Effects of imperfect unipolarity on the ionization of Rydberg atoms by subpicosecond half-cycle pulses

Rydberg atoms are ionized by nearly unipolar, subpicosecond electromagnetic pulses. Deviations from a perfectly unidirectional pulse are found to alter substantially the ionization probability as a function of peak field. Quantitative agreement between classical theory and experiment is achieved if the pulse imperfections are significantly attenuated.