Researchers at Harvard have demonstrated a new type of technology called the quantum cascade laser nanoantenna, that might be used to design smaller, possibly tabletop, microscopes, capable of visualizations of details on the “nanometric” scale, including the chemical composition of a cell.
The laser’s 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.
“There’s 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 [Professor at Harvard’s School of Engineering and Applied Sciences].
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 rely on an ultra sharp metallic tip scanned across the sample surface at nanometric distances, can provide ultrahigh spatial resolution but applications are so far strongly limited by the use of bulky lasers with very limited tunability and wavelength coverage.
“By combining Quantum Cascade Lasers with optical antenna nanotechnology we have created for the first time an extremely compact device that will enable the realization of new ultrahigh spatial resolution microscopes for chemical imaging on a nanometric scale of a wide range of materials and biological specimens,” says Capasso.