HotLoop optimization of petawatt laser focal spot via a twin-focus scheme

Achieving diffraction-limited focusing of high-power laser pulses to generate ultrahigh intensities is crucial for developing compact laser-driven particle accelerators and exploring strong-field quantum electrodynamics. However, accurately diagnosing and optimizing the focal spots of petawatt (PW) laser pulses remains a significant challenge. In this work, we present an experimental methodology utilizing a twin-focus scheme to precisely characterize the intensity distribution and wavefront of focused PW femtosecond laser pulses, and employ it to elucidate their power-dependent evolution. Furthermore, we optimize the focal spots at full power via our in situ wavefront correction method called “HotLoop,” achieving a Strehl ratio of 0.80 for 1 PW laser pulses. Consequently, the cutoff proton energies in laser proton acceleration experiments are significantly enhanced. The success of this approach underscores the necessity of in situ high-energy wavefront correction for ultrahigh-intensity laser–matter interactions.