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What is the function of the laser field lens of the laser marking machine?

The flat-field focusing lens, also called field lens, f-theta focusing lens(F-Theta Objective Lens), is a professional lens system whose purpose is to form a uniform focused spot of the laser beam in the entire marking plane, which is the most important part of a laser marking machine. One of the accessories.

The main functions of the laser field lens of the laser marking machine are:

1. Improve the ability of the edge beam to enter the detector;
2. Make the non-uniform illumination on the photosensitive surface of the detector uniform;
3. In the same main optical system, the additional laser field lens will reduce the area of ​​the detector; if the same area of ​​the detector is used, the field of view can be enlarged and the incident flux can be increased;

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When selecting a field lens, the main technical parameters considered are working wavelength, entrance pupil, scanning range and focusing spot diameter.

Working wavelength: It mainly depends on the wavelength of the laser. The field is actually coated at a given laser wavelength. If the field lens is not used within the given wavelength range, the field lens will be burned by the laser.

Entrance pupil: If a single lens is used, the mirror is placed at the entrance pupil, and the diameter of the maximum usable beam is equal to the diameter of the entrance pupil.

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Scanning range: The larger the range that the field lens can scan, the more popular it is for users. However, if the scanning range is increased, the focus spot becomes larger, and the distortion degree also increases. In addition, to increase the scanning range, the focal length and working distance of the field lens must also be increased. The increase of the working distance will inevitably lead to the loss of laser energy. Also, the diameter of the focused spot is proportional to the focal length, which means that if the scanning range is increased, the diameter of the focused spot will increase, and the spot will not be narrow enough, and the power density of the laser will drop very quickly (the power density is the second power of the spot diameter Inversely proportional), which is not conducive to processing. Therefore, the user should choose the most suitable field lens according to different processing areas, or spare several field lenses with different scanning ranges.

Focused spot diameter: For a scanning system with incident laser beam diameter D, field lens focal length F and beam quality factor Q, the focused spot diameter d = 13.5QF/D (mm). Therefore, a beam expander can be used to obtain a smaller focused spot.