APS News

New Optical Devices, Techniques Highlight Laser Science Meeting

3-D reality, a new technique for internal fingerprints, and a fiber-optic probe for detecting precancerous cells were among the highlights at the 2004 Frontiers in Optics/Laser Science XX meeting, the annual meeting of the Optical Society of America, held October 10-14 in Rochester, NY. The Laser Science XX meeting serves as the annual meeting of the APS Division of Laser Science and provides an important forum for the latest work on laser applications and development, spanning a broad range of topics in physics, biology and chemistry.

The conference plenary session featured three visionary speakers and a keynote presentation from Senator Hillary Rodham Clinton (D-NY). Kerry Vahala of Caltech provided a tour of tiny devices for confining and controlling light. Watt Webb of Cornell University discussed recent advances in imaging and studying tiny biomolecular structures using the whole range of the electromagnetic spectrum.

The University of Rochester's Emil Wolf traced optics history from the 1860s to the 21st century to present a new development in which he played a major part: a recently developed unified theory of coherence and polarization, two key properties of light waves. Senator Clinton also spoke, touching on the impact of optics in the state of New York.

Finding a Vein. Finding a vein, necessary for administering intravenous solutions, can often be difficult. A new device, called a Vein Contrast Enhancer (VCE), uses sensitive infrared sensing to find the vein beneath the skin and then also projects the rather spooky vein image back onto the patient's wrist. This makes it appear as if the veins were lying right on top, making it easy for a nurse to make an injection.

An array of light-emitting diodes shines infrared light at the subject. Since red blood cells absorb the light, whereas surrounding tissues scatter it, the veins appear dark. The scattered light passes through some filters and then is captured by a sensitive TV camera, processed by computer, and rendered as a sort of movie at a rate of 30 frames per second. These images can be projected onto the subject through a careful aligning process to register the surface projection with subcutaneous anatomy.

No Cell Left Behind. How can a surgeon be sure that no cancer cells are left behind during surgery? Or what if some cancer patients could skip exploratory surgery and have suspicious areas examined with an endoscope? Irving Bigio of Boston University, and clinical collaborators in London, may have an answer. His team has constructed a fiber-optic probe inserted through an endoscope that will measure via spectroscopy the structural properties of cells in tissue. For example, cancerous cells can be identified by changes in size or density of sub-cellular components like the nuclei. Bigio's research takes the spectroscopic measurements in vivo and collects real-time measurements. Then a surgical biopsy is done. To make it clinically practical, diagnostic algorithms would need to be created to process the information in real time, and larger-scale studies would need to be done to prove efficacy.

An Internal Fingerprint. In the movie Minority Report, the main character has his eyeballs swapped out in order to fool a biometric retina scanner. Robert Rowe of Lumidigm, Inc. has introduced a system for fingerprint identification that is almost as hard to fool. The new sensor uses multiple colors of light to measure the subsurface structure of the finger, sending visible light and very near infrared light into the finger. This new development builds on work that shows that tiny capillaries under the fingerprint also have distinctive patterns, and the blood that the capillaries carry can be easily detected by the light sensor. They've even tested it against fake fingers to ensure that the system can't be spoofed. The system could easily integrate into some of today's fingerprint scanners. The spoof-detection technology should be available in mid-2005.

Detecting Early Signs of Cancer. Patients with chronic diseases that may lead to cancer need a means for monitoring tissue health, without invasive and non-definitive biopsies. Adam Wax of Duke University has developed a way to detect pre-cancerous cells in intact tissues in just one second with a technique called angle-resolved low-coherence interferometry (a/LCI).

To find pre-cancerous cells, the a/LCI device looks beneath the tissue surface and measures cell features with a sensitivity smaller than the wavelength of light.

One of the earliest changes in pre-cancerous cells is that the cell's nucleus enlarges, which changes its light-scattering properties, and this can be seen by a/LCI. The interferometer records the angular distribution of light scattered by a small region of tissue, even beneath the tissue surface where cancer begins. It measures the frequency variations of the light returned and in one fell swoop acquires the entire light-scattering pattern over a wide range of angles, instead of acquiring measurements one by one, which used to take five minutes per measurement. Wax anticipates that the first clinical trials in human subjects with esophageal cancer will begin in about two years.

3-D Reality Without the Real. Conventional 3-D displays force our eyes to do two conflicting things at the same time, for instance, pointing our eyes to look at something that appears to be far away, but having to focus the lenses of our eyes up close. But this unnatural eye pose is tiring and gives people headaches. It's easier and natural for our eyes to focus at the same place that we're pointing them. Brian Schowengerdt at the University of Washington's Human Interface Technology Laboratory has a new 3-D display, called True 3-D, that matches what's most easy on the eyes.

With the True 3-D scanned-light display, light from different objects seems to come from different distances in space. This is made possible by a tiny stretchable mirror made of a thin membrane, just 10 millimeters across, coated with aluminum. The deformable mirror stretches on command to change the focus of each pixel of light as the display projects different objects. Just one tiny mirror can control all the pixels in the display as it scans by changing the focus of that beam very quickly—in this case, twice as fast as the display refreshes. Viewers can converge their eyes and focus their eyes at the same distance—just like when viewing real objects. Also as in real life, no screen is needed to see the objects—the display changes the light's intensity and color, so "a high-resolution full-color picture can be painted right onto the retina," Schowengert said.

Shedding New Light on Embryonic Cell Development. Chi-Kuang Sun of the National Taiwan University presented a new high-resolution optical technique for imaging the embryonic development of living organisms non-invasively in their natural environments.

Demonstrated in the zebrafish, the technique could potentially be applied to following the development of human stem cells. Infrared laser light safely penetrated all the way through the zebrafish embryo and yielded highly detailed images (400-nanometer resolution) of its interior, enough to discern important cell features such as the neural tubes, structures which later develop into the spinal cord, spine, and brain.

Called "harmonic optical microscopy," the technique scans infrared laser light across the living specimen, which then generates light in the second and third harmonics. Detectors capture this "higher harmonic" light to build up images of the specimen. By using light that does not get absorbed by the embryo, Sun could continuously image the embryo for 12 hours without heating it or otherwise damaging its viability.

James Riordon, Ben Stein and Phil Schewe contributed to this article.