Researchers have developed an ultra-fast experimental camera that uses an optical diffraction gating mechanism to capture millions of images per second.
Based on off-the-shelf components, the method is less expensive than commercial high-end high-speed cameras. It could be useful in a range of applications from monitoring drug delivery in humans to LiDAR systems for autonomous vehicles, say researchers from Concordia University (Montreal, Québec, Canada), Institute national de la recherche scientifque (Québec City, Québec, Canada) and Meta Platforms (Menlo Park, CA, USA). They published the results of their work in the journal Optica (bit.ly/3GuwLQN).
How Does it Work?
Called diffraction-gated real-time ultra high-speed mapping, or DRUM, photography, the method captures images at a rate of 4.8 million frames per second with a sequence depth of seven images and a temporal resolution of 0.37 µs.
Cameras use a gate, such as a shutter, to control when light hits a sensor. In the DRUM method, the gate is opened and closed in rapid succession before the sensor reads out an image.
To accomplish this technique, the researchers use a digital micromirror device, or DMD, to produce a fast flipping motion that acts as a time gate, extracting sequential frames from the scenes being imaged.
DMDs, which are mass-produced optical components in projectors, are readily available.
Components
The researchers used a 473-nm continuous wave laser from CNI Laser (Changchun, China) as the light source. A CF Achro finite objective lens from Nikon (Tokyo, Japan) collects the light, which then is reflected by a beam splitter (BF250) from Thorlabs (Newton, MA, USA) to form an image on an intermediate image plane.
These results then are processed by another system composed of a stereoscopic objective lens from Olympus (Shinjuku, Japan) and a DMD (AJD-4500), consisting of an array of micromirrors, from Ajile Light Industries (Ottawa, Ontario, Canada).
The diffraction orders, or frames, created from the second process are then relayed by a third imaging system, which is composed of two lenses from Thorlabs, to a CMOS camera (CP70-1HS-M-1900) from Optronis (Kehl, Germany), which records a snapshot.
With DRUM photography, the camera’s exposure is synchronized with the flipping motion of the DMD.
“The key feature of DRUM photography is its ability to spatially separate and temporally gate successive 2D images in the optical domain while satisfying the imaging condition between the object and the sensor. It allows for the sensitive mapping measurement of a single ordinary CMOS sensor by directing these sequential frames onto different areas,” the researchers wrote in the journal article.
Testing the Camera
To demonstrate the utility of the DRUM method, the researchers observed bubbles created with laser pulses in liquid, bubbles in a carbonated drink, and a short laser pulse onto a single-layer cell from an onion.
“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. 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 such as high sensitivity,” concludes Jinyang Liang, assistant professor at the Institut national de la recherche scientifique.
