Optical Probing of Laser-Produced Plasma Channeling Experiments on the OMEGA EP laser system

Steven Ivancic Laboratory for Laser Energetics, University of Rochester Advised by Doctor Wolfgang R. Theobald and Professor David D. Meyerhofer

Hopeman 224

Optical probing allows for the direct observation of fluid dynamics in transparent media such as gases and plasmas.  Light pressure from an intense (100 Trillion Watt) laser pulse drives a tremendously intense shockwave (> 1000 km/s) into ionized coronal plasma of a laser ablated target.  This talk describes experiments that demonstrate the transport of high intensity (> 10¹⁷ W/cm²) laser light through a mm-size inhomogeneous kJ-laser produced plasma up to overcritical density. The multi-kJ high intensity light evacuates a conical shaped cavity with a radial parabolic density profile that is observed using a novel optical probing technique, Angular Filter Refractometry (AFR). The cavity in the plasma forms in less than 100 ps using a 20 TW laser pulse and bores at a velocity of 2 µ m/ps.  The experimentally measured depths of the cavity are consistent with a ponderomotive hole boring model.  The experiments show that 100-ps IR pulses with an intensity of ~ 5 x 10¹⁷ W/cm² produced a channel up to the critical density, while 10-ps pulses with the same energy but higher intensity did not propagate as far.  In this seminar, the design of the optical probe used to make these measurements and a new technique for analysis will also be discussed.  A  10-ps, 263-nm (4ω) laser was built to probe plasmas produced on OMEGA EP. AFR allows the measurement of large phase excursions in the probe beam (100’s of radians per mm) and maintains a 3 micron resolution over the field of view.  The data obtained from the AFR diagnostic and channeling experiment provide new insights into high intensity laser-matter interactions, with applicability in a variety of applications: controlled thermonuclear fusion schemes, acceleration of light ions and directed energy systems.