Very often the word LASER - (Light Amplification by Stimulated Emission of Radiation) is used undifferentiated. In our opinion it is important to know that there are different kinds of laser, that differ fundamentally, especially in terms of appropriability for the intended job. Laser doesn´t equal Laser and the consideration must be focused on the specific application.
We are here concentrating on marking / engraving of mineral and organic glasses, lenses and molds (moulds) in optics / ophthalmics. The glasses, lenses and molds (moulds) are lucent for certain wavelengths, meaning they do not (or hardly) absorb radiation. The chosen wavelength of the laser should allow the energy to be effective on the surface instead off passing it. Additionally the laser must be capable of engraving mineral and organic substrates as well as a variety of coatings likewise in high quality, so the laser source must fulfill a diversity of requirements.
There are different lasers that can generate a more or less usable wavelength, differentiated by solid state laser like Nd-YAG lasers and gas lasers like CO2 lasers and Excimer lasers. For marking / engraving in optics / ophthalmics the Excimer laser with a wavelength of 193nm is the ideal laser source, not only because of the engraving quality but also for its cost effectiveness, a factor that must not be disregarded.

The lasers in detail:

CO2 Laser:
CO2 lasers, also known as infrared lasers, work with wavelengths of about 10,000nm. They act by focused thermal energy meaning they melt and burn (destroy) the surface, what very much restrains their applicability in optics / ophthalmics. Minerals (e.g. silicate glass) suffer microcracks through this thermal impact that may lead to crack or burst under stress. Application for organic material is limited to a few types. The thermal stress leads to an enduring physical surface alteration. Together with the poor reproduceability and the strong roughness being created during the engraving this leads to unsatisfying results. Above all the marking / engraving is not stable (thermically reversible). Because of this, the marking / engraving in optics / ophthalmics with a CO2 laser is to be regarded extremely critical, especially when the substrate needs to be coated later on. Regular tinting is, due to the altered surface, impossible. Engraving on or through AR-Coating or in Transition is not satisfying. Microencoding (e.g. for tracing or branding) can not be achieved with a justifiable effort using a CO2 laser.
Considering all this, the CO2 laser is not qualified for the implementation in optics / ophthalmics, although it may appear low priced in purchase and operation at first view.

YAG Laser:
YAG (Yttrium aluminium garnet) lasers belong to the solid state lasers, also called DPSS (Diode Pumped Solid State) lasers with a basic wavelength of 1,064nm. Almost any material that is used in optics / ophthalmics is lucent for this wavelength and might only be engraved with complex pretreatment. The thermal part of this wavelength is very high and would also cause roughness and microcracks on organic and mineral substrates. Through frequency tuning, meaning the merging of harmonic oscillations, a YAG laser can produce shorter wavelengths like 532nm, 355nm, 266nm or 212nm. This is done by using specific, very expensive crystals, that only have a very limited lifetime and need to be adjusted extremely accurate.
With decreasing the wavelength the price of the laser source and its maintenance intensity rise disproportionately, the quality and stability of the beam, however, decrease disproportionately. YAG lasers cannot perform microengraving and microencoding because the beam is too big and too unstable.

Excimer Laser:
Excimer Lasers, also known as UV Lasers, belong to the family of pulsed gas lasers. They are available in various wavelengths, which is determined by the gas used. The 193nm version is the ideal laser source for marking and engraving (including microengraving and microencoding) in optics and ophthalmics and does neither cause any thermal stress nor roughness or microcracks. The use for microencoding with character heights down to 30µ is, adequate technological adaption implied, achievable very cost-effective. The engraving is applied through the phenomenon of cold ablation. The material is removed in molecular mode and is not burned, as it is done with CO2 or YAG lasers. Excimer lasers with a wavelength of 193nm can gently engrave / mark almost any material.
The old prejudices against Excimer lasers because of the gas needed for operation are completely baseless when talking about modern systems like the KEPETS ULM family, far from it, these machines exceed by far even the highest requirements and security regulations like the ones in the US. Even if machine security is concerned, the KEPETS ULM-family is the predominant leader. KEPETS uses only laser sources that are manufactured to our guidelines. These laser sources can only be found in the KEPETS ULM-family. They are characterised by excellent performance, highest reliability (we guarantee 850,000,000 pulses) and an extremely low amount of maintenance. That is why laser systems from the KEPETS ULM-family achieve the lowest unit costs for engraving, including all costs like investment, maintenance and operational costs. We offer special Guarantee Agreements wherein we commit to bearing all arising costs during the contract duration, ensuring the forecasted unit costs.