Evaluation of a novel laser-system operating at 1940 nm for weed control and determining the influence of biological and operational factors

BACKGROUND: This study evaluates a novel laser-based pulse-system for weed control characterized by two primary innovations: a thulium-doped yttrium aluminum perovskite (Tm:YAP) laser operating at a 1940 nm wavelength aligned with the peak water absorption band to maximize photothermal efficiency and the implementation of pulsed laser operation. The system's efficacy was examined across varying weed species (dicots and monocots), growth stages (2–3, 4–5, and 7–8 leaf stages), and target locations (growth meristem and stem), alongside technical parameters including beam diameter (0.1–4.7 mm) and exposure time (0.25–2.5 s) and compared against a continuous-wave (CW) system. RESULTS: Targeting the plant stem was significantly more effective than the meristem with mean biomass (proportion of control) values of approximately 0.0 and 0.25, respectively, following a treatment of 1.5 s with beam diameter of 1.6 mm. Across the majority of tested parameters, the pulsed configuration demonstrated no significant advantage over the CW system. Early treatment of the dicot Solanum nigrum at the 2–3 leaf stage resulted with 6% survival using energy density of only 1.5 J mm⁻² (0.25 s exposure). However, sensitivity varied greatly by species; Abutilon theophrasti was significantly more susceptible than grass species (e.g., Sorghum halepense), and had a higher effective dose for a 50% response (ED₅₀). CONCLUSION: While pulsed and CW modes yielded similar results, indicating that total energy delivery governs the thermal response, the 1940 nm wavelength demonstrated superior energy efficiency compared to previously reported systems. These findings provide a solid foundation for developing energy-efficient, site-specific robotic weeding technologies.