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Cover Picture
In our experiment, the GaN laser diode output radiation at โผ 448 nm was collimated by an aspherical lens (f = 4.5 mm, 0.55 NA, ARC = 400 -600 nm) and subsequently focused into the active medium by a noantireflection-coated lens with a 50 mm focal length resulting in a spot size of about 60 ฮผm. For tunable laser operation, V-folded laser resonator consisting of a pump mirror (M1), output folded mirror (M2), and an end mirror (M3) with 5 m, 50 mm, and 5 m radii of curvature, respectively, was used. The reflectance of all the mirrors was greater than 99.9% in the 720 -747 nm spectral range. M1 -M2 and M2 -M3 distances were 30 mm and 80 mm, respectively. As a tuning element, Lyot filter placed inside M2 -M3 arm at Brewster's angle was employed. The active medium mounted on a copper heat sink was situated closest to the pump mirror, i.e., the location of the cavity beam waist. In order to shield unabsorbed pump radiation, laser radiation was detected behind the glass plate filter with T โผ 0% at โผ 448 nm. (Cover picture: M. Fibrich, J. ล ulc, et al., pp.