Date of Award

12-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Electrical Engineering

Committee Member

Dr. Eric G. Johnson, Committee Chair

Committee Member

Dr. John Ballato

Committee Member

Dr. Liang Dong

Committee Member

Dr. Joe Watkins

Committee Member

Dr. Lin Zhu

Abstract

In this work, the amplification of higher order modes, mainly focused on optical vortices that carry orbital angular momentum (OAM), were demonstrated and discussed in a Ho:YAG rod amplifier and Ho:YAG single crystal fiber (SCF) amplifier at 2 μm. Both experiments and simulations were carried out to understand the propagation, amplification and phase preservation of optical vortices in solid state amplifiers. A 3-D propagation model combining semi-vectorial BPM and steady state rate equations was used to verify the experimental results and to simulate the high power amplification. The amplification of optical vortices was experimentally demonstrated in a Ho:YAG rod amplifier for both – the case of incoherently multiplexed seeds and the case of coherently multiplexed seeds. A matched filter was used to evaluate the phase of the amplified seed beams and it is proven that the important phase information of the seeds was preserved through the amplification process. Pump beam profile engineering is also discussed for optimizing the gain for a desired seed beam. The amplification of optical vortices were also demonstrated in a Ho:YAG SCF amplifier. The SCF has a small diameter and a large surface-to-volume ratio to ensure guidance for both pump and seed beams. The optical spectroscopic properties, small signal gain and lasing characteristics of the Ho:YAG SCF were investigated. Then the amplification of higher order vortices was demonstrated in the SCF as well. The high power operation potential of the SCF amplifier is also discussed together with the associated thermal issues. With improved SCF fabrication techniques, SCF exhibits great potential to function as a high power multimode amplifier.

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