Transient absorption measurement of laser-accelerated ion bunch radiolysis on sub-ps timescales

Abstract

Modern laser-based accelerators for ions reach peak kinetic ion energies of > 100MeV, over 1MA of total beam currents with only a few picoseconds of bunch duration in close vicinity to the target at ≈ 1 Hz repetition rate and with a high controllability. Thus, the number of potential applications is growing rapidly. This raises a high interest in the processes of ion-matter-interactions in the energy deposition region of these ultra-intense particle bunches. In our recent experiments we investigated these interactions by single-shot time-resolved optical streaking of the energy deposition region of laser-accelerated proton bunches in liquid water. The absolute timing reference provided by the x-rays emitted from the laser-plasma-interaction and the sub-ps time resolution revealed that ionized electrons solvate > 20 ps delayed compared to experiments with lower deposited energy density. In this paper we discuss first approaches to explain these observations by micro-dosimetric considerations regarding the background molecules excitation of vibration states and polarization. This is highly relevant for applications, e.g. to understand the FLASH-effect in radio-biology. We further present the planned experiments at the Centre for Advanced Laser Applications where these phenomena will be investigated in more detail with advanced diagnostics.