High average power fiber laser system for attosecond science

Abstract

The process of high harmonic generation allows for up-conversion of infrared laser light towards the EUV or soft X-ray region. If very short (few-cycle) laser pulses are employed and their carrier envelope phase (CEP) is well controlled the generation of so-called isolated attosecond pulses becomes feasible. Today’s few-cycle laser technology relies on Ti:Sapphire laser systems and hollow fiber based post-compression. The output power of such lasers is typically below 1 W and the repetition rate is limited to a few kilohertz due to thermo-optical limitations of the Ti:Sapphire amplifiers. In this contribution we present a different approach combining the advantages of fiber laser technology with nonlinear frequency conversion. A high power femtosecond fiber laser system serves as pump laser for an ultrabroadband optical parametric amplifier. As a result we are able to generate intense CEP-stable pulses with only two optical cycles duration at repetition rates up to 0.6 MHz. The excellent beam quality ensured by the fiber based pump laser enables focusing of these pulses to high intensities, thus, allowing for the generation of high harmonics and attosecond pulses at exceptionally high repetition rates. We will present the design of the laser system and discuss specific challenges such as the broadband signal generation, the temporal synchronization of the pump laser and the carrier envelop phase stabilization. In addition, experimental results on high repetition rate XUV continuum generation will be presented, demonstrating the feasibility of our approach.