Propagation of intense Bessel beams in underdense plasmas and applications

Propagation of intense Bessel beams in under-dense plasmas (plasmas with densities below critical density) has been investigated in ambient and gas jet cases. For zero-order Bessel beams (J₀), a resonant self-trapping and enhanced absorption process was investigated. This resonance depended not only on the plasma density, but also on Bessel beam angle and wavelength. We applied high power fifth order Bessel beams ( J₅) to generate plasma waveguides with the smallest radius bound modes (∼4 microns) to date, without the need for shock expansion as in this group's earlier work with J₀ beams. A 1D hydrodynamic code was developed to simulate the interaction of intense Bessel beams with neutral gas and under-dense plasma; the simulation results were in good agreement with the experimental results for moderate intensity laser pulses.; Neutral gas at the ends of plasma waveguides made by Bessel beams in ambient gas has been a problem for applications involving intense pulse injection and EUV (extreme ultraviolet) generation. To solve this problem, a high repetition rate gas jet was developed, in which plasma waveguides were generated by high power Bessel beams and probed using interferometry. The spectra of EUV emission exiting from the end of pump laser-injected plasma waveguides was examined for the first time, and it was found that the EUV radiation output was closely related to the coupling efficiency. The extra heating from laser pulses injected into and guided in the plasma waveguide resulted in enhanced radiation from the highest observed ionization stages.