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INRS camera catches sight of transient events

20 Sep 2023

New approach to time-gating lowers cost of imaging for biological samples or lidar.

A project at Quebec's INRS research center has developed a camera platform that could allow cheaper ultrafast imaging for multiple applications by using off-the-shelf components.

Reported in Optica, the new device is intended to addresses some current constraints in high-speed imaging, including parallax errors and potential damage from pulsed illumination.

"Our camera uses a completely new method to achieve high-speed imaging," said Jinyang Liang from INRS.

"It has an imaging speed and spatial resolution similar to commercial high-speed cameras, but uses off-the-shelf components that would likely cost less than a tenth of today’s ultrafast cameras which can start at close to $100,000."

The breakthrough has been named diffraction-gated real-time ultrahigh-speed mapping (DRUM) photography, and uses optical diffraction as the mechanism for controlling the camera's gating. Liang's Laboratory of Applied Computational Imaging (LACI) realized that rapidly changing the tilt angle of a suitable diffraction grating could generate several replicas of the incident light traveling in different directions.

This effect can effectively be used to gate out individual frames at different time points in an imaging operation, with the selected frames then synchronized with camera exposure to form an ulrafast movie. Turning this idea into a working camera required a multidisciplinary team that brought together expertise in areas such as physical optics, ultrahigh-speed imaging and MEMS design.

"Luckily it is possible to accomplish this type of swept diffraction gate using a digital micromirror device (DMD), a common optical component in projectors, used here in an unconventional way," said Liang. "DMDs are mass-produced and require no mechanical movement to produce the diffraction gate, making the system cost-efficient and stable."

Benefits for any CCD or CMOS camera

INRS built a platform in which an off-the-shelf DMD was employed to create the gated illumination, effectively time-gated at the sub-microsecond level according to the project's published paper.

The team used this as the basis for a DRUM camera with a sequence depth of seven frames, capturing seven frames in each short movie. After characterizing the system’s spatial and temporal resolutions the researchers used it to record cavitation dynamics in distilled water, and laser ablation of onion cells as a model of biological imaging.

In the water experiment, DRUM time-lapse images showed the evolution of a plasma channel and the development of a bubble in response to a pulsed laser. Images of the onion cells revealed details of the anisotropic damage caused by the laser, arising from small-scale rapid variations in the plasma created at the surface.

The next steps could include improvements to the imaging speed and sequence depth, along with ways to capture color information and to apply the same imaging principles to other applications such as lidar. Clinical use in nano-surgery or laser-based cleaning applications could also follow.

"In the long term, I believe that DRUM photography will contribute to advances in biomedicine and automation-enabling technologies such as lidar, where faster imaging would allow more accurate sensing of hazards," said Liang. "However, the paradigm of DRUM photography is quite generic. In theory it can be used with any CCD and CMOS cameras without degrading their other advantages."

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