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SPIE Professional April 2011

Laser Research Advances

More than 50 years after the invention of the laser, laser research continues to make advances in sensing, medical diagnostics, and other areas.

Lasers ID skin cancer

A team at Duke University has developed a promising two-laser microscopy technique that could help doctors better diagnose melanoma, the deadliest form of skin cancer, while potentially saving thousands of lives and millions of dollars in unnecessary biopsies each year.

The tool probes skin cells using two lasers to pump small amounts of energy into a suspicious mole. Scientists analyze the way the energy redistributes in the skin cells to pinpoint the microscopic locations of different skin pigments.

For the first time, scientists have the ability to identify substantial chemical differences between cancerous and healthy skin tissues, says SPIE member Thomas Matthews, a Duke graduate student who helped develop the technique.

Matthews and his collaborators, who include SPIE members Martin Fischer, and Warren S. Warren, director of Duke's Center for Molecular and Biomolecular Imaging, will present an invited paper on "Differentiation of eumelanin and pheomelanin in skin lesions using transient absorption microscopy" at SPIE/OSA European Conferences on Biomedical Optics in May. Their results also appear in the 23 February Science Translational Medicine.

Air laser senses bombs

Princeton University engineers have developed a laser-sensing technology that may allow soldiers to detect hidden bombs from a distance and scientists to better measure airborne environmental pollutants and greenhouse gases.

A practical "air laser" would be a powerful tool for remote measurements of trace amounts of chemicals in the air, determining how many contaminants or explosive vapors are in the air and the identity and location of those contaminants.

Laser Research Team
Research team from Princeton that developed the "air laser" technology includes James Michael (left), a doctoral student, and Arthur Dogariu, a research scholar.
Photo by Frank Wojciechowski

"We are able to send a laser pulse out and get another pulse back from the air itself," says Richard Miles, professor of mechanical and aerospace engineering at Princeton, the research group leader, and co-author of a paper to be presented at SPIE Defense, Security, and Sensing in April. "The returning beam interacts with the molecules in the air and carries their fingerprints."

The new technique uses a UV laser pulse. The returning beam of light is not just a reflection or scattering of the outgoing beam. It is an entirely new laser beam generated by oxygen atoms whose electrons have been excited to high-energy levels.

Miles collaborated on a paper published in the journal Science with three other researchers from Princeton: Arthur Dogariu, lead author on the paper; James Michael, a doctoral student; and SPIE member Marlan Scully, a professor who holds a joint appointment at Texas A&M University.

Miles, Dogariu, and Michael will present their research on remote air lasing for trace detection at the Advanced Environmental, Chemical, and Biological Sensing Technologies conference at SPIE Defense, Security, and Sensing in Orlando 25 April.

Anti-laser made from loss

Yale University scientists have reported the development of an "anti-laser," in which incoming beams of light interfere with one another in such a way as to perfectly cancel each other out.

The device, which team leader A. Douglas Stone calls a coherent perfect absorber (CPA), takes the laser concept in reverse: In a normal laser, the beam is created by feeding light or electricity through a gain medium like gallium arsenide, with reflectors positioned to keep the beams bouncing through. As the light bounces back and forth, the medium adds more photons to the mix and one of the reflectors is partially transparent to let the amplified beam through the laser.

The structure of the anti-laser device is similar except the incoming laser is countered with a beam that's the opposite of itself, and the medium, silicon, is optimized to make the beam experience a loss of coherence rather than a gain. The result is that the two beams dissipate in the medium and the energy is released as heat.

The discovery could pave the way for a number of novel technologies with applications in everything from optical computing to radiology.

Stone and co-authors Wenjie Wan, Yidong Chong, Li Ge, Heeso Noh, and Hui Cao published their findings, "Time-Reversed Lasing and Interferometric Control of Absorption," in the journal Science in February.

Have a question or comment about this article? Write to us at spieprofessional@spie.org.

DOI: 10.1117/2.4201104.12

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