A catheter system to ablate target matter within a mammalian body using light energy is described. The system may include an open-ended catheter tip through which a liquid light guide medium flows to the target matter, where at least a portion of the liquid light guide medium exiting the catheter tip creates a fluid optical channel to transmit the light energy from the catheter tip to the target matter. The system may also include a catheter lumen whose distal end includes the open-ended catheter tip, a light source to generate the light energy, and a liquid light guide medium source fluidly coupled to the catheter lumen. The liquid light guide medium source may include a reservoir of the liquid light guide medium that includes a magnesium chloride solution or a lactated Ringer's solution.
