High-speed holographic microscopy for fast-propagating cracks in transparent materials

A compact flexible sub-nanosecond framing photographic system

A novel high-speed multi-frame photographic system is presented in this paper. The system demonstrates exceptional compactness and flexibility, requiring only the introduction of a cavity comprising multiple beam-splitters in the optical path to enable multi-frame imaging of sub-nanosecond events. The number and temporal delay of frames can be easily adjusted by adjusting the distance and angle between beam-splitters. These capabilities are demonstrated by observing the laser ablation process, highlighting the great potential for application in capturing ultrafast time-evolving events such as optical breakdown, the evolution of laser-produced plasmas, and the propagation of shock waves.

Six-pack holographic imaging for dynamic rejection of out-of-focus objects

Six-pack holography is adapted to reject out-of-focus objects in dynamic samples, using a single camera exposure and without any scanning. By illuminating the sample from six different angles in parallel using a low-coherence source, out-of-focus objects are laterally shifted in six different directions when projected onto the focal plane. Then pixel-wise averaging of the six reconstructed images creates a significantly clearer image, with rejection of out-of-focus objects. Dynamic imaging results are shown for swimming microalgae and flowing microbeads, including numerical refocusing by Fresnel propagation. The averaged images reduced the contribution of out-of-focus objects by up to 83% in comparison to standard holograms captured using the same light source, further improving the system sectioning capabilities. Both simulation and experimental results are presented.

Pulsed digital holography system recording ultrafast process of the femtosecond order

We report, for the first time to our knowledge, a pulsed digital microholographic system with spatial angular multiplexing for recording the ultrafast process of the femtosecond order. The optimized design of the two sets of subpulse-train generators in this system makes it possible to implement a digital holographic recording with spatial angular multiplexing of a frame interval of the femtosecond order, while keeping the incident angle of the object beams unchanged. Three pairs of amplitude and phase images from the same view angle digitally reconstructed by the system demonstrated the ultrafast dynamic process of laser-induced ionization of ambient air at a wavelength of 800 nm, with a time resolution of 50 fs and a frame interval of 300 fs.

Holographic recording of fast events on a CCD camera

We report on holographic recording of nanosecond events on a conventional CCD camera. Three frames of an air-discharge event, with resolution of 5.9 ns and frame interval of 12 ns, are recorded in a single CCD frame. Each individual frame is reconstructed by digital filtering of the CCD frame, since successively recorded holograms are centered at different carrier frequencies in the spatial frequency domain.