Towards an ytterbium based frequency frequency synthsizer

Attosecond pulses are sought for experiments enlightening intra-atomic and intermolecular phenomena in attosecond or femtosecond time scale. These pulses can only be obtained via high-harmonics generation in gases with the current technology. The cut-off energy of the harmonics increases non-linearly with the wavelength of the driving laser, whereas the conversion efficiency sinks drastically. Here, we will present the first developments of a laser driver system for high-harmonics generation applications, capable of answering these challenges via a broadband spectrum covering several octaves with high energy.Attosecond science highly depends on the electric field of the driving laser and is very sensitive to the carrier-envelope phase stability. As the phenomena occur past a certain threshold of the electric field, single-cycle pulses are best adapted. The spectrum of these pulses, a few femtosecond long in time, covers several hundreds of nanometers. Pulse compression in a highly non-linear fiber achieves few femtosecond long pulses at a 100´s µJ energy level, but is not scalable to broader spectra and higher energies. A broader spectral coverage is obtained via non-linear conversion of a hundred nanometers to one octave initial broad spectrum. Due to the limitations in energy of this kind of conversion, the resulting pulses, with energies lower than the µJ level, have to be amplified afterwards with optical parametric amplifiers.We will use a waveform synthesizer based on parallel amplification: a broadband, low energy pulse generated via passively CEP stable white-light generation will be split spectrally into several channels and amplified separately to higher energies via parametric amplification. The CEP-stable white-light is driven by a sub-picosecond Yb:KYW regenerative amplifier delivering >5 mJ energy. The parametric amplification will be divided in several stages, the first ones being pumped with the remaining energy from the regenerative amplifier and the last ones with the output of a cryogenically cooled Yb:YAG composite thin-disc amplifier. The technique for the recombination of the channels to generate a sub- to single cycle pulse will be finally discussed