Surface plasmon enhanced transient thermoreflectance

Abstract

Ahct. It is shown that optically excited surface plasmons can k used for measurements of the surface temperature of a metal with nanosecond the resolution. This method is closely related to transient thermoreflectance, but its sensitivity is considerably higher. We give a survey on the mechanisms involved, briefly discussing the dependence on the sample properties. Experimental confirmation of the proposed sensitivity enhancement as well as the time resolution is presented. PACS: 07.60, 42.80, 61.80 Transient thermoreflectance is a well established technique for observing temperature changes at a metal surface with high temporal resolution [I, 21. It employs as a probe the thermally induced change in the optical constants of the metal by measuring the intensity of a Iight beam being reflected at the surface under consideration. However, since the optical constants of the metal are not very sensitive to the temperature, signals obtained are usually small, and enhancement of the sensitivity of the method would be desirable. In this paper we demonstrate a modified transient thermoreflectance setup using an attenuated total reflectance technique. When the conditions for optical excitation of surface plasmons are fulfilled, the thermoreflectance signal becomes resonantly enhanced, thus increasing the sensitivity of the measured light intensity to changes of the surface temperature. We elaborate on the feasibility of this effect for performing fast high sensitivity measurements of temperature changes at a metal surface. 1. Theory Optical excitation of surface plasmons by means of the socalled Kretschmann setup has been described by many authors [3-51: the sample is formed by a metal fdm with a thickness of several tens of nanometers, evaporated onto the base of a glass prism. The surface to be studed is the interface between the metal and the vacuum. On illu