Fig. 2
From: Synthesized complex-frequency excitation for ultrasensitive molecular sensing
Direct observation of molecular vibration infrared signals and the enhancement effect of synthesized complex-frequency waves. a Schematic illustration of molecular infrared spectroscopy measurements. The infrared beam is incident upon the molecular film, spin-coated on the Si substrate, to excite the infrared fingerprint vibrational signal. b Optical microscope image showing the deposition of DON molecules on Si substrate. After spin coating, the molecules recrystallize into raised particle shapes. Scale bar: \(10\; \mathrm{\mu m}\). c Vibrational extinction spectrum of DON molecules. The gray curve represents the experimentally measured extinction spectrum, while the black curve represents the extinction spectrum enhanced by the CFW technique. The vertical dashed lines mark the positions of the characteristic vibrational peaks of C-O-H bending vibration (1410 cm-1, 1425 cm-1 and CH3 bending vibration (1442 cm-1)