Flat field focusing mirror, also known as field mirror or f-theta focusing mirror, is a professional lens system that aims to form a uniform size focusing spot of laser beam throughout the entire marking plane. Simply put, it is a focusing mirror that focuses at any point in a certain plane, while a regular focusing mirror has only one point of focus, which is the center point. It is one of the most important accessories of a laser marking machine. Field mirrors can be divided into f-theta lenses and telecentric lenses. Due to the high cost and expense of telecentric lenses, F-theta lenses are mainly used in industrial laser marking machines. In the absence of deformation, the position of the focal point depends on the focal length of the lens and the tangent of the deflection angle. The position of the focal point only depends on the focal length and deflection angle, which simplifies the calculation method of focal point positioning. What specific functions does the flat field focusing mirror of a laser marking machine have?
1. Improve the ability of edge beam to incident onto the receiver;
2. In the same main optical system, additional field mirrors will reduce the area of the receiver; If the same receiver area is used, the field of view can be expanded to increase the incident flux;
3. Unify the non-uniform illumination on the photosensitive surface of the receiver.
What are the main technical parameters of the field mirror? Let's understand the specific technical parameters of the field mirror and what are the main technical parameters we should consider when selecting the field mirror? The main considerations are the working wavelength, incident pupil, scanning range, and focal spot diameter.
Working wavelength: It mainly depends on the wavelength of the laser, and the field mirror is coated at a given laser wavelength. If the field mirror is not used within the given wavelength range, it will be burned out by the laser.
Entrance pupil: If a single lens is used, the reflector is placed at the entrance pupil, and the diameter of the usable beam is equal to the diameter of the entrance pupil.
Scanning range: The larger the range that the field mirror can scan, the more popular it is among users. But if the scanning range is increased, the focus point will become larger, and the distortion will also increase. In addition, by increasing the scanning range, the focal length and working distance of the field mirror should also be increased. The extension of working distance inevitably leads to the loss of laser energy. The diameter of the focused light spot is directly proportional to the focal length, which means that increasing the scanning range will result in an increase in the diameter of the focused light spot. If the light spot is not clustered finely enough, the power density of the laser will decrease very quickly (the power density is inversely proportional to the second power of the light spot diameter), which is not conducive to processing. So users should choose the most suitable field mirrors based on different processing areas, or reserve several field mirrors with different scanning ranges.
Focusing spot diameter: For scanning systems with incident laser beam diameter D, field mirror focal length F, and beam quality factor Q, the focusing spot diameter d=13.5QF/D (mm). So using a beam expander can obtain a smaller focused spot. This product is mainly used in laser marking machines, Stage lighting, scientific experiments and laser measuring instruments.