An apparatus and a method for operating a sealed high intensity illumination lamp configured to receive a laser beam from a laser light source. The lamp includes a sealed chamber configured to contain an ionizable medium having a plasma sustaining region, and a plasma ignition region. A high intensity light egress window emits high intensity light from the chamber. A substantially flat ingress window located within a wall of the chamber admits the laser beam into the chamber. The lamp includes means for controlled increasing and decreasing a pressure level within the sealed chamber while the lamp is producing the high intensity illumination.