Single-shot nanosecond-resolution multiframe passive imaging by multiplexed structured image capture

Simultaneous imaging of CH*, C2∗, and temperature in flames using a DSLR camera and structured illumination

Measurement of chemical species and temperature mapping in flames is essential to understanding the combustion process. Multiple cameras are conventionally employed for measurement in such scenarios making the experimental setup not only cost-intensive but also challenging. To circumvent this, structured illumination (SI)-based methods are reported for multispecies chemiluminescence (CL) imaging using a single camera. In this paper, we demonstrate four-channel SI-based imaging for simultaneous snapshot C H ∗ and C2∗ CL imaging and two-color pyrometry for temperature profiles in a butane diffusion flame. We demonstrate our approach using individual species and multiple species imaging. Taking the advantage of the axisymmetric nature of the flame, the Abel transform is performed on the line-of-sight averaged images to obtain deconvoluted images. The deconvoluted maps of temperature are compared with the temperature data obtained by using a physical thermocouple probe.

Single-shot ultrafast terahertz photography

Multidimensional imaging of transient events has proven pivotal in unveiling many fundamental mechanisms in physics, chemistry, and biology. In particular, real-time imaging modalities with ultrahigh temporal resolutions are required for capturing ultrashort events on picosecond timescales. Despite recent approaches witnessing a dramatic boost in high-speed photography, current single-shot ultrafast imaging schemes operate only at conventional optical wavelengths, being suitable solely within an optically-transparent framework. Here, leveraging on the unique penetration capability of terahertz radiation, we demonstrate a single-shot ultrafast terahertz photography system that can capture multiple frames of a complex ultrafast scene in non-transparent media with sub-picosecond temporal resolution. By multiplexing an optical probe beam in both the time and spatial-frequency domains, we encode the terahertz-captured three-dimensional dynamics into distinct spatial-frequency regions of a superimposed optical image, which is then computationally decoded and reconstructed. Our approach opens up the investigation of non-repeatable or destructive events that occur in optically-opaque scenarios.

Single-shot imaging with multiple frames through delaying optical images

A single-shot imaging system with multiple frames has been developed, which can record sequential multiple frames by delaying multiple optical images with fiber bundles and then capturing the images with a single intensified camera. The observed optical object is imaged through four lenses onto the end faces of four sets of fiber bundles. These fiber bundles with different lengths can provide different delays for delivering optical images, which determine the inter-frame separation times. The optical images exported from the fiber bundles are captured with a single intensified CMOS camera simultaneously. This imaging system has been applied for investigating the dynamic x-ray spot of the rod-pinch diode via a combination of scintillators, which are used to convert x-ray images to optical images. Four sequential x-ray images in a single shot have been obtained, which show the dynamic development of the rod-pinch x-ray spot. The results experimentally reveal the dynamics of the electrons flow bombarding the rod, which roughly agrees with the theoretical modeling of the rod-pinch diode.

Fast HDR image generation method from a single snapshot image based on frequency division multiplexing technology

Traditional high dynamic range (HDR) image generation algorithms such as multi-exposure fusion need to capture multiple images for algorithm fusion, which is not only slow but also occupies a lot of storage space, which limits the application of multi-exposure fusion technology. In this paper, the frequency division multiplexing method is used to separate the sub-images with different exposure values from a single snapshot image successfully. The resolution of HDR images generated by this method is almost the same as that of the traditional multiple exposure methods, the storage space is greatly reduced and the imaging speed is improved.

Spatial-frequency encoded imaging of multangular and multispectral images

Modern imaging techniques increasingly require signals to be collected from multiple viewpoints and spectral bands to realize multi-dimensional and multi-species detections. For this purpose, multiple cameras are commonly required. Each camera collects signals from one viewpoint or one spectral band, resulting in a considerable experimental cost. Based on frequency modulation, this work proposes an encoded-imaging technique that can record multangular and multispectral images in one acquisition. The signals recorded from different viewpoints and spectral bands are superimposed in the spatial domain, while being separate in the frequency domain. This allows us to extract individual images based on their respective frequency components. In this work, a proof-of-concept experiment was conducted. The high correlation coefficient between the superimposition of the extracted images and a normal superimposed image demonstrates the effectiveness of this technique. In addition, an improved mathematical formulation was proposed to describe the higher spatial-frequency components, which were considered merely to be residual lines in previous studies. The proposed encoded-imaging technique may have potential for multangular and multispectral imaging, which is especially useful for tomographic reconstructions.

Long sequence single-exposure videography using spatially modulated illumination

Frequency recognition algorithm for multiple exposures (FRAME) is a single-exposure imaging technique that can be used for ultrafast videography, achieved through rapid illumination with spatially modulated laser pulses. To date, both the limit in sequence length as well as the relation between sequence length and image quality are unknown for FRAME imaging. Investigating these questions requires a flexible optical arrangement that has the capability of reaching significantly longer image sequences than currently available solutions. In this paper we present a new type of FRAME setup that fulfills this criteria. The setup relies only on (i) a diffractive optical element, (ii) an imaging lens and (iii) a digital micromirror device to generate a modulated pulse train with sequence lengths ranging from 2 to 1024 image frames. To the best of the authors' knowledge, this is the highest number of temporally resolved frames imaged in a single-exposure.

A versatile, low-cost, snapshot multidimensional imaging approach based on structured light

The behaviour and function of dynamic samples can be investigated using optical imaging approaches with high temporal resolution and multidimensional acquisition. Snapshot techniques have been developed in order to meet these demands, however they are often designed to study a specific parameter, such as spectral properties, limiting their applicability. Here we present and demonstrate a frequency recognition algorithm for multiple exposures (FRAME) snapshot imaging approach, which can be reconfigured to capture polarization, temporal, depth-of-focus and spectral information by simply changing the filters used. FRAME is implemented by splitting the emitted light from a sample into four channels, filtering the light and then applying a unique spatial modulation encoding before recombining all the channels. The multiplexed information is collected in a single exposure using a single detector and extracted in post processing of the Fourier transform of the collected image, where each channel image is located in a distinct region of the Fourier domain. The approach allows for individual intensity control in each channel, has easily interchangeable filters and can be used in conjunction with, in principle, all 2D detectors, making it a low cost and versatile snapshot multidimensional imaging technique.

Single-shot ultrafast sequential holographic imaging with high temporal resolution and a large field of view

A compact system for single-shot sequential holographic imaging (SSSHI) with high temporal resolution and a large field of view is proposed. In this system, a specially designed sequence pulse train generator with a group of diffractive gratings inserted is adopted to simultaneously generate the probe pulse train and the reference pulse train required for recording a single-shot spatial frequency division multiplexing hologram. The system successfully overcomes the walk-off effect of the ultrashort pulse laser in SSSHI and, hence, effectively avoids the influence of the short coherence of ultrashort pulses on the spatial resolution (or field of view) of SSSHI; the complexity of the system and the difficulty in the precise synchronous alignment of the probe and the reference pulses also can be greatly reduced. An experimental setup of the system was constructed, and a SSSHI of dynamical air plasmas induced by a femtosecond pulse laser is successfully realized.