Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Effect of front surface engineering on high energy electron, X-ray and heavy ion generation from Relativistic laser interaction with thick high-Z targets

J. Twardowski, C. Kuz, A. S. Bogale, Z. Su, A. Lee, R. Kaur, M. Eder, Y. Noor, D. P. Broughton, Md Kazi Rokunuzzaman, R. Hollinger, A. Blackston, J. Strehlow, A. Baraona, P. Spingola, G. Tiscareno, D. Hanggi, B. Unzicker, C. -S. Wong, G. K. Ngirmang, F. N. Beg, D. Schumacher, E. Chowdhury

Abstract

Relativistic lasers on solid targets generate hot electrons, and other secondary particles. These particles can be used for radiography, cancer therapy, or isochoric heating. A lower density or structured coating on high-Z targets can improve laser-target energy coupling and subsequently enhance overall particle emission. In this work performed at the Scarlet Facility, a $10^{21}$ W/cm$^2$ intense pulse was incident on front surface coatings on 1 mm thick Ta. These coatings include a 12 $μ$m plastic coating, a 50 $μ$m thick foam coating, and a Au nanowire (NW) coating. Post-damage craters are correlated with reflected light on a MACOR screen, illustrating that less absorption in a target is directly tied to smaller craters. Additionally, more absorption in a target also leads to more MeV electrons and X-rays. Bare targets performed the best for electron and MeV X-ray generation, with X-rays of 30 MeV detected, as coatings tested were too thick and thus experienced lower intensities. Due to this larger spot size, foam and NW-coated targets generated the greatest heavy ion acceleration. Particle-in-cell simulations tested on bare and plastic-coated targets illustrate that $\sim μ$m thick plastic coatings perform better than bare Ta. These results underline the importance of density and thickness control of coatings on high-Z materials. In the future, post-damage crater analysis could provide an easy way to benchmark absorption in a sample, and could later be compared against absorption estimates from particle-in-cell simulations.

Effect of front surface engineering on high energy electron, X-ray and heavy ion generation from Relativistic laser interaction with thick high-Z targets

Abstract

Relativistic lasers on solid targets generate hot electrons, and other secondary particles. These particles can be used for radiography, cancer therapy, or isochoric heating. A lower density or structured coating on high-Z targets can improve laser-target energy coupling and subsequently enhance overall particle emission. In this work performed at the Scarlet Facility, a W/cm intense pulse was incident on front surface coatings on 1 mm thick Ta. These coatings include a 12 m plastic coating, a 50 m thick foam coating, and a Au nanowire (NW) coating. Post-damage craters are correlated with reflected light on a MACOR screen, illustrating that less absorption in a target is directly tied to smaller craters. Additionally, more absorption in a target also leads to more MeV electrons and X-rays. Bare targets performed the best for electron and MeV X-ray generation, with X-rays of 30 MeV detected, as coatings tested were too thick and thus experienced lower intensities. Due to this larger spot size, foam and NW-coated targets generated the greatest heavy ion acceleration. Particle-in-cell simulations tested on bare and plastic-coated targets illustrate that m thick plastic coatings perform better than bare Ta. These results underline the importance of density and thickness control of coatings on high-Z materials. In the future, post-damage crater analysis could provide an easy way to benchmark absorption in a sample, and could later be compared against absorption estimates from particle-in-cell simulations.
Paper Structure (10 sections, 1 equation, 10 figures, 6 tables)

This paper contains 10 sections, 1 equation, 10 figures, 6 tables.

Table of Contents

  1. Introduction
  2. Experimental setup
  3. Experimental Results
  4. Laser-target coupling
  5. Electrons
  6. MeV X-rays
  7. Ta ions
  8. Particle-in-cell simulation
  9. Discussion
  10. Conclusion

Figures (10)

  • Figure 1: (a) Experimental setup with an angle of incidence of 28°. The MACOR screen is rotated 50°, and was placed directly next to the focusing optic. The CR-39 is placed behind the target in the laser axis, with a horizontal slit cut out for the electron wide angle spectrometer (eWASP). The filter stack spectrometer (FSS) is placed outside of the chamber and in the laser axis. (b) Front view of 5.1 $\times$ 5.1 cm CR-39, and its mylar coating thickness. (c) Side view of eWASP, where the electrons enter the slit in +$\vv{z}$, $\vv{B}$ is in -$\vv{y}$. (d) Side view of FSS, with the IP numbers labeled above the FSS. The majority of the filters are nylon-66, while some are tungsten (W).
  • Figure 2: Measured pre-pulse contrast of Scarlet (cross correlation) versus other high power lasers, with the peak of the pulse occurring at 0 ps.
  • Figure 3: (a) Example crater on plastic-coated Ta. Ta strip is 5 $\times$ 20 $\times$ 1 mm. Crater on bare Ta target with the (b) surface in focus, (c) bottom of crater in focus. Both crater depth and diameter varied with the target tested. Note that the focal spot had a 1/e2 diameter of 4.2 $\mu$m
  • Figure 4: Representative MACOR images for all samples tested. The f/2 focusing optic is in the bottom left of each image. The microscope objective used for front-side imaging is casting a shadow on the MACOR screen, and partially obscuring the front CR-39. MACOR images of NWs were the most variable in intensity.
  • Figure 5: Electron spectra taken at 0°, directly along the laser axis. The dashed line is the same target wheel, but the back IP instead of the bottom. A single pump shot on bare Ta is featured. The back IP for the foam target may have been loaded incorrectly into the detector. The back IP for the NW target was not loaded correctly and is not shown.
  • ...and 5 more figures