  Recent experiments have shown that femtosecond filamentation plasmas generate
ultra-broadband RF radiation. We show that a novel physical process is
responsible for the RF: a plasma wake field develops behind the laser pulse,
and this wake excites (and copropagates with) a surface wave on the plasma
column. The surface wave proceeds to detach from the end of the plasma and
propagates forward as the RF pulse. We have developed a four stage model of
these plasma wake surface waves and find that it accurately predicts the RF
from a wide range of experiments.
