The team achieved the milestone by focusing the beam more tightly; it used an off-axis parabolic mirror to focus a 28 cm laser beam onto a spot that was only 1.1 microns wide. Only a clean laser beam with no wavefront distortion can achieve this diffraction-limited tight focus level. To achieve this level of cleanliness, the team used a set of deformable mirrors to correct wavefront distortion. CoReLS 4-PW laser is a femtosecond, ultra-high power Ti:Sapphire laser based on chirped pulse amplification technology. The low-energy femtosecond pulse from the front end is stretched into nanosecond pulses by the pulse stretcher, and then amplified to 4.5 J by the two power amplifiers, and then amplified to 112 J by the two boost amplifiers. The size of the laser beam is increased along its path by a series of beam expanders: 25 mm directly after the power amplifier, 65 mm at the entrance of the first booster amplifier, 85 mm at the entrance of the second booster amplifier, and 280 mm at the pulse The entrance to the compressor. In the pulse compressor, the laser pulse is recompressed to 20 fs, and the peak power after compression is as high as 4 PW. After the final booster amplifier, the researchers placed the first deformable mirror with a diameter of 100 mm to correct the wavefront distortion accumulated to the front end to the final beam expander. A second deformable mirror with a diameter of 310 mm is installed behind the pulse compressor, beam delivery line and target area. In the target chamber, the PW laser beam is tightly focused by an f/1.1 off-axis parabolic mirror, and its effective focal length is 300 mm. In order to image and characterize the focal point, the focused beam is collimated by the objective lens. Then it is divided into two beams by a beam splitter for focal spot and wavefront characterization. Use the camera to monitor the focus of the reflected laser beam. "This high-intensity laser will enable us to examine astrophysics phenomena in the laboratory, such as electron-photon and photon-photon scattering," said Chang Hee Nam, director of CoReLS and professor at Gwangju Institute of Science and Technology. "We can use it to experimentally test and obtain theoretical ideas, some of which were first proposed about a century ago." He added that he believes that intensity lasers are particularly useful for extremely strong field quantum electrodynamics, which is mainly based on theory. Home processing. The research was published on Optica (www.doi.org/10.1364/optica.420520).