Transform-Limited Attosecond Pulse Generation Through Atto-Chirp Compensation by Material Dispersion

Abstract

High harmonics are a unique light source with ultrashort duration and superb spatial coherence in the extreme ultraviolet and X-ray region. Though regularly spaced broad harmonic spectra are suitable for generating very short pulses, they suffer from the inherent chirp due to the harmonic generation process. Here we proposed and demonstrated the method to compensate for the attosecond chirp by propagating the harmonic pulses through a medium with negative group delay dispersion. In a single Ar gas cell, we showed that the chirp compensation could be achieved in the same harmonic generation cell, obtaining near transform-limited 206-as pulses. We could demonstrate also the generation of much shorter 63-as pulses by obtaining the harmonics from Ne and by compensating for the attosecond chirp in the second gas cell of Ar. The chirp compensation in gaseous media is, thus, very effective and powerful in obtaining near transform-limited attosecond pulses—very valuable for attosecond science.