Extreme contrast, ultrahigh intensity laser-solid interaction - Impulsive excitation and direct observation of the ponderomotive push

Ultrahigh intensity, femtosecond laser pulse interaction in high energy density plasmas is attracting great attention for the basic science it reveals and applications in particle acceleration, bright hard x-ray emission and simulation of astrophysical scenarios [1]. Recent experiments have explored the interaction of "extreme" contrast (well below 10^{-12} at 100 picosecond), relativistic intensity femtosecond laser pulse interaction with solids [2]. Here we present the ultrafast dynamics of the high energy density plasma created by a high intensity, femtosecond laser pulses at 400 nm [3] created by second harmonic generation of 800 nm pulses from a Ti-Sapphire laser with a contrast of 10^{-9} at 100 picosecond. Measurements include Doppler spectrometry [4] and wavefront sensing [5]. Experimental and simulation results demonstrate instantaneous excitation of the solid density surface and the launch of a very strong shock by the radiation pressure of the pulse. The wavefront measurement directly reveals the ponderomotive deformation of the critical surface by the pump pulse and its time evolution captured through phase modifications of a time delayed probe. The results offer possibilities for shaping plasma mirrors for generating even higher intensities.

[1] J. J. Rocca et al., OPTICA, 11, 437 (2024)

[2] C. Aparajit etal., Phys. Rev. Res. (in press, 2025)

[3] C. Aparajit et al, Opt. Lett. 46, 3540 (2021)

[4] K. Jana et al., Phys. Rev. Res.3, 033034 (2021)

[5] Sk. Rakeeb et al., Opt. Lett. (in press, 2025)