Experimental progress in all-optical diagnosis of the laser wakefield of a plasma channel

Summary form only given. As an alternative to radio-frequency (RF) based linear accelerators (linacs), laser driven plasma based accelerators are being studied at various universities and laboratories around the world. In analogy with RF linacs, the laser plasma accelerator needs to consist of an injector, an accelerating structure with longitudinal electric fields which provides mode control for the accelerating fields as well as guiding for the laser, and a suitable laser driver. Recently, a novel scheme for producing a plasma channel has been implemented, which substantially reduces the energy requirement on the laser system. Called the ignitor-heater scheme, the plasma channel formation, which occurs via shock expansion of heated plasma, is accomplished by distributing the task of ionization and inverse bremsstrahlung heating between two laser pulses, rather than the standard single pulse. Each pulse is separately optimized to perform its function. A Ti-sapphire laser system provides the 75 fs, 10-20 mJ ignitor pulse, the 160 ps, >100 mJ heater pulse and several probe beams, both at the fundamental wavelength and frequency doubled to 400 nm, for diagnosis of the channel parameters.