The Allegra femtosecond laser system is the main driver for high harmonic and plasma x-ray secondary sources at ELI-Beamlines operating at a 1 kHz rep rate. The system is based on OPCPA technology and consists of seven amplification stages pumped by thin-disk picosecond lasers. It is designed to reach 30 mJ output in the first phase of operation and to be ramped up to 50 mJ by engaging an additional pump laser. The amplified pulse is compressed to sub-20fs by an array of chirped mirrors and higher order dispersion is pre-compensated for by a Dazzler AOPDF in the front-end. In this paper we present the overview of Allegra system and the current status of deployment with a special focus on the high average power OPCPA in vacuum.
Simultaneous spatially and temporally focussing (SSTF) of ultrashort pulses allows for an unprecedented control of the intensity distribution of light. It has therefore a great potential for widespread applications ranging from nonlinear microscopy, ophthalmology to micro-machining. SSTF also allows to overcome many bottlenecks of ultrashort pulse micro-machining, especially non-linear effects like filamentation and self-focussing. Here, we describe and demonstrate in detail how SSTF offers an additional degree of freedom for shaping the focal volume. In order to obtain a SSTF beam, the output of an ultrafast laser is usually split by a grating into an array of copies of the original beam, which we refer to as beamlets. The ratio of the beamlet array width to the width of the invidual beamlet is the beam aspect ratio. The focal volume of the SSTF beam can now be tailored transversally by shaping the cross-section of the beamlets and axially by choosing the right beam aspect ratio. We will discuss the requirements of the setup for a successful implementation of this approach: Firstly, the group velocity dispersion and the third order dispersion have to be compensated in order to obtain a high axial confinement. Secondly, the beamlet size and their orientation should not vary too much spectrally. Thirdly, beamlet and SSTF focus should match. We will hence demonstrate how SSTF allows to inscribe tailored three-dimensional structures with fine control over their aspect ratio. We also show how the SSTF focus can be adapted for various glasses and crystals.