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.

We report the first experimental demonstration of a novel plasma diagnostics method using the single-shot THz detection method. In this experiment, a broadband single THz pulse is generated by focusing two-color (400 nm and 800 nm in wavelength) laser pulses in air and the THz pulse is sent through an inductively-coupled plasma with a density of 10 ¹³ –10 ¹⁴ cm ⁻³ which is in the modern tokamak plasma density range. Phase shift of the THz pulse is measured by the single-shot THz detection method and the instant plasma density information is obtained from the phase shift. The result is compared with that of the existing THz time domain spectroscopy method and it is found that both results are in good agreement. It implies that the proposed method in this paper can provide a new plasma diagnostics tool which can be used for dynamically changing plasmas.

In the THz-based plasma diagnostics, plasma information can be deduced via measurement of the THz phase shift in the frequency domain. However, little study has been reported on how THz waveforms in the time domain can be used for plasma diagnostics. Hence, we performed studies on the time-domain THz waveforms from the calculation through the plasma model and compared them with the experimental result. For this experiment, intense THz pulses were generated by focusing two-color femto-second (fs) laser pulses in air and they were sent through an inductively-coupled argon plasma source which was powered by RF with a frequency of 13.56 MHz. The comparison results show that the waveform comparison method (plasma model) in the time domain can provide the electron density information successfully, implying that the plasma density diagnostic method based on the waveform comparison works properly. Furthermore, the collision frequency data from our experiment reveals that the plasma model should include more factors to describe the observed phenomena.

In the agricultural and food industries, there is an urgent need for large-capacity and high-efficiency plasma-activated water (PAW) production technology. Regarding this matter, we demonstrate the mass production of PAW with high efficiency based on reverse vortex flow (RVF) gliding arc (GA) plasma with an input power of 4 kW or higher. With the current system, the production capacity of the PAW with pH 3.0 is 1000 L/h for distilled water and 500 L/h for tap water. The amount of NO $_{3}^{-}$ ion in the PAW was 60 g/kWh, which is ten times higher than that of a dielectric barrier discharge (DBD) method. The produced PAW tends to show a higher acidity for a longer storage time.

Microwave surface-wave plasma (SWP) provides relatively higher ion density and radical species density than RF plasma, making it a promising plasma source for semiconductor fabrication. However, its plasma uniformity is compromised due to the non-uniform field distribution as the microwave wavelength is typically shorter than chamber dimensions. This could be a bottleneck as the practical application of SWP in semiconductor fabrication demands a large-area plasma with a high uniformity. In this work, we propose field agitation by applying the phase difference of 0° and 180° between the two input microwaves in the chamber to enhance the plasma uniformity. The chamber, optimized for the TM 130 mode at 2.458 GHz, successfully produces a large-area SWP with a diameter of 450 mm under 800 W absorption power and 200 mTorr argon pressure. The measurement results show that the system is capable of yielding enhanced uniformity of large-area SWP while maintaining high ion density.

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.