We present the characterization of intensity distributions and beam wavefront along the caustic of an iodine photodissociation laser beam at the Prague Asterix Laser System.Its 700 J, 300 ps laser pulse was attenuated by neutral density optical filters and focused by an f /2.2 aspherical lens.In multiple planes at and around the focus position (7 Rayleigh length), we measured fluence distributions by far-field imaging with a nonlinearity-corrected camera.We used these measurements to retrieve the beam wavefront by phase retrieval algorithm with dynamic input-output mixing (PhaRe).We then propagated the beam to the focus position and to the lens position.The calculated peak intensity at the focus position was 7.9 10 18 W/cm 2 and 300 J (43% of the pulse energy) was contained within the intensity region above the relativistic intensity threshold of 0.8 10 18 W/cm 2 @ 1315.2 nm.
Jelínek et al. (Tue,) studied this question.