Crack growth behavior of silicate thin films prepared by pulsed laser deposition

Er-doped silicate thin films were deposited by the pulsed laser deposition technique, starting from an Er-doped silicate glass of composition: 65%SiO ₂ - 3%Al₂O₃, - 11%Na₂O - 10%PbF ₃ - 10%LaF₃ - 1%ErF₃. The irradiations were performed with an ArF excimer laser (pulse length - 30 ns) in a dynamic flow of oxygen at a pressure of 5 Pa. The laser fluence at the target surface was about 2 J/cm². The films were deposited on pure silica substrates, either at room temperature or heated to 200°C. The morphology of the films was studied by using optical microscopy, scanning electron microscopy and atomic force microscopy. The optical transmission of the films in the NIR-visible-UV regions (200-2500 nm) was recorded by using a double beam spectrophotometer. The optical spectra were analyzed by a computer code to evaluate the refraction index n and the extinction coefficient k along with the film thickness. The optical transmission was performed soon after the deposition and after one month to evaluate the aging effects. The films deposited at room temperature presented cracks over all the area of the film when submitted to SEM inspection or ion etching. Films deposited at 200°C remained undamaged. Optical waveguides were fabricated in the films deposited at 200°C by ion etching. Very low losses (down to 0.74 dB/cm) were measured by the prism coupling technique.