https://doi.org/10.1140/epjd/s10053-023-00678-6
Regular Article – Ultraintense and Ultrashort Laser Fields
Intense laser pulse interaction with a nanofoil and generation of energetic protons in underdense upstream plasma
1
Department of Physics, MNIT Jaipur, 302017, Jaipur, Rajasthan, India
2
Department of Physics, AIAS, Amity University, 201313, Noida, UP, India
Received:
10
November
2022
Accepted:
16
May
2023
Published online:
12
June
2023
An analytical formalism is developed to study the radiation pressure hole boring ion acceleration of a CH foil in an underdense upstream plasma. The laser quickly converts the foil into an overdense plasma and exerts a strong forward ponderomotive force on the electrons. The electrons are pushed to the rear and detach from the ions to form a thin electron layer, followed by a hydrogen ion layer and a distant carbon ion layer. The triple layer of electrons, protons and carbon ions is accelerated by the radiation pressure; the space charge field plays an intermediary role in accelerating the ions. In the frame of the electron layer, moving with velocity 
, the upstream protons appear to be moving backward with velocity -. They get reflected back in the fast moving intense space charge field of the triple layer, acquiring velocity . In the lab frame, these protons have a velocity nearly twice the velocity of the electron layer. For a Gaussian (in time) laser pulse, a parabolic density profile of the upstream plasma is seen to produce a proton beam with narrow energy spread. For a normalized laser amplitude 
, one may obtain 180 MeV protons in a parabolically decreasing density profile of scale length 
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