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Intensification of electrons escaping from an intense laser-produced plasma is demonstrated by using double femtosecond laser pulses. The electron density distribution at the rear surface of a laser-irradiated foil target is controlled by preirradiation to suppress sheath field growth and to expand the plasma into which the fast electrons are released. Consequently, the number of electrons escaping from the plasma that have an energy of 380 keV increases by a factor of 7. The experimental results are well explained by numerical simulations of a foil plasma with a preformed plasma and analytical evaluations considering the plasma expansion.

Thin metal wires are known to be a low loss and very low dispersion terahertz (THz) waveguide. Recently, generation of a strong THz surface wave was demonstrated by irradiating a wire surface with a ultrahigh intensity femtosecond laser [1]. Such THz light sources driven by femtosecond laser induced plasma are expected to have a high potential as a power scalable source. Picosecond magnetic field pulses from such strong THz sources are promising for advanced researches on magnetic and spintronic materials. In this study, for the first time, we demonstrated the magneto-optical (MO) sampling measurement of strong THz surface waves using a terbium gallium garnet (TGG) polycrystalline ceramic. We observed a strong Faraday rotation of 60 mrad at the maximum, but the time resolution was limited to a few tens of picoseconds due to the thick MO medium.

We have demonstrated that a pulsed electromagnetic wave (Sommerfeld wave) of subterahertz frequency and 11-MV/m field strength can be induced on a metal wire by the interaction of an intense femtosecond laser pule with an adjacent metal foil at a laser intensity of 8.5×10^{18}W/cm^{2}. The polarity of the electric field of this surface wave is opposite to that obtained by the direct interaction of the laser with the wire. Numerical simulations suggest that an electromagnetic wave associated with electron emission from the foil induces the surface wave. A tungsten wire is placed normal to an aluminum foil with a gap so that the wire is not irradiated and damaged by the laser pulse, thus making it possible to generate surface waves on the wire repeatedly.

It has been demonstrated that the electric field associated with electrons generated by an intense femtosecond laser pulse in a foil can induce intense sub-THz surface wave on a wire waveguide adjacent to the foil.

Alpha particles generated by 7Li(p,α)4He and 19F(p,α)16O reactions are selectively detected in the presence of abundant primary protons by reducing the proton sensitivity of CR-39 using a potassium hydroxide-ethanol-water (PEW) etching solution. These nuclear reactions are induced in a LiF crystal using the laser-accelerated protons (4 × 1011 protons/pulse with a maximum energy of 3.3 MeV) generated and accelerated by the interaction of a 40-fs laser pulse with a polyethylene thin film target at a peak intensity of 5 × 1019 W/cm2. Subsequent etching of the CR-39 in the PEW solution (KOH: 17 wt. %; C2H5OH: 25 wt. %; H2O: 58 wt. %) permits the selective detection of 4.0 MeV alpha particles, which is independently confirmed by an experiment using alpha particles from an 241Am source. The described method is expected to be useful for research into nuclear reactions in laser plasma.

We have investigated the generation of terahertz (THz) waves from an argon cluster plasma produced by laser pulses of various durations. THz energy depends on laser pulse duration and reaches a peak at a pulse duration of ∼250 fs. This dependence of THz energy on laser pulse duration is attributed to the plasma density produced by the rising edge of the pulse. By irradiating clusters with collinear double laser pulses, we demonstrate that the THz energy can be increased by controlling the plasma density. Optimizing the delay time of the collinear double laser pulses increases the THz energy by ∼2.5 times that with simultaneous irradiation of collinear double laser pulses.

We review an efficient method for strong terahertz surface wave generation by relativistic-intensity (>1018 W/cm2) laser pulses. Ultrafast field propagation along a metal wire driven by a femtosecond laser pulse with a relativistic intensity is characterized by femtosecond electron deflectometry and electro-optic sampling. We found that the field propagating at the speed of light is a half-cycle transverse-magnetic surface wave excited on the wire and a considerable portion of the kinetic energy of laser-produced fast electrons can be transferred to the sub-surface wave.

