Effect of frequency blueshift on the plasma channel

周波数ブルーシフトのプラズマチャネルへの効果

小瀧 秀行; 林 由紀雄; 森 道昭; 神門 正城; Koga, J. K.; Bulanov, S. V.

Kotaki, Hideyuki; Hayashi, Yukio; Mori, Michiaki; Kando, Masaki; Koga, J. K.; Bulanov, S. V.

In laser-plasma interactions, there is a phenomenon of blueshifting of the laser pulse. The frequency blueshift has two mechanisms, which are ionization blueshift and photon acceleration. In addition, relativistic self-focusing is one of the important physics for laser-plasma interaction. When the laser power is high enough, the laser pulse self-focuses. In plasma, the laser pulse is self-focused with frequency blueshift. The plasma channel ends when the laser power becomes smaller than the critical power for self-focusing. The effect of the frequency blueshift is studied in order to elucidate the plasma channel length limitation. The experiments have been performed with a Ti:sapphire laser system. The laser pulses with 133 mJ energy are focused onto a 3-mm-diameter helium gas-jet by an off-axis parabolic mirror. The pulse width of the laser pulse is 40 fs. The result shows that the laser pulse in plasma is blueshifted and the plasma channel length is limited due to the spectrum shift.