Optimization of THz Radiation Generation from a Laser Wakefield Accelerator

Ultrashort terahertz pulses with energies in the muJ range can be generated with laser wakefield accelerators (LWFA), which are novel, compact accelerators that produce ultrashort electron bunches with energies up to 1 GeV [1] and energy spreads of a few-percent. Laser pulses interacting with a plasma create accelerated electrons which upon exiting the plasma emit terahertz pulses via transition radiation. Because these electron bunches are ultrashort ( < 50 fs), they can radiate coherently (coherent transition radiation-CTR) in a wide bandwidth (~1-10 THz) yielding high intensity terahertz pulses [2]. In addition to providing a non-invasive bunch-length diagnostic [3] and thus feedback for the LWFA, these high peak power THz pulses are suitable for high field (MV/cm) pump-probe experiments. Here we present energy-based measurements using a Golay cell and an electro-optic technique which were used to characterize these THz pulses.