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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 laser (SP laser) and ultra-short pulse laser (USP laser) have special demands on optical elements. SP lasers emit narrowband light with a bandwidth of approx. 1 nm. As the peak power can be very high, non-linear effects (colour centres, self-focusing) in certain glass materials can occur. USP lasers in the femtosecond regime have a broad spectral width which makes the use of special glasses necessary to minimize the pulse broadening.
For SP and USP lasers, glasses with low dispersion or fused silica lenses are recommended. In addition, ghost reflections, i. e. spurious, unwanted images formed by small amount of reflected light, can be problematic for scan mirrors and lens elements and should therefore be avoided. The scan lenses offered (marked with a point) are optimised for these demands.
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