Optimization of an All Normal Dispersion Fiber Laser and a Gain Managed Nonlinear Amplifier

Abstract

Ultrafast laser systems are used in a wide variety of modern laser research. The combination of an all-normal dispersion fiber laser and a gain-managed nonlinear fiber amplifier makes for inexpensive and easy to build system that can generate ultrashort pulses with high average power. In this thesis I explore the improvements and optimizations made to such a system for use in making a two-color laser amplifier system, to be used for projects such as multi frequency Raman generation. An all-normal dispersion fiber mode-locked laser was developed for our group, but modifications were necessary to improve both the ease of mode-locking and extend the duration of self-sustaining. Spectral filtering is the key aspect of the mode-locking operations of an all-normal dispersion fiber laser and it is the mode-locking that generates the ultrashort pulses. This spectral filtering was optimized to improve the ease of mode-locking. The pulses at the output of the mode-locked laser were found to be too long to allow the maximum spectral broadening in the gain-managed nonlinear amplifier. Compression of these pulses with a grating compressor caused the amplified spectrum to be significantly broadened by the nonlinear optical interaction in the fiber. The resulting spectra of the nonlinear amplifier were analyzed as a function of seed power and pump power (up to an upper limit before the introduction of incoherent noise that seeds Raman scattering creating a red shoulder on the spectrum). The result of these investigations is an optimized laser system that produces a train of pulses with energy of 176nJ, a bandwidth exceeding 100nm, and an uncompressed pulse duration of approximately 6ps. The system can now deliver the needed energy and bandwidth for the two-color amplification experiments that will be conducted in the future with this laser system.