Scanning photoacoustic microscopy using photothermal radiometric detection

A thin film structure exposed to pulsewise illumination may experience pulsating temperature variations in its surface layers. The amplitude of those temperature fluctuations depends on the absorption spectrum of the sample and may be measured photothermally by observing similar pulsations in the thermal reradiation. The scanning photoacoustic microscope is based on this concept by incorporating a focused laser beam as the illumination source. With either He-Ne-3.39 μm- or CO2-10.6 μm-laser lines a spatial resolution of better than 0.1 mm can be achieved. For photothermal detection PXE-ceramics is used as infrared detector. Microscopy is carried out by recording the output of the lock-in amplifier as the sample is scanned mechanically in the x-y-plane. The aim of the work is the application of the photoacoustic technique to the evaluation of thermal properties of thin layered structures simulating human skin tissue. In collaboration with the medical school of the University of Heidelberg the possibility of developing a new specific thermographic method will be studied which should be applied for medical diagnosis of cancerous skin tissue and for temperature regulation studies of breast skin tissue for mamma cancer screening.