SURFACE LASER CLEANING

Weed and Biofilm Treatment with Laser Technology

The rapid development of AI-based image recognition is opening new possibilities for highly selective laser treatment. Two particularly interesting fields are:

• Agricultural weed control
• Biofilm treatment on monuments, stone and other sensitive surfaces

Although these applications are very different, they share an important principle: recognize the biological target, locate it precisely and deliver only the laser energy required to create the desired biological effect.

Laser Weed Control

Laser weed control is currently the best-known application.

The effectiveness of the process depends on several factors, including the type and development stage of the weed, laser wavelength, required dwell time, spot size, energy density and the exact location where the laser energy is applied.

The basic principle is thermal. Laser energy is absorbed by the plant tissue and converted into heat. Sufficient localized heating can damage the cells and disrupt the plant's ability to continue growing.

This makes optical absorption an important factor when selecting the laser wavelength.

Plants provide two particularly interesting absorption targets:

Plant pigments
Visible wavelengths, including blue and green light, interact strongly with plant pigments and can therefore be considered for selective energy deposition in green plant tissue.

Water contained in the plant tissue
Water has strong absorption bands in the infrared. Wavelengths in the approximately 2–3 µm region can therefore provide strong surface absorption with relatively limited penetration depth.

CO₂ lasers also operate at wavelengths that are strongly absorbed by water-containing biological tissue. However, for an industrial machine, the laser source itself is only part of the equation. Size, efficiency, beam delivery, scanner compatibility, maintenance and integration all influence the final choice of technology.

AI Recognition Changes the Process

The most important development may not be the laser itself, but the combination of the laser with AI-based machine vision.

Instead of treating the complete surface, a vision system can identify individual plants and potentially classify different weed species.

The next challenge is even more interesting: determining where the laser should fire.

For effective weed treatment, the system should identify the critical growing region of the plant, including the meristem or other vulnerable tissue, and calculate the coordinates required to direct the laser scanner toward this target.

The complete process becomes:

Detect → Identify → Localize → Select treatment parameters → Target → Irradiate → Verify

Different weeds could eventually receive different laser recipes. The system could automatically adjust wavelength, power, spot size, dwell time, scanning strategy or number of exposures according to the identified plant and its development stage.

This transforms laser weeding from simple thermal treatment into a selective optical treatment process controlled by AI.

Laser Treatment of Biofilm

The same philosophy can potentially be applied to bacterial, fungal, algal and other biological films growing on monuments and stone surfaces.

However, there is one major difference.

With weed control, damage to the biological target is intentional. With monument conservation, we want to affect the biological contamination without damaging or unnecessarily altering the underlying historical material.

The objective is therefore not necessarily laser cleaning.

Instead, the objective can be controlled biological treatment.

For example, when a biofilm is present on marble, the process could be designed to selectively heat the biological layer while keeping the laser fluence below the threshold at which the marble itself is modified, discoloured or ablated.

A thermal imaging system could provide an additional feedback loop. Rather than applying a fixed laser dose, the system could monitor the surface temperature during treatment and continuously regulate the laser output and scanning speed.

The principle becomes:

AI vision identifies the biofilm → scanner positions the beam → laser delivers controlled energy → infrared camera measures temperature → control software adjusts the treatment in real time.

A target temperature, for example around 60°C for a specific biological organism, should not be considered universal. The required temperature and exposure time depend on the organism, substrate, moisture conditions and treatment objective and therefore need to be experimentally validated.

Protecting the Original Surface

For restoration applications, the operating window is critical.

There are effectively two thresholds:

Biological damage threshold
The minimum laser dose required to sufficiently deactivate or destroy the targeted biological material.

Substrate damage threshold
The laser dose at which the marble, stone, pigment, patina or other original material begins to undergo an unacceptable physical, chemical or visual change.

A successful treatment process must operate safely between these two thresholds.

This is where wavelength selection, pulse duration, fluence, spot size, scanning speed, temperature monitoring and AI recognition all become important.

From Laser Cleaning to Intelligent Laser Treatment

This represents an interesting evolution of laser technology.

The future system does not simply switch a laser ON and move it across a surface. It first understands what is present and where it is located.

AI vision provides the eyes.
The scanner provides the positioning.
The laser provides the energy.
Thermal imaging provides feedback.
Software controls the complete treatment process.

The result could be a new generation of intelligent laser systems capable of treating biological targets with high spatial selectivity while minimizing the impact on the surrounding material.

At P-Laser, we see significant potential in combining laser technology, machine vision, AI recognition and closed-loop process control to develop dedicated treatment processes for agriculture, conservation and other biological surface applications.

.