news GOVERNMENT AND SOCIETY humidity. They have a narrow bandwidth, and their emission wavelength is very reproducible. They also generate much higher power than their predecessors (~8 mW vs 10–100 µW). “Now you can dream of doing cheap spectroscopy based on optical sensing because you have the source,” says Faist, who is now at the University of Neuchâtel (Switzerland) and is a co-founder of the company Alpes Lasers, which develops and commercializes QC laser technology. Most applications of QC lasers are for gas sensing. Sharpe and his colleagues at PNNL and the Stevens Institute of Technology are working with Lucent researchers to develop high-resolution chemical vapor methods for noninvasive medical diagnostics and for law enforcement applications. Richard Zare’s group at Stanford University has used QC lasers for cavity ring-down spectroscopy, and the spin-off company Information Diagnostics won a NIST grant to develop the method further. In addition, the Jet Propulsion Laboratory is developing QC laser spectrometers to sample the atmospheres of Mars, Venus, and several planetary satellites. The Geneva, Switzerland-based company Orbisphere has taken an even bigger step and incorporated a QC laser into its commercial photoacoustic spectroscopy instrument for gas analysis. Work in liquid sensing also is beginning. Last year, Faist, Antoine Müller, and colleagues at the Univesity of Neuchâtel and the Swiss Federal Institute of Technology reported large electrical tuning ranges— 40 cm–1 and 20 cm–1—for a QC laser at –10 ˚C and room temperature, respectively (Appl. Phys. Lett. 1999, 75, 1509–1511). This feature is useful for spectroscopy of liquids or solids, which may have wide absorption features. In addition, the Neuchâtel researchers and co-workers at the Vienna University of Technology
(Austria) have used QC lasers for flow injection and observed a 50-fold improvement over results obtained with an FT-IR (Anal. Chem. 2000, 72, in press). Bidirectional lasers. The bidirectional semiconductor laser is expected to follow in the footsteps of its unipolar predecessor and break new ground in differential spectroscopy, which requires two wavelengths. “Before the bidirectional laser, we had worked on two-color lasers,” says Gmachl. “But they emitted two wavelengths at the same time, and then you had the problem of peeling apart those two wavelengths in some way.” This problem disappears with the bidirectional laser because the wavelengths alternate in time, depending on the applied polarity. Bidirectional lasers use exactly the same materials as earlier QC lasers, Gmachl says, but the layers are designed for “double use”. At one polarity, everything is normal—the active region generates photons, and the injector region transports electrons. “[But] if we change the polarity, these two types of regions change their tasks,” she explains. The structures could emit at the same wavelength in both directions, but decoupling them produces two independent lasers in a single device. And because the polarities can be switched very rapidly (in hundreds of picoseconds), the device should be useful for many applications. “In hindsight, it looks very intuitive. You look back and say, ‘What a waste of layer structure!’,” Gmachl says. But the bidirectional laser required a special design that became obvious only after the researchers decided to alternate the wavelengths in time, she explains. To Gmachl, that is precisely the advantage of working with QC lasers. “Once you have the goal in mind,” she says, “quantum cascade lasers, by being designer materials, allow you to go for it.” Elizabeth Zubritsky
National Nanotechnology Initiative In his fiscal year 2001 budget, President Clinton is requesting $227 million to create a new National Nanotechnology Initiative (NNI). The initiative is designed to boost basic research in nanoscale science and engineering, with roughly 70% of the proposed funding earmarked for universities. One goal of NNI is to create centers and networks of excellence that would encourage the shared use of academic facilities. Funding also would be set aside for developing a nanotechnology infrastructure, including instrumentation, modeling, simulation, and user facilities. In addition, studies of the ethical, legal, social, and economic impact of nanotechnology would be supported. If approved, the National Science Foundation would receive an added $217 million; the Department of Defense and the Department of Energy each would receive ~$100 million more; and the National Institutes of Health, NASA, and the Department of Commerce would receive increases of $18–36 million.
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