Mounting an optical antenna atop a QC laser can sharpen its resolution up to 100-times smaller than the wavelength of its light--that is, 70 nanometers for a seven micron laser. Spectral-photonic scanners utilizing this more focused quantum-cascade laser could image the submicron chemical composition of surfaces in real-time--from semiconductors to medical samples. Capasso has applied for U.S. patents on what he claims is a new class of photonic-scanning device, which he invented in collaboration with doctoral candidates Nanfang Yu and Ertugrul Cubukcu.

Capasso's optical antenna consists of two gold rods, 1.2-microns long, with a 100-nanometer gap between them integrated above the QC laser. When set to seven microns, the laser can power a spectral scanner that reveals chemical composition. Ordinarily, a seven-micron laser could only be focused to a spot no smaller than seven microns. But by focusing the laser with the optical antenna, a spot less than 100 nanometers across can be produced, enabling sub-micron resolution in measurements of chemical composition by merely scanning the laser across a sample.

Capasso and his group at Bell Labs invented the quantum cascade laser in 1994--a semiconductor laser that's smaller than bulk-crystal or gas lasers. The QC laser is created by stacking alternating layers of semiconductor materials on top of each other--varying their thickness to tune for specific wavelengths.

In conventional lasers, an electron emits a single photon by jumping from the semiconductor's conduction band to its valence band. But a QC laser arranges its layers to realize from 25 up to 75 quantum wells--each at a progressively lower energy level. When an electric current flows through the QC laser, electrons cascade down the energy staircase, emitting a photon at each step.

QC lasers are being customized for a variety of applications, from spectral scanners for semiconductor metrology, pollution monitoring, chemical sensing and medical diagnostics, to homeland security.