Optical absorption photoacoustic measurements for determination of molecular symmetries in a dichroic organic-film.

A novel approach to specify symmetries and main optical axes in anisotropic polymeric films is proposed. This method is based on the analysis of the optical absorption via the pulsed laser photoacoustic (PLPA)technique in a common polarizer film, while rotating the polarizer axis at normal incidence. Since the PLPA-signals are directly proportional to the optical absorption, it is shown that a symmetric and complementary Malus's law can be obtained over full root mean square (RMS)- and correlation (CA)-analysis of the PLPA-signals. Such data processing reveals the main material directions of the constituting film molecules defining the symmetry structure of the sample. PLPA-results were compared to the pure optical transmission experiments and show unambiguous information, allowing this technique to be used in nonstandard and opaque polymeric films, where the analysis of the optical measurements represents a difficult task, and in general, in anisotropic media. (C) 2008 Optical Society of America