15 February 2011 All-in-quartz optics for low focal shifts
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Abstract
High laser power levels in combination with increasing beam quality bring optics performance into focus, particularly with regard to systems with low focal shifts along the optical axis. In industrial applications, this often influences the overall performance of the process, especially if the focal shift is comparable to or in excess of the Rayleigh length. It is commonly accepted that the focal shifts are of thermal nature where lens material, lens coating, geometry and surface contamination all contribute to the direction and extent of the focal shifts. In this paper we will present a novel design of lens packages where a patented all-in-quartz concept is explored. By mounting quartz lenses in hermetically sealed quartz tubes and applying water cooling on the perimeter of the quartz tubes we will reduce or eliminate a number of contributing factors to focal shift problems. The hermetic sealing, carried out in a clean-room environment, will minimize lens surface contamination. Differences in thermal expansion between lens and housing are eliminated as the lens and housing will be of the same material. Absorption of scattered laser light will be efficient as the energy is removed quickly by cooling water and not absorbed by fixed surroundings. Finally, indirect heating from the housing transmitted by radiation and convection to the lenses is avoided. Values of the normalized System Focal Shift Factors (SFSF) for the all-in-quartz optics will be compared to standard lens assemblies at multi-kW laser power levels.
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Mats Blomqvist, Ola Blomster, Magnus Pålsson, Stuart Campbell, Frank Becker, Wolfram Rath, "All-in-quartz optics for low focal shifts", Proc. SPIE 7912, Solid State Lasers XX: Technology and Devices, 791216 (15 February 2011); doi: 10.1117/12.874597; https://doi.org/10.1117/12.874597
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