Nearfield optics with solid immersion lenses and sharp metal probes

Abstract

We discuss two methods for achieving optical resolution beyond the diffraction limit in air. The first method, the solid immersion lens (SIL), improves optical resolution by increasing the numerical aperture (NA) beyond 1.0, the usual limit in air, to a maximum of n, the refractive index of the SIL. We present experimental results with a scanning optical microscope (/spl lambda/=400 nm) based on a micromachined silicon nitride SIL that demonstrates optical resolution /spl sim/1.9 times better with the SIL than without. Specifically, the microfabricated silicon nitride SIL improves the optical edge response from /spl sim/190 nm to /spl sim/100 nm. The second method for improving resolution is based on the strongly enhanced electric field at the surface of a nanoparticle illuminated with light whose wavelength corresponds to the particle's plasmon resonance. We present finite difference time domain (FDTD) calculations showing that the electric field intensity at the sharp apex of a triangular nanoparticle is enhanced by more than two orders of magnitude over the incident intensity in a very small region (< 10 nm).