Researchers at Washington University in St.Louis have built what they claim is the world's fastest 2D receive-only camera, which is able to capture images at a rate of up to 100 billion frames per second. Using a technique called Compressed Ultrafast Photography (CUP), the researchers have so far taken photographs of a number of properties of light propagation and behavior that are already pushing the dimensional limits of fundamental physics.
Although other cameras in use in physics laboratories have laid claim to higher speeds – the University of Tokyo’s STAMP system at 4.4 trillion FPS, being one notable example – the Washington University model achieves its incredible frame rate without the aid of sequential illumination. That is, in sequential illumination an ultra-short laser pulse is split into a series of discrete separate pulses, each in different spectral bands, which illuminate the target object as successive flashes so that the entire scene may be captured using stroboscopic acquisition.
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In the case of the new CUP system, it is a receive-only device that does not require sequential flashes of light, but rather captures high-speed images more akin to the method used in high-speed photography, where an object with its own luminescence – such as a laser, in this instance – is able to be captured frame-by-frame as it passes the lens and its image is captured.
As a result, the CUP system can capture a range of luminescent objects as a single camera shot that not only captures exceedingly fleeting images, but also provides measurements of their spatial and time co-ordinates. To demonstrate the system’s capabilities, the researchers captured four transitory phenomena of a single laser pulse. Namely: laser pulse reflection, refraction, faster-than light propagation (of what is known as "non-information"), and photon racing in two media.
"For the first time, humans can see light pulses on the fly," said Professor Lihong Wang, the research team leader. "Because this technique advances the imaging frame rate by orders of magnitude, we now enter a new regime to open up new visions. Each new technique, especially one of a quantum leap forward, is always followed a number of new discoveries. It’s our hope that CUP will enable new discoveries in science – ones that we can’t even anticipate yet."
The CUP system is an expansion on existing technology known as a streak camera, an ultrafast detection device that measures the variation in intensity of a measured light pulse over time. However, streak cameras only record in one dimension, so Wang and his team expanded this into two dimensions by configuring new control algorithms and adding some extra components of their own.
To help expand images into a 2D view, the CUP system lens captures photons emitted by the luminescent object being imaged, and then sends them through a tube to a digital micromirror device (DMD). This DMD is only around 15 mm (0.6 in) in diameter and contains about 1 million micromirrors, with each micromirror being just 7 microns square.
The micromirrors are then used to encode the image and reflect the photons to a beam splitter, which then propels them to an especially widened slit on the streak camera. The photons are then transformed into electrons, and sheared by two electrodes to convert time to space. That is, the electrodes apply a varying voltage, so the electrons arrive at dissimilar times and at different vertical positions. Finally, all for the resulting information is then sent to a Charge Coupled Device (CCD) to capture the information and pass it on for analysis.
This entire process takes just 5 nanoseconds, or 5 billionths of a second.
Possible applications for this new imaging technology include the areas of biomedicine, where it can be employed in imaging fluorescent proteins, or astronomy, where the ultrafast and super-high-resolution capture of luminescent objects is particularly important.
"Fluorescence is an important aspect of biological technologies," said Professor Wang. "We can use CUP to image the lifetimes of various fluorophores, including fluorescent proteins, at light speed. Combine CUP imaging with the Hubble Telescope, and we will have both the sharpest spatial resolution of the Hubble and the highest temporal solution with CUP. That combination is bound to discover new science."
The research was published in the journal Nature