A fluid stream is directed toward tissue to generate a plurality of shedding clouds. The fluid stream can be scanned such that the plurality of shedding clouds arrive a different overlapping locations. Each of the plurality of shedding clouds can remove a portion of the tissue. In many embodiments, an apparatus to ablate tissue comprises a source of pressurized fluid, and a nozzle coupled to the source of pressurized fluid to release a fluid stream, in which the fluid stream generates a plurality of shedding clouds.

An apparatus to treat a patient, the apparatus comprises a carrier having a proximal end and a distal end, an optical fiber to couple to a light source, a fluid delivery element comprising a nozzle having an orifice on the distal end, and an alignment structure to align the optical fiber with the orifice. A distance extends between the alignment structure and the orifice, such that the light beam emitted from the optical fiber diverges so as to allow energy transmission and fluid flow through the orifice. In some embodiments, the apparatus to ablate tissue comprises a source of pressurized fluid, and the nozzle is coupled to the source of pressurized fluid to release a fluid stream.

A catheter system for treating a treatment site within or adjacent to a vessel wall includes a light source, a balloon, a light guide, and an optical analyzer assembly. The light source generates light energy. The balloon is positionable substantially adjacent to the vascular lesion. The balloon has a balloon wall that defines a balloon interior that receives a balloon fluid. The light guide receives light energy from the light source at a guide proximal end and guides the light energy toward a guide distal end and into the balloon interior. The optical analyzer assembly is configured to optically analyze light energy emitted from the guide proximal end of the light guide.