Abstract

Fluorescence detection with subwavelength resolution is important in biological applications¹ such as the observation of a membrane selectively labeled with dye molecules. Photon scanning tunneling microscopy (PSTM), which is also called scanning near-field optical microscopy (SNOM),² enables us to detect fluorescence with the resolution determined by the tip diameter at the apex of the fiber probe. In comparison with the illumination mode in PSTM, the most favorable quality of the collection mode is that probe-sample distance can be controlled by all-optical means without a feedback mechanism based on shear force, which may damage samples. It is, therefore, essential to estimate the resolution and the sensitivity of PSTM as fluorescence microscopy. Also, local detection of fluorescence with a fiber tip is an attractive subject in quantum optics. The approach of the tip to a fluorescent material in the near-field region will largely modify its radiation modes. This modification leads to a change of its radiation pattern and of its lifetime, which offers the possibility of highly effective collection of fluorescence. From these viewpoints, we here report the fluorescence imaging of dye-doped 110-nm microspheres, and we estimate the pickup efficiency, which demonstrates that the fiber tip acts as something like a nanometric integrating tip in collecting fluorescence.

© 1995 Optical Society of America