Ultrafast Coherent Raman Scattering at Plasmonic Nanojunctions

• Published in: Journal of physical chemistry. C Vol. 120; no. 37; pp. 20943 - 20953
• Main Authors: Crampton, Kevin T, Zeytunyan, Aram, Fast, Alexander S, Ladani, Faezeh T, Alfonso-Garcia, Alba, Banik, Mayukh, Yampolsky, Steven, Fishman, Dmitry A, Potma, Eric O, Apkarian, V. Ara
• Format: Journal Article
• Language: English
• Published: American Chemical Society 22.09.2016
• Subjects: autocorrelation; nanospheres; physical chemistry; Raman spectroscopy
• ISSN: 1932-7447; 1932-7455; 1932-7455
• DOI: 10.1021/acs.jpcc.6b02760

Surface-enhanced coherent anti-Stokes Raman scattering (SECARS) measurements carried out on individual nanosphere dimer nantennas are presented. The ν-domain and t-domain CARS measurements in the few-molecule limit are contrasted as vibrational autocorrelation and cross-correlation, respectively. We show that in coherent Raman spectroscopies carried out with ultrashort pulses, the effect of surface enhancement is to saturate stimulated steps at very low incident intensities (100 fJ in 100 fs pulses), and the principal consideration in sensitivity is the effective quadratic enhancement of spontaneous emission cross sections, σ* = (E L/E o)2σ. Through multicolor femtosecond SECARS measurements we show that beside enhancement factors, an effective plasmon mode matching consideration controls the interplay between coherent electronic Raman scattering on the nantenna and vibrational Raman scattering on its molecular load. Through extensive measurements on individual nantennas, we establish the tolerable average and peak intensities that can be used in ultrafast measurements at nanojunctions, and we highlight a variety of plasmon-driven chemical and physical channels of signal and sample degradation.