Instrument Development: Spectral Fluctuation Raman Spectroscopy

With the support of the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Hendrik Utzat of the University of California, Berkeley, is developing a new optical instrument to measure time-dependent fluctuations in the vibrational spectra of single molecules. These spectral fluctuations provide insights into how molecular bonds are distorted, how molecules interact with surfaces, and how polymer chains change conformation. However, especially fast fluctuations—on the nano- to millisecond timescale—have largely eluded quantitative measurement. Professor Utzat and his team will build an apparatus called Spectral Fluctuation Raman Spectroscopy (SFRS), which will enable precise measurement of Raman spectral fluctuations across a broad range of timescales, including those currently inaccessible with existing techniques. The data generated by this instrument will help researchers better understand molecular interactions, potentially leading to improved catalysts, functional materials, and pharmaceuticals. The project will contribute to building a competitive, quantum-literate U.S. workforce through training opportunities for high school and college students in spectroscopy, quantum optics, instrument engineering, and data science. Technically, the project integrates photon-correlation and interferometric methods into surface-enhanced Raman spectroscopy (SERS) to quantify spectral fluctuations with sub-microsecond to millisecond resolution. The technique measures spectral correlation functions of Raman photons, allowing temporal resolution to be decoupled from detector frame rates. To achieve this, the project will harness cutting-edge superconducting nanowire single-photon detectors (SNSPDs) and interferometry. The instrument will be benchmarked using established SERS model systems to assess its ability to detect vibrational dephasing and molecular switching processes. The method is designed as a general platform for measuring time-dependent vibrational spectral diffusion in single-molecule systems. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.