A novel diode laser system for photodynamic therapy

In this paper a novel diode laser system for photodynamic therapy is demonstrated. The system is based on linear spatial filtering and optical phase conjugate feedback from a photorefractive BaTiO₃ crystal. The spatial coherence properties of the diode laser are significantly improved. The system provides an almost diffraction limited output which is efficiently coupled into a 50 μm core diameter fiber. The optical power transmitted through the fiber is increased by a factor of six when the feedback is applied to the diode laser. 85 percent of the power from the freely running laser diode is extracted in a high-quality beam and 80 percent of the output power is extracted through the fiber. The power transmitted through the fiber scales linearly with the power of the laser diode, which means that a laser diode emitting 1.7 W multi-mode radiation would provide 1 W of optical power through a 50 μm core diameter fiber. The system is compact, portable, stable, and easy to operate.