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Target Test Diagnostics Richard Brownsword Engineering, Rutherford Appleton Laboratory

Target Test Diagnostics Richard Brownsword Engineering, Rutherford Appleton Laboratory. Target Surface Velocities Problem : to measure surface displacement remotely in a time-resolved manner for an arbitrary surface material. Velocity Interferometry (VISAR) :

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Target Test Diagnostics Richard Brownsword Engineering, Rutherford Appleton Laboratory

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  1. Target Test Diagnostics Richard Brownsword Engineering, Rutherford Appleton Laboratory

  2. Target Surface Velocities • Problem : to measure surface displacement • remotely • in a time-resolved manner • for an arbitrary surface material

  3. Velocity Interferometry (VISAR) : • laser interferometric technique • time resolution may be ~ 1 ns • compensates for changes in surface reflectivity

  4. Velocity Interferometry (VISAR) : Detector Laser Frequency ω Sample Fixed mirror Beamsplitter Velocity u(t) Etalon Length L Refractive index n Fixed mirror

  5. Velocity Interferometry (VISAR) : • recombines beams at beamsplitter with delay •  = (2 L / c)( n - 1/n ) • beat frequency  (t) = ω [u(t) – u(t - )] / c • time and velocity resolution determined by etalon (L, n) • optical fibre etalons offer flexibility

  6. Derivation of velocity : • VISARs measure acceleration : Δu in time  • fringe constant Kf = o /  (ms-1) • fringe count fc  Δu • u (t) = u (t - ) + Δu (t)

  7. VISAR Simulations :surface velocity G. Skoro

  8. VISAR Simulations :VISAR signal Detection limit

  9. Background emission • Expect source temperature ~ 2000 K • VISAR laser  = 1.55 m • (1) Narrow-band interference filter  ~ 500:1 discrimination • (2) Background subtraction module

  10. Conclusion • Velocity interferometry : • has potential for remote measurement of surface displacement for a range of different materials and surface velocities • 0.01 ms-1 @ 10 ns ?

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