Spherical lens, sapphire

This system consists of a symmetrical pair of lens elements connected by a small volume of liquid. Each lens consists of a single spherical interface between the liquid and a lens rod. The lens element is formed by polishing a small concave spherical surface in the end of a sapphire rod. At the opposite end of the rod, a thin film piezoelectric transducer is centered on the axis of the lens surface. 

Fig. 2.1. A lens for high-resolution acoustic microscopy in reflection. The central transparent part is a single crystal of sapphire, with its c-axis accurately parallel to the axis of the cylinder. The sandwich structure at the top is the transducer, with the yellow representing an epitaxially grown layer of zinc oxide between two gold electrodes. The pink shaded areas within the sapphire represent the plane-wavefronts of an acoustic pulse they are refracted at the lens cavity so that they become spherical in the coupling fluid. A lens for use at 2 GHz would have a cavity of radius 40f[Pg.8]

Spherical ball lenses have been used as collimators in fibre optic connectors. Sapphire spheres with a high refractive power are industrially produced in a wide range of diameters (Sandoz SA, Cugy, Switzerland Rubis Precis, Charquemont, France). Light emitted from a fibre can be focused with this lens type onto the sample site (Figure 12A). Rol found a maximal performance when the ratio of the back surface distance to the fibre and the radius of the... 

Considering the presence of acoustic energy loss, a material having a high velocity compared with that of a coupling medium and low attenuation (e.g., fused quartz or sapphire) is generally selected. The selection of the material directly relates to the design of the lens in terms of spherical aberration that needs to be minimized. 

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