A catheter system includes a catheter having an elongate shaft, a balloon and a light guide. The balloon expands from a collapsed configuration to a first expanded configuration. The light guide is disposed along the elongate shaft and is in optical communication with a light source and a balloon fluid. A first portion of the light guide extends into a recess defined by the elongate shaft. A protection structure is disposed within the recess and is in contact with the first portion of the light guide. The light source provides pulses of light to the balloon fluid, thereby initiating plasma formation and rapid bubble formation within the balloon, thereby imparting pressure waves upon a treatment site. The protection structure can provide structural protection from the pressure waves to the first portion of the light guide.