Photo-thermal transient stress observed by sub-nanosecond pump-probe technique with the surface plasmon resonance

Abstract

Photoacoustic microscopy (PAM) has attracted attention as a non-invasive observation tool for biomedical studies. However, the spatial resolution is unsuitable for precise imaging of a single cell due to the characteristics of the ultrasonic transducer. In recent years, the surface plasmon resonance (SPR) sensor has been reported as a technique with a high-spatial resolution and ultra-flat frequency response. SPR is expected to be the future optical detector for photoacoustic imaging. As a first trial, using a Kretschmann-configuration SPR sensor (Ag (53 nm)/BK7 glass prism), we observed the photo-thermal transient stress and the consequent change in refractive index using the sub-nanosecond pump-probe technique. The signal intensity of the thermo-elastic stress produced by the pump beam excitation was measured by changing the incident angle of the probe beam. The spot diameter of the probe beam was 5 μm. The highest intensity signal was observed at the SPR angle (46.5 deg.) of the plasmon resonance. Results suggest that the SPR sensor effectively enables the non-contact and non-destructive measurements of the thermo-elastic stress. Further researches will implement the SPR sensor for tissue characterization by attaching biological samples on the Ag surface.