With a high peak power and high pulse energy, the physical effect of the interaction between picosecond petawatt laser and matter is related to key factors such as pulse signal-to-noise ratio, focusing power density, and spatio-temporal control accuracy. This paper presents a comprehensive study of these three factors, as well as the associated limiting mechanism, key technologies, and latest development of the SG-II-UP picosecond petawatt laser. This provides has a guiding role in improving the performance of petawatt lasers. For the load limitation of picosecond petawatt lasers, the damage threshold of optics, optical field degradation, and cleanliness control are analyzed, and the new trend of pulse amplification and compression technology based on plasma optics in exploring the load bottleneck of the high-power laser is reviewed. In addition, advancing the high-efficiency, high-energy and high-repetition-rate picosecond petawatt laser technology research is crucial to the transition of picosecond petawatt lasers from laboratory to a wider range of applications.

This study aimed to improve the overall performance of the SG-II-UP picosecond petawatt laser. The intricate challenge of signal-to-noise ratio in the pulse generation system of the picosecond petawatt laser was systematically addressed. Through the engineering application of picosecond optical parametric amplification technology, a significant reduction in parametric fluorescence was achieved, amounting to four orders of magnitude. Concurrently, two distinct groups of pre-pulses, attributed to the non-linear process between the primary pulse and post-pulses associated with the B-integral in a nanosecond optical parametric amplification, were identified and eliminated. This resulted in a three-orders-of-magnitude reduction in the pre-pulse amplitude. The optimization of key parameters of the adaptive optics system and the implementation of a comprehensive closed-loop control strategy for the entire laser beamline significantly improved the typical focal spot of the SG-II-UP picosecond petawatt laser to 17.0 μm×20.8 μm, corresponding to a peak focusing power density of 1.4×10²⁰ W/cm². During the laser-driven proton acceleration experiments conducted in 2021, the maximum cutoff energy of the proton beam reached up to 70 MeV. These results illustrate a significant enhancement in the overall performance of the SG-II PW laser facility.

Additionally, a verification experiment was conducted on chirped pulse amplification utilizing a multi-pass amplification configuration. This research comprehensively investigated challenges associated with pencil-beam pre-pulses, amplified spontaneous emission, focusing capabilities, and anti-laser isolation during the commissioning of a picosecond-petawatt laser integration beamline (PPLIB) at the SG-II-UP facility. The suppression of the pre-pulses from pencil-beams in the subsequent multi-pass chirped-pulse amplification (CPA) was achieved by optimizing the timing sequence of the Plasma electrode pockels cell (PEPC). This optimization is anticipated to boost the contrast by over 20 dB. The focusing laser power density of this multi-pass chirped-pulse amplification configuration achieved an improvement of approximately sevenfold through a novel wavefront control system. The experiment demonstrated an output capability of 4126 J/3.3 nm via chirped pulse amplification in a single beam, thereby establishing a technical foundation for the development of the second picosecond petawatt laser at SG-II-UP.

Moreover, a series of advanced laser technologies were developed at SG-II-UP. A closed-loop control method for the laser pointing stability by adopting high-speed camera combined with fast-steering mirror in a high-power laser facility was proposed and demonstrated using the SG-II-UP picosecond petawatt laser. The implementation of this approach resulted in an improvement in beam pointing stability of more than three times. Correspondingly, the root-mean-square value of the pointing uncertainty decreased from 2.80 to 0.63 μrad. Further enhancements in the focusing power density of the petawatt laser systems were achieved through the study of dynamic chromatic aberration pre-compensation schemes and curved plasma mirrors.

High-power laser facilities, capable of providing extremely high temperature and pressure conditions, serve as a critical scientific infrastructure for fundamental research, advanced science and technology, and national defense and security. To satisfy the demand in cutting-edge fields such as precision backlight probes, fast ignition and proton imaging, and to improve the brightness and quality of laser generated secondary rays and particle sources (X-rays, electrons, protons and etc.), the SG-II-UP PW, a representative of picosecond petawatt lasers, has developed a series of advanced laser technologies in the aspects of pulse signal-to-noise ratio, focusing power density and spatio-temporal coupling accuracy. Owing to the limited load capacity of the picosecond petawatt laser, several strategies such as improving component damage thresholds, effectively suppressing optical field degradation, and implementing closed-loop control of cleanliness can significantly enhance its output capacity. The anticipated advancements in new technologies such as pulse amplification and compression based on plasma optics can potentially overcome the current bottlenecks in the development of high-power lasers, including picosecond petawatt lasers.

In the future, the trajectory of picosecond petawatt laser research is expected to evolve from a singular emphasis on achieving peak power in discovery science to a dual focus on both high average and high peak powers in applied science. The advent of high-efficiency, high-energy, and high-repetition rate picosecond petawatt laser technology is set to revolutionize the developmental paradigm for high power laser systems. This transformation will influence all aspects of high-power laser systems, including laser materials, optical components, and laser configurations.