Quantitative spectroscopy of micron-thick liquid films

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Abstract
We demonstrate a new sensitive spectroscopic technique for highly transparent micron‐thick liquid films sandwiched between transparent substrates. A pulsed dye laser irradiates the film, producing (via the optoacoustic effect) a transient ultrasonic wave which is launched into the substrate and detected by a piezoelectric transducer bonded to the substrate. This technique is illustrated by measuring the absorption lines of films of aqueous solutions of rare‐earth ion, and absorptions ∼10−5 can be detected presently. This technique should open up new opportunities to study the spectra of chemi‐ or physi‐adsorbed species on surfaces.