Observation of laser ablation of silicon as a function of pulse length at constant fluence via time-resolved x-ray spectroscopy

Journal Article · 13 December 2023 · Physics of Plasmas

DOI: https://doi.org/10.1063/5.0164950 · OSTI ID:2280852

Joshi, T. R.  ^[1]; Bailly-Grandvaux, M.  ^[2]; Turner, R. E.  ^[2]; Spielman, R. B.  ^[3]; Garay, J. E.  ^[2]; Beg, F. N. ^[2]

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1. University of Rochester, NY (United States); Laboratory for Laser Energetics, University of Rochester
2. University of California San Diego, La Jolla, CA (United States)
3. University of Rochester, NY (United States)

We investigate the ablation of silicon as a function of laser pulse length at a constant fluence using time-resolved x-ray spectroscopy data obtained from OMEGA EP experiments at the University of Rochester's Laboratory for Laser Energetics. Our targets consisted of three-layer planar structures composed of Si (50 μm), Cu (25 μm), and SiO₂ (500 μm) layers. The Si layer was irradiated by a 351-nm laser with varying pulse widths of 250 ps, 500 ps, 1 ns, and 10 ns while maintaining a constant fluence of ~27.9 kJ/cm². Electron temperatures and densities of the ablated plasma were determined by analyzing the time-resolved x-ray spectroscopy data through a comparison of experimental measurements with synthetic results obtained from Si atomic calculations in a steady state and non-local thermodynamic equilibrium. These calculations were computed using PrismSPECT. Additionally, radiation-hydrodynamics simulations with FLASH are used to generate simulated plasma-density and plasma-temperature profiles, which are then compared with the experimental measurements. Our analyses reveal that increasing the laser pulse length at a constant fluence results in a decrease in electron temperatures and densities. Furthermore, the longer pulses with lower intensities lead to deeper ablation regions before reaching the peak ablation but lower ionization balances in the silicon layer. Furthermore, these findings emphasize the critical role of laser pulse length in plasma ablation and shock generation for laser-impulse studies.

• Research Organization: University of Rochester, NY (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: NA0003856
• OSTI ID: 2280852
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 12 Vol. 30; ISSN 1070-664X
• Publisher: American Institute of Physics (AIP)Copyright Statement
• Country of Publication: United States
• Language: English