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A tailored-pulse-imploded core with a diameter of 70  μm is flashed by counterirradiating 110 fs, 7 TW laser pulses. Photon emission (>40  eV) from the core exceeds the emission from the imploded core by 6 times, even though the heating pulse energies are only one seventh of the implosion energy. The coupling efficiency from the heating laser to the core using counterirradiation is 14% from the enhancement of photon emission. Neutrons are also produced by counterpropagating fast deuterons accelerated by the photon pressure of the heating pulses. A collisional two-dimensional particle-in-cell simulation reveals that the collisionless two counterpropagating fast-electron currents induce mega-Gauss magnetic filaments in the center of the core due to the Weibel instability. The counterpropagating fast-electron currents are absolutely unstable and independent of the core density and resistivity. Fast electrons with energy below a few MeV are trapped by these filaments in the core region, inducing an additional coupling. This might lead to the observed bright photon emissions.

Nanoparticle formation via laser ablation in liquid is known to produce functional materials. However, there have been few applications of this technique to the synthesis of electrochemical catalysts for energy conversion. Herein, we report the detailed effects of femtosecond laser ablation in water on the structure and activity of a catalyst intended to promote the electrochemical oxygen evolution reaction (OER) in association with water oxidation. The femtosecond laser ablation of submicron‐sized Co–CoO particles induced a drastic size reduction (from approximately 500 to 5 nm) to give highly dispersed CoO nanoparticles. X‐ray absorption near edge structure (XANES) and X‐ray diffraction (XRD) data demonstrated that these particles also contained Co3O4 and CoO(OH) but not metallic Co. These 5 nm‐CoO nanoparticles showed higher mass‐based‐activity and lower over‐potential values than those of submicron‐sized Co–CoO during the OER in a nearly neutral solution. XANES data suggest that Co containing Co2O3 and Co(OH)2 formed during the OER functioned as the actual OER catalyst.

A method of in situ elemental analysis of the electrode surface in electrolytic solution is proposed. The method is based on the measurement of emission spectra from the plume induced by the laser ablation of an electrode surface. A Cu-Zn binary system electrodeposited on a Pt plate has been employed to demonstrate the applicability of this method to electrode surfaces, and quantitative analysis of the sample surface has been attempted. Also, some improvement is shown for the pulse-to-pulse fluctuation in the measurement of relative intensity by using several spectral lines instead of a single line for each element.