Nonlinear Raman spectroscopy is a versatile method to enhance the intensities of Raman scattering. It requires an intense light field that can be provided by a liquid droplet acting as a high-quality optical cavity. Here, colliding droplets were used as a novel optical cavity to enhance the intensity of Raman scattering. Specifically, multiorder stimulated Raman-scattered light was generated with significant intensity from colliding droplets of carbon tetrachloride (CCl). The intensities of the Raman bands were analyzed with a simple theory that roughly reproduced the experimental spectrum. Overall, the method facilitates Raman spectroscopy of molecules in liquids because of its high sensitivity and resolution.
Chemical reactions at the interface of reactive solutions are of importance for a full understanding of solution reactions. We investigate the chemical reaction induced by the collision of two droplets. The extent of the reaction is measured by analyzing spectra and images of the Raman scattered light emerging from the interface of the colliding droplets of H 2 SO 4 and NH 3 aqueous solutions. The obtained product concentration is lower than that expected from a simple diffusion model. The result indicates that a fresh interface is produced at the periphery of the mixing region of the colliding droplets. This study provides the basis to extend this method to measure rapid chemical reactions at the interface of colliding droplets.
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