A device is disclosed herein which may comprise a droplet generator producing droplets of target material; a sensor providing an intercept time signal when a droplet reaches a preselected location; a delay circuit coupled with said sensor, the delay circuit generating a trigger signal delayed from the intercept time signal; a laser source responsive to a trigger signal to produce a laser pulse; and a system controlling said delay circuit to provide a trigger signal delayed from the intercept time by a first delay time to generate a light pulse that is focused on a droplet and a trigger signal delayed from the intercept time by a second delay time to generate a light pulse which is not focused on a droplet.