Akira Tsunemi

Complete removal of paint from metal surface by ablation with a TEA CO2 laser

For high-speed metal surface cleaning, we applied TEA CO2 laser pulses to ablate painted materials on metal surfaces and examined the efficiency of removal under different surface and irradiation conditions. Surfaces treated with a line-focused laser beam were analyzed with an energy dispersive X-ray analyzer and inspected with optical microscopic observation. Although paints were selectively ablated from the metal surface, the cleaning efficiency was found to depend on surface conditions of substrates. An application of a small amount of dimethyl formamide was effective for completely removing of resin without scorching the surface.

Micropatterning of Quartz Substrates by Multi-WavelengthVacuum-Ultraviolet Laser Ablation

Photoablation of synthetic fused quartz by simultaneous irradiation of multi-wavelength beams of a vacuum-ultraviolet (VUV) laser using high-order anti-Stokes Raman scattering is described. The VUV laser, which emits widely spread Raman-shifted lines from 133 nm to 594 nm, is ideal for effective laser ablation of the fused quartz. The well-defined patterns with a cross-sectional profile of a rectangular shape are formed by using a contact mask at an ablation rate as high as 13 nm/s. An effective absorption coefficient of 3.4×10-5 cm-1, which indicates that the multi-wavelength irradiation effect has an important role in the process, is obtained.

Enhanced Raman conversion by a two‐longitudinal‐mode beam in the para‐hydrogen Raman laser

Using a longitudinally mode‐controlled transversely excited atmospheric CO2 laser, we studied the conversion characteristics of single‐, two‐, and multimode pump pulses in a para‐H2 Raman laser. In the small signal region, two‐ and multimode pump pulses showed higher Raman conversion efficiencies. In the saturation region, however, output energies pumped with single‐ and two‐mode pulses exceeded those pumped with multimode pulses. Consequently, the two‐mode pumping was the most efficient within the limit of pump energies used in the experiment. The results are explained in relation to the mode‐mixing effect for the correlated pump and Stokes beams.

Short-Pulse Generation in the Transient Raman Regime with a Parahydrogen Raman Laser

Generation of Stokes pulses as short as 1 ns has been observed in the transient rotational Raman conversion of CO2 laser pulses with a multiple-pass Raman cell. The capability of producing pulses with energies up to 100 mJ in the 13–17 µm region was demonstrated. The experimental results were found to be consistent with theoretical predictions of the Stokes pulse width and the conversion efficiency in transient scattering.

Analysis of Effective Interaction Length for Crossing Beams in a Para-Hydrogen Raman Laser

The amplification by stimulated rotational Raman scattering in para-hydrogen was studied for the pump and Stokes beams which crossed each other with a small angle. The dependence of amplification gain on crossing angles was explained using a plane wave model with three dimensional overlaps.

Precise measurement of the rotational Raman gain coefficient in para-hydrogen by the large-signal method

The plane-wave gain coefficient of stimulated rotational Raman scattering in para-H(2) was determined for CO(2) laser-pumping pulses. Difficulties caused by lowered substantial gain for stimulated scattering in the infrared region were overcome by measuring converted energies instead of powers in the large-signal region. The measured gain coefficients showed excellent agreement with theoretical values.