Ultra-sensitive surface absorption spectroscopy using sub-wavelength diameter optical fibers

摘要

The guided modes of sub-wavelength diameter air-clad optical fibers exhibit apronounced evanescent field. The absorption of particles on the fiber surfaceis therefore readily detected via the fiber transmission. We show that theresulting absorption for a given surface coverage can be orders of magnitudehigher than for conventional surface spectroscopy. As a demonstration, wepresent measurements on sub-monolayers of 3,4,9,10-perylene-tetracarboxylicdianhydride (PTCDA) molecules at ambient conditions, revealing theagglomeration dynamics on a second to minutes timescale.