Spectral broadening for ultrashort focused pulses / SBUF

Abstract:

Spectral broadening of ultrashort laser pulses was proposed as a up-scaling peak power path in PW-class laser system and was an intense field of research in the last 10 years. While spectral broadening is well understood for example in optical fibre, extended 2D in space and 1D in time models to include wavefront and pulse duration distortions for non-gaussian beams after spectral broadening are still missing.

The project’s first major objective is to introduce a model for the description of the spectral broadening of pulses with 2D beam profile and to create numerical instruments and methods ready to i) provide a prediction for the spatio-spectral composition of cm-size beams after spectral broadening in thin films and ii) describe propagation of such pulses in free space and also after a focusing mirror, in the confocal region.

The starting point to describe the spatio-temporal structure of the spectrally broadened ultrashort laser pulses in the confocal region is reference [1]. In particular, we will extend the calculation method developed for the studies on spatio-temporal couplings, by including also the non-linear contribution to the wavefront of the pulse. We already made Gauss beamlets decomposition that allows us to perform simulations such as helical beams propagation. By extending the method to include spectral amplitude and phase modulations we will be able to predict the spot size and achievable intensity in the focus, essential for example in non-linear QED experiments studies.

The final result is the detailed amplitude and phase of the spectrally broadened pulses in the whole volume of interaction, starting from the measured beam profiles and temporal-spectral description of the collimated pulse in accessible regions outside of the focus. An immediate result would be an estimation of the irradiance (intensity) of such spectrally broadened pulses in the focus. Another possible application is to perform pulse shaping and beam shaping in order to obtain the highest possible irradiance in the focal region, in the range of 20PW/arm using SB. Beam optimization is proposed in order to obtain the highest irradiance in the focal region.

The second major objective of the project is to demonstrate the experimental characterization and analysis of the spectral broadening effect on the intensity distribution in the cofocal region for ultrashort pulses available at ELI-NP. We will use in-house qualified non-linear thin films and we will measure intensity distribution in focus, adapting hardware developed in previous ELI-RO project ProPW 3/2016. Measurements for spatio-temporal characterization with INSIGHT device, or similar, can complement the benchmarking of the code and validate the model developed within the present proposal. The 3D+1D field strength validated in this way becomes a realistic input for particle-in-cell calculations which are used for modeling ELI-NP experiments at 1015-1023 W/cm2 intensities.

1. A. Talposi and D. Ursescu, "Propagation of Laser Beams by Decomposition into Gaussian Beamlets," CLEO Europe 2019, Munich, Germany, 2019, pp. 1-1, doi: 10.1109/CLEOE-EQEC.2019.8873404.