Direct Measurement of Evanescent Wave Interference with a Scanning Near-field Optical Microscope

Evanescent wave interference is studied theoretically and experimentally. The interference patterns were directly measured with a scanning near-field optical microscope. The acquired image of the interference pattern is clear and has better contrast than that previously acquired with a photon-scanning tunnelling microscope or lasertrapped particles. The spatial period of the interference fringes is 180 nm, which agrees with the theoretical value. The results indicate that the probe of the scanning near-field optical microscope has a resolution beyond 100nm. The relation between the evanescent field intensity and the distance is also measured. When the separation between the probe and the interface is up to 18Ohm, the intensity can decrease to 1/e of the maximum.