High-resolution X-Ray spectromicroscopy methods were used for investigations of fs laser interaction with N2O cluster media. Elongated (up to 8.5 mm) femtosecond laser self-channeling in N2O cluster media under sufficiently low laser intensity (0.5-4x1017 W/cm2) was observed. Results are revealing a strong macroscopic effect on laser beams owing to their interaction with a gas of clusters. This has occurred at moderate pulse intensities, so the effect is unrelated to either relativistic self-focusing or ponderomotive filamentation. Enough homogeneous multicharged ions plasma with bulk electron temperature around 100 eV was observed along the plasma channel. The spectral lines shapes of the H- and He-like Oxygen ions demonstrated the presence of strong "blue wings", which are caused by Doppler-shifted lines radiation from the essential fraction of ions (~10-2 - 10-3) with energies 0.1 - 1.5 MeV. The slope of Doppler-shifted lines radiation is good approximated by ~300 KeV ion temperatures.
A series of experiments has been performed to investigate the interaction of intense laser pulses with cryogenic noble gas droplets. Understanding of the time scales for this interaction is important for optimization of extreme ultraviolet (EUV) sources for next-generation lithography that utilize laser-produced plasmas. The temporal character of the plasma formed by the irradiation of micron-sized argon and krypton droplets with intense 200-mJ, 100-ps laser pulses was investigated using a pump-probe scheme. The evolution of the droplet plasma was assessed by monitoring delay-dependent x-ray and EUV emission, and by imaging frequency-doubled probe light scattered from the interaction region. Depending on the spectral region of interest and the droplet characteristics, the effective plasma lifetime extends from a few hundred picoseconds to several nanoseconds. These results are explained in terms of the plasma expansion, excitation emission, and recombination emission time scales.
Theoretical analysis and preliminary experiment on ionization instability of intense laser pulses in ionizing plasmas are presented. The ionization instability is due to the dependence of the ionization rate on the laser intensity and scatters the laser energy off the original propagation direction.
A recently developed laser-produced plasma channel is shown to be a promising means to produce an efficient, compact soft x-ray laser. The channel provides a route for efficient high power laser pumping through optical waveguiding of the pump. The channel also acts as a waveguide for generated soft x-rays, since it has wavelength independent mode structure. Channel creation and guided laser pulses of moderate duration and energy can be highly effective in driving nonequilibrium behavior of these plasmas to generate substantial population inversions.
We present results from a 1-D plasma dynamics calculation, describing the evolution of strongly heated material in the vicinity of a solid-vacuum interface. We find that the radiation emitted by the hot material in the range hν > kTe, where Te is the initial peak plasma temperature, comes primarily from the region of the original step function interface. This emission is dominated by recombination radiation. The emitted radiation pulse is extremely short; the cooling at the interface is dominated by expansion. It is seen that thermal conduction minimally affects the radiation pulse intensity and duration.
In these proceedings, we report on a time-resolved investigation of the hydrodynamics of a laser-produced plasma. A sub-100ps pulse is focused into a chamber filled with xenon for various pulse energies and pressures. This pulse (the pump pulse) forms a plasma, which is probed by a second pulse (the probe pulse) with a variable delay of up to 2.5 ns. The gradients in the plasma density profile produce a lensing effect on the probe pulse. The beam transmitted through the plasma is viewed with a CCD camera. The diffraction pattern of the probe pulse can be seen by subtracting the image of the first pulse beam from the image produced by the two-pulse beam.