A laser therapy system having improved effectiveness in surgical use, particularly in laser angioplasty, can be formed by employing a pulsed source of radiation. The pulsed energy source is preferably an excimer laser having a coherent beam of ultraviolet radiation and preferably is employed in conjunction with a dye laser to produce an output beam which is tunable over a wide portion of the ultraviolet and visible spectrum. The output beam is coupled via a novel coupling device to an optical fiber disposed within a surgical instrument, for example, a percutaneous catheter. The operative components are sealed in a gas-tight, liquid-tight housing. An electronic controller monitors and adjusts the output energy density, duration, and pulse repetition rate. In operation, a pulsed, high energy beam of extremely short duration is available to remove atherosclerotic plague with less damage to the underlying tissue and less chance of perforating the blood vessel wall.