Intense XUV sub-fs pulses using extreme soliton dynamics in hollow-core fibers

阿秒长的明亮超紫外脉冲的产生在各种应用中具有重要意义。目前，唯一的方法是采用高次谐波产生（HHG），其具有相当低的转换效率。这里，提出了一种替代方法，根据初步模拟，允许在波长低至50 nm时，对于持续时间短于500的脉冲，转换效率高达5%。该方法是基于光学克尔效应，并利用动力学的几个周期的强烈脉冲在现代空芯“可果美”光纤充满氦。从光纤中的孤子传播产生新频率是众所周知的，但是这里通过使用a）极短的输入脉冲和B）最高可能强度来利用根本上新的机制。传播几厘米后，此类脉冲将发射XUV范围内的共振辐射。 通过在预电离气体中的线性传输，可以补偿XUV脉冲的啁啾。成功的关键是准备大约几个周期的短脉冲。5 fs的持续时间，约20 µJ的能量，这将通过自制的OPCPA设置来实现。

Generation of bright attosecond-long XUV pulses is of immanent importance for various applications. Currently, the only way is to employ high harmonic generation (HHG), which suffers from rather low conversion efficiencies. Here, an alternative approach is proposed, allowing, according to preliminary simulations, for up to 5 % conversion efficiency to pulses with durations shorter than 500 as at wavelengths down to 50 nm. The method is based on the optical Kerr effect and exploits dynamics of few-cycle intense pulses in modern hollow-core "kagome" fibers filled with helium. Generation of new frequencies from soliton propagation in fibers is well known, but here a fundamentally new regime is exploited by using a) extremely short input pulses and b) highest possible intensities. After a few cm of propagation, such pulses will emit resonant radiation in the XUV range. The XUV pulses chirp can be compensated by linear propagation in a pre-ionized gas. Critical for success is the preparation of few-cycle short pulses of approx. 5 fs duration with around 20 µJ of energy, which will be accomplished by a home-built OPCPA setup.