As energy is injected into matter it eventually reaches the plasma state where electrons are

separated from ions. The importance of electrostatic interaction in a plasma is determined

by the plasma parameter Γ which is the ratio of electric potential energy to thermal energy.

Space plasmas and plasmas created in Tokomaks are dilute and have Γ << 1. The

transport properties of strongly coupled plasmas where Γ > 1 are not understood and are

especially important for understanding instabilities in inertial connement fusion experiments.

Dense plasmas with Γ > 1 are accessible in table top experiments via sonoluminescence,

sparks and laser breakdown of dense gases. In this thesis, plasma is generated in

1-10 bar hydrogen gas using a high power femtosecond laser between pulse widths of 130-

320fs. By measuring the plasma via CCD images, spectral and bandpass emission, as well

as transmitted laser spectra, a transition from tunneling ionized plasma at low pressure

to cascade breakdown at high pressure is observed. Dense tunneling plasma is imaged directly for the first time and shown to have a uniform structure. This plasma is proposed as an ideal candidate for the study of dense plasma hydrodynamics.