Mar 8 2019
A novel imaging technique recently developed by researchers is capable of capturing images at speeds of around 1.5 million frames per second (fps) utilizing traditional imaging sensors usually restricted to 100 fps.
The COSUP system uses a traditional camera together with a galvanometer scanner and a digital micromirror device to achieve high-speed imaging. (Image credit: Xianglei Liu and Jinyang Liang, Institut National de la Recherche Scientifique)
This breakthrough technology could enable capturing ultra-fast events for applications like slow-motion scenes in films or biomedical research.
At the Institut National de la Recherche Scientifique (INRS) in Canada, scientists elucidated their latest technique, known as compressed optical-streaking ultra-high-speed photography, or COSUP for short, in The Optical Society (OSA) journal, Optics Letters. To demonstrate the power of COSUP, they used this technology for capturing the transmission of one laser pulse that has a width of just 10 ms.
COSUP has a wide range of potential applications because it can be integrated into many imaging instruments from microscopes to telescopes. Using different CCD and CMOS cameras with COSUP also allows the method to be used for a wide range of wavelengths and for acquiring various optical characteristics such as polarization.
Jinyang Liang, Study Corresponding Author and Assistant Professor, Institut National de la Recherche Scientifique.
According to the researchers, the novel COSUP system may also benefit sports videography and the movie industry, where high-speed cameras are utilized for capturing rapid and detailed movements for playback in slow motion. The team is also exploring the option to reduce the size of the system so that high-quality slow-motion video capture can be performed through a smartphone.
Faster imaging
While present-day cameras are extremely sensitive and can be employed with a broad range of wavelengths, their speed is normally less due to the imaging sensor. Similarly, dedicated high-speed cameras are known to have limiting trade-offs, for example, one-dimensional imaging, recording just a few frames at high speeds, a costly and bulky setup, or low resolution.
The scientists created the COSUP system to overcome these difficulties by integrating a computational method known as compressed sensing with an imaging technique referred to as optical streak imaging.
COSUP has specifications similar to existing high-speed cameras with an imaging speed that is tunable from tens of thousands of frames per second to 1.5 million frames per second. We used off-the-shelf components to create a very economical system.
Jinyang Liang, Study Corresponding Author and Assistant Professor, Institut National de la Recherche Scientifique.
To carry out the COSUP method, compressed sensing is applied so that each temporal frame of a scene is spatially encoded with a digital micromirror device (DMD). Through this process, the capture time of each frame is labeled similar to an exclusive barcode. A scanner is subsequently employed to carry out temporal shearing, producing an optical streak image—in other words, a linear image from which a light’s temporal properties can be figured out—that is recorded with a conventional camera in one shot.
Even though the streak image contains a mixture of 2D space and time information, we can separate the data using reconstruction because of the unique labels attached to each temporal frame. This gives COSUP a 2D imaging field of view that can record hundreds of frames in each movie at 1.5 million frames per second and a resolution of 500 × 1000 pixels.
Xianglei Liu, Study Lead Author and Doctoral Student, Institut National de la Recherche Scientifique.
Capturing a single laser pulse
To demonstrate COSUP, the investigators imaged a couple of short-lived events through a CMOS camera. In the initial experiment, four laser pulses were fired, each having a pulse width of 300 ms through a mask containing the letters USAF. Applying COSUP with an imaging speed of 60,000 fps, the team successfully recorded this event with 240 frames. When the researchers increased the imaging speed to 1.5 million fps, it allowed them to record a single 10-microsecond laser pulse that transmitted via the USAF mask.
In the next experiment, the scientists detected the location of a fast-moving ball pattern. By utilizing COSUP at an imaging speed of 140,000 fps, they were able to record the shape and the spatial position of the ball pattern over time. In addition, they determined the ball’s centroid in every temporal frame and evaluated it against the known location, which revealed that COSUP may precisely detect the position of the ball.
The team is now planning to utilize a COSUP system to determine the phosphorescence lifetimes of each nanoparticle, which can possibly be used for producing an optical nanothermometer that would support photodynamic therapy—a light-based medical treatment.
The researchers are also working on applying COSUP to enhance the imaging of neurons’ membrane voltage, which can help in finding out the cellular mechanisms fundamental to brain functions. However, such an imaging is rather difficult because the process cannot be repeated and is fleeting, and also only a minimal light is produced by the indicators used. “Using COSUP with highly sensitive cameras such as an electron-multiplying CCD would enable the real-time, fast imaging required for this application,” Liang said.
The investigators are also exploring ways to miniaturize the bench-top system so that it can be used outside and can ultimately be integrated into smartphones. In this regard, they have started an industrial partnership with Axis Photonique to further improve COSUP as a commercial product.