Apparatus for the treatment of a target tissue with a laser beam in which the target tissue is immersed in a liquid medium within a body lumen. The laser device is configured to provide one or more laser pulses which are configured by a controller to have an energy sufficient to form one or more vapor bubbles in the liquid medium at the distal delivery end of the fiber. The one or more pulses are configured by the controller to: first, cause a vapor bubble to be formed distally of the distal end portion of the endoscope and around the distal delivery end of the optical fiber； second, cause a second bubble to be formed distally of the first bubble； and, third, inflate the second bubble as the first bubble has begun to collapse to expand an amount sufficient to displace a substantial portion of the liquid medium from the space between the distal delivery end of the fiber and the target tissue.
