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 Harvard's 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 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.
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.
Quantum cascade (QC) lasers were invented and first demonstrated by Capasso and his group at Bell Labs in 1994. These compact millimeter length semiconductor lasers, which are now commercially available, are made by stacking nanometer thick layers of semiconductor materials on top of each other. By varying the thickness of the layers one can select the wavelength of the QC laser across essentially the entire infrared spectrum where molecules absorb, thus custom designing it for a specific application.
In addition by suitable design the wavelength of a particular QCL can be made widely tunable. The range of applications of QC laser based chemical sensors is very broad, including pollution monitoring, chemical sensing, medical diagnostics such as breath analysis, and homeland security.
Source: Harvard University
Related stories:
The brightest, sharpest, fastest X-ray holograms yet
The pinhole camera, a technique known since ancient times, has inspired a futuristic technology for lensless, three-dimensional imaging. Working at both the Advanced Light Source (ALS) at the U.S. Department of Energy's Lawrence Berkeley National Laboratory, and at FLASH, the free-electron laser in Hamburg, Germany, an international group of scientists has produced two of the brightest, sharpest x-ray holograms of microscopic objects ever made, thousands of times more efficiently than previous x-ray-holographic methods.
Nano sculptures in gold
If someone is charged up, the colour of their face might change, but they don't immediately pull off one of their arms, only to reattach it as a third leg. With some molecules, however, the situation is quite different - for example, in a gold cluster with seven atoms. In a charged state, the atoms arrange themselves differently than when they are uncharged.
Scientists demonstrate highly directional semiconductor lasers
Applied scientists at Harvard collaborating with researchers at Hamamatsu Photonics in Hamamatsu City, Japan, have demonstrated, for the first time, highly directional semiconductor lasers with a much smaller beam divergence than conventional ones.
Ultrafast look into atoms and molecules
New record in ultrafast metrology: Physicists at Max-Planck Institute of Quantum Optics and the Ludwig-Maximilians-University Munich are the first to produce light pulses lasting only 80 attoseconds.
Terahertz laser source at room temperature
“There is a growing interest in utilizing terahertz radiation, or T-rays, for a variety of applications,” Mikhail Belkin, a scientist at Harvard University, tells
PhysOrg.com. “The terahertz region is a part of the electromagnetic spectrum that lies between the radio waves and infrared/visible light.”
Bright sparks make gains towards plastic lasers of the future
Imperial researchers have come one step closer to finding the 'holy grail' in the field of plastic semiconductors by demonstrating a class of material that could make electrically-driven plastic laser diodes a reality.
The Photonic Beetle: Nature Builds Diamond-Like Crystals For Future Optical Computers
Researchers have been unable to build an ideal “photonic crystal” to manipulate visible light, impeding the dream of ultrafast optical computers. But now, University of Utah chemists have discovered that nature already has designed photonic crystals with the ideal, diamond-like structure: They are found in the shimmering, iridescent green scales of a beetle from Brazil.
New mid-infrared lasers show doubled efficiency
Researchers at the Center for Quantum Devices at the McCormick School of Engineering at Northwestern University have recently doubled the efficiency of infrared lasers under the U.S. Defense Advanced Research Projects Agency’s Efficient Mid-wave Infrared Lasers (EMIL) program.
