F-theta lens with fused silica lenses
for high power lasers, focal length 420 mm
With increasing beam quality of lasers with high average power of several kilowatts, thermal induced focus shift in collimation, beam guiding and focusing optics become more and more apparent. In that case, high quality fused silica lenses with low absorption coating should be used. Fused silica has superior performance concerning transmission and thermal stability. Considering a simple setup with collimator and focusing lens, the focal shift can be easily one Rayleigh range if a 1 kW laser is used. Scan lenses without fused silica lenses can have a focus shift of more than on order of magnitude.
Sill Optics now offers a fused silica scan lens with 420 mm focal length for wavelengths within 1030 nm to 1090 nm. The spot size variation in the 280 mm x 280 mm scan field is less than 10%. The usable beam diameter is 14 mm enabling a spot size of 60 µm. The lens has the article number S4LFT1420 and will be available soon.
