Picosecond electron deflectometry of laser-induced plasmas

We demonstrate a method for real-time imaging of the field distribution in laser-induced plasmas with picosecond temporal resolution. The plasma is generated by a 50 fs laser pulse focused in nitrogen gas jet, and is then probed by a picosecond electron pulse synchronized with the laser. Pump-probe images of the electron beam at different delay times are recorded on a CCD camera. The electric and magnetic fields are reconstructed by comparing the recorded patterns with numerical simulations. We have observed a cloud of hot electrons expanding away from a central core of positively charged ions, and the appearance of strong magnetic fields near the boundaries of the gas jet. In the case of a plasma generated in low density nitrogen (10$^{13}$ cm$^{-3})$, we observed that even low energy electrons can escape from the plasma volume.