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Lenses used in combination with XY galvanometer scanners are called ƒ-theta lenses, plane field objectives or simply scan lenses. ƒ-theta lenses are used in various applications from industrial material processing, drilling, welding of synthetic material and cutting in addition to medical and biotechnology (confocal microscopy, ophthalmology) to science and research. The design and the quality of the optical components are playing a decisive role.
Standard lenses focus the laser beam on a spherical plain in contrast to an ideal flat or plane field. The use of ƒ-theta lenses provides a plane focusing surface and almost constant spot size over the entire XY image plane or scan field. The position of the spot on the image plane is directly proportional to the scan angle. The scan length specifications in this catalogue are based on mirror spacings of typical scan heads. For other scan systems the parameter “aperture stop” defines the distance of the geometrical centre between the mirrors to the mechanical edge of the lens housing.
Short pulse lasers and ultra-short pulse lasers, but also lasers with high average power issue a exceptional challenge for lenses. Processed are strongly influenced by the characteristics of regular optical glasses. For instance thermal effects change both the beam shape and the working distance. At this point fused silica presents its crucial advantage by lower sensitivity to thermal effects in comparison to optical glasses and is therefore highly recommended for the use with the named laser sources above.
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