<title>Laser heat-up of near-field probe tip</title>

Abstract

The work includes theoretical analysis of heat-up of an optical near-field probe with laser radiation passing through it. Stationary solution is found regarding the probe heating due to partial absorption of the radiation by the metal film and linear heat exchange between the probe and its environment. Temperature space distribution down the tapered part of the probe is found. The threshold power of continuous radiation leading to melting of the probe is estimated. INTRODUCTiONNear-field optical microscopes (NFSOM) have been undergoing intensive development the last ar1 . NFSOM can be used not only for imaging and spectroscopic purposes but also for providing superlocal force action of light on a sample. NFSOM probe is the key element defining the maximum power that can be delivered to the sample surface and structure of nearfield radiation acting on the sample. That is why consideration of the probe heating by laser radiation passing through it becomes important if marginal parameters of superlocal light action are to be found. As input light power increases, heating of the probe leads to deformation of the probe followed by damage, limiting the maximum applicable light power. SETTING OF THE PROBLEM.NFSOM fiber probes are usually formed by stretching or chemical etching of an optical fiber. Such probes generally have intricate shape, hut as a first approximation assume that probe consists of two parts (Fig. 1). One part (denoted II in Fig.l) is a half-closed cylinder of diameter d and the other part (I) represents a cone with the element angle y. The cone is bounded with two radii r0 and r1. The cone part of probe is cladded with a thin metal film.128 / SPIE Vol. 2384 0-8194-173 1-9/95/$6.00 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/27/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

Microscale Spatially Resolved Thermal Response of Si Nanotip to Laser Irradiation

“…Moreover, the laser in the Si tip will be reflected back and forth inside the tip when it encounters the surface. The light is trapped in the geometry as in Al-coated fiber for aperture NSOM. , In the apex, although the electric field is high enough outside, the electric field inside is relatively low. Near the apex zone, the surface of the tip exposed to the incident laser is smaller than that of the blunt zone.…”

“…12À14 In aperture NSOM, during the process of passing light through the aperture, a large portion of the incident laser is trapped in the tip area, causing tip heating. 1,2 As heat accumulated near the tip apex, the probe could be damaged as a result of thermal stress caused by different thermal expansions of the fiber and aluminum coating of the coaxial tip. 3À5 For an apertureless tip, a very strong electromagnetic field is created in the vicinity of the tip apex, which may cause nanoscale heating effects in the tip.…”

“…When an external laser illuminates a nanoscale tip, heating effect arises from absorption of light. This thermal phenomenon happens in near-field scanning optical microscopy (NSOM), − apertureless NSOM, , tip-enhanced Raman spectroscopy (TERS), laser-assisted scanning tunneling microscope (STM)/atomic force microscope (AFM)-assisted surface modification and nanofabrication, − and high density data storage. − In aperture NSOM, during the process of passing light through the aperture, a large portion of the incident laser is trapped in the tip area, causing tip heating. , As heat accumulated near the tip apex, the probe could be damaged as a result of thermal stress caused by different thermal expansions of the fiber and aluminum coating of the coaxial tip. − For an apertureless tip, a very strong electromagnetic field is created in the vicinity of the tip apex, which may cause nanoscale heating effects in the tip. , Mamin and Rugar first used a laser-heated AFM tip and cantilever to create a series of 100 nm depth pits on polymer substrates . Hamann et al used a laser-heated AFM tip magnetic recording method, which is beyond traditional limits, to heat a magnetic material and write less than 40 nm pits, corresponding to a data density of 400 Gbit/inch 2 .…”