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Mapping transient electric fields with picosecond electron bunches

Significance Transient electric fields driven by intense lasers and particle beams play a key role in a number of applications from plasma-based particle accelerators to implosion dynamics of inertial fusion targets. Here, a method to map the 3D transient field structures with high resolutions both in time and space by use of picosecond electron bunches is presented. It is applied to measure the transient field evolution induced at a solid surface irradiated by a short pulse laser. This method can be applied to monitor field structures with much higher strength, which may find wide application in relevant research fields. Transient electric fields, which are an important but hardly explored parameter of laser plasmas, can now be diagnosed experimentally with combined ultrafast temporal resolution and field sensitivity, using femtosecond to picosecond electron or proton pulses as probes. However, poor spatial resolution poses great challenges to simultaneously recording both the global and local field features. Here, we present a direct 3D measurement of a transient electric field by time-resolved electron schlieren radiography with simultaneous 80-μm spatial and 3.7-ps temporal resolutions, analyzed using an Abel inversion algorithm. The electric field here is built up at the front of an aluminum foil irradiated with a femtosecond laser pulse at 1.9 × 1012 W/cm2, where electrons are emitted at a speed of 4 × 106 m/s, resulting in a unique “peak–valley” transient electric field map with the field strength up to 105 V/m. Furthermore, time-resolved schlieren radiography with charged particle pulses should enable the mapping of various fast-evolving field structures including those found in plasma-based particle accelerators.