Description
The acceleration of ions to MeV energies via the Target Normal Sheath Acceleration mechanism remains limited by the slow scaling of the ion energies with the laser intensity. In this work, we present a pathway to overcome this limitation using micrometric bar targets ("μ-bars"). We have recently demonstrated [1,2] that intense laser irradiation of μ-bars narrower than the laser waist, achieve 3-times higher ion cutoff energies compared to traditional flat foil targets.
In addition, μ-bars enable cascaded laser ion acceleration (CLIA), a scheme designed to increase ion energies by re-accelerating them across multiple stages. Previous experimental realizations of CLIA using flat foils failed because a millimeter-scale separation was required to be able to fit more than one laser beam. This excessive distance caused the ion bunch to disperse significantly.
Here, we present an experimental setup designed to realize a CLIA scheme at the 20 TW NEPTUN laser facility. The open geometry of μ-bars allows for the placement of two targets with only micron-scale separation. This proximity ensures that the ion bunch launched by the first μ-bar remains compact upon entering the re-acceleration sheath of the second target. We detail the experimental configuration, supported by numerical simulations using the EPOCH particle-in-cell code.
[1] Elkind, Michal, et al. "Intense laser interaction with micro-bars." Scientific Reports 13.1 (2023): 21345.
[2] Elkind, Michal, et al.”Ion acceleration from micrometric targets immersed in an intense laser field." Communications Physics 8.1 (2025): 315