A new methodology able to model and reconstruct the transverse trace space of low-emittance electronudbeams accelerated in the bubble regime of laser-plasma interaction is presented. The single-shotudmeasurement of both the electron energy spectrum and the betatron radiation spectrum is shown toudallow a complete measurement of the transverse emittance, including the correlation term. A noveludtechnique to directly measure the betatron oscillation amplitude distribution is described and tested at theudSPARC-LAB test facility through the interaction of the ultrashort ultraintense Ti:Sa laser FLAME with audHe gas-jet target. Via the exposed technique the beam transverse profile is also retrieved. From the study ofudthe electron transverse dynamics inside the plasma bubble, the nonlinear correlation between the betatronudamplitude and the divergence, i.e. the angle with respect the acceleration axis, is found. The angularuddistribution of the electron beam inside the bubble is retrieved. The knowledge of the trace-space densityudallows a more accurate measurement of the transverse emittance with respect to previous paradigms.
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