Self-guided laser wakefield acceleration using ablated plasma targets

Laser wakefield acceleration (LWFA) was studied using ablated plasmas as the target medium. A low density laser-ablated plasma (carbon and fluorine) was produced by focusing a 100 mJ, 10 ns pulse from a Nd : YAG laser onto the surface of a plastic target to a peak intensity of 3 × 1010 W cm−2. A 30 fs interaction pulse from the HERCULES Ti : sapphire laser system with 30 TW laser power subsequently irradiated the plasma at a peak intensity of 3 × 1018 W cm−2. The plasma density profile was varied in situ by changing the time delay between the two laser pulses. It was observed that electron energies up to 120 MeV with monoenergetic features were observed. For larger delays, the electron beam charge increases while the transmittance of the interaction pulse decreases. This correlation suggests that pump depletion occurs due to wake excitation. The use of an ablated plasma target enables LWFA operation at much higher repetition rates due to the fast plasma dynamics and adds flexibility of plasma parameters such as temperature, charge state and ion composition.