Research On Fiber Optic Coupling For The High-power Nd:YAG Laser Beam

Fiber optic transmission of high power laser beam has opened a new dimension for laser material processing. The Nd:YAG laser in combination with the optical fiber increases the automation and the flexibility of laser processing. The aim of fiber transmission is definitely to deliver laser power through optical fiber with losses as low as possible. The main influencing on the efficiency of transmission system is coupling losses. The alignment of laser beam to fiber end face and degradation of beam quality can increase the coupling losses. This paper analyzes their effects to the coupling efficiency. To laser processing delivery system, beam quality of fiber output laser is extraordinary important because it influences the quality of processing. Beam quality of the output laser is dependent on not only the fiber's structural parameter but also the launching conditions of laser. Calculations show that the near-field profile of the output beam is strong function of the laser launching conditions.For fiber coupling system, study of focusing characteristic of high-power Nd: YAG laser is the precondition of designing coupling system. If a Nd: YAG laser runs at high pump power, laser resonator will generate multimode beam due to thermal lens of active rod. The higher pump power is, the bigger divergence occurs and the smaller Rayleigh range is. With the multimode beam transformations theory, the influence of degradation of beam quality on the optical coupling system was analyzed. For single lens, the change of beam quality lead to the varity of dimension and positions of spot of focused Nd:YAG laser. A telescopic system can produce constant dimension and position of beam waist.Special fiber delivery system was designed for high-power Nd:YAG laser, which assure the alignment of laser beam to fiber end face as well as avoid laser-damage. Coupling efficiency experiments were performed.