Fig. 2: CUSP imaging of an ultrafast linear optical phenomenon.

a Schematic of the system used to impart both spatial and temporal chirps to the incoming pulse train using a pair of reflective diffraction gratings (G1 and G2). Each sub-pulse has a positive temporal chirp and illuminates the sample successively. b Selected frames from the reconstructed 70-Tfps movie of the spatially and temporally chirped pulse train sweeping a group of letters. Each frame is cropped from the full field of view to reduce blank space. A 2D map uses color to represent illumination wavelength and grayscale to represent intensity. Intensity is normalized to the maximum, and its color map is saturated at 0.5 to display weak intensities better. See the entire sequence in Supplementary Movie 1. Scale bars: 1 mm. c Temporal profile of the light intensity at \((x_1, y_1)\) (white arrow in b) from the state-of-the-art T-CUP (red dashed line), CUSP (black solid line) and the transform limit (cyan dash-dotted line) calculated based on the CUSP curve in the spectral domain. Inset: normalized light intensity profiles from CUSP and T-CUP in the first 2 ps. d Spatially integrated total intensity over wavelength for five sub-pulses (magenta lines). The reference spectrum (green line) was measured by a spectrometer.