Fig. 1. The optical setup and principle of high-frequency enhanced compressed active photography (H-CAP). (a) The optical setup of the H-CAP system. (b) The sampling principle of R-code and (c) H-code in the spatial and frequency domain. (d) The ultrafast phenomena are reconstructed from the compressed image by using a reconstruction algorithm.

Fig. 2. Simulation results of H-code and R-code. (a) Forward model of high-channel photography. (b) The compressed images of 200 frames collected under different codes and corresponding Fourier transform. (c) Reconstruction results of light reflection under different codes. (d) The comparison of the light intensity center extracted from the reconstruction results of H-code and R-code with the original data. (e) The beam length calculated according to the reconstruction results of different codes.

Fig. 3. Characterization of static experimental results. (a) The original image of the object. (b) The compressed image of the object with 100 frames. (c) Reconstruction results of ‘UPL’ and ‘Laser’ under different captured frames. (d) The correlation between the reconstruction result in (c) and the original object. (e) Reconstruction results of the resolution target under different captured frames. (f) The intensity curves of vertical stripes in (e).

Fig. 4. Imaging of the self-focusing of optical pulses in Kerr medium. (a) The experimental schematic of optical pulse self-focusing. (b) Reconstruction results of optical pulse self-focusing under different codes. (c) Scatter plot of spots along x direction and corresponding Gaussian fitting curves (every 8 frames in the reconstruction results of H-code). (d) Scatter plot of transverse spot sizes and corresponding Gaussian fitting curves (every 8 frames in the reconstruction results of R-code). (e) The velocity of beam in CS₂ is calculated according to (c) and (d). (f) The intensity curves of the spot along the y direction. (g) The variation of beam width with travel time (according to the full width at half maximum (FWHM) of the curve in (f)). The red box indicates the self-focusing area.

Fig. 5. Double-pump pulse induced ultrafast ablation process of silicon surface. (a−c) The reconstructed dynamic process of the double-pulse ablation of silicon surface when the inter-pulse delay time τ is 0 ps, 6.7 ps and 13.3 ps. (d) The curves of the relative reflectivity of the center of the excitation region over time under different pulse delay. (e) The change on the depth of the ablation area with the number of shots when the delay between pulses is 6.7 ps and the observation time is 260 ps.