Fig. 1. Inverted cross-sectional AFM image of a chemically etched longitudinally written waveguide. The laser was operated at a repetition rate of 250 kHz and an average power of 175 mW. The scan rate was 100 µm/s. The width of the flat-topped region is ≈ 1.7 µm.

Fig. 2. Index of refraction profiles (arbitrary units) across the longitudinally written waveguide shown in Fig.1 and obtained using the chemical etching/AFM and microreflectivity techniques.

Fig. 3. Average AFM etch depth (1%HF,6 minutes) as a function of induced index change measured using microreflectivity averaged across the width of five waveguides written with an aspherical lens using a femtosecond laser power of 250mW and under the following conditions: (◆) 15°, 100µm/s, (■) 15°,50µm/s, (▲) 10°,100µm/s, (▪) 10°, 50 µm/s and (●) 6°, 50µm/s. The line shown in the figure is the best line visually through the data and the origin. The error bars indicate the experimental uncertainty on the AFM and microreflectivity data, which is higher for the lower index changes.

Fig. 4. Inverted AFM image of the cross-section of an etched tapered conical structure in a silica glass sample. The etch depth (before inversion) was ≈ 40 nm over the entire conical structure. The structure was produced by focussing (NA=0.65) a 30 mW, 100 kHz laser beam ≈ 150 µm below the top surface and translating the sample perpendicular to the laser beam at a scan rate of 25 µm/s. The sample was then cut in two pieces transverse to the scan direction. One of the inside surfaces was polished then etched (1% HF for 3 min) and placed under the AFM. The focussed femtosecond laser light entered from the top of the image.