Takayoshi Norimatsu

Ultrathin amorphization of single-crystal silicon by ultraviolet femtosecond laser pulse irradiation

The mechanisms of amorphization for crystalline Si (c-Si) induced by ultraviolet femtosecond laser irradiation are described in this paper. The wavelength of the laser pulse was 267 nm, which is the third harmonics of a Ti:sapphire laser. We performed a laser scanning microscopy and a transmission electron microscopy for surface and structural analysis and imaging pump-probe measurements to investigate the dynamics of the process. From the analyses, we confirmed that the thickness of the amorphized layer was quite uniform and there is no lattice defect under the amorphized section. The thickness of the amorphous Si (a-Si) layer was 7 nm and the threshold fluence of the amorphization was 44 mJ/cm2. From the Imaging Pump-Probe measurement it was revealed that the melting time is less than 1 ns and ultra high speed melting and re-solidification process was occurred. The melting depth estimated by the Imaging Pump-Probe measurement was 7 nm. The melted portion completely corresponded to the amorphized section.

Design and Analysis on Face-Cooled Disk Faraday Rotator for High Average Power Lasers

A novel, scalable Faraday rotator has been designed for high-average-power lasers in a gas-cooled multi-disk scheme. The concept with a negligible thermal distortion and birefringence is feasible up to 10 kW/cm2 enough below fracture limit.

Thermal Birefringence in Cylindrical Faraday Rotator under High Average Power Lasers

Detailed computation and experimental results of thermal birefringence loss in TGG and glass based Faraday rotator rod was presented. These data will be useful for designing a laser system and a thermally compensated Faraday rotator.