PROCEEDINGS ARTICLE | October 4, 2011
Proc. SPIE. 8168, Advances in Optical Thin Films IV
KEYWORDS: Mirrors, Sputter deposition, Metals, Dielectrics, Optical coatings, Ion beams, Process control, Deposition processes, Disk lasers, Laser systems engineering
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.
