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October 02, 2008

Imaging and laser related roundup: 25 million barcodes per second and lensless cell counting


1. Building on a series of recent breakthroughs in ultrafast analog-to-digital conversion, UCLA engineers have designed a bar code reader that is nearly a thousand times faster than any device currently in use.

The new imaging technique, developed by researchers at the UCLA Henry Samueli School of Engineering and Applied Science, enables the detection of ultrafast, non-repetitive transient phenomena in real time and can produce one-dimensional bar codes with a frame rate on the order of 25 million frames per second.

Conventional bar code readers use one of two approaches to acquire an image of the bar code. In one, a laser beam is scanned over the code to measure the intensity of the light reflected back by the black-and-white pattern. In such devices, the activity of the mechanical scanner limits the image-acquisition speed to less than 1,000 frames per second. In the second type, a digital camera, such as a CCD- or CMOS- based device, takes a picture of the code, which is then recognized by the computer. The frame rate of these devices is limited to about 1,000 frames per second by the refresh rate of the CCD or CMOS image sensor.

The new technology, dubbed the CWEETS Scanner (chirped wavelength electronic encoded time domain sampling), first maps the one-dimensional bar code image onto the spectrum of an ultrashort laser pulse and then maps that into an amplitude-modulated waveform that is captured with a single optical-to-electrical converter.








Counting shadows: A new cell counter uses the imaging chip from a digital camera to record the “shadows,” or diffraction signatures, from cells in blood and other samples. Simple algorithms allow cells to be identified and counted because each cell type has a unique signature. In this image taken with the cell counter, yeast cells are circled in blue, red blood cells are circled in red, and beads are circled in green. Credit: Aydogan Ozcan

2. Also from UCLA, a lensless imaging system finds and recognizes the shadows of T cells and bacteria.

Clinical tests for identifying and counting normal and bacterial cells in blood and other samples can tell doctors the source of a bacterial infection or help them monitor the immune health of people with HIV. But conventional cell counting is costly and time-consuming. A simple, lensless imaging system being developed by researchers at the University of California, Los Angeles, uses a chip like the one found in a digital camera to count and distinguish different types of cells in blood and drinking water, and simple algorithms to identify and count the cells. The imager could be carried in a device the size of a cell phone and used to monitor water quality and to provide cheap diagnostics in rural and underdeveloped areas.

"What we record is not an image but a diffraction signature," says Aydogan Ozcan, an assistant professor of electrical engineering at UCLA who's developing the cell counter. The blurred, pixellated images created by his cell counter are of such low quality that Ozcan doesn't call the system a microscope. But these images contain just enough information to identify and count cells, which is all that's needed for many clinical


3. Fiber lasers advance with better diode technology. 25% efficient conversion of electricity from the wall into laser power for high power kilowatt level fiber lasers.

Recent developments in high-power fiber-laser technology are closely related to improvements in high-brightness fiber-coupled pump laser diodes. Today it is possible to build kilowatt-level fiber lasers operating at 1 µm, based on standard commercial fiber, components, and 976 nm laser diodes. Advances in eye-safe fiber-laser technology indicate that the same path is likely at 2 µm based on thulium-doped fibers and 790 nm diode technology.

Based on the diode data in the previous section, the current high-brightness 976 nm diodes have an approximate 45% electrical-to-optical (E-O) efficiency making the total amplifier E-O efficiency around 35%. Further improvements are anticipated as the diode material improves.

This pump technology, coupled with the latest advances in highly efficient Tm-doped fibers [Thallium-doped], has allowed eye-safe fiber laser technology to approach 25% wall-plug efficiency and further improvements are likely as diode material continues to mature at these new operating wavelengths.


4. Low power liquid lens: an adjustable-focus lens made of two drops of water could be used in small cameras.

Researchers at Rensselaer Polytechnic Institute, in Troy, NY, are proposing a type of liquid lens--made of only two drops of water--that changes shape when bombarded with sound waves. Using sound requires much less power than previous methods and could, with improvements in resolution, make the lens attractive for use in small surveillance cameras and cell phones.

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