A pulse laser is configured for projecting a pulsed laser beam at a target site on a fluid film atop a workpiece for laser shock peening the workpiece. The fluid film is monitored by a probe laser which projects a probe laser beam at the target site, and an optical detector which detects reflection of the probe beam from the target site. The pulse laser is coordinated by the detector in order to emit the pulsed beam in response to the condition of the monitored film.