Our research

The recently established ZNE-Ag CRC brings together a wide range of experts, ranging from farmers, members of agricultural industry and business people to researchers from universities and government agencies. They all share the aim to promote ways to substantially reduce environmentally damaging emissions of greenhouse gases such as methane (CH4) and nitrous oxide (N2O) from Australian agriculture.

One of the first research projects approved by the CRC is led by Macquarie University, aiming to provide an innovative, field-deployable way to quantitatively measure emissions of CH4 in air from ruminant animals such as beef cattle and dairy cows, in order to evaluate the CRC’s ways to reduce emissions of CH4 from ruminant animals such as beef cattle and dairy cows, using measures such as feed additives.

The ZNE-Ag CRC requires MOPL to develop a sensor that is CH4-specific, affordable, accurate, reliable, rugged and compact – criteria that are not all met at present by commercially available instruments.

The MOPL approach adopts a sensitive, CH4-specific form of Wavelength Modulation Spectroscopy (WMS), based on optoelectronics. Narrowband tunable infrared laser light passes through a cylindrical cell containing CH4-laden ruminant breath. This is drawn up from an identified animal through a 24-faced polygon reflector with a 4.5-m laser-beam path forming a 21-pointed star.

The limit of detection for concentrations of CH4 in air is found to be lower than 1 part in 106. Also used are lab-based WMS experiments that use a pulsed solenoid valve to simulate eructations of CH4 in air; notably, these indicate that we have sufficient detection sensitivity and temporal response to discern individual ruminant eructations.

Towards the end of the first year (2025) of this 3-year ZNE-Ag CRC project, we are preparing to take our WMS system out of the lab and into the field, to monitor real animals. Initial field trials in 2026 of our field-ready, wifi-connected WMS instruments are to be conducted in a respiration-chamber at University of New England (Armidale, NSW) and then elsewhere on a dairy farm, in collaboration with Agriculture Victoria.

Beyond that, there is the challenging prospect of open-paddock measurements.

Read our pre-CRC publication: Laser-based sensing of trace-level methane in agricultural and environmental air, a four-page paper presented at 17th International Conference on Sensing Technologies (9–11 December 2024).

Cavity ringdown (CRD) spectroscopy is a highly sensitive method used to detect trace gases. It works by passing laser light through a highly reflective optical cavity. As the light reflects thousands of times between mirrors, even very weak molecular absorption can be measured with exceptional precision. The rate at which the light fades, or ‘rings down' reveals the gas absorption properties.

Our researchers have advanced CRD spectroscopy using compact, optical fibre-based designs that feature rapidly swept optical cavities, miniature tunable diode lasers and telecommunications-grade components. These innovations have madee it possible to measure gases accurately and in real time with robust, portable systems.

A major development is the use of optical heterodyne detection, which combines the transmitter and receiver in a single module linked by optical fibres to one or more CRD cavities. This setup has enabled environmental gas sensing over long distances of up to tens of kilometres.

A recent major project, in partnership with the CSIRO Livestock Methane Research Cluster, used CRD spectroscopy to monitor greenhouse and agricultural emissions. The technology supports remote detection of gases such as methane from livestock and ammonia from soils and waste, helping create more sustainable agricultural and environmental practices.

Read our publication: Remote open-path cavity-ringdown spectroscopic sensing of trace gases in air, based on distributed passive sensors linked by km-long optical fibers.

For many years, the MOPL research group has conducted advanced laser-based experiments to explore how molecules interact and transfer energy after spectroscopic excitation. Using high-performance pulsed lasers, our researchers prepare small molecules in specific quantum states, allow them to undergo controlled gas-phase collisions, and then analyse their final states with laser-induced fluorescence (LIF).

For short time intervals between the pump and probe laser pulses, this method allows precise identification of features in complex molecular spectra. As the time delay increases, the technique reveals how molecules exchange energy during collisions, providing insights into molecular dynamics and reaction pathways. By continuously scanning the delay, our researchers can build detailed kinetic models that describe these processes.

An early instance of MOPL’s pioneering work in this area has included infrared–ultraviolet (IR–UV) double-resonance spectroscopy of formaldehyde-d₂ (D₂CO). Using a tunable CO₂ laser for excitation and a pulsed dye laser for probing, the group has identified new features in the molecule’s spectra and characterised how it transfers rotational and vibrational energy.

Such studies have uncovered highly efficient rovibrational coupling caused by Coriolis interactions, improving our understanding of molecular collisions and photochemical behaviour.

Other MOPL work in this area have entailed the use of molecular beams and coherent-Raman excitation.

Read our publication: Collision-induced rovibrational energy transfer in small polyatomic molecules: the role of intramolecular perturbations.

Optical parametric oscillators (OPOs) convert laser light of one colour, called the pump, into two new beams of light known as the signal and idler. This process happens inside a special nonlinear crystal, such as BBO, PPKTP or PPLN, placed within an optical cavity. When the light waves inside the crystal are aligned correctly, energy is transferred efficiently between them, allowing precise control of the new wavelengths produced.

MOPL researchers have developed OPO technology to improve wavelength control, stability and efficiency. Traditional tuning methods use optical components that can limit performance or damage the crystal. To address this, MOPL created modular, injection-seeded OPO systems, where a finely tuned laser controls the output wavelength without reducing efficiency.

These systems can generate multiple wavelengths at once, enabling advanced spectroscopic sensing applications such as measuring gas temperatures. In collaboration with the Australian National University (ANU), MOPL has also developed tunable, narrowband deep-ultraviolet OPO sources for high-resolution spectroscopy. This work has revealed fine details in the spectra of atomic xenon and molecular oxygen, showcasing the potential of MOPL’s OPO technology for cutting-edge optical and atomic research.

Read our publication: Two-photon excitation of two Rydberg levels of O2 above 95 130 cm–1: rotational state dependence of predissociation linewidths

The MOPL research group uses fibre-optical technology to transmit stable light and frequency signals over long distances. This supports high-precision measurement and sensing in science and industry.

Through an ARC-funded Linkage Project, MOPL has developed new methods for transferring radio-frequency and optical frequency signals through standard optical fibres with very high accuracy. These advances have addressed major challenges in radio astronomy and precision measurement.

A key achievement is a phase-conjugate photonic system for transferring radio-frequency signals over optical fibre. This technique provides a reliable and cost-effective way to synchronise radio telescope arrays used in Very Long Baseline Interferometry (VLBI), reducing the need for multiple expensive hydrogen-maser frequency standards.

In partnership with CSIRO’s Australia Telescope National Facility, MOPL researchers have successfully demonstrated two-way frequency transfer over about 310 kilometres between the Narrabri and Mopra observatories in New South Wales. The system maintained excellent signal stability even while sharing live telecommunications traffic, confirming its practicality for large-scale use.

This breakthrough, featured in Optics and Photonics News, highlighted MOPL’s leadership in advancing photonic and fibre-based technologies for precision science and national research infrastructure.

Read our publication: Long-distance telecom-fiber transfer of a radio-frequency reference for radio astronomy.