We report the generation of 63 J of broadband pulse energies at 0.1 Hz from the J-KAREN-P laser, which is based on an OPCPA/Ti:sapphire hybrid architecture. Pulse compression down to 30 fs indicates a peak power of over 1 PW. High temporal contrast of ${10}^{12}$ prior to the main pulse has been demonstrated with 10 J output energy. High intensities of ${10}^{22}\mathrm{W}/{\mathrm{cm}}^2$ on target by focusing a 0.3 PW laser with an $f/1.3$ off-axis parabolic mirror have been achieved. Fundamental processes of laser matter interaction at over ${10}^{22}\mathrm{W}/{\mathrm{cm}}^2$ intensities belong to a new branch of science that will be the principal research task of our infrastructure.

J-KAREN-P is a high-power laser facility aiming at the highest beam quality and irradiance for performing state-of-the art experiments at the frontier of modern science. Here we approached the physical limits of the beam quality: diffraction limit of the focal spot and bandwidth limit of the pulse shape, removing the chromatic aberration, angular chirp, wavefront and spectral phase distortions. We performed accurate measurements of the spot and peak fluence after an f/1.3 off-axis parabolic mirror under the full amplification at the power of 0.3 PW attenuated with ten high-quality wedges, resulting in the irradiance of ~10²² W/cm² and the Strehl ratio of ~0.5.

Nuclear reactions between protons and boron-11 nuclei (p–B fusion) that were used to yield energetic α-particles were initiated in a plasma that was generated by the interaction between a PW-class laser operating at relativistic intensities (~3 × 10¹⁹ W/cm²) and a 0.2-mm thick boron nitride (BN) target. A high p–B fusion reaction rate and hence, a large α-particle flux was generated and measured, thanks to a proton stream accelerated at the target’s front surface. This was the first proof of principle experiment to demonstrate the efficient generation of α-particles (~10¹⁰/sr) through p–B fusion reactions using a PW-class laser in the “in-target” geometry.

Accelerating relativistic mirrors have long been recognized as viable settings where the physics mimic those of the black hole Hawking radiation. In 2017, Chen and Mourou proposed a novel method to realize such a system by traversing an ultra-intense laser through a plasma target with a decreasing density. An international AnaBHEL (Analog Black Hole Evaporation via Lasers) collaboration was formed with the objectives of observing the analog Hawking radiation, shedding light on the information loss paradox. To reach these goals, we plan to first verify the dynamics of the flying plasma mirror and characterize the correspondence between the plasma density gradient and the trajectory of the accelerating plasma mirror. We will then attempt to detect the analog Hawking radiation photons and measure the entanglement between the Hawking photons and their “partner particles”. In this paper, we describe our vision and strategy of AnaBHEL using the Apollon laser as a reference, and we report on the progress of our R&D concerning the key components in this experiment, including the supersonic gas jet with a graded density profile, and the superconducting nanowire single-photon Hawking detector. In parallel to these hardware efforts, we performed computer simulations to estimate the potential backgrounds, and derived analytic expressions for modifications to the blackbody spectrum of the Hawking radiation for a perfectly reflecting point mirror, due to the semi-transparency and finite-size effects specific to flying plasma mirrors. Based on this more realistic radiation spectrum, we estimate the Hawking photon yield to guide the design of the AnaBHEL experiment, which appears to be achievable.

An approach for accelerating a quasimonoenergetic proton bunch via a hemispherically converging collisionless shock created in laser-cluster interactions at the relativistically induced transparency (RIT) regime is studied using three-dimensional particle-in-cell simulations. By the action of focusing a petawatt class laser pulse onto a micron-size spherical hydrogen cluster, a crescent-shaped collisionless shock is launched at the laser-irradiated hemisphere and propagates inward. The shock converges at the sphere center in concurrence with the onset of the RIT, thereby allowing the proton bunch to be pushed out from the shock surface in the laser propagation direction. The proton bunch experiences further acceleration both inside and outside of the cluster to finally exhibit a quasimonoenergetic spectral peak around 300 MeV while maintaining a narrow energy spread ($\sim 10\%$) and a small half-divergence angle ($\sim 5°$) via the effect of the RIT. This mechanism works for finite ranges of parameters with threshold values concerning the laser peak intensity and the cluster radius, resulting from the synchronization of the multiple processes in a self-consistent manner. The present scheme utilizing the internal and external degrees of freedom ascribed to the spherical cluster leads to the proton bunch alternative to the plain target, which allows the operation with a high repetition rate and impurity free.

We experimentally explore the generation of pre-pulses by post-pulses, created through internal reflection in the optical components, by the nonlinear process associated with the B-integral in the laser chain of the petawatt (PW) facility J-KAREN-P. At a large time delay between the main and the post-pulses, we have found that the pre-pulses are not generated from their counterpart post-pulses at an identical time difference before the main pulse, and the temporal shapes of the pre-pulses are greatly distorted asymmetrically. We have also observed that the peak intensities of the pre-pulses are drastically suppressed compared to the expected value at a small time delay. We briefly describe the origins of the pre-pulses generated by the post-pulses and demonstrate the removal of the pre-pulses by switching to optical components with a small wedge angle at our PW laser facility.