Time-dependent density functional theory for strong electromagnetic fields in crystalline solids

時間依存密度汎関数法による結晶中の強電磁場の記述

矢花 一浩*; 杉山 健*; 篠原 康*; 乙部 智仁; Bertsch, G. F.*

Yabana, Kazuhiro*; Sugiyama, Takeshi*; Shinohara, Yasushi*; Otobe, Tomohito; Bertsch, G. F.*

時間依存密度汎関数法とMaxwell方程式を結合させ結晶シリコンと強い電磁場の相互作用の記述を行った。その結果、レーザーの強度によって幾つかの違った応答領域が見られた。比較的弱いレーザーは誘電関数に従った応答を見せるが、レーザー強度が210W/cmを超えると非線形な応答が見られる。この領域では1原子あたりのエネルギー吸収量が1eVを超え、反射率の変化が見られる。さらに強いレーザーではプラズマが生成されそれによる反射が見られた。

We apply the coupled dynamics of time-dependent density functional theory and Maxwell equations to the interaction of intense laser pulses with crystalline silicon. As a function of electromagnetic field intensity, we see several regions in the response. At the lowest intensities, the pulse is reflected and transmitted in accord with the dielectric response, and the characteristics of the energy deposition is consistent with two-photon absorption. The absorption process begins to deviate from that at laser intensities 10 W/cm, where the energy deposited is of the order of 1 eV per atom. Changes in the reflectivity are seen as a function of intensity. When it passes a threshold of about W/cm, there is a small decrease. At higher intensities, above 210 W/cm, the reflectivity increases strongly. This behavior can be understood qualitatively in a model treating the excited electron-hole pairs as a plasma.