Detection and Characterization of GeV-class electrons from nonlinear laser wakefield

Recently, monoenergetic electron beams are obtained with intense, short-pulse laser interacting with tenuous (underdense)[1, 2], a few centimeters plasma via laser wakefield acceleration (LWFA) mechanism [3]. Almost all the experiments utilize relatively long focal length focusing devices, of which the F-numbers (ratio of the focal length to the laser diameter) more than 10. The normalized peak laser field a0=eE/(mcw) is not greater than 5 usually, where e, E, m, c, and w are elementary charge, electric field of a laser, electron mass, speed of light, laser angular frequency, respectively. However, a large f-number detracts from the compactness of LWFA. Furthermore, a recipe for the generation of quasimonoenergetic electron beans also requires not-so-strong laser intensities at vacuum as high as ~2. We investigated experimentally highly nonlinear regime around a0~10. The nonlinear regime is not well explored recently and the benefits of the nonlinear regime might be its high gradient and a capability to accelerate high current electrons.