Endcapping of high-power 3 µm fiber lasers.

Fiber tip photodegradation through OH diffusion currently limits the long term operation of high-power fiber lasers and amplifiers operating near 3 µm. To address this issue, we investigate the resistance to OH diffusion of fluoride and oxide endcaps manufactured out of ZrF$_4$4, AlF$_3$3, GeO$_2$2, SiO$_2$2 and Al$_2$2O$_3$3 fibers. To this extent, the endcaps are spliced at the output of a 20 W continuous-wave fiber laser operating at 2.8 µm and their degradation over a 100 h time period is monitored. While the fluoride-based endcaps underwent failure during the first 10 h, their oxide counterparts survived the experiment, although showcasing degradation which was reflected as an increase of the endface temperature over time. To overcome this issue, we propose a novel method to completely suppress OH diffusion which consists in sputtering a nanoscopic diffusion barrier film made of silicon nitride (Si$_3$3N$_4$4) on the output face of the endcap. The effectiveness of the approach is validated on Al$_2$2O$_3$3, ZrF$_4$4 and AlF$_3$3 endcaps which show no sign of degradation after being used for more than a 100 h at the output of a 3 µm high-power fiber laser.

30 W fluoride glass all-fiber laser at 2.94 µm.

We report the demonstration of a 2938 nm erbium-doped fluoride glass fiber laser delivering a record output power of 30.5 W in continuous wave operation. The passively cooled all-fiber laser cavity based on intracore fiber Bragg gratings has an overall laser efficiency of 16% as a function of the launched pump power at 980 nm and a single-mode output beam quality of M2<1.2. This power scaling demonstration of a fiber laser operating near the vibrational resonance of water is likely to have a significant impact on several biomedical applications.

Fabrication of high-quality VO2 thin films by ion-assisted dual ac magnetron sputtering.

The technique of cathodic ac dual magnetron sputtering along with the high energy ionic bombardment is known to yield high-quality thin films in terms of their uniformity and high density. This technique has been applied for the first time to achieve thermochromic VO2 thin films that show a high optical and electrical contrast between normal and switched states. In this two-step process Vanadium metal films were deposited and subsequently oxidized in optimum conditions to achieve stoichiometric VO2 films. Typical films switched between more than 40 % to less than 5 % transmission in the infrared region while undergoing an electrical sheet resistance change between 1 × 10(5) and 1 × 10(2) Ω/cm(2). The application potential of such VO2 films in integrated optics is deemed high.