World's fastest camera
relies on an entirely new type of imaging
Ultrafast, light-sensitive video
cameras are needed for observing high-speed events such as shockwaves,
communication between living cells, neural activity, laser surgery
and elements of blood analysis. To catch such elusive moments,
a camera must be able to capture millions or billions of images
continuously with a very high frame rate. Conventional cameras
are simply not up to the task.
Now, researchers at the UCLA Henry
Samueli School of Engineering and Applied Science have developed
a novel, continuously running camera that captures images roughly
a thousand times faster than any existing conventional camera.
In
a paper in the April 30 issue of Nature (currently
available online), UCLA Engineering researchers Keisuke Goda,
Kevin Tsia and team leader Bahram Jalali describe an entirely
new approach to imaging that does not require a traditional
CCD (charge-coupled device) or CMOS (complementary metal-oxide
semiconductor) video camera. Building on more than a decade
of research on photonic time stretch, a technique for capturing
elusive events, the team has demonstrated a camera that captures
images at some 6 million frames per second.
"The most demanding application
for high-speed imaging involves fast events that are very rare,
rogue events or the proverbial needle in the haystack —
in other words, unusual events that carry important information,"
said Jalali, a professor of electrical engineering and principal
investigator of the project.
One of the applications he envisions
for the camera is flow cytometry, a technique used for blood
analysis. Traditional blood analyzers can count cells and extract
information about their size, but they cannot take pictures
of every cell because no camera is fast and sensitive enough
for the job. At the same time, images of cells are needed to
distinguish diseased cells from healthy ones. Today, pictures
are taken manually under a microscope from a very small sample
of blood.
But what if you needed to detect
the presence of very rare cells that, although few in number,
signify the early stages of a disease? Circulating tumor cells
are a perfect example. Typically, there are only a handful of
them among a billion healthy cells; yet these cells are precursors
to metastasis, the spread of cancer that causes about 90 percent
of cancer mortalities.
"The chance that one of these
cells will happen to be on the small sample of blood viewed
under a microscope is negligible," Jalali said. "To
find these rogue cells — needles in the haystack —
you need to analyze billions of cells, the entire haystack.
Ultra-high-speed imaging of cells in flow is a potential solution
for detection of rare abnormal cells."
The new imager operates by capturing
each picture with an ultrashort laser pulse — a flash
of light only a billionth of a second long. It then converts
each pulse to a serial data stream that resembles the data in
a fiber optic network rather than the signal coming out of a
camera. Using a technique known as amplified dispersive Fourier
transform, these laser pulses, each containing an entire picture,
are amplified and simultaneously stretched in time to the point
that they are slow enough to be captured with an electronic
digitizer.
Click
here to see a video of how the camera works
on UCLA's Youtube Channel
The fundamental problem in performing
high-speed imaging, Jalali says, is that the camera becomes
less and less sensitive at higher and higher speeds. It is simple
to see why: At high frame rates, there is less time to collect
photons in each frame before the signal becomes weaker and more
prone to noise. The new imager overcomes this because it is
the first to feature optical image amplification.
"Our serial time-encoded amplified
microscopy (STEAM) technology enables continuous real-time imaging
at a frame rate of more than 6 MHz, a shutter speed of less
than 450 ps and an optical image gain of more than 300 —
the world's fastest continuously running camera, useful for
studying rapid phenomena in physics, chemistry and biology,"
said research co-author Goda, a postdoctoral researcher in the
group.
One such phenomenon the group has
studied with the new camera is laser ablation, an important
technology that is the basis of laser medicine. The camera can
capture laser ablation happening in real time, providing important
clues for understanding the process and optimizing its effectiveness.
"Unlike other high-speed imaging
methods, our approach does not require cooling of the camera
or high-intensity illumination — problems that plague
conventional CCD and CMOS cameras," said Kevin Tsia, a
graduate student in the group and a co-author of the research.
The study was funded by the Defense
Advanced Research Project Agency (DARPA), the U.S. Department
of Defense's central research and development organization.
###
Wileen Wong Kromhout
April 29, 2009