This note points out a missed correction to the math on p. 5648 of [Appl. Opt.5, 5647 (2016)APOPAI0003-693510.1364/AO.55.005647].

By electron deflectometry with intense femtosecond laser accelerated electron pulses, it has been observed that the acceleration and emission of electrons from a metal wire induces generation of strong sub-THz surface wave on the wire.

Irradiating a metal wire with an intense femtosecond laser pulse induces a terahertz (THz) surface wave that travels along the wire. Here, the characteristics of the THz surface wave generated by the laser–wire interaction are investigated in detail by using an electro-optical method to determine the dependence of surface wave properties on laser energy and wire diameter. The surface wave is distributed by the Hankel function in the wire radial direction. On the wire surface, the electric field is estimated to be MV/cm. The peak electric field of the surface wave and the conversion efficiency from laser energy to surface wave energy are found to be proportional to the laser energy raised to the power of 0.67 and 0.3, respectively.

It has been demonstrated that the interaction between argon clusters and intense femtosecond double laser pulses with appropriate intervals in time and space provides important properties for terahertz electromagnetic wave generation, namely, high forward directivity, power enhancement, and linear polarization with a variable direction. Irradiating argon clusters with double pulses (1 and 3 mJ, 40 fs, 810 nm) in 133-ps and 40-μm intervals results in terahertz wave emission in the forward direction that is 10 times greater than that for a single pulse. The polarization direction of terahertz electromagnetic waves can be varied by changing the relative focal positions of the first and second pulses.

Laser pulse contrast exceeding 1011 was demonstrated on a kilojoule-class petawatt laser for fast ignition experiments (LFEX) laser system [J. Phys. IV France133, 81 (2006)10.1051/jp4:2006133016] by implementing a 2 in. plasma mirror. Laser beams of up to 1.2 kJ striking the plasma mirror with a pulse duration of 1.5 ps were reflected and focused onto a target without significant distortions in the focal spot. Transmitted light from the plasma mirror reveals that it has a high reflectivity 2 ps before the main peak. The estimated laser pulse contrast at the target was 1011 at 1 ns before the main peak. No preformed plasma was observed with an optical interferometry diagnostics, but in the experiment without a plasma mirror a preplasma was clearly observed. The energetic proton was generated from a 0.1 μm thick CH film showing excellent pulse contrast. This technique constitutes a promising method to enhance the LFEX laser system performance in fast ignition experiments.

To efficiently eliminate picosecond pre-pulses that accompany ultrashort pulses emitted from high-power chirped-pulse-amplification laser systems, we have developed a high-performance plasma mirror system. By reducing the reflectivity of the antireflection coating on the substrate for the plasma mirror to the limit of current technology (∼0.006%), we achieved the highest pre-pulse contrast enhancement reported to date for a single plasma mirror of 10sup4/supat 1 ps before the pulse peak. By optimizing the laser incidence to the plasma mirror and the laser fluence, the reflectivity of the plasma mirror has been improved to 70%. The contrast improvement indicates extensibility to 100 PW class lasers by doubling this plasma mirror system. Contrast enhancement of 10sup8/supshould be possible without a serious reduction in energy (no more than 50%).

Irradiating double pulse-laser beams into cluster gas, THz wave emission is enhanced 10 times as much as that for a single laser beam. The emission polarization is rotatable by changing directivities of the two beams.

Thin metal wires are known to be a low loss and very low dispersion terahertz (THz) waveguide [1]. Recently, generation of a strong THz surface wave was demonstrated by irradiating a wire surface with a ultrahigh intensity femtosecond laser [2]. Such THz light sources driven by femtosecond laser induced plasma are expected to have a high potential as a power scalable source. However, the characteristics and mechanism of the laser-plasma driven surface wave generation on wires are not fully understood. In this study, for the first time, we quantitatively measured the waveforms of THz surface waves depending on radial position, wire diameter, and laser pulse energy by using electro-optical (EO) sampling technique.