Plasma expansion into a waveguide created by a linearly polarized femtosecond laser pulse

We demonstrate the efficient generation of 4 mm and 8 mm long plasma waveguides in hydrogen and helium. These waveguides have matching spots sizes for 13 to 34 μm laser beams. The plasma waveguides are created by ultra-short laser pulses (sub-picosecond) of moderate intensities, ∼1015–1016 W cm−2, that heat the plasma to initial temperatures of tens of eV in order to create a hot plasma column that will expand into a plasma waveguide. We have determined that the main heating mechanism when using fs laser pulses and plasma densities ∼1018–19 cm−3 is Above Threshold Ionization. Detailed time and space electron density measurements are presented for the laser produced plasma waveguides.