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Project A.1.1

High-power sub-MHz-rate femtosecond VIS-MIR sources

High-power sub-MHz-rate femtosecond VIS-MIR sources are pursued in two sub-projects: i) multi-stage broadband OPA using a sub-MHz, sub-ps Yb:YAG regenerative amplifier (REGEN) as the pump source and ii) CEP-stabilised yJ-scale few-cycle pulse generation from an Yb:YAG-oscillator/fibre-chirped-mirror-compressor system.

i) Several spectroscopic applications desire powerful femtosecond pulses at variable repetition rate and pulse energy. This goal will be achieved by developing a broadband OPA system pumped by a REGEN at a variable rate between100 KHz and 1 MHz.

The sub-picosecond 1030-nm pulses and their second, third and fourth harmonic will serve as a versatile pump for driving thin-crystal broadband OPA stages in the MIR (1500-3000 nm), NIR (700-1500 nm), VIS (500-700 nm) and UV-VIS (350-500 nm), respectively. With their seed derived from a common broadband front-end these stages will provide synchronised few-cycle pulses at microjoule energies and sub-MHz repetition rates. In close collaboration with Project B.3.1 these channels will be phasecoherently recombined for ultrabroad-band waveform synthesis. A collaboration with the group of A. Leitensdorfer (Konstanz) will strongly support our efforts of the MIR extension of the OPA spectrum.

ii) The broadband CEP-stable seed for the multi-channel OPA system will be generated in the simplest and most robust scheme: by spectral broadening of the passively mode-locked sub-ps Yb:YAG oscillator output (developed during the 1st fp and to be further improved with optimised saturable reflectors) in a double-stage large-mode-area monomode fiber followed by chirped mirrors, an approach successfully demonstrated with a 500-nJ Ti:Sa oscillator. Both parts of the project will be carried out in close collaboration with Project A.2.1 within which the Goals A.2a and A.2b bear special relevance to the work proposed here. This light source will have a widespread applicability including photoelectron emission microscopy and femtosecond electron diffraction for the study of electron dynamics (B.3c-f).

By the sub-MHz repetition rate the required data acquisition (or exposure) time will be greatly reduced, allowing also for pump-probe spectroscopy of biological molecules.