Guide For Choosing The Right Co2 Laser Lens

The focusing lens is an indispensable part of the laser machine, when you choose a focusing lens raw materials, diameter, focal length, and coating are the core factors 

In order to achieve high-quality engraving and precise cutting with your laser cutter, the laser beam is directed through a series of mirrors and through the focus lens.

The focus lens narrows or “focuses” the laser beam to a very small, precise spot that will enable graphic images to be engraved or cut with extremely accurate results.

Raw materials

According to the material Co2 laser focusing lens can be divided into zinc selenide, gallium arsenide, and germanium lens. Zinc Selenide (ZnSe) has the lowest absorption of the common CO2 transmitting materials. therefore, the material of choice for high-power applications. It is also the only material that transmits visible light, a requirement for the use of a HeNe alignment laser.

Gallium Arsenide (GaAs) is the material of choice in dirty or high- splatter environments. It has a relatively high hardness which helps repel debris particles. It also has a high thermal conductivity which helps transmit heat away from embedded particles.

Germanium (Ge) can only be used in low power applications because it is subject to thermal runaway. As temperature increases, its absorption increases, which leads to thermal failure in high power applications. Ge used to be the lowest cost CO2 lens material because its widespread use in the semiconductor industry created a large supply. 

Zinc selenide lenses can be divided into PVD and CVD according to different growth methods of raw materials. Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD) are two processes used to produce a very thin layer of material, known as a thin film, onto a substrate.If you want to know more details of znse materials,kindly click here.

We can choose the appropriate focusing lens according to the different applications:

Lens Diameter

Higher power lasers require larger diameter lenses to prevent thermal overload. At any given focal length, a larger diameter lens will yield a smaller focused spot if the incoming beam is expanded to fill the larger lens. In a word, the higher the power, the larger the diameter of the lens.

Parameters:

Focal length

Focal length affects both spot size and depth of focus. In general, a shorter focal length will produce a smaller focused spot and a shorter depth of focus. Usually, the specified focal length is a compromise between desired spot size, penetration depth, and workpiece clearance.

CO2 laser systems are typically equipped with one particular focal lens – one that is generally good for most engraving and cutting applications. One and a half-inch, two-inch, or four-inch lenses are all commonly used with laser systems. Which lenses are right for which applications?

1.5-inch lens

·    Optional lens for high-resolution engraving.

·    Recommended for raster engraving above 600 DPI resolutions.

·    Recommended for small font or fine detail engraving.

·    Produces a spot size of 0.003 to 0.0065 inches in diameter.

·    Good cutting lens for thin (less than 1/16 inch) material.

2-inch lens

·    Standard lens on most laser systems.

·    Multipurpose for both engraving and cutting applications.

·    Recommended for raster engraving from 300 DPI to 600 DPI resolutions.

·    Produces a spot size of 0.004 to 0.007 inches in diameter.

2.5-inch lens

· Most commonly used for laser systems.

· Multipurpose for both, engraving and cutting applications.

· Graphics with medium detail and resolution.

· About 63.5mm of thickness, for a majority of works.

4-inch lens

·    Produces focused beam over a longer vertical distance

·    Specialty lens typically used for engraving within the recessed area (bowl or plate).

·    Used for cutting thick materials.

As an important conclusion, you can see that the more delicate and detailed the graphics are, Shorter focal lens should be. For cutting thick materials, lenses of maximum size are recommended.

Important considerations

The lens you need is directly related to your application. These are some important considerations that will define the lens you must use:

• The output of your laser device (laser beam wattage).
• Material and purpose (cutting or engraving).
• The detail level of the graphics.
• The thickness of the material.

                         ———Relevant data provided by bescutter，Epiloglaser

Lens Coating

Chemically vapor deposited ZINC SELENIDE (CVD ZnSe) is the material of choice for use as optical components in high powered CO2 lasers due to its low bulk absorption at 10.6 microns. Its index of refraction homogeneity and uniformity offers excellent optical performance for use as protective windows or optical elements in high resolution forward looking infrared (FLIR) thermal imaging equipment. This material has also been used as small windows and lenses in medical and industrial applications, such as thermometry and spectroscopy. 

