RESUMEN
Ion-beam techniques, i.e., ion-beam sputtering for material deposition or ion beam etching for a controlled modification of surfaces, are well established for planar thin-film processing. The primary beam of ions exiting a broadband source typically used exhibits a macroscopic spatial beam profile. In general, the beam profile is considered an undesirable but unavoidable feature of the ion source, as it may introduce inhomogeneities in the thickness of the deposited thin-film or the etched surface. Ways of circumventing these effects are sought, e.g., by using rotating substrates or large ion sources compared to the size of the substrate. Here, we demonstrate that an active control of the spatial beam profile may become advantageous when attempting to achieve homogeneous coatings on nonplanar substrates or to etch nonplanar macroscopic structures, e.g., when coating free-form optics.
RESUMEN
A polarization-independent optical sensor is created by fabricating a concentric gold ring grating with a period of 900 nm on the end facet of an optical fiber. The sensing function of this miniaturized device is realized by sending white light as a probe to the gold rings and collecting the response signal in the back-reflection through the optical fiber. A pronounced peak due to the Rayleigh anomaly of the gold ring grating is observed in the reflection spectrum, the center wavelength of which is sensitive to the change in the environmental refractive index of the fiber end facet. Theoretical analysis not only shows excellent agreement with the experimental results, but also gives insights into the mechanisms of this kind of sensor. Using the center position of the Rayleigh peak as the response signal, a high sensitivity dλ/dn of 900 nm per unity refractive index is realized for this sensor and a resolution of Δn/n ≈ 1% is demonstrated in preliminary experiments. The sensitivity is solely determined by the period of the grating.