Pulse laser for rust removal of steel, choose single-mode or multi-mode?

You may start with a small-scale test before making your selection.

Test Parameters:
Beam type: Multimode (shaped to top-hat), Multimode (unshaped), Single-mode
Scanning speed (v): 0.1, 0.2, 0.5 m/s
Laser power ratio (if adjustable): 100% (300 W), 70% (210 W), 40% (120 W)
Number of scanning passes: 1, 2, 3

Evaluation Metrics:
Rust removal rate (measured as residual rust percentage by weight)
Substrate surface damage (examined via microscopic inspection, color change, and hardness testing)
Surface roughness
Post-treatment appearance uniformity
Spatter, fumes, and post-processing requirements
Cost/Time Statistics:
Processing time and energy consumption per square meter

Prioritize efficiency, thoroughly remove rust, and have unlimited requirements for the surface of the substrate → Choose single-mode.
Priority should be given to substrate protection and it must be non-destructive → Choose multimode.

For a 30mm width, multimode is the better choice. It provides more even energy distribution and higher efficiency. Single-mode has a smaller spot, so it takes multiple passes to cover 30mm — which can cause uneven results, striping, or localized burning.