Laureate
Prof. Dr. Federico Capasso, Harