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Plenary Lecture

Laser-based microfabrication and metrology of laser-driven inertial fusion targets

Friday (26.06.2020)
14:00 - 14:40 Room 1

14:00 - 14:40

While high-power lasers enable laser-driven inertial fusion and high-energy-density–physics

experiments, low- power lasers are increasingly used to make and characterize the targets at

micro/nanoscales for those experiments. The feature of particular importance is the high power

density achievable with femtosecond lasers, which provides the spatial resolution that is needed to

apply additive manufacturing and a new generation of characterization techniques to this field.

 

Millimeter-size plastic shells with smooth surfaces and submicrometer cellular (foam) structures

are made using the two-photon polymerization process. While this application is in its infancy, the

potential to make targets more deterministically, consistently, and efficiently than existing

methods is compelling. The goal is to make structures with a surface smoothness 50-nm rms and

feature sizes 0.5 ❍m over dimensions up to 5 mm; the process conditions needed to achieve this and

the capabilities and current limitations of this technique are described.

 

A second application of lasers in this field is in the traditional role of ablation to produce

structured surfaces and precise pinhole-aperture arrays. These structures are used to increase

x-ray emission from a surface and to produce high-resolution imaging systems to better diagnose

laser-driven implosions.

 

A third application is to use coherent anti-Stokes Raman spectroscopy (CARS) to produce a 3-D

topographical map of the elemental composition of a laser-fusion target. Initial experiments

demonstrated micrometer-scale imaging of a 0.9-mm-diam polystyrene shell to identify the presence

of voids in the material; this was achieved by sectional imaging to scan horizontal 2-D slices

vertically through the target and detecting the presence or absence of Raman-active bands of C-H

stretching bonds at 2800 to 3000 cm–1. This application is being extended to image the distribution

of the hydrogen isotopes inside the fuel layer of the polystyrene shell—which is a shell of frozen

deuterium and tritium. These data will provide greater resolution and sensitivity than the

technique, tunable infrared diode laser spectroscopy, to address an important question that until

now could not be diagnosed.

Speaker:
Prof. David Harding
University of Rochester
Additional Authors:
  • Sarah Fess
    University of Rochester
  • Mark Bonino
    University of Rochester
  • Robert Earley
    University of Rochester
  • Dr. Craig Sangster
    University of Rochester
  • Dr. Michael Campbell
    University of Rochester
  • Prof. Yongfeng Lu
    University of Nebraska Lincoln
  • Dr. Peixun Fan
    University of Nebraska Lincoln
  • Dr. Xi Huang
    University of Nebraska Lincoln

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