1 Optical probing of preplasmas produced by the Vulcan-PW-solid interaction

We present results obtained in experiments in which the Vulcan Petawatt laser pulse was interacting with solid targets under different contrast conditions. The pre-plasma produced by the amplified spontaneous emission was characterized by imaging the interaction zone which was back-lighted by a short probe pulse. When no contrast improvement was employed, the scale length was as large as 5 µm which effectively increased the initial target thickness by a factor of two.