K-α x-ray measurements using a high-resolution highly annealed pyrolytic graphite crystal spectrograph have been performed for ultrashort intense laser foil interaction. Experiments were performed using Ti:sapphire laser of 25 fs duration, intensity of 1 × 1019 W cm−2 and 7 µm Cu foil target. Using the observed laser-to-x-ray conversion, the fast electron conversion efficiency was estimated to be ∼1%. Intensity scaling of x-ray conversion was used to establish the role of the J × B mechanism of fast electron generation. Furthermore, through parametric studies, the role of refluxing and reacceleration of electrons in x-ray generation is also established. Finally, the role of polarization (p vs. s) is also observed and briefly discussed.
Characterisation of a laser plasma betatron source for high resolution x-ray imaging