How to Adjust the Focal Length of Laser Marking Machine Correctly?

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When using a laser marking machine, it will involve the problem of correct adjustment of the focal plane. Equipment manufacturer will emphasize the importance of focal length during equipment installation training and sample adjustment. Laser engraving on the correct focal plane is a key factor for the equipment to perform properly.

First of all, before knowing the proper debugging method, we first understand the correct definition of focal length.

What is the Focal Length of the Laser?

Focal length, is a measure of the concentration or divergence of light in an optical system. It refers to the distance from the center of the lens to the focal point of the light.

After the laser is reshaped, it will be irradiated with a parallel beam to the focusing field lens. Conventional laser marking equipment mostly uses convex lens. The convex lens is optically refracted to focus the parallel light beam to a focal point. Form the focal plane.

The vertical distance from the optical center of the convex lens to the focal plane is what we call the focal length. We generally use F= to represent its focal length. Most of the laser equipment matching the focusing field lens will have a mark on it. For example: F=163; F=254, etc. The focusing field lens is a very important optical accessory in laser marking equipment.


The common focusing methods of laser marking machines on the market can be divided into front focus and back focus.

Dynamic front focus, that is, the focusing step is placed before the deflection of the galvo, which can form a larger marking area. We focus on the latter, that is, back focus.

The laser generates laser light and is incident on the galvo deflection lens, and cooperates with the control software to form our preset marking pattern path. The galvo lens refracts the laser to the focusing lens, focusing the energy to the focal plane to complete the laser engraving.

The focused beam of the laser is like a cone-shaped needle. Therefore, in order to make the laser energy sharper, the only thing to do is to shake the Z-axis of the laser marking machine up and down to adjust it to the focal plane.

However, when the focused centripetal beam passes through the focal point, due to the characteristics of the laser (good monochromaticity, good coherence, good directivity, and high brightness), the beam will not end or change phase. They will continue to scatter after crossing. Therefore, if the laser focal plane is too high or too low, the correct focal plane will be missed. Only on the correct focal length plane, the laser spot is the smallest, the energy is the strongest, and the sound and color are the brightest after the laser reaches the object.

Some Conventional Debugging Methods for Adjusting the Focal Length of Laser Markers

After fully understanding the theoretical knowledge related to laser focal length, let’s enumerate a few conventional methods of finding the focal length.

1.Continuous light test

Draw a square or circle about one centimeter on the marking software. After regular filling, adjust the laser energy to a larger value in the laser setting parameter column, try to use low frequency as much as possible, and then check continuous marking. Place a metal business card or the like on the surface of the product where the laser is projected, continue to mark the light, shake the Z-axis up and down until the laser hits the metal business card with the strongest energy, the clearest sound, and the brightest color, which is basically the focal length. Too high or too low to test several times to find a suitable focal length.

metal card marking

This method is more suitable for 1064nm wavelength fiber laser marking machine, semiconductor laser marking machine, end pump laser marking machine, 355nm ultraviolet laser marking machine, 532nm green laser marking machine, etc. For the CO2 laser marking machine, draw a box in the marking software, and continuously emit light on a piece of white paper, shake the Z axis. When the line on the paper is the thinnest, it is the focal plane.

2.Measuring the focal length

After the laser engraving machines manufacturer informed the focal length data, you can record it. Then every time you switch the product, you can directly lean one end of the steel rule against the surface of the product. The scale value refers to a certain reference surface on the field lens, and just shake it up and down to the scale data.


This method is applicable to all laser markers, but one drawback is that if the position of the product that needs laser engraving is concave or not fit into the steel ruler, this method is not very practical.

3.Double red light on the point to take the value

This method requires the equipment itself when the factory has the corresponding hardware configuration. Install one or two oblique red lights next to the galvo, from some principles of right triangles, use a fixed right-angle side and two overlapping hypotenuses to find the other right-angle side on the plane where the focal length is located. You only need to shake up and down until the two red light indicator points coincide to quickly find the focal length.

Double red light

Although this method is convenient and fast, it requires the laser marking mahcines manufacturer to cooperate with this device. In addition, if it is not properly adjusted or shifted in the middle, it is easy to cause misleading and form the wrong focal length.

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