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.
The propagation characteristics of the circular Airy beam (CAB) modified with low-pass filtering is investigated in details in this paper. Based on a modification of the angular spectrum of CAB, we get a new kind of CAB constructed with low frequency spectrum, which is called “LCAB” for short. A suitable low-pass filter is introduced to cut off the high frequency angular spectrum and maintain the low frequency domain mainly affecting the front light rings of CAB. Two apodization parameters are employed to optimize the low-pass filtering, which influence the propagation characteristic of the LCAB. Fortunately, the abruptly autofocusing property, the most important property of CAB, is still maintained in LCAB. What is more, the initial ring number and the focal spot length can be controlled by adjusting the two apodization parameters. If the two apodization parameters are appropriately chosen, one can form an elegant optical needle which plays an important role in optical manipulations. The numerical results show that the less front light rings are, the longer the optical needle is. It should be noted that the width of the optical needle will increase as long as the length increases, and lead to the decline of the maximum intensity of the optical needle.
We demonstrated a single-shot quasi-on-axis digital holography which is capable of simultaneously capturing two-step phase-shifting interferences. A dual-channel interferometer was employed to monitor the Gouy phase-shifting between two orthogonal polarized references which was introduced by two confocal lenses. A new algorithm was derived for reconstruction the complex field of the object’s wavefront according to the feature of Gouy phase-shifting. Simulation was carried out and recover software was also made. The proposed approach can also be applied to single-shot quasi-onaxis digital holography for real time measurement.
KEYWORDS: Digital holography, Holograms, High speed photography, Charge-coupled devices, Fourier transforms, Holography, Digital recording, 3D image reconstruction, Optical filters, Diffraction
In this paper, the characteristics of Fraunhofer digital holography are investigated. With Fraunhofer digital holography,
we could simplify the calculational and reconstructed process. Moreover, the spectrum of the hologram did not contain
the original images and the limitation of recording frame caused by the size of objects was reduced. The number of
recording frame could be increased, especially for the objects of concentrative spectrum. Thus, with Fraunhofer digital
holography, it could not only simplify the process of reconstruction and calculation, but also improve the framing
capability in high-speed photography.
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