Single-frame complete spatiotemporal measurement of complex ultrashort laser pulses
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Today one of the frontiers in light measurement is to measure ultrashort pulses from ultrafast laser systems, which demonstrate extremely fast temporal variations, and are necessarily associated with large spectral bandwidths by Fourier transform. In addition to the temporal and spectral structures, ultrashort pulses can also be complex in space. Especially, the field can have spatiotemporal couplings which relate pulse temporal profile to spatial coordinates. Therefore, a complete spatiotemporal measurement technique is needed. In this work, we demonstrate our study on measuring complex ultrashort pulses by development of a method, called Spatially and Temporally Resolved Intensity and Phase Evaluation Device: Full Information from a Single Hologram (STRIPED FISH). Based on digital holography, this simple single-frame method can measure the complete spatiotemporal intensity I(x,y,t) and phase ϕ(x,y,t) of pulses at a particular z-plane. By experiments, we investigated sub-picosecond chirped pulse beating, pulses from multimode optical fibers, ultrafast lighthouse effect and so on, using STRIPED FISH. We also performed numerical simulations to understand the effects of different spatiotemporal distortions on STRIPED FISH trace. With its improved apparatus, processing algorithm, and display method, STRIPED FISH offers a simple and compact solution to monitor, measure, and display spatiotemporal structures in ultrashort pulses.