Development of photothermal near-field scanning optical microscope photothermal near-field scanning optical microscope

Photothermal near-field scanning optical microscope (PT-NSOM) which gives lateral resolution below the diffraction limit has been developed. The substances are excited by the evanescent wave emitted from the small aperture (around 100 nm φ) of the metal-coated optical fiber probe, resulting in a formation of refractive index change, or the so-called thermal lens. The probe laser light introduced coaxially with the excited one is deflected by it and the intensity at the center of the transmitted component of the probe light is measured by a photodiode. The NSOM image based on photothermal phenomena of Au colloids with diameter of 250 nm has been taken and the lateral resolution is estimated to be less than 150 nm.