Pulse Stretching, Compression and Supercontinuum Generation in a Mode-locked Erbium Fibre Laser
Date
2024
Authors
Matulick, Andrew
Editors
Advisors
Ganija, Miftar
Boyd, Keiron
Boyd, Keiron
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Thesis
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Abstract
Understanding the non-linear optical physics involved with pulse stretching and compression enables the production of lasers for applications in research, medical, industrial, spectroscopy and chirped pulse amplification systems. The aim of this research is to provide a comprehensive investigation of pulse stretching and compression techniques with both diffraction gratings and optical fibre. In this research a coherent supercontinuum source was developed, through amplification, to produce high energy femtosecond pulses from an erbium doped fibre laser. The amplifier stage utilised non-linear effects to increase the optical spectrum and reduce the pulse duration through non-linear pulse compression and soliton fission. Supercontinua have attracted continuous research interest due to their applications in spectroscopy, tomography, metrology, and sensing. Various pulse stretching and compression techniques involving optical fibre and diffraction gratings were studied. Numerical modelling is utilised and verified with experimental pulse stretching results. Other techniques were then used for pulse compression to achieve near time-bandwidth limited pulses. These pulses were 410 fs at a 23.8 MHz repetition rate with a central wavelength of 1561.4 nm and an average power of 120.2 mW. The numerical modelling was then used in the development of the supercontinuum source. The supercontinuum enabled the increased spectral bandwidth needed for further pulse compression. The erbium fibre laser was amplified to produce a supercontinuum through strong nonlinear interactions to extend from 1550 nm beyond 2000 nm. The system was modelled using the non-linear Schrödinger equation to provide an understanding of the underlying physics behind the supercontinuum generation. This simulation showed that the supercontinuum was generated through soliton dynamics. Initially, soliton fission occurs and there is a continuous shift to longer wavelengths due to the Raman soliton experiencing Raman soliton self-frequency shift and cross-phase modulation. The output of this source was multiple soliton-like pulses at 14.5 fs duration and 2.3 W of average power. The pulse energy contained within a single Raman pulse was 59.6 nJ for a total estimated peak power of 3.63 MW.
School/Discipline
School of Physics, Chemistry and Earth Sciences
Dissertation Note
Thesis (MPhil) -- University of Adelaide, School of Physics, Chemistry and Earth Sciences, 2025
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