  Numerical simulations of laser-plasma interactions demonstrate the generation
of axially polarized electromagnetic pulses (EMPs) that radiate away energy
with a characteristic frequency determined by the plasma frequency, in the THz
range for typical laser wakefield acceleration experiments. This is confirmed
by full 2D electromagnetic particle-in-cell simulations, as well as by a
ponderomotively-driven reduced model that captures the EMP generation
essentials. When the laser's pulse length matches the plasma wavelength, that
pulse's fractional energy losses to the wakefield are independent of the pulse
width, while the losses to the EMP are inversely dependent on the pulse width.
