Rare Earth Doped High Power Fiber Lasers And Amplifiers PDF Download

This thesis is related to the spectroscopic and optical properties of doped optical fibers used as a laser amplifier for short laser pulses at high repetition rates emitting around 2 μm. Therefore short pulses created by a laser diode are amplified in thulium-doped optical fibers combining the benefits of a direct electronic control of the laser diodes' parameters and the robust setup of an optical fiber system that can easily be integrated. After the development of a high-current pulse generator especially adapted to the 2 μm laser diodes used, pulses of > 7 ns with peak powers in the Watt range could be generated. Due to the modal behaviour of these laser diodes only 2 mW of peak power could be launched into a single-mode fiber. By comparing different fiber glasses, a heavy metal fluoride glass could be identified as the optimum host for the ions thulium and holmium emitting around 2 μm. Due to the development of a numerical simulation tool based on rate equations and radiation transport equations the fiber parameters such as core diameter, fiber length etc. could be optimized, minimizing the amplified spontaneous emission (ASE) created inside the fiber. Based on this simulation a laser system consisting of cascaded fiber amplifiers could be realized. I emits short laser pulses (20-30 ns) at high repetition rates (up to 125 kHz) and peak powers of up to 5 kW. In contrast to Q-switched lasers the pulse width created is independent of the repetition rate. By using these pulses at 1.87 μm as an optical pump for a Cr2+:ZnSe laser, efficiencies of up to 22% could be reached at an emission wavelength of 2.5 μm.