Figure 1. Principle scheme of the laser-plasma lens.

(a) An electron beam is accelerated in the first gas jet (accelerator), then it enters free space where it diverges and is eventually focused in the second gas jet (lens). The same laser triggers a wakefield in both gas jets. Electron spectra are measured using an electron spectrometer consisting of a dipole magnet and a phosphor screen, imaged by a CCD camera. (b) Phase spaces at the end of the acceleration (I), drift (II) and focusing (III) stages.