’Breaking Barriers’ 2007 CLEO/QELS Theme

New optics concepts and phenomena that rely on "classical" optics are recently becoming part of researchers' fundamental tools, said Ben Stein, a senior science writer and editor at the American Institute of Physics who moderated a panel, "New Fundamentals Breaking Scientific Barriers," at a press luncheon held Tuesday at CLEO/QELS.

"The basic framework for optics hasn't changed much since the 20th century, but after the invention of the laser in the 1960s, things really took off in the optics industry," he said.

Among researchers that is breaking those barriers is Thorlabs, which is demonstrating an adaptive scanning optical microscope (ASOM), already on the market, which won the 2007 PhAST/Laser Focus World Innovation Award. Scott Barry, a Thorlabs application engineer, presented research the company has conducted for the past six months that merges many technologies into a single instrument.

The PhAST (Photonic Applications, Systems and Technologies) award was presented at the CLEO/PhAST plenary session on Monday. The PhAST conference runs concurrently with CLEO/QELS.

Mike Duncan, PhAST co-chair, said, "The ASOM is truly a unique innovation in microscopy. Its application will have a significant impact in a variety of areas."

Barry said the current trend toward larger and larger systems made of small and smaller components has created "a real need in microscopy for wide field of view. This technology allows us to sidestep classical design limits and alignment issues."

The ASOM combines classical microscopy principles with state-of-the-art adaptive optic technology to eliminate the traditional trade-off between magnification and field of view. The ASOM system offers an unprecedented 40-mm diameter field of view with consistent resolution of ~1£ gm throughout. A unique optical scanning technique completely eliminates mechanical motion of the object (specimen) during the image capture process, making it significantly faster than translation stage-based approaches.

This optical, rather than mechanical, nature of the scanning process necessitates constant use of the system's scan lens at "off-axis" trajectories, an operating condition that introduces distortion of optical waves reaching the microscope as the scan axis departs from the microscope's optical axis. In a conventional optical design, such a condition would result in visual distortions and blurriness of captured images, thereby reducing the system's capability to resolve images.

The device, which functions much like a dynamic funhouse mirror, Barry said, is made up of tiny microelectromechanical systems (MEMS), allowing it to operate 10 to 100 times faster than current automated microscopes without disturbing the specimen. The instrument can quickly -- in about 1 to 2 seconds -- scan an entire slide and allow a user to zoom in on specific areas of interest. Applications could include medical imaging, e.g., biopsy slides, machine vision and inspection systems, biological research and pharmaceutical investigation, he said.

The technology was invented at the Center for Automation Technologies and Systems (CATS) at Rensselaer by Ben Potsaid, John Wen and Yves Bellouard, with some funding from the National Science Foundation. (See also: Rensselaer Licenses Microscope Technology to Thorlabs)

Imaging Via Hemaglobin

"Catching Cancer's Spread by Watching Hemoglobin" was the topic of Warren S. Warren -- a Duke University professor of chemistry and radiology and director of the Duke Center for Molecular and Biomolecular Imaging -- who is working on an advance that can potentially assist with cancer diagnosis: an optical technique that provides high-resolution, three-dimensional images of blood vessels by taking advantage of the natural light-absorbing properties of hemoglobin, the red-blood-cell molecule that carries oxygen throughout the bloodstream. Clinically, the imaging technique can potentially be used to detect the spread of cancer, particularly melanoma, since angiogenesis -- the growth of new blood vessels from existing ones -- often signals the proliferation of tumors.

"Two-Photon Absorption Imaging of Hemoglobin Presentation Start/End Time" a paper presented at CLEO Tuesday morning by Dan Fu (coauthors: Thomas E. Matthews, Tong Ye, Gunay Yurtsever, Warren S. Warren), discussed how the Princeton/Duke team demonstrated that both oxyhemoglobin and deoxyhemoglobin has sequential two-photon absorption properties that can serve as endogenous contrasts in microvasculature imaging; they can also be differentiated through their different excited state dynamics.

Warren said the imaging technique can eventually be done in a doctors office. It is performed now on an isolation table, but "miniaturization is so dramatic, we could readily imagine something could be built in 1 tp 2 years. Within a year, we could be building devices with which we could start clinical trials. We have proposals to do that in progress."

He added, "The hard part is thinking outside the box. Magnetic resonance imaging (MRI) has become an important imaging method, but for the first 25 years, every radiologist looked at it as a film, instead of on a computer."

He said the most obvious target for the new technique is the imaging of melanin, which makes melanoma cells appear pigmented so biopsies can be performed in situ, with the potential for earlier diagnosis of the disease.

THz at 25 Meters, Shortest Light Pulse

Panelist Alan Lee, a graduate student with the Massachusetts Institute of Technology's Quantum Cascade Terahertz Laser Group, discussed "Real-Time, Transmission-Mode, Terahertz Imaging Over a 25-meter Distance with a 4.9 THz Quantum-Cascade Laser," presented Thursday at CLEO/QELS (Authors: Lee, Qi Qin, Sushil Kumar, Benjamin Williams, and Qing Hu of MIT; and John L. Reno of Sandia National Laboratories.

Terahertz (THz) radiation, or far-infrared light, is potentially very useful for security applications, as it can penetrate clothing and other materials to provide images of concealed weapons, drugs or other objects. However, THz scanners must usually be very close to the objects they are imaging. Lee said doubts have lingered over whether it is possible to use THz waves to image objects that are far away, because water vapor in air absorbs THz radiation so strongly that most of it never reaches the object to be imaged.

The team demonstrated the first real-time THz imaging system that obtains images from 25 meters away. The technique takes advantage of the fact that there are a few "windows," or frequency ranges, of the terahertz spectrum that do not absorb water very strongly. The MIT-Sandia group designed a semiconductor-based device known as a "quantum cascade laser" that delivers light in one of these windows (specifically, around 4.9 THz). They shine this light through a thin target with low water content (for example, a dried seed pod), and a detector on the other side of the sample records an image.

A cryorefrigerator maintains the laser at a temperature of 30 Kelvin, where it produces 17 mWs of power (as opposed to the mWs of power typical of pulsed THz sources) in order to provide enough Thz radiation to obtain a decent image. Increasing the power of the lasers and sensitivity of the detectors can potentially enable imaging of thicker objects or imaging of the reflected light, which would be more practical for security applications. In addition, the development of high-operating-temperature quantum cascade lasers, which operate without the use of cryogenic materials, may also increase the availability of this approach. In the nearer term, this approach may enable sensing of chemical residues or contaminants in the air, Lee said.

"The Shortest Light Pulse Ever" was the topic of Mauro Nisoli, associate physics professor at the Politecnico of Milan and team leader (attosecond science) at the National Laboratory for Ultrafast and Ultraintense Optical Science (ULTRAS CNR-INFM). Researchers in Italy have created the shortest light pulse yet published -- a single isolated burst of extreme-ultraviolet light that lasts for only 130 attoseconds (billionths of a billionth of a second). Shining this ultrashort light pulse on atoms and molecules can reveal new details of their inner workings, providing benefits to fundamental science and potential industrial applications.

MorePhAST Awards

In addition to the award given to Thorlabs, four products received honorable mentions:

A pulse shaper that can automatically measure and compensate phase distortions that broaden femtosecond laser pulses (Biophotonic Solutions)
Kitty Hawk ultrafast coherent optical receiver (Discovery Semiconductors)
The Phzaaler, a dual-mode ultrafast pulse-shaping and ultrafast pulse measurement system that enables the collection and comparison of measurement results using a single instrument (Fastlite)
The first 10-W femtosecond fiber laser (PolarOnyx)

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