Experimental demonstration of plasmonic- and electronic-enhancement-free coherent Raman spectroscopy of ångström-scale ultrathin molecular systems. Credit: Institute for Molecular Science / Toshiki Sugimoto Conventional spontaneous Raman spectroscopy of interfacial molecules typically requires plasmonic or electronic enhancement, limiting accessible systems. A nonlinear coherent Raman method now enables direct, high sensitivity detection without such requirements. A time-frequency engineered optical design suppressed strong substrate background signals by four orders of magnitude, allowing Raman detection of ångström scale ultrathin interfacial molecular layers. This method opens new opportunities for real-time operando observations in electrochemistry, catalysis, adhesion, and molecular devices. Why ultrathin interfaces are difficult Molecular vibrations provide direct fingerprints of chemical bonding, molecular structure, and intermolecular interactions.…