A novel method for the direct and sensitive analysis of powder samples has been developed by utilizing the characteristics of a transversely excited atmospheric (TEA) CO(2) laser. In this study, a powder sample was placed in a container and covered by a metal mesh; the metal mesh functions to control the blowing-off of the powder. The container was then perpendicularly attached on a metal surface. When a TEA CO(2) laser (1.5 J, 200 ns) was focused on the metal surface, a large hemispherical gas plasma (radius of around 8 mm) with long emission lifetime (several tens of microseconds) was produced without ablating the metal surface. The high-speed expansion force of the gas plasma samples the powder covered by the metal mesh and fine powder particles are sent into the gas plasma region to be dissociated and excited. Sensitive semi-quantitative analysis was made on organic powder samples such as powdered rice, starch, seaweed (agar), and supplements. The detection limit of heavy metals of Cr in powdered mineral supplement was approximately 0.55 mg/kg.

A third harmonic of a Nd-Yttrium Aluminum Garnet laser (355 nm, 10–50 mJ, 7 ns, 10 Hz) was focused in air or He gas at atmospheric pressure to produce microgas plasma. Two flat electrodes (25 mm×25 mm) were arranged in parallel with a 1.5 cm separation to allow the microgas plasma to be sandwiched by the electrodes. A DC voltage was supplied to the electrodes and the induced current due to the generated laser plasma was detected using an oscilloscope. The characteristics of the induced current were studied by changing parameters such as supplied voltage (50–700 V), laser pulse energy (2–50 mJ) and the type of gas, and compared with the optical emission characteristics. A similar experiment was carried out on the target plasma by placing a small rod sample (diameter of 2 mm) of various materials such as brass, iron, aluminum, plastic and wood, near the focusing point between the electrodes. It is stressed that the induced current signal is very useful for monitoring of the laser processing, that is, to determine the precise focusing condition and to identify the moment when the laser beam begins to penetrate the sample.

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A special technique for the modification of laser-induced breakdown spectroscopy (LIBS) has been developed to improve the spectral quality of hydrogen emission from a solid sample in helium gas at atmospheric pressure. In this technique, the plasma was generated by focusing a fundamental Nd-YAG (yttrium aluminum garnet) laser into a surrounding helium gas. The helium atoms excited to their metastable states would then serve to excite the atoms of the solid material vaporized by using another Nd-YAG laser. When properly synchronized, the resulting hydrogen emission line of H I 656.2 nm shows a dramatic improvement of the emission intensity and the spectral quality over what was obtained by conventional LIBS technique. This study further reveals that this improvement is mainly due to the role of the metastable excited state in a helium atom, which allows the delayed detection to be performed at a favorable moment when the charged particles responsible for the strong Stark broadening effect in the plasma have mostly disappeared.

To clarify the excitation mechanism of hydrogen in transversely excited atmospheric-pressure (TEA) CO2 laser-induced helium gas plasma, atomic emission characteristics of H, C, F, and He were studied using a Teflon sheet (thickness of 2 mm) attached to a metal subtarget. The TEA CO2 laser (750 mJ, 200 ns) was focused on the Teflon sheet in the surrounding He gas at 1 atm. Atomic emissions of H, C, F, and He occurred with a long lifetime, a narrow spectrum width, and a low-background spectrum. The correlation emission intensity curves of H–He and F–He indicated a parabolic functions. To explain the emission characteristics, we offered a model in which helium metastable atoms (He*) play an important role in the excitation processes; namely, atoms collide with helium metastable atoms (He*) to be ionized by the Penning effect, and then recombine with electrons to produce excited states, from which atomic emissions occur.