Solid immersion lenses

Past strategies for increasing the storage capacity of optical disks were based on a reduction of A and an increase in NA, as can be seen from Table 12.1. In principle, a reduction in the spot size can be achieved with the aid of solid immersion lenses. This as yet not practically exploited technique, operating with a hemispherical or a Weierstrass superspherical lens placed near the recording medium (< 100 nm), yields a reduced spot size, S, as is evident from Eqs. (12-2) and (12-3), respectively, where n denotes the refractive index of the lens [8],... 

Spot size reduction of an optical beam is generally limited if focussing in air is considered due to the NA limit of unity. If the angular spectrum of the waveguide mode field comes close to or exceeds this limit, two ways can be eonsidered. The first one is to widen the mode field by a 2D-taper in such a way that it comes close to a diameter which is available with focus formation in air. The second one is to focus in a high index lens material, and to attach the lens to the lO-chip, finally, just similar to what is achieved with a solid immersion lens. The principal geometry is shown in figure 15. 

I. Ichimura, S. Hayashi, and G. S. Kino, High-density optical recording using a solid immersion lens, Applied Optics 36, 4339-4348 (1997). 

Figure 19. Tapered gold rectangular aperture. The aperture is filled with the glass of the solid immersion lens with refractive index 1.5.

With the microfocus instrument it is possible to combine the weak Raman scattering of liquid water with a water-immersion lens on the microscope and to determine spectra on precipitates in equilibrium with the mother liquor. Unique among characterization tools, Raman spectroscopy will give structural information on solids that are otherwise unstable when removed from their solutions. 

Figure 7 shows two designs of coverslip-form solid-immersion micropshere superlens we have proposed, a flat-top design (Fig. 7a), and a hemisphere-top design (Fig. 7b), both having a thickness similar to standard coverslip which is small enough for the superlens to be directly inserted into the gap between conventional microscope s objective lens and sample. The hemisphere-top curved surface in the design Fig. 7(b) is used to reduce the effect of total internal reflection from a flat surface. 

The new lens is also less sensitive to the environment change owing to encapsulation which separates microspheres and the environment. The solid-immersion design has great commercial potential which will be discussed in the outlook session below. 

One of the significant advantages of Raman spectrometry is that it is based on visible or near-IR radiation that can he transmitted lor a considerable distance (as much as 100 m or more) through optical fibers. Figure 18-9 shows the arrangement of a typical Raman instrument that uses a fiber-optic probe. Here, a microscope objective lens is used to focus the laser excitation beam on one end of an excitation liber of a fiber bundle. These libers bring the excitation radiation to the sample. I ibers can be immersed in liquid samples or used to illuminate solids. A second fiber or liber bundle collects the Raman scattering and transports it to... 

In this chapter, we have seen how a sandwiched film can promote adhesion on a surface. We have examined the cstahlishment of an adhesive contact between a deformable elastomer lens and a rigid planar solid - -whether it is in motion or at rest immersed in a non-wetting liquid. 

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