Experimental ionization of atomic hydrogen with few-cycle laser pulses*

We report the first experiments on ionisation of atomic hydrogen using few-cycle laser pulses. Light from an amplified titanium:sapphire laser system is compressed in a hollow-core fiber to produce 6 fs, 100 $\mu$J pulses. These pulses are focused through a beam of atomic hydrogen at peak intensities up to $10^{15} {\mbox W}/{\mbox cm}^2$. The resulting photoelectrons are energetically filtered by an electrostatic repeller and the high-energy electrons are detected by a channeltron, yielding a measurement of the integrated electron energy spectrum above the repeller voltage. The data are compared to theoretical electron spectra computed by a matrix iteration method.