3 October 2011 Coatings for thin-disk laser systems
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Abstract
The operation of thin-disk laser (TDL) systems relies on diode pumping of thin disks of laser active material. The thickness of such laser disks ranges between about 50 and 300 micrometers depending on the absorption coefficient and the number of pump passes. High performance optical coatings deposited on the front and back surface of the disks are essential for efficient TDL operation. Two types of coatings are necessary: On the rear surface, a high finesse HR coating is required to reflect both laser and pumping radiation. On the front surface, a low loss antireflective coating allows to transmit the laser radiation under (near) normal incidence and the pumping radiation under oblique incident angles. Besides the optical properties, the coating system on the TDL substrate has to fulfil specific mechanical and, especially for the HR coating, thermal requirements. At the Laser Zentrum Hannover, a cluster deposition tool has been developed to deposit coatings for TDL systems. This cluster deposition tool consists of a substrate load lock system for inspection and in-situ pre- and post-treatment of the substrates, a second chamber for the deposition of low loss dielectric coatings with Ion Beam Sputtering (IBS) technique, and a third section for the deposition of metal layers, which can be employed as reflective layers or for soldering purposes. The dielectric deposition chamber is equipped with an RF ion source for the deposition of discrete materials or material mixtures. Thus, discrete high low stacks or rugate filter systems can be deposited. The process is controlled via an optical Broad Band Monitor (BBM). Moreover, an in situ stress measurement system based on an online measurement of the bending of the substrate allows for an estimation of the mechanical stress in the material.
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St. Günster, St. Günster, D. Ristau, D. Ristau, B. Weichelt, B. Weichelt, A. Voss, A. Voss, } "Coatings for thin-disk laser systems", Proc. SPIE 8168, Advances in Optical Thin Films IV, 81680J (3 October 2011); doi: 10.1117/12.897000; https://doi.org/10.1117/12.897000
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