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Multibeam Lasers Emit in IR

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CAMBRIDGE, Mass., Nov. 30, 2009 – An international team of applied scientists has demonstrated compact, multibeam and multiwavelength lasers emitting in the infrared. Typically, lasers emit a single light beam of a well-defined wavelength; with their multibeam abilities, the new lasers have potential uses in chemical detection, climate monitoring and communications.

The research was led by postdoctoral researcher Nanfang Yu and Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering, both at the Harvard School of Engineering and Applied Sciences (SEAS); Hirofumi Kan, general manager of the Laser Group at Hamamatsu Photonics; and Jérôme Faist, professor at ETH Zürich.

MultibeamLaser.jpg
A computer rendering of one of the prototype multibeam, multifunctional lasers demonstrated by the team. The new laser emits several highly directional beams with the same wavelength near 8 µm, which requires two coherent beams. (Image: Capasso and Yu)

In one of the prototypes demonstrated by the team, the new laser emits several highly directional beams with the same wavelength near 8 µm, a function very useful for interferometry, which requires two coherent beams: a probe beam and a reference beam. The probe beam interacts with a sample and recombines with the reference beam to reveal optical properties of the sample. A second type of laser emits multiple small divergence beams with different wavelengths (9.3 and 10.5 µm) into different directions.

“We have demonstrated devices that can create highly directional laser beams pointing in different directions either at the same or at different wavelengths,” said Capasso. “This could have major implications for parallel high-throughput monitoring of multiple chemicals in the atmosphere or on the ground and be used, for example, for studying hazardous trace gases and aerosols, monitoring greenhouse gases, detecting chemical agents on the battlefield and mapping biomass levels in forests.”

The more versatile laser is a descendant of the quantum cascade laser (QCL), invented and first demonstrated by Capasso, Faist and their collaborators at Bell Labs in 1994. Commercially available QCLs, made by stacking ultrathin atomic layers of semiconductor materials on top of one another, can be custom designed to emit a well-defined infrared wavelength for a specific application or be made to emit simultaneously multiple wavelengths. To achieve multiple beams, the researchers patterned the laser facet with metallic structures that behave as highly directional antennas and then beam the light in different directions.

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“Having multibeam and multiwavelength options will provide unprecedented flexibility. The ability to emit multiple wavelengths is ideal for generating a quantitative map of the concentration of multiple chemicals in the atmosphere,” said Kan. “Profiles of these atmospheric components – as a function of altitude or location – are critically important for environmental monitoring, weather forecasting and climate modeling.”

Though the researchers demonstrated the idea using mid-infrared semiconductor lasers emitting wavelengths in the 8- to 10-µm range, the concept can be generalized to lasers emitting other wavelengths in the near-infrared and terahertz spectrum, or to passive optical components such as optical fibers. For example, nanostructures can be patterned on the facet of optical fibers to help build microendoscopes for in vivo diagnostics, they said.

The findings appeared online in the Oct. 23 issue of Applied Physics Letters and will appear as a Dec. 7 cover story.

The team’s co-authors included graduate students Mikhail A. Kats and Markus Geiser, research associate Christian Pflügl, all from SEAS; and Qi Jie Wang, now an assistant professor at Nanyang Technical University in Singapore; researchers Tadataka Edamura, Shinichi Furuta and Masamichi Yamanishi, all from Hamamatsu Photonics; and researchers Milan Fischer and Andreas Wittmann, both from the Institute of Quantum Electronics, ETH Zürich.

The work was partially supported by Air Force Office of Scientific Research and Harvard’s Center for Nanoscale Systems, a member of the National Nanotechnology Infrastructure Network.

For more information, visit: www.seas.harvard.edu






Published: November 2009
Glossary
beam
1. A bundle of light rays that may be parallel, converging or diverging. 2. A concentrated, unidirectional stream of particles. 3. A concentrated, unidirectional flow of electromagnetic waves.
infrared
Infrared (IR) refers to the region of the electromagnetic spectrum with wavelengths longer than those of visible light, but shorter than those of microwaves. The infrared spectrum spans wavelengths roughly between 700 nanometers (nm) and 1 millimeter (mm). It is divided into three main subcategories: Near-infrared (NIR): Wavelengths from approximately 700 nm to 1.4 micrometers (µm). Near-infrared light is often used in telecommunications, as well as in various imaging and sensing...
nano
An SI prefix meaning one billionth (10-9). Nano can also be used to indicate the study of atoms, molecules and other structures and particles on the nanometer scale. Nano-optics (also referred to as nanophotonics), for example, is the study of how light and light-matter interactions behave on the nanometer scale. See nanophotonics.
nanotechnology
The use of atoms, molecules and molecular-scale structures to enhance existing technology and develop new materials and devices. The goal of this technology is to manipulate atomic and molecular particles to create devices that are thousands of times smaller and faster than those of the current microtechnologies.
optical fiber
Optical fiber is a thin, flexible, transparent strand or filament made of glass or plastic used for transmitting light signals over long distances with minimal loss of signal quality. It serves as a medium for conveying information in the form of light pulses, typically in the realm of telecommunications, networking, and data transmission. The core of an optical fiber is the central region through which light travels. It is surrounded by a cladding layer that has a lower refractive index than...
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
quantum cascade laser
A quantum cascade laser (QCL) is a type of semiconductor laser that operates based on the principles of quantum mechanics. It is a versatile and powerful device used for emitting coherent light in the mid-infrared to terahertz range of the electromagnetic spectrum. Quantum cascade lasers were first proposed by Federico Capasso, Jerome Faist, Deborah Sivco, Carlo Sirtori, Albert Hutchinson, and Alfred Cho in 1994. Key features and principles of quantum cascade lasers: Quantum cascade...
terahertz
Terahertz (THz) refers to a unit of frequency in the electromagnetic spectrum, denoting waves with frequencies between 0.1 and 10 terahertz. One terahertz is equivalent to one trillion hertz, or cycles per second. The terahertz frequency range falls between the microwave and infrared regions of the electromagnetic spectrum. Key points about terahertz include: Frequency range: The terahertz range spans from approximately 0.1 terahertz (100 gigahertz) to 10 terahertz. This corresponds to...
wavelength
Electromagnetic energy is transmitted in the form of a sinusoidal wave. The wavelength is the physical distance covered by one cycle of this wave; it is inversely proportional to frequency.
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