Pulsed Tm-fiber (Thulium) lasers for weed killing

Traditional weed control using herbicides is becoming increasingly problematic. Pestilent weeds reduce productivity in agriculture by damaging crops and reducing yield in a multi-billion-dollar farming industry. Current methods of weed control resort to the use of herbicides and toxic substances that persist in soil and are detrimental to humans and wildlife.

The use of CO2 lasers to prevent or delay weed growth has been demonstrated as an eco-friendly and economically viable alternative. The concept has already been proven with CO2 lasers mounted on land-based vehicles for short-row crops like vegetables. In 2022 OzGrav awarded a $25,000 Seed grant to a team led by OzGrav student Zachary Holmes, to investigate extending laser weed-killing capabilities to taller field crops such as grains and grasses, orchards, or vineyards, which has not yet been demonstrated. The proposed system is readily adaptable to replace other pesticides and has greater potential for mounting on a drone to improve speed and non-invasiveness.

The cost-effectiveness of laser-based weed killing depends critically on the laser parameters and SWAP (Size, Weight, and Power) performance. Laser weed killing exploits the very high water content and very low reflectance in the 1.90-1.94 µm band. This project will use a Thulium (Tm) fiber laser to determine the optimum laser parameters (wavelength, beam diameter, average power, pulse width) for weed killing.

The laser weed-killing demonstration is also a pathway towards translating research into single-frequency laser diode-seeded Tm-fiber amplifier sources into a commercialisable laser weed-killing unit for mounting on an autonomous vehicle. The project is in collaboration with the Weed Science Research Group in the School of Agriculture, Food & Wine at the University of Adelaide (UoA).

We will configure, test and optimise the laser system, and then install it at Waite Research Institute. Our team includes ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) experts in fiber laser development:

• Zac Holmes, PhD student in the field of laser source design and stabilisation with first-class honours in mechanical engineering, who has designed and successfully demonstrated a seed source and Tm:fiber amplifier concept for future adaptation;
• Dr Sebastian Ng, co-chair of the OzGrav Quantum Program with extensive experience in fiber laser development, and space applications team leader at QuantX Labs, translating terrestrial laser and quantum technologies for satellite payloads;
• Prof Peter Veitch, Head of School of Physical Sciences and OzGrav Adelaide node leader with a proven track record of coordinating and undertaking research in laser systems for environmental, industrial, and defence applications; and
• Emeritus Prof Jesper Munch, a longstanding member of the Australian optics community with invaluable contributions to the fields of high-power lasers, nonlinear optics, and gravitational wave detection.

The team also includes University of Adelaide School of Agriculture, Food & Wine – experts in weed control research:

• Dr Andrew Hennesey, Image and Data Analyst specialising in the classification of hyperspectral vegetation datasets;
• Dr Jenna Malone, a senior postdoctoral fellow in the Weed Science Research Group researching the understanding and management of herbicide-resistant weeds;
• Dr Darren Plett, the Technology and Development Lead at the Plant Accelerator researching phenotyping technologies to improve agricultural crop productivity; and
• Prof Timothy Cavagnaro, an expert in management of soil ecological processes with a great degree of experience in cross-disciplinary technologies and techniques.

The team proposes to use a Tm-fiber laser source to research the optimum parameters (wavelength, beam diameter, average power, pulse width) for laser weed killing of flat-leaf weeds. Our proposed demonstration with a Tm-fiber laser source is also a pathway toward mounting onto an autonomous vehicle for field testing.

The vehicle is equipped with Artificial Intelligence (AI) weed detection and locating capabilities, including a scanner to direct the pulsed laser beam(s) towards the target weed. A likely field test of the system will be laser weed killing in a vineyard through collaboration with the Australian Wine Research Institute. Further collaboration will be initiated with autonomous vehicle experts in the UoA’s School of Mechanical Engineering and AI experts at the UoA and Australian Institute of Machine Learning (AIML), who are currently developing AI detection systems for other applications. The team will pursue further funding to progress this study beyond the proof-of-concept phase.