Harvard University engineers demonstrate quantum cascade laser n...( Cambridge Mass. October 22 2007 In...)

Cambridge, Mass. October 22, 2007 In a major feat of nanotechnology engineering researchers from Harvard University have demonstrated a laser with a wide-range of potential applications in chemistry, biology and medicine. Called a quantum cascade (QC) laser nanoantenna, the device is capable of resolving the chemical composition of samples, such as the interior of a cell, with unprecedented detail.

Spearheaded by graduate students Nanfang Yu, Ertugrul Cubukcu, and Federico Capasso, Robert L. Wallace Professor of Applied Physics, all of Harvards School of Engineering and Applied Sciences, the findings will be published as a cover feature of the October 22 issue of Applied Physics Letters. The researchers have also filed for U.S. patents covering this new class of photonic devices.

The lasers design consists of two gold rods separated by a nanometer gap (a device known as an optical antenna) built on the facet of a quantum cascade laser, which emits invisible light in the region of the spectrum where most molecules have their tell tale absorption fingerprints. The nanoantenna creates a light spot of nanometric size about fifty to hundred times smaller than the laser wavelength; the spot can be scanned across a specimen to provide chemical images of the surface with superior spatial resolution.

Theres currently a major push to develop powerful tabletop microscopes with spatial resolution much smaller than the wavelength that can provide images of materials, and in particular biological specimens, with chemical information on a nanometric scale, says Federico Capasso.

While infrared microscopes, based on the detection of molecular absorption fingerprints, are commercially available and widely used to map the chemical composition of materials, their spatial resolution is limited by the range of available light sources and optics to well above the wavelength. Likewise the so-called near field infrared microscopes, which rel
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