Variable wavelength photoacoustic microscopy

Imaging with a variable wavelength photoacoustic (PA) microscope is a technique that permits the characterization of surface-improved materials, layered materials, etc. The authors present theoretical and experimental studies of the modulation frequency dependence and the image for a layered sample using a variable-wavelength PA microscope. The theoretical predictions are compared with experimental results on a PA signal as a function of modulation frequency for a layered polypropylene film when varying the wavelengths. Good agreement was obtained for varied wavelengths. Examples are presented of photoacoustic images obtained with the variable-wavelength PA microscope. These show a change of PA signal caused by the alteration of the layer which absorbs the incident light.