尾松 孝茂

我々は,側面励起Nd:YVO_4スラブバウンス増幅器からなる高平均出力ピコ秒レーザを励起光源として,擬似位相整合デバイスである周期分極反転定組成タンタル酸リチウム結晶(PPSLT : periodically poled stoichiometric lithium tantalite)を用いた光パラメトリック発生器/増幅器を開発した.このシステムを用いて最大出力1.1W (励起光8.1W入射時)の1.5μm帯ピコ秒パルス光発生に成功した.このときの光-光変換効率は13.8%,発生した1.5μm光のピーク強度は0.3MWに達した.

We found that the optical vortex could fabricate a nano-scaled metal needle (nano-needle). Optical vortices, having a helical (twisted) wavefront owing to a phase singularity, carry an angular momentum. The angular momentum of the optical vortices is transferred to the melted (or vaporized) metal during ablation process, resulting in the formation of the nano-needle. The tip curvature of the nano-needle with a height of 8.4 μm was measured to be <50nm, corresponding to less than one-twentieth of the laser wavelength (1064nm). We also demonstrated the fabrication of a two-dimensional 5 × 5 nanoneedle array. The direction of the nano-needle could be also controlled by changing an incident angle of the optical vortex onto the metal target.

Metal microneedles have been attractive in many fields including nano-scopic imagers, energy-saving field emission displays, and biomedical nano-electro mechanical systems. Several methods for fabrication of metal microneedles have been proposed. However, they involve mostly a bottom-up technique based on several chemical processes, and their time and cost efficiencies are limited. In recent years, we have proposed a new method of microneedle fabrication on metal surface based on laser ablation with optical vortex pulses[1,2]. This technique is capable of forming a metal microneedle by deposition of merely a few laser pulses onto a metal target, significantly saving the time and cost of fabrication of two-dimensional metal microneedle arrays. The resulting needles show a height of 10 m above the target surface and a tip diameter of less than 0.5 m. © 2011 IEEE.