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Type: Thesis
Title: Advancing Mid-IR Lasers
Author: Malouf, Andrew
Issue Date: 2019
School/Discipline: School of Physical Sciences
Abstract: The mid-IR spectral region is important in a wide range of applications. Many molecules have unique characteristic absorption features in this region due to strong vibrational transitions. Mid-IR lasers, tuned to these absorption lines, are an excellent source for detecting trace gases such as air pollutants for environmental monitoring, biomarkers in exhaled human breath for medical diagnosis, and trace explosives for security. Furthermore, the mid-IR region includes two atmospheric transmission windows, 3 μm– 5 μm and 8 μm– 13 μm, which overlap with the strong absorption lines of many molecules. These transmission windows may be exploited with differential absorption lidar technology to remotely detect atmospheric gases. New and exciting applications for mid-IR lasers will open up as mid-IR lasers become more powerful, stable, tunable, and ultrafast. This thesis details three approaches to advancing mid-IR lasers and their uses. Firstly, a feasibility study is presented that assesses the detectability of diesel exhaust emissions in the atmosphere using differential absorption lidar from an airborne platform. This technology could be developed to identify and monitor major sources of air pollution at any location accessible by an aircraft. The study shows that carbon monoxide is a suitable target gas in the 2.3 μm wavelength band, while nitrogen dioxide and formaldehyde are suitable targets in the 3.5 μm band. Secondly, a numerical model is presented that simulates the physical processes in 3.5 μm dual-wavelength pumped fibre lasers. The model, validated against three experiments reported in literature, provides time domain analysis of ionic energy state populations, predicts laser performance, and has become a valuable tool for the optimisation of fibre laser design. The model was adapted to study Q-switching behaviour of these lasers with high temporal resolution. Finally, this thesis presents a detailed characterisation of graphene under high intensity radiation to understand its suitability for passively mode-locking mid-IR lasers. Intensity dependent transmission measurements were performed on trilayer graphene in the 1.55 μm– 3.50 μm spectral region using a 100 fs laser source and the z-scan technique. The measured saturation intensities were combined with others reported in literature to find that saturation intensity depends on the third power of photon energy in the femtosecond regime while longer pulses show a square root dependence. Furthermore, multilayer graphene is shown to exhibit two-photon absorption as well as saturable absorption when subjected to high intensity radiation. Two-photon absorption limits the effective modulation depth and can be detrimental to mode-locking mid-IR lasers. This explains why lasers beyond the 3 μm wavelength band have not been mode-locked using multilayer graphene.
Advisor: Ottaway, David
Henderson-Sapir, Ori
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2020
Keywords: Laser
differential absorption lidar
diesel exhaust gas detection
dual-wavelength pumping
modelling fibre lasers
saturable absorber
saturable absorption
two-photon absorption
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at:
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