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Short pulse laser damage testing on nitrocellulose and polyimide thin films in vacuum with application to laser debris shields

High intensity lasers require novel debris mitigation techniques in laser-target experiments. For a PW class system (500 J in 500 fs at 1054 nm), the debris shield thickness is limited by the accumulated B-integral that the laser acquires in transmission. In our case, this sets an upper limit of 500 micron for the debris shield thickness if the added Bintegral is to stay below 1.5. Therefore we have started to investigate the optical properties of various thin films such as Nitrocellulose, Mylar, and Polyimide with respect to their application as laser debris shields. Those results were presented during the last conference in 2007[1] and it was shown that Nitrocellulose and Polyimide are well suited. Damage testing was not performed at this time. We now present short pulse (500 fs at 1054 nm) laser damage testing on these thin films in vacuum. Energy, pulsewidth, beamsize and phase were closely monitored during the damage testing experiments. Nitrocellulose was measured to damage at 1.33 J/cm2. Polyimide showed signs of damage at 133 mJ/cm2 and began to fully penetrate the film at 670 mJ/cm2. Surprisingly, these films do not rupture with tens of closely spaced damage sites being present which makes them ideal candidates for short pulse laser debris shields. Damage testing procedure and apparatus as well as the damage site morphology will also be discussed.