Cold Laser Marking
Key Takeaways
- Ultra-short pulses remove material faster than heat spreads, which is what eliminates burn zones.
- Femtosecond and picosecond lasers are the tools; the mechanism is cold ablation rather than melting.
- Micron-scale resolution with no charring, discolouration or soot.
- Essential where heat would be unacceptable — medical implants, PCBs, thin films and precision plastics.
Cold Laser Marking
Cold laser marking uses short-wavelength ultraviolet light — typically 355 nm — to mark a polymer by breaking chemical bonds directly, rather than by heating the material until it degrades. The process is often called athermal or photochemical marking. It is not literally cold, but the heat-affected zone is small enough that thermally sensitive parts can be marked without melting, charring or distortion.
The Physical Basis
Photon energy rises as wavelength falls. A 1064 nm infrared photon carries roughly 1.2 eV — far too little to break a covalent bond, so its energy simply becomes heat. A 355 nm ultraviolet photon carries about 3.5 eV, which is comparable to the dissociation energy of a carbon–carbon bond in a polymer backbone.
At that energy the absorbed photon can sever the polymer chain outright. Material is removed or altered by photolytic bond scission, with only a modest thermal component. Two consequences follow, and they are the whole reason the technique exists:
- A very small heat-affected zone, so no melt rim, no charred halo, no crazing and no dimensional distortion.
- Strong absorption by most polymers. Nearly all organic polymers absorb well in the UV, even those that are effectively transparent at 1064 nm. That means high-contrast marks on natural, clear and light-coloured resins without compounding in a laser additive.
Cold Marking Versus Infrared Marking
| UV / cold marking (355 nm) | Fiber / infrared (1064 nm) | |
|---|---|---|
| Mechanism | Photochemical bond scission | Thermal degradation |
| Heat-affected zone | Minimal | Moderate to significant |
| Additive needed on natural resins | Often not | Usually yes |
| Feature resolution | Finer — shorter wavelength focuses smaller | Coarser |
| Marking speed | Lower | Higher |
| Capital and running cost | High | Moderate |
Where It Is Specified
- Medical devices — UDI marks that must survive autoclave, gamma or EtO sterilisation without compromising the substrate, and without an additive that would complicate biocompatibility approval.
- Thin-walled and film components, where infrared marking would deform or perforate the part.
- Transparent and light-coloured polymers, where infrared marking gives little or no contrast — see laser marking clear and transparent plastics.
- Fine codes and micro-marking, where a tight heat-affected zone preserves the cell definition that machine vision depends on.
- Additive-free applications, where regulatory, food-contact or optical requirements rule out compounding in an absorber.
The source is normally a frequency-tripled vanadate (Nd:YVO4) laser. Against its advantages, weigh higher capital cost, lower throughput and the finite service life of frequency-conversion optics. For pigmented and filled engineering resins that already mark well thermally, a fiber laser remains the more economical answer — the comparison is developed in UV laser marking vs fiber laser marking.
Related Terms and Reading
- UV laser marking vs fiber laser marking
- Vanadate laser
- Pharmaceutical and medical manufacturing
- Plastics laser marking solutions
Applying this in production
The Sabreen Group provides independent engineering support for UV cold marking qualification for medical, optical and heat-sensitive components. If you are specifying a process, qualifying a material or troubleshooting a production problem, our engineering services team can help. Contact us to discuss your application.
Frequently Asked Questions
What makes cold laser marking “cold”?
Unlike thermal laser systems, cold laser marking uses ultra-short pulses in the femtosecond and picosecond range that remove material faster than heat can spread through it. Because there is no time for thermal diffusion, burn zones are eliminated.
Is cold laser marking better than traditional laser marking?
It depends on the application. Cold laser marking is superior when working with delicate, heat-sensitive or micro-scale parts where thermal damage would be unacceptable. For general production marking on robust substrates, conventional thermal marking is faster and far more economical.
What lasers are used for cold marking?
Typically femtosecond and picosecond lasers. These ultrafast sources combine extremely short pulses with high peak power, which is the combination that enables precision ablation without heat accumulation.
Can cold laser marking be used on plastics?
Yes, and it is particularly suited to plastics prone to melting or discolouration under heat. It produces sharp, high-contrast marking on materials such as polyimide, polycarbonate and ABS that are sensitive to thermal input.
Is cold laser marking permanent?
Yes. The marks created are permanent and abrasion resistant, and are unaffected by moisture, chemicals or UV exposure, because the change is made in the material itself rather than applied to its surface.
