Investigations on laser marking of plants and fruits

• We marked plants and fruits with encoded patterns using direct laser marking.
• We examined the influence of laser and plant parameters on the marking success.
• The minimal size of a pattern depended on the laser energy applied.
• The surface damage and infestation risk was low with adjusted laser parameters.
• Image processing was used for the re-identification of laser marked 2D patterns.

High traceability has become more and more important for worldwide logistics of horticultural products as the flow of goods rises steadily. Barcode stickers are widely used on product packaging or on the product itself. Direct product marking could be an option, to improve marking safety and to increase protection against forgery. Therefore, this paper investigates the benefits of direct laser marking and identifies the factors influencing the achievement of useable markings. The studies were conducted by testing various laser wavelengths (193–10,600 nm) to mark a simple 9 mm2 sized 2-D barcode on the surface of apple fruits and rhododendron cuttings. Depending on the laser wavelength, the process steps of laser marking, the risk of fungal infection and the marking pattern alteration due to product storage were investigated. The marking process (laser energy, laser wavelength, pattern size, pattern design, etc.) considerably influences the representation accuracy of the patterns used, which is important for later image processing. By using suitable laser marking energies per pattern, it is possible to minimise the damaging of product surfaces, and correspondingly the risk of fungal infection. This leads to an applicable codification of individual horticultural products.