High-Speed Field-Resolved Infrared Fingerprinting of Particles in Flow

Among quantitative multi-species molecular analysis techniques, broadband vibrational spectroscopy uniquely combines the advantages of minimum sample preparation, non-destructive, label-free acquisition of the chemically-specific signal, and the potential of ultra-short acquisition times. Raman spectroscopy has showcased the classification of cells according to their broadband vibrational spectra [1], [2]. While profiting from orders-of-magnitude larger cross-sections of fundamental vibrational modes, the use of infrared (IR) spectroscopy for such applications has so far been precluded by the strong IR absorption of liquid water in the context of the low brilliance of contemporary radiation sources and modest detectivity as well as dynamic range of available broadband IR detectors. Recently, field-resolved spectroscopy (FRS) [3] employing brilliant, waveform-controlled femtosecond-laser-based IR sources, along with field-sensitive detection now approaching ultimate sensitivity [4] and a linear detection over an unprecedented range of intensities [5], has revealed a route toward overcoming these limitations.