PIC-simulation of ultra-intense laser plasma interaction with silica microspheres

Mass limited targets (MLT) in laser plasma interaction (LPI) is a reliable pathway to achieving warm and hot dense matter (WDM/HDM) states. The effects of ultra-high intensity laser light on various geometric arrangements of silica microspheres as MLT were investigated using 2D and 3D EPOCH particle-in-cell code. Multiple target configurations were used with one, two, and three 1 µm diameter silica sphere(s), where the laser, with 10²⁰ W/cm² peak intensity, 400 nm wavelength, 40 fs pulse duration and a 1 µm beam waist radius, is focused onto a single sphere. Initial conditions were charge-neutral and room temperature (300 K), with both Si and O atoms set to field ionize using a semi-classical tunneling ionization model, and releasing electrons in strong accelerating fields. All simulations were carried out up to 1000 fs. Comparison of single vs multiple sphere cases show that the spheres not directly hit by the laser exhibit different charged particle dynamics. The results showed all particle species ejected from the rear in distinct geometric patterns (“jets”) several hundred fs after laser impact in the three-sphere configuration where the laser is focused onto the middle sphere only. Ionization of adjacent spheres with minimal dispersion is also demonstrated.