, and Huazhong University of Science and Technology also obtained IAP generation. To better realize the application of attosecond light pulses in multiple fields and make them serve more users, in September 2017, the Institute of Physics, CAS built a large ultrafast dynamic and image system as one of the four extreme conditions of the “Synergetic Extreme Condition User Facility (SECUF)”, with the support of National Major Basic Science Infrastructure Projects. The attosecond laser station is responsible for the generation and application of IAPs based on high harmonic generation with a pulse duration less than 100 as in extreme ultraviolet (XUV) and is equipped with time-resolved angle-resolved photoelectron spectrometer (ARPES), photoelectron microscope (PEEM), cold target recoil-ion momentum spectrometer (COLTRIMS) and other terminal devices. Thus, this provides users time resolution from attosecond to femtosecond and momentum, and energy resolution measurements are conducted for studying ultrafast dynamics of physical, chemical, and biological materials on an atomic scale.

According to the construction content and goal of attosecond laser stations, we have constructed four attosecond and femtosecond light sources in the XUV range. Each beam contains an XUV light source designed specifically for application experiments with its end station. The first beam employs the high-energy few-cycle fs laser as the driving laser to produce broadband XUV isolated attosecond light for attosecond photoelectron spectroscopy and attosecond transient absorption spectroscopy. This will be adopted to study the electron dynamics in atoms, molecular and condensed matter by utilizing attosecond streaking and transient absorption. The second XUV beam leverages the high repetition rate and high power fs laser as the driving laser to produce narrowband femtosecond XUV pulses for time-resolved ARPES to study the electronic dynamics on the timescale of fundamental correlations and interactions in condensed matter. The third beam adopts high-energy few-cycle fs lasers at 10 kHz to produce broadband XUV pulses for attosecond coincidence spectroscopy in a COLTRIMS to research the ultrafast dynamics and reactions in atomic and molecular systems. The fourth beam utilizes high repetition rate few-cycle lasers to produce broadband attosecond XUV pulses for time-resolved PEEM to study the ultrafast dynamics of plasmons in nanostructures and surfaces of solid materials with high temporal and spatial resolutions simultaneously.

After five years of development of four XUV beams and their end station, the attosecond laser station can output XUV coherent radiation with photon energy of nearly 100 eV and IAPs with pulse width of 86 as. The time-resolved ARPES beam employs a femtosecond laser with an average power of 280 W in 57 fs at repetition rate of 500 kHz to produce high-order harmonics of 20-50 eV. A narrowband high-order harmonic light source is selected by a monochromator and combined with a femtosecond IR laser to form a pump-probe pulse, which is jointly focused on the ARPES sample. The generated photoelectrons are detected by an energy analyzer. By scanning the precise delay between the pump light and detection light, the time resolution is demonstrated to be 125.75 fs, with the energy resolution of 43.9 meV. The minimum temperature of the sample is 3.8 K. As for PEEM, the spatial resolution of PEEM with 21.6 eV high harmonic light source generated by few-cycle lasers at 100 kHz is demonstrated to be 20 nm. As for COLTRIMS, the momentum resolution of electrons is 0.03 a.u., and the momentum resolution of ions is 0.04 a.u. All four beams in the attosecond laser station work normally and are provided for users. For further development, we will develop the sub-50-as XUV light source using mid-IR fs lasers at 2.2 μm. We will also develop time-resolved ARPES based on TOF (time-of-flight spectrometer)-ARPES and momentum microscopes to realize fs resolved, high energy resolved, and spatial resolved measurements.

The attosecond laser station, which has four XUV beamlines with its own end station, was built in Huairou District, Beijing as a condition of SECUF. Based on few-cycle femtosecond pulses and HHG technology, the experimental station can provide IAPs with a pulse duration of less than 100 as in the XUV range. Meanwhile, time-resolved ARPES, PEEM, COLTRIMS, and other end stations are included to help users study fundamental ultrafast processes in physics, chemistry, biology, and material sciences with temporal resolution from femtosecond to attosecond on atomic scale.