強レーザー場中NOの非断熱回転励起と角度依存イオン化のコヒーレント相関ダイナミクス

Coherent correlation dynamics between nonadiabatic ionization and angle-dependent ionization of NO in intense laser fields

板倉 隆二; 長谷川 宗良*; 黒崎 譲; 横山 淳; 大島 康裕*

Itakura, Ryuji; Hasegawa, Hirokazu*; Kurosaki, Yuzuru; Yokoyama, Atsushi; Oshima, Yasuhiro*

強レーザー場中の分子は、非断熱回転励起とイオン化を同時に起こす。イオン化には配向角度依存性があり、イオン化によって中性分子の回転波束は変形する。本研究は、フェムト秒強レーザーパルス照射後のNO分子の回転状態分布を測定するとともに、時間依存シュレーディンガー方程式を解くことによってイオン化と回転励起の相関を議論する。

When neutral molecules are partly ionized in intense laser fields (I 35 TW/cm), a hole in the rotational wave packet of the remaining neutral NO is created by the ionization, whose rate depends on the alignment angle of the molecular axis with respect to the laser polarization direction. Rotational state distributions of NO are experimentally observed and then the characteristic feature that the population at higher J levels is increased by the ionization can be identified. Numerical calculation for solving time-dependent rotational Schrdinger equations including the effect of the ionization is carried out. The numerical results suggest that NO molecules aligned perpendicular to the laser polarization direction are dominantly ionized at the peak intensity of I = 42 TW/cm, where the multiphoton ionization is preferred rather than the tunneling ionization.