High-precision spatiotemporal profiler of femtosecond laser pulses

The precise spatiotemporal characterization of broadband ultrafast laser beams is essential for accurate laser control and holds significant potential in photochemistry and high-intensity laser physics. Existing methods for spatiotemporal characterization, such as frequency-resolved optical gating (FROG) and compressed ultrafast photography (CUP), are often spatially averaged or suffer from limited spatial resolution. Recent advances in imaging techniques based on multiplexed ptychography have enabled high-spatial-resolution diagnostics of ultrafast laser beams. However, the discrete spectral assumption inherent in multiplexed ptychographic algorithms does not align with the continuous spectral structure of ultrafast laser pulses, leading to significant crosstalk between different wavelength channels (WCs). This paper presents a method to reduce the bandwidth of each wavelength channel through spectral modulation, followed by the discretization of the continuous spectrum using interference techniques, which significantly improves the convergence and accuracy of the reconstruction. Using this method, the experiment accurately measured chromatic dispersion, spatial chirp, and other spatiotemporal coupling effects in femtosecond laser beams, achieving a spatial resolution of 9.4 μm, close to the pixel size resolution limit of the angular spectrum method.