国立大学法人東京農工大学大学院工学研究院の宮地悟代准教授は、同大学大学院生の立田実花氏（当時）、飯田悠斗氏（当時）とともに、半導体電子デバイスとして利用されるシリコン表面にフェムト秒レーザーを照射することにより、表面を金属化させた後に、もう一つのフェムト秒レーザーパルスを照射することによって表面プラズモンを効率良く励起することに初めて成功しました。これにより効率良くナノ領域をアブレーションできるため、新しいナノ加工技術への基礎物理過程として期待されています。

掲載論文情報

掲載誌：Scientific Reports

出版日：2023年10月27日付（電子版）

論文名：Enhancement of plasmonic coupling on Si metallized with intense femtosecond laser pulses

著者名：Mika Tateda , Yuto Iida* & Godai Miyaji*

DOI　：https://doi.org/10.1038/s41598-023-45968-6

Using a pump–probe technique, the reflectivity of a silicon grating surface irradiated with intense femtosecond (fs) laser pulses was measured as a function of the incidence angle and the delay time between pulses. After irradiating the surface with an intense s-polarized, 400 nm, 300 fs laser pulse, the reflectivity measured with a weak p-polarized, 800 nm, 100 fs laser pulse exhibited an abrupt decrease for an incidence angle of ~ 24°. The depth of the dip was greatest for a delay time of 0.6–10 ps, for which the reflectivity around the dip was highest. The surface was also found to be ablated most strongly for the conditions causing the deepest dip for a delay time of 5–10 ps. Surface plasmon polaritons (SPPs) on silicon metallized by the intense pulse are resonantly excited by the subsequent pulse, and the strong coherent coupling between the subsequent pulse and SPPs excited on the molten Si surface produced by high-density free electrons induces strong surface ablation due to the intense plasmonic near-field. The results clearly show that fs pulses can be used to significantly modulate the nature of nonmetallic materials and could possibly serve as a basic tool for the excitation of SPPs on nonmetallic materials using ultrafast laser–matter interactions.

2023.10