How to determine the focal length  
There are many different types co2 laser machine can be available from LaserMen. The co2 laser machines are widely used in different industries. It is favored by many customers for its reasonable price, easy operation, and engraving cutting function.      
Many new customers do not understand how the co2 laser machine works or they want to know the co2 laser machine working principle. For the co2 laser machine, the co2 glass laser tube is the laser source. The picture below showing how the laser beam ultimately works on the processed material.

Different types laser machines have their corresponding Mirror Alignment Guide. If you have bought our co2 laser machines, we provide the video and guidance. It the basic operation.
Which is the actual focal length ? What are the common focal lengths?
First, the picture showing how to measure the actual focal length.  

Different lenses have different local lengths, and depths of cutting. If a lenses' focal length is long, the focused point will be further away, so the cutting thickness will be greater.
Lenses have two parameters, diameter and focal length. The diameters we use are 20mm (for the Ordinary co2 laser machines) and 25mm (for the hybrid co2 laser machine).    
The focal lengths we usually use are 50.8mm, 63.5mm and 101.2mm.  
Now, we believe you have known well about our co2 laser machine, and we also have fiber laser cutting machine, laser marking machines, laser welding machines and other laser products. If you are interested in, please feel free to contact us.