Rajagopalan UMA MAHESWARI,¹ Shuji MONONOBE,² Hitoshi TATSUMI,^2,3 Yoshifumi KATAYAMA² and Motoichi OHTSU^1,4

¹Kanagawa Academy of Science and Technology KSP East 408, 3-2-1, Sakado, Takatsu-ku, Kawasaki, Kanagawa, 213 Japan, ²Department of Autonomic Physiology, Medical Research Institute, Tokyo Medical and Dental University, Chiyoda-ku, Tokyo, 101 Japan, ³gThe Intelligence and its Origin,h PRESTO, Japan Science and Technology Corporation, Japan, ⁴Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259, Nagatsuda, Midori-ku, Yokohama, Kanagawa 226 Japan

(Received August 17, 1996; Accepted September 3, 1996)

We propose an illumination mode near-field optical microscope operated under an optical feedback for imaging biological specimens in their natural environment. For feedback control, rapidly varying evanescent signal has been generated over the sample surface. It has been found that evanescent signal can be profitably used as a control signal by utilizing its sample feature dependent discrimination sensitivity. Neurons have been successfully observed both in air and in liquid with a resolution well beyond the diffraction limit.

Key words : near-field optical microscope, illumination mode, evanescent feedback, sample feature dependent discrimination sensitivity, nanometric protruding tip

*This paper was originally presented at the first Asia-Pacific Workshop on Near Field Optics, which was held on August 17 and 18, 1996 at Seoul Education and Culture Center, Seoul, Korea, organized by Condensed Matter Research Institute, Seoul National University.