Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

The paper reports recent experiments using the VULCAN Nd:glass amplifier. Chirped pulse amplification has been used in solid state laser systems to avoid the power limit set by nonlinear self phase modulation and self focusing that would otherwise prevent amplification of ultrashort pulses to high peak powers. The operation of a laser diode pumped oscillator based on NdxLa1-xMgAl11O19 (Nd:LMA or LNA) is reported.

Abstract:

A high brightness krypton fluoride Raman laser (wavelength 0.268 μm) generating 0.3 TW, 12 ps pulses with 20 μrad beam divergence and a prepulse of less than 10-10 has been focused to produce a 10 μm wide line focus (irradiances ≃ 0.8-4X1015 W cm-2) on plastic targets with a diagnostic sodium fluoride (NaF) layer buried within the target. Axial and lateral transport of energy has been measured by analysis of x-ray images of the line focus and from x-ray spectra emitted by the layer of NaF with varying overlay thicknesses. It is shown that the ratio of the distance between the critical density surface and the ablation surface to the laser focal width controls lateral transport in a similar manner as for previous spot focus experiments. The measured axial energy transport is compared to MEDUSA [J. P. Christiansen, D. E. T. F. Ashby, and K. V. Roberts, Comput. Phys. Commun. 7, 271 (1974)] one-dimensional hydrodynamic code simulations with an average atom post-processor for predicting spectral line intensities. An energy absorption of ≃10% in the code gives agreement with the experimental axial penetration. Various measured line ratios of hydrogen- and helium-like Na and F are investigated as temperature diagnostics in the NaF layer using the RATION [R. W. Lee, B. L. Whitten, and R. E. Strout, J. Quant. Spectrosc. Radiat. Transfer 32, 91 (1984)] code. © 1994 American Institute of Physics.

Abstract:

The hydrodynamic behavior of a Ta exploding foil using a double pulse in order to achieve favorable conditions for a Ni-like collisional x-ray laser with moderate driver energy have been examined in detail. It is shown that plasma conditions required for high gain lasing can be produced with ×4 reduced laser power as compared with Maxon's scheme [Phys. Rev. Lett. 70, 2285 (1993)], provided that the second pulse is correctly timed and is delivered before transparency of the target to the incident laser light. This makes water window x-ray lasers within the reach of many moderately sized laser installations. © 1994 American Institute of Physics.