Broadband Laser Sees Infrared

Portable system can identify explosives and toxins

2 min read
Broadband Laser Sees Infrared
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A new laser could lead to fast and easy detection of explosives or toxins and may help NASA explore other planets.

The broadband quantum cascade laser can cover a vast swath of wavelengths in the infrared, making quick work of detecting chemical signatures. It’s also tiny and portable and works at room temperature, so it can replace bulky, complex lasers that are used for IR spectroscopy but that aren’t easy to carry out in the field.

“With one diode I can have access to any wavelength I want from 6 to 10 [micrometers],” says Manijeh Razeghi, director of the Center for Quantum Devices at Northwestern University. “We can have simultaneously different wavelengths to get fingerprints for different molecules.”

The laser consists of six separate stages, made with alternating layers of aluminum-indium-arsenide and gallium-indium-arsenide. The first stage produces higher-energy photons, with wavelengths in the 6-µm range. Those pass into the next stage, with some of them stimulating photons in the 7-µm range that have somewhat lower energy, and some of them passing through. The process continues through the stages to at the end the laser emits wavelengths from 5.9 to 10.9 µm. The trick, Razeghi says, lies in carefully designing the laser so that, though their wavelengths vary, all the photons emerge with the same power. She and her team describe the work in a recent paper in the journal Optics Express.

That region of the infrared spectrum is where many molecules have their natural resonant frequencies; it’s easy to identify a particular molecule by seeing what wavelength of light it interacts with. Razeghi says that because her laser produces spectrally narrow lines of laser light over such a wide range, it can pick out all sorts of substances that might be of interest. For instance, it might be used to test for small traces of explosives on cars as they drive by government buildings. The work was funded in part by the Department of Homeland Security and the Naval Air Systems command because of its potential security uses. NASA, which could use the system to identify, say, the constituents of Martian soil, also helped fund the research.

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3D-Stacked CMOS Takes Moore’s Law to New Heights

When transistors can’t get any smaller, the only direction is up

10 min read
An image of stacked squares with yellow flat bars through them.
Emily Cooper

Perhaps the most far-reaching technological achievement over the last 50 years has been the steady march toward ever smaller transistors, fitting them more tightly together, and reducing their power consumption. And yet, ever since the two of us started our careers at Intel more than 20 years ago, we’ve been hearing the alarms that the descent into the infinitesimal was about to end. Yet year after year, brilliant new innovations continue to propel the semiconductor industry further.

Along this journey, we engineers had to change the transistor’s architecture as we continued to scale down area and power consumption while boosting performance. The “planar” transistor designs that took us through the last half of the 20th century gave way to 3D fin-shaped devices by the first half of the 2010s. Now, these too have an end date in sight, with a new gate-all-around (GAA) structure rolling into production soon. But we have to look even further ahead because our ability to scale down even this new transistor architecture, which we call RibbonFET, has its limits.

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