Er:YAG Lasers for Methane and Wind Sensing

The impact of climate change has become increasingly important in recent years. Many countries are transitioning to renewable energy sources to curb global warming. However, renewable energy is still unreliable on a large-scale, which could lead to grid-instability. We will consider two methods of facilitating this transition: first, the use of “cleaner” fossil fuel sources to supplement the power grid and second, the development of methods to make green energy sources more reliable. Natural gas is a popular fossil fuel for this transitory phase; it has a low carbon footprint compared to oil if it is fully combusted during use. However, a primary constituent of natural gas is methane, which has a global warming potential 25 times greater than carbon dioxide. If methane emissions during production, storage, and transport exceeds 3%, then the benefit of gas as a transitory fossil fuel is lost. We propose a laser resonator for use in an Integrated Path Differential Absorption LIDAR (IPDA) LIDAR system capable of detecting fugitive emissions over natural gas pipelines from a light aircraft. The goal for this system is a dual-pulsed Q-switched Erbium-doped Yttrium Aluminium Garnet (Er:YAG) laser source that produces two injection-seeded laser pulses, one of which is tuned “off” the methane absorption line, and one which is tuned “on” the line. The laser is frequency stabilised using the Pound-Drever-Hall (PDH) frequency stabilisation method to “lock” two low-power diode lasers to the Er:YAG resonator to produce reliably injectionseeded pulses. The laser designed and built in this thesis produces two free-running pulses each with energies of 0.9mJ within 3 µs of each other at a repetition rate of 3 kHz. This system uses a novel Q-switching method, wherein the laser lases continuous wave (CW) prior to the engagement of the switch. This laser design was adapted to a wind LIDAR system to increase the reliability of wind energy generation. Wind energy has the potential to become a major energy source in Australia, and new wind farms are being built across the country. However, wind energy generation is subject to sudden drops in wind speed, which have the potential to cause blackouts. We propose a ground-based, Q-switched Doppler LIDAR capable of measuring wind speed and direction. The outgoing pulses are backscattered off the incoming wind and compared to a reference signal. The Doppler shift of the return signal gives an indication of wind speed and direction. This laser will provide an early-warning system for wind farm, so that they can predict their output to the national grid and prevent black and brownouts. The laser is an Er:YAG based laser sensor, frequency stabilised using a novel application of the PDH technique. The laser produces injection-seeded pulses at 1645nm with pulse energies of > 1mW at a 4 kHz repetition rate.

Author dc:creator

• Watzdorf, Sarah Martha

Advisors dc:contributor.advisor

• Ottaway, David
• Veitch, Peter

• Er:YAG
• methane sensing
• DIAL
• lidar
• IR
• lasers
• methane
• wind

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/2440/142632

OAI identifier oai:identifier

oai:digital.library.adelaide.edu.au:2440/142632