Abstract
Low-intensity laser prepulse (<10
13
W/cm
2, ns duration) are a major issue in experiments on laser-generation of protons, often limiting the performances of proton sources produced by high-intensity lasers (≈10
19
W/cm
2, ps or fs duration)
Several effects are associated to the prepulse and are discussed in this contribution:
i)
Destruction of thin foil targets by the shock generated by the laser prepulse
ii)
Creation of preplasma on target front side affecting laser absorption
iii)
Deformation of target rear side
iv)
Whole displacement of thin foil targets affecting focusing condition
In particular, we show that under oblique high-intensity irradiation and for low prepulse intensities, the proton beam is directed away from the target normal. Deviation is towards the laser forward direction, with an angle that increases with the level and duration of the ASE pedestal. Also, for a given laser pulse, beam deviation increases with proton energy.
The observations are discussed in terms of Target Normal Sheath Acceleration, in combination with a laser-controllable shock wave locally deforming the target surface.