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. 2018 Feb 23;7:17180. doi: 10.1038/lsa.2017.180

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Copyright © 2018 The Author(s)

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Mode-locked Ho:YAG thin-disk oscillator. HR, high-reflection mirrors; R1 and R2, concave spherical mirrors; KM, Kerr medium; HD, high dispersion mirrors; H, hard aperture; OC, output coupler. The oscillator contains a wedged Ho:YAG thin disk with a thickness of ~200 μm and 2.5 at.% Ho doping, housed within a multi-pass pump head (TRUMPF Laser GmbH). The pump spot diameter on the thin disk is 2.5 mm. The thin disk is placed as a folding mirror in a cavity based on a Z-shaped design. A pair of 45° high-reflection mirrors folds the beam path to provide eight passes through the thin disk per round trip. A 1 mm-thick sapphire plate acting as the Kerr medium is placed at the focus between two concave mirrors (R1 and R2). The total anomalous group delay dispersion per round trip is −16000 fs², introduced by a pair of chirped mirrors with up to 4 bounces on each surface. A water-cooled copper plate with a circular hole is placed near an end mirror as a hard aperture to aid the stabilization of KLM. The total cavity length is ~1960 mm, corresponding to a repetition rate of 77 MHz. Inset: the beam profile of the oscillator output.