Kim Munnyon, Lee Changmin, Shin Pyoungsik, Joo Taiha
Opt Express. 2024 Oct 7;32(21):36577-36585. doi: 10.1364/OE.537904.
Ultrashort pulses with a duration of ∼10 fs are crucial to fully resolve nuclear motions in molecules and materials. Here, we employ nonlinear pulse compression using photonic crystal fiber in the near-infrared region to generate ultrashort pulses at a high repetition rate with significant pulse energy. Femtosecond pulses centered around 1200 nm from a cavity-dumped optical parametric oscillator are compressed to a duration of 15 fs. The pulse energy reaches several tens of nanojoules, sufficient for wavelength conversion via nonlinear processes. Second harmonic generation produces clean 13 fs pulses at around 600 nm with pulse energy of 4 nJ. The effectiveness of nonlinear pulse compression using photonic crystal fiber for ultrafast time-resolved spectroscopy is demonstrated through time-resolved fluorescence (photoluminescence) and transient absorption apparatus, utilizing the second harmonic as pump pulses. Specifically, a time resolution of ∼20 fs is achieved in a time-resolved fluorescence experiment, enabling the recording of nuclear wave packets over 1200 cm by spontaneous fluorescence. The high repetition rate at the megahertz level significantly improved the signal quality.
持续时间约为10飞秒的超短脉冲对于充分解析分子和材料中的核运动至关重要。在此，我们利用近红外区域的光子晶体光纤进行非线性脉冲压缩，以高重复率产生具有显著脉冲能量的超短脉冲。来自腔倒空光学参量振荡器的中心波长约为1200nm的飞秒脉冲被压缩至15飞秒的持续时间。脉冲能量达到几十纳焦，足以通过非线性过程进行波长转换。二次谐波产生在600nm左右产生了持续时间为13飞秒、脉冲能量为4nJ的干净脉冲。利用二次谐波作为泵浦脉冲，通过时间分辨荧光（光致发光）和瞬态吸收装置，证明了光子晶体光纤用于超快时间分辨光谱的非线性脉冲压缩的有效性。具体而言，在时间分辨荧光实验中实现了约20飞秒的时间分辨率，从而能够通过自发荧光记录超过1200cm的核波包。兆赫兹级的高重复率显著提高了信号质量。
