The relationship between the laser beam, beam expander, F-θ lens and galvo scanner?

What are the important parts of laser equipment parts?

Laser beam

The laser beam size generally refers to collimated light, not parallel light. We often say laser output beam size is several millimeters, for example coherent CO2 laser is generally 1.8±0.2mm, pulsed fiber laser is 7mm.However, continuous fiber laser is a point light source, like incandescent light bulbs, is hard to tell output beam diameter. Only lasers that emit collimated light could be called “laser beam size”. Or we could look at the laser parameter table, there is a parameter called “output beam diameter (mm)”, or 1/e².

Beam expander

Beam expanders are optical devices used to increase the laser beam diameter while maintaining its collimation (keeping the beam rays parallel). The divergence angle is reduced by 1/X after X beam expander. Smaller divergence angle leads to smaller focal spot by using same focusing lens. Below are advantages of beam expander:

  1. Increased beam diameter is useful in applications where a larger beam size is required, such as in laser cutting, drilling, or precise material processing. Larger beam diameter leads to smaller focused spot.
  2. By spreading the laser energy over a larger area, beam expanders can help reduce the power density of the beam. This can prevent damage to optical components and samples in high-power laser applications.
  3. Amplified beam in laser show system.

In industrial laser machines, the main functions of the beam expander are: reduce divergence angle; Expanding the beam size to achieve smaller focal spot; reduce power density to ensure longer lifetime of galvo mirrors.

Galvanometer scanner

The aperture of galvo scanner (10mm 12mm 20mm, etc.) is how much laser beam that the area of galvo mirror could reflect. The smaller the galvo mirror, the smaller laser beam can be reflected, vice versa. But larger aperture, the greater the weight of galvo (larger motors and mirrors), the scanning speed will be slower than smaller aperture galvo.

Why choose large aperture galvo? This is because precision processing requires laser beam with a smaller divergence angle, so a large -magnification beam expander will be used. If a large -magnification beam expander is used, the larger aperture galvo is needed. Precision and working speed are a contradiction. We can only choose one.

F-theta lens

In brief, F-theta lens is a focusing mirror, which every point in a specified field at the focal length is a focusing point. Of course, this statement is not rigorous. In general, Input beam diameter of F-θ lens≥Galvo aperture, otherwise the laser will goes into the lens edge or leak, the edge part will be shallower than the middle.

The relationship between the above four is: Laser beam size x beam expander≤Galvo aperture ≤ F-theta lens input beam diameter.

How to choose suitable laser equipment parts?

RequirementsLaser sourceBeam expanderGalvo apertureF-θ lens input beam
High-speed production lineCO2 Synrad Vi303X10mm>10mm
Precision markingCO2 Synrad Vi304X12mm>12mm
Flying markingReci V22X10mm>10mm
Precision markingReci V24X/6X20mm/30mm20mm/30mm
Deep engraving200W Pulsed laser2X quartz14mm>14mm quartz; Or 10mm(avoid full-format marking, reduce the working field labelled in lens. Eg.150*150mm reduce to 110*110mm)
Deep engraving500W Pulsed laser3.5~4X water cooling quartz30mm water cooling quartz30mm water cooling quartz