Advanced Materials’ CVD ZINC SELENIDE is chemically inert, non-hygroscopic, highly pure, theoretically dense, and easily machined. It has extremely low bulk losses due to absorption and scatter, has a high resistance to thermal shock, and is stable in virtually all environments.

Manufactures from Zinc Selenide (CVD-ZnSe) the following optics: blanks, protective windows, windows, domes, wedges, right angle prisms, ATR prisms, cylindrical and spherical lenses, CO2 optics (mirrors, Brewster windows, lenses, meniscuses), spherical microlenses (hemisphere and balls) and ZnSe witness samples. These products are used for infrared IR applications including CO2 laser optics.

offers Evaporation Grade Zinc Selenide (CVD-ZnSe), size less than or equal to 6 mm, purity: 99.5%.

Spectrum transmission charts of CVD-ZnSe laser grade windows below:

A good antireflection coating will increase the transmittance of the focusing lens, greatly improve the cutting performance and extend the spanlife.

Lens Shapes

Meniscus lenses and Plano-convex is the regualar shapes of focusing lens .Meniscus lens for CO2 laser and infrared optical system Concave-convex lens can reduce spherical aberration and produce the smallest collimated incident light focus.

If you want to know more details,try to read this article ZnSe lenses for CO2 laser: plano-convex vs convexo-concave

According to our long-term use experience, the Meniscus lenses performs better than the plano-convex focusing lens, which is also one of the most popular reasons in the market.

When removing the laser lens, firstly stop the machine for a period of time and wait for the laser lens to cool down before removing it. When removing the lens, do not use hard pliers, clips or other tools to scratch the lens. Gently remove with medical finger cots. After disassembly, place it on a cotton work surface, wait for the lens to cool down, and then start blowing to wipe the lens. Because the fast alcohol volatilization speed will make the lens cool down quickly, this will affect the life of the laser lens if it is not good for the overheated lens.

Maintaining Lens 

CO2 laser optics take a severe beating in normal use, whether the applicationiscutting,markingor welding.A zinc selenide lens is a means of focusing a CO2 laser beam on a substrate. These lenses typically form the barrier between the sealed optical chain leading back to the laser resonator and the spatter that arises from the laser’s work.

How to clean the lens of laser engraving machine?

First, use an air ball to blow off the floats on the surface of the lens, especially the lens with tiny particles and floccules on the surface. This step is necessary. But never use air compressor, because the air will contain oil and water droplets, which will deepen the pollution of the lens.

In the second step, use acetone (or alcohol, preferably acetone) to clean the lens lightly. This grade of acetone is almost anhydrous, which reduces the possibility of lens contamination.

The cotton ball must be dipped in acetone and the lens must be cleaned under light and moved in a circular motion. Once the cotton swab is dirty, it must be replaced. The cleaning should be done at one time to avoid the formation of ridges.

If the lens has two coated surfaces, such as a lens, each surface needs to be cleaned in this way. The first side needs to be placed on a layer of clean lens paper for protection.

If acetone cannot remove all the dirt, then use acid vinegar to clean it. Acid vinegar cleaning uses the dissolution of dirt to remove dirt, but it will not cause damage to the optical lens. This acid vinegar can be experimental grade (diluted to 50% strength), or white vinegar with 6% acetic acid for household use. The cleaning procedure is the same as that of acetone, and then acetone is used to remove the acid vinegar and dry the lens. At this time, the cotton ball should be changed frequently to completely absorb the acid and hydrate.

What are the advantages of correct cleaning of laser engraving machine lenses?

When the lens is properly cleaned and operated, its service life and performance will undoubtedly improve significantly. Taking some preventive and maintenance measures in this article will ensure that the laser engraving machine works longer and performs better.

Precautions for the use of laser engraving machine lenses?

1. Never install the lens with your bare fingers, wear finger cots or rubber gloves.

2. Do not use sharp instruments to avoid scratches on the lens surface.

3. Do not touch the film when taking the lens, hold the edge of the lens.

4. The lens should be placed in a dry and tidy place for testing and cleaning. There should be several layers of cleaning paper towels or wipes, and several sheets of cleaning tissues.

5. The user should avoid talking above the lens and keep food, beverages and other potential pollutants away from the work environment.

Here is some videos to help you learning :co2 lens cleaning,ophir optics.

All of the above opinions are not for commercial purposes. Any errors, we’d happy to revise it.