field lensAccording to wavelength, it can be mainly divided into 1064nm field mirror (also known as YAG field mirror), 10.6-micron field mirror (also known as CO2 field mirror), 532nm field mirror (also known as green field mirror), and 355nm field mirror (also known as ultraviolet field mirror); According to the design concept, it can be divided into f-theta lens and telecentric lens. Telecentric lens has a high cost and is mainly suitable for f-theta lens in industrial systems.

The main technical parameters of a field lens include: operating wavelength, entrance pupil, scanning range, and focused spot diameter. Working wavelength: mainly depends on the wavelength of the laser, and the lenses of the field lens are coated at the given laser wavelength. If the field mirror is not used within the given wavelength range, it may be burned out by the laser or the required laser transmittance may be very low. Incident pupil: also known as maximum incident spot. If a single mirror is used, the reflector is placed at the entrance pupil, and the maximum available beam diameter is equal to the diameter of the entrance pupil. The larger the entrance pupil, the smaller the diameter of the focused spot produced by the focusing mirror. Therefore, in situations where precise marking is required, we will consider using field mirrors with larger entrance pupils, such as fine marking and galvanometer welding. Scanning range: The larger the range that the field lens can scan, the more popular it is among users. But if the scanning range is increased, the focused light spot will become larger and the distortion will also increase. In addition, the scanning range should be increased, and the focal length and working distance of the field lens should also be increased. The extension of working distance inevitably leads to the loss of laser energy. The diameter of the focused spot is directly proportional to the focal length, which means that as the scanning range increases, the diameter of the focused spot also increases. If the spot is not focused fine enough, the power density of the laser will decrease very quickly (the power density is inversely proportional to the square of the spot diameter), which is not conducive to processing. So users should choose the most suitable field lens according to different processing areas, or spare several field lenses with different scanning ranges. Focal length: It is related to the working distance to some extent, but not equal to the working distance. Focusing spot diameter: For a scanning system with incident laser beam diameter D, field lens focal length F, and beam quality factor Q, the focusing spot diameter d=13.5QF/D (mm). So using a beam expander can result in a smaller focused spot.