Hydrodynamical and optical properties of the plasma waveguide

The linear optical guiding properties of the laser-produced plasma waveguide were experimentally investigated. Time and space resolved interferometry measurements of the electron density profile allowed the determination of the channel size, depth, and the local uniformity of the guide. This information was used to completely characterize the guiding of moderate intensity laser pulses injected into the guide, where moderate intensity is defined as below the threshold for further ionization of the preformed plasma. The observed guided intensity profiles of end-coupled and tunnel-coupled pulses compared favorably with calculations of the quasi-bound modes based on the measured electron density profiles. For end-coupling, quasi-bound mode selection was determined by the input beam size and coupling angle with no observed frequency selection. This was in contrast to the frequency and angle selective tunnel coupling. For a given spectrum of allowed quasi-bound modes, end-coupling tended to select lower order modes while tunnel-coupling selected the highest available.;Detailed time- and space-resolved electron density measurements were made on the plasma waveguide. A density depression suitable for optical guiding was observed to develop within the first few hundred picoseconds after plasma creation, during which rapid cooling occurred. At longer times the plasma expansion closely followed that of a cylindrical blast wave, with further cooling due to expansion work.;In addition, time- and space-resolved measurements of the electron density profiles of a laser-driven concentric implosion were performed for the first time to our knowledge. The implosion was the result of the interaction of a second line-focused laser pulse with an existing plasma waveguide. The two-pulse absorption and ionization significantly exceeded that due to a single pulse of the same total energy, with the second pulse being almost completely absorbed when the initial waveguide was allowed to expand and cool. The observed end-coupled guided pulse transmission showed a prompt enhancement due to the increased barrier height and thickness. The laser-driven hydrodynamic response of the plasma (compression and relaxation waves) resulted in additional guided mode control over the delay method for single-pulse created waveguides.