Fig. 1: Near-petahertz fieldoscopy.

a, An ultrashort pulse excites molecules at their NIR resonances. Here, the molecules inside a cuvette represent the sample under scrutiny, while the surrounding molecules represent atmospheric water vapour molecules. The transmitted field accumulates dispersion during propagation and contains the global molecular response of both the sample and the environment. A second short pulse at higher frequencies is used for up-conversion and generation of a delay-dependent signal in a nonlinear crystal, where the correlation signal is directly proportional to the electric field of the excitation pulse. The measured electric contains the ultrashort excitation pulse, the delayed response of the liquid spanning over several picoseconds, and a long-lasting response of atmospheric gases lasting for hundreds of nanoseconds. By time filtering and subsequent data analysis, the molecular response can be decomposed to the short-lived liquid and long-lived gas responses. b, The biologically relevant vibrational modes at NIR spectral range. Different compounds, including proteins, carbohydrates, lipids, polyphenols and alcohols, are associated with the shown bands. Associated bonds are described in the legend below the plot, where ‘str’ refers to stretching vibration and ‘bend’ refers to bending vibration. The numbers 1 and 2 indicate the first and second overtones, while the plus sign (+) indicates combination bands. The values were taken from ref. ¹⁶. The liquid and gas responses shown in the figure are enhanced for better visibility.