Investigation of ultraintense femtosecond laser-plasma interactions through omega and 2 omega imaging and spectroscopy

A laser-plasma interaction experiment was performed in order to match effec tive conditions for wake-field electron acceleration. A 30-fs pulse was mad e to interact with a preformed plasma generated via the exploding foil tech nique from a 1-mum-thick plastic film. The irradiance of the femtosecond pu lse in the plasma was 10(20) Wcm(-2). The interaction conditions were inves tigated via imaging and spectroscopy at the fundamental and the second harm onic of the laser frequency, both forward and backward. Our data clearly sh ow that conditions suitable for electron acceleration are achieved close to the propagation axis and can be easily reproduced from shot to shot. In co ntrast, significant growth of instabilities occurs at the boundaries of the interaction region. These observations are consistent with a preliminary e vidence of forward acceleration of high-energy electrons. Optical, X-ray, a nd gamma -ray data obtained for different positions of the foil target with respect to the laser focal plane further support this promising scenario.