Imaging of refractive index change by the reflection-mode scattering-type scanning near-field optical microscope: Simulation and observations

The response of the reflection-mode scattering-type scanning near-field optical microscope (RS-SNOM) to the refractive index change was investigated numerically and experimentally. Numerical results indicated that the signal of the RS-SNOM reflected the optical property of the sample and the image resolution was drastically improved in an ac mode SNOM image. The experimental results using alternating layers of GaAs and Al0.55Ga0.45As sample were in quite good coincidence with the numerical results and the spatial resolution of the RS-SNOM reached 10 nm in the case of ac mode SNOM operation. (C) 1999 American Institute of Physics. [S0021-8979(99)08004-4].