A XeCl excimer laser (20 ns, 15–70 mJ) has been focused on a Zn plate in surrounding gas at low pressures (100–1500 Pa). The characteristics of the resultant plasma are examined with the use of a unique time-resolved spectroscopic method. A density jump in the distribution of Zn atoms is clearly observed, which indicates the generation of a shock wave. Furthermore, it is proved that the relationships among the displacement length of the front of the emission of the Zn neutral emission line, the pressure of the ambient gas, and the energy of the laser pulse are in good agreement with the theoretical result for a blast wave explosion. An application is also presented to show that the plasma induced by a blast wave is excellent as a light source for emission spectrochemical analysis because of its very low background emission intensity.

Ultrashort electromagnetic waves (600 fs width) from superconducting YBCO thin films have been observed by irradiating current-biased samples with femtosecond optical laser pulses (80 fs width). The Fourier component of the pulse extends up to ∼2 THz. The characteristics of the radiation are studied and the radiation mechanism is ascribed to the ultrafast supercurrent modulation by the laser pulses, which induce the nonequilibrium superconductivity.

A transversely excited atmospheric-pressure (TEA) CO2 laser beam has been focused on a Zn plate at reduced ambient gas pressure. It is demonstrated that reflection and diffraction phenomena take place in the laser plasma when the free expansion of the laser plasma is limited by an obstructing material placed in front of the target. These findings strongly support the shock wave model for explaining the mechanism in forming a laser plasma.

A TEA CO2 laser beam (500 mJ, 100 ns) has been focused on a Zn target at reduced ambient gas pressures. In order to confine the laser plasma into a limited space, a tube (7 × 7 × 20 mm) has been placed just in front of the target, and the laser beam has been focused through the tube on the target. The time-resolved spatial distributions of Zn emission lines show that emission intensity increases quickly with a distinct jump near the front of the plasma and that the emissions take place only in a limited thin layer. It is also shown that the displacement of the emission front is proportional to 0.6 power of time. These experimental results support the supposition that the plasma is excited by a plane shock wave induced by the laser bombardment. This laser plasma confinement technique shows the possibility of improving the sensitivity in laser microprobe spectrochemical analysis.

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