Acousto-optically driven lensless single-shot ultrafast optical imaging

Optical design of spectral filtering system in sequentially timed all-optical mapping photography for enhancing temporal resolution

Ultrafast imaging is crucial for understanding phenomena in the femtosecond to nanosecond time domains. Among ultrafast imaging techniques, sequentially timed all-optical mapping photography utilizing spectral filtering enables single-shot acquisition of ultrafast images with high spatial resolution and high quality. However, conventional designs based on Fourier optics struggle to achieve high temporal resolution while maintaining high pixel resolution, because the spatial-spectral dependence in this configuration makes laser wavelengths within each frame broad, resulting in longer exposure times. Here we propose an optical design that minimizes the bandwidth of laser wavelengths within each frame to achieve high temporal resolution by collimating the beam incident on the diffractive optical element. Numerical analysis showed that increasing the magnification of the imaging system before the diffractive optical element sufficiently narrows the bandwidth within each frame compared to the conventional designs. We experimentally demonstrated the effectiveness of the proposed configuration, achieving a bandwidth of 0.9 nm and a wavelength interval of 2.1 nm. These spectral properties enabled imaging with a 1.4 ps frame interval and an exposure time of 0.8 ps, which is 40% of the exposure time in the conventional Fourier configuration with similar setup parameters. Furthermore, the proposed configuration maintained a high pixel resolution of 480 pixels × 480 pixels for each of the five frames and was successfully applied to visualize laser ablation of glass. This article presents a highly spatiotemporally resolved imaging method for the detailed analysis of ultrafast phenomena such as laser ablation, shockwaves, and electric discharges.

Discrete Illumination-Based Compressed Ultrafast Photography for High-Fidelity Dynamic Imaging

Compressed ultrafast photography (CUP) can capture irreversible or difficult-to-repeat dynamic scenes at the imaging speed of more than one billion frames per second, which is obtained by compressive sensing-based image reconstruction from a compressed 2D image through the discretization of detector pixels. However, an excessively high data compression ratio in CUP severely degrades the image reconstruction quality, thereby restricting its ability to observe ultrafast dynamic scenes with complex spatial structures. To address this issue, a discrete illumination-based CUP (DI-CUP) with high fidelity is reported. In DI-CUP, the dynamic scenes are loaded into an ultrashort laser pulse train with controllable sub-pulse number and time interval, thus the data compression ratio, as well as the overlap between adjacent frames, is greatly decreased and flexibly controlled through the discretization of dynamic scenes based on laser pulse train illumination, and high-fidelity image reconstruction can be realized within the same observation time window. Furthermore, the superior performance of DI-CUP is verified by observing femtosecond laser-induced ablation dynamics and plasma channel evolution, which are hardly resolved in the spatial structures using conventional CUP. It is anticipated that DI-CUP will be widely and dependably used in the real-time observations of various ultrafast dynamics.

Sequentially timed all-optical mapping photography with quantitative phase imaging capability

Sequentially timed all-optical mapping photography (STAMP) is considered a powerful tool to observe highly dynamic events; however, its application is significantly hindered by its incapability to acquire quantitative phase images. In this work, by integrating diffraction phase microscopy (DPM) and STAMP, we achieve ultrafast single-shot quantitative phase imaging with a frame rate of up to 3.3 trillion fps. The performance of the system is evaluated using a homemade phase module. Experimental results show that the system can accurately record the propagation of laser filamentation in air. We believe our method will greatly enhance the capability of STAMP to measure highly transparent targets.

Tutorial on compressed ultrafast photography

Significance

Compressed ultrafast photography (CUP) is currently the world's fastest single-shot imaging technique. Through the integration of compressed sensing and streak imaging, CUP can capture a transient event in a single camera exposure with imaging speeds from thousands to trillions of frames per second, at micrometer-level spatial resolutions, and in broad sensing spectral ranges.

Aim

This tutorial aims to provide a comprehensive review of CUP in its fundamental methods, system implementations, biomedical applications, and prospect.

Approach

A step-by-step guideline to CUP's forward model and representative image reconstruction algorithms is presented with sample codes and illustrations in Matlab and Python. Then, CUP's hardware implementation is described with a focus on the representative techniques, advantages, and limitations of the three key components-the spatial encoder, the temporal shearing unit, and the two-dimensional sensor. Furthermore, four representative biomedical applications enabled by CUP are discussed, followed by the prospect of CUP's technical advancement.

Conclusions

CUP has emerged as a state-of-the-art ultrafast imaging technology. Its advanced imaging ability and versatility contribute to unprecedented observations and new applications in biomedicine. CUP holds great promise in improving technical specifications and facilitating the investigation of biomedical processes.

Single-shot optical imaging with spectrum circuit bridging timescales in high-speed photography

Single-shot optical imaging based on ultrashort lasers has revealed nonrepetitive processes in subnanosecond timescales beyond the recording range of conventional high-speed cameras. However, nanosecond photography without sacrificing short exposure time and image quality is still missing because of the gap in recordable timescales between ultrafast optical imaging and high-speed electronic cameras. Here, we demonstrate nanosecond photography and ultrawide time-range high-speed photography using a spectrum circuit that produces interval-tunable pulse trains while keeping short pulse durations. We capture a shock wave propagating through a biological cell with a 1.5-ns frame interval and 44-ps exposure time while suppressing image blur. Furthermore, we observe femtosecond laser processing over multiple timescales (25-ps, 2.0-ns, and 1-ms frame intervals), showing that the plasma generated at the picosecond timescale affects subsequent shock wave formation at the nanosecond timescale. Our technique contributes to accumulating data of various fast processes for analysis and to analyzing multi-timescale phenomena as a series of physical processes.

Fabric computing: Concepts, opportunities, and challenges

With the advent of the Internet of Everything, people can easily interact with their environments immersively. The idea of pervasive computing is becoming a reality, but due to the inconvenience of carrying silicon-based entities and a lack of fine-grained sensing capabilities for human-computer interaction, it is difficult to ensure comfort, esthetics, and privacy in smart spaces. Motivated by the rapid developments in intelligent fabric technology in the post-Moore era, we propose a novel computing approach that creates a paradigm shift driven by fabric computing and advocate a new concept of non-chip sensing in living spaces. We discuss the core notion and benefits of fabric computing, including its implementation, challenges, and future research opportunities.

Simple system for realizing single-shot ultrafast sequential imaging based on spatial multiplexing in-line holography

We present a simple system for realizing single-shot ultrafast sequential imaging based on spatial multiplexing in-line holography. In this system, we propose to combine a specially designed mini-reflector delay-line array with digital in-line holography. The former including a group of adjustable mini-reflectors can easily generate an array of probe sub-pulses that can be controlled independently in the propagation direction and time delays. The object beams formed by the different sub-pulses will propagate and fall on different recording regions of the image sensor to generate a single-shot spatial-multiplexing in-line hologram. The geometry of the digital in-line holography can simplify the complexity of the system and enable complex amplitude imaging. In addition, the time resolution of this system is limited only by the pulse duration, which allows this system to study the dynamic processes with the femtosecond order. In an experiment about the laser-induced air plasma, our proposed system achieves nine frames sequential holographic images with the frame rate of 7.5 trillion frames per second (Tfps).

Lensless ultrafast optical imaging

Lensless single-shot ultrafast optical imaging is realized by integrating an acousto-optic programmable dispersive filter with spectrally filtered sequentially time all-optical mapping photography, which enables independent control of frame rate, frame intensity, and exposure time with a simple system design.