Temperature profile measurements of near-field optical microscopy fiber tips by means of sub-micronic thermocouple

The present paper deals with the experimental measurement of temperature al ong various shapes of fiber tips used as near-field optical microscope prob es. An ultra-small thermoelectric couple makes it possible to detect the ti p temperature as far as the junction dimension remains smaller than the loc al investigated area. The couple is a 0.5 mu m Pt and Pt-Rh 10% welded wire s, whose dynamic and dimensional characteristics allow the investigation of the thermal behaviors of tapers under steady-stare and periodic excitation modes (bandwidth near 1 kHz). Temperature profiles along these fiber tips (up to 400 mu m from the apex) are shown and discussed. Confirming some aut hors' results, dramatic temperature increases due to an internal heating ca n occur for some configurations. Such temperatures can play a key role in t he imaging process. because of the resulting behaviors of the apex, mainly due to its thermal expansion. Indeed, variation of the aperture diameter an d thermoelastic interaction with the sample surface could explain some arte facts in the resulting images. (C) 2000 Editions scientifiques et medicales Elsevier SAS.