Ultrabroadband phase-matching optical-parametric chirped-pulse amplification with a diverged pump beam

発散角付き励起光による超広帯域位相整合光パラメトリックチャープパルス増幅

赤羽 温; 小川 奏; 青山 誠; 張本 鉄雄*; 山川 考一

Akahane, Yutaka; Ogawa, Kanade; Aoyama, Makoto; Harimoto, Tetsuo*; Yamakawa, Koichi

波長1000nm付近の一段光パラメトリックチャープパルス増幅(OPCPA)において、励起光に角度分散をつけることで従来より大幅な広帯域増幅を実現した。実験ではフォトニック結晶ファイバーによって帯域幅400nm以上でパルス幅1ps程度の白色光に変換したシグナル光と、低温冷却型Yb:YLF再生増幅器よって増幅され、パルス圧縮・波長変換された中心波長510nm, 1.1ps, 1mJの励起光を長さ7mmのBBO結晶中で交差角1.2度で重ね合わせ、シグナル光を増幅した。この時BBO結晶手前に配置されたf=560mmとf=-560mmのレンズペアによって励起光の発散角を調整した。実験の結果、強度76GW/cm、発散角1.6mradの収束励起光に対して従来の2倍の400nmの広帯域増幅光を得た。増幅利得も1.210と高く、高強度数サイクルパルス発生に非常に有効な増幅技術であることが確認できた。

We have demonstrated ultrabroadband optical-parametric chirped-pulse amplification around 1000 nm wavelength with diverged pump beam. In experiment, seed signal pulse with over 400 nm bandwidth and about 1 ps duration, which was broadened by photonic-crystal fiber, and pump pulse with 510 nm center wavelength, 1.1 ps duration and 1 mJ energy, which was generated by cryogenically-cooled Yb:YLF pump laser were overlapped in BBO crystal with 1.2 deg internal crossing angle. The divergence of the pump beam was adjusted by a pair of collimating lenses (f1 = +560 nn, f2 = -560 mm) inserted before BBO crystal. With 1.6 mrad divergence of pump beam, we have observed 400 nm ultrabroadband amplified signal, which is twice of our previous OPCPA experiment with collimated pump beam. Parametric gain with 76 GW/cm was measured as high as 1.210 in this experiment, which is sufficient for intense few-cycle laser pulse generation with this scheme.