By coherently superimposing two chirped vortex pulses with frequency differences and conjugate topological charges, a tunable ultrafast rotating optical field is generated. The interfering device is an asymmetric Michelson interferometer. There are three parameters to regulate the ultrafast rotating optical field: the topological charge difference ∆l; the chirp constant C; the optical path difference of the two interference pulses Δt. The experiment obtained the dynamic image of the rotating optical field by the nonlinear sampling ultrafast imaging, the rotational angular velocity measured in the experiment is 2.368 Trad/s, which are in good agreement with the theoretical calculations. Two nonlinear imaging mechanisms, sum-frequency generation (SFG) and optical parametric amplification (OPA), are applied for ultrafast nonlinear sampling. The results show that at the same rotational angular velocity of the rotating optical field, the image quality of OPA imaging is better than that of SFG imaging. These rotation optical fields at Trad/s level have important potential applications in particle acceleration, vortex THz wave generation, laser fine machine, etc.
We report a framing imaging based on noncollinear optical parametric amplification (NCOPA), named FINCOPA, which applies NCOPA for the first time to single-shot ultrafast optical imaging. In an experiment targeting a laser-induced air plasma grating, FINCOPA achieved 50 fs-resolved optical imaging with a spatial resolution of ∼83 lp / mm and an effective frame rate of 10 trillion frames per second (Tfps). It has also successfully visualized an ultrafast rotating optical field with an effective frame rate of 15 Tfps. FINCOPA has simultaneously a femtosecond-level temporal resolution and frame interval and a micrometer-level spatial resolution. Combining outstanding spatial and temporal resolutions with an ultrahigh frame rate, FINCOPA will contribute to high-spatiotemporal resolution observations of ultrafast transient events, such as atomic or molecular dynamics in photonic materials, plasma physics, and laser inertial-confinement fusion.
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