Compact Pulsed High Power Rare- Earth Doped Fiber Optic Laser

The objective of this work is to develop a small, reliable, low cost pulsed fiber optic laser. The fiber will be rare-earth doped and will deliver pulses of several megawatts with a width of ten nanoseconds. Fiber optic communications has already stimulated the development of low power cw fiber lasers and high power fiber amplifiers. In this proposal, we present an approach to use fiber lasers in a high power pulsed mode. We will use a double clad fiber configuration because it is currently the most promising design for high power fiber lasers. We will focus our efforts on Nd3+ doped silica fibers because this combination achieves the highest output power at the present time. However, we will experiment with different fiber materials and rare-earth dopings, as well as optimize the length of the fiber for each combination. Because the projected peak output power is in the range of megawatts, damage thresholds of the different materials have to be investigated. To generate pulses in the ten nanosecond range we propose using a KD*P modulator for Q-switching. The end mirrors can be formed by dielectric coatings on the fiber ends or UV induced fiber-gratings. A high power fiver optic laser with integrated Q-switch will have several advantages over solid state lasers consisting of bulk optical elements: The coupling of the pump light is simpler and the cooling of the active material is more efficient, because of the bigger surface to volume ratio in the fiber. Therefore, thermal lensing is reduced and fundamental mode operation is possible over a wide power range.