Picosecond electron deflectometry of optical-field ionized plasmas

Abstract: We demonstrate a new method of investigating optical field ionized (OFI) plasmas which allows their dynamics to be studied with ultrahigh temporal resolution and yields information not accessible by other methods. Ultrashort electron pulses with an energy of 20 keV are directed onto an OFI nitrogen plasma generated by a 50 fs titanium-sapphire laser pulse. Deflection of the electrons by the fields resulting from charge separation yields images of the expanding plasma. Pump-probe experiments of the plasma expansion capture changes within a few picoseconds with high spatial resolution. Analysis of the images reveals features not seen in previous studies: an expanding cloud of relatively hot electrons and electron lobes at the entrance and exit of the laser.