Sources and Diagnostics for Attosecond Science

Abstract: Ultrafast science refers to physical events that happen on the femtosecond (1 fs=10^-15 s) and attosecond (1 as=10^-18 s) timescales. Generation of attosecond pulses is usually achieved by interacting high-intensity femtosecond pulses with matter (typically gases), in a process called high-order harmonic generation (HHG). Under the correct conditions, this process leads to the creation of sub-fs pulses in the extreme ultraviolet (XUV) region. The work presented in this thesis focuses around generating, characterizing, and applying ultrashort light pulses, both in the femtosecond and attosecond domain. The first part describes the effort on the femtosecond laser sources, with emphasis on carrier-envelope phase (CEP) stability and control, and temporal and spatial characterization. An existing high-power (30 fs, 6 mJ) laser system was successfully CEP-stabilized, using an acousto-optic programmable dispersive filter (AOPDF) for CEP control. CEP detection at kilohertz rates is also demonstrated. A method for the characterization of ultrashort laser pulses, based on a glass wedges and chirped mirror compressor, has been developed and demonstrated on pulses in the few-cycle regime. This technique, together with spectral interferometry, has been used to characterize in space and time femtosecond laser pulses, in the optical / near-infrared domain. The second part deals with the HHG sources and applications. The spatial coherence of one of the HHG sources, together with its high photon flux, has allowed us to perform single-shot holography in the extreme ultraviolet (XUV) domain. Another HHG source, with lower power but higher repetition rate, was used for the characterization of properties of argon and helium atoms. For this, a technique typically used for the temporal characterization of attosecond pulse trains, RABBITT (reconstruction of attosecond beating by interfering two-photon transitions) was used, allowing us to study the phase of a resonant two-photon ionization in helium, and to measure photoemission delays in argon.