A capillary gas cell for laser wakefield acceleration was developed with the aid of three-dimensional computational fluid dynamics simulations. The gas cell was specially designed to provide upward density tapering in the longitudinal direction, which is expected to suppress the dephasing problem in laser wakefield acceleration by keeping the accelerated electrons in the acceleration phase of the wake wave. The density-tapered capillary gas cell was fabricated by sapphire plates, and its performance characteristics were tested. The capillary gas cell was filled with a few hundred millibars of hydrogen gas, and a Ti:sapphire laser pulse with a peak power of 3.8 TW and a pulse duration of 40 fs (full width at half maximum) was sent through the capillary hole, which has a length of 7 mm and a square cross section of 350 × 350 µm². The laser-produced hydrogen plasma in the capillary hole was then diagnosed two-dimensionally by using a transverse Mach–Zehnder interferometer. The capillary gas cell was found to provide an upward plasma density tapering in the range of 10¹⁸ cm⁻³–10¹⁹ cm⁻³, which has a potential to enhance the electron beam energy in laser wakefield acceleration experiments.

Axion-like particles (ALPs) have been searched for with a quasi-parallel stimulated resonant photon-photon collider sensitive to the sub-eV mass range by focusing two-color near-infrared pulse lasers into a vacuum. In this work, we have developed a specialized coronagraphy to mitigate the dominant background photons from optical elements by introducing an eclipse filter. The observed number of signal-like photons was found to be consistent with residual background photons from optical elements through an additional test by degrading the focal point overlapping factor between the two lasers. We then extended the exclusion region in the relation between ALP-photon coupling, g/M, and the ALP mass m, reaching the most sensitive point g/M = 5.45 × 10 ⁻⁷ GeV ⁻¹ at m = 0.15 eV for pseudoscalar ALPs.

The ASE (amplified spontaneous emission) level in a laser system consisting of an oscillator and a regenerative amplifier is very important, for example, in the interaction of an intense laser pulse and a thin foil, so a lower ASE level is always required. In this paper, we propose a new method to achieve a lower ASE level, which can be obtained by spectral matching of the seed laser beam and the ASE in a CPA (chirped-pulse amplification) Ti:sapphire laser system. In this method, two baffles are used to control the seed pulse spectrum by blocking a portion of the seed beam in a grating stretcher and it was found that the spectral matching method can reduce the temporal contrast ratio (after the regenerative amplifier) by a factor of 10 in a few hundred picosecond scale. This kind of spectral matching method is simple and it can be easily employed for other CPA laser systems to enhance the contrast ratio.

We developed a compact Ti:sapphire laser amplifier system in our laboratory, generating intense laser pulses with a peak power of >1 TW (terawatt), a pulse duration of 34 fs (femtosecond), a central wavelength of 800 nm, and a repetition rate of 10 Hz. The laser amplifier system consists of a mode-locked Ti:sapphire oscillator, a regenerative amplifier, and a single-side-pumped 4-pass amplifier. The chirped-pulse amplification (CPA)-based laser amplifier was found to provide an energy of 49.6 mJ after compression by gratings in air, where the pumping fluence of 1.88 J/cm² was used. The amplified spontaneous emission (ASE) level was measured to be lower than 10⁻⁷, and ps-prepulses were in 10⁻⁴ or lower level. The developed laser amplifier system was used for the generation of intense THz (terahertz) waves by focusing the original (800 nm) and second harmonic (400 nm) laser pulses in air. The THz pulse energy was shown to be saturated in the high laser energy regime, and this phenomenon was confirmed by fully electromagnetic, relativistic, and self-consistent particle-in-cell (PIC) simulations.

We review prevalent fabrication techniques for targets used in high-power and high-intensity single-beam laser experiments, emphasizing their applications and performance. Solid targets include free-standing metallic and carbon films of various thicknesses for particle acceleration studies involving proton and carbon beams and micro-/nano-structured surfaces, as well as near-critical-density materials, such as foams, which enhance laser absorption and coupling, and boron targets for proton–boron fusion experiments. The resulting gamma and proton beams enable applications in isomer production, proton therapy, societal applications and fundamental studies. The use of gas targets for electron acceleration via the laser wakefield acceleration mechanism is discussed, as are cryogenic clusters undergoing Coulomb explosion. Finally, liquid, cryogenic and tape target systems are presented as high-repetition-rate and application-oriented solutions, offering high reproducibility and long-term operation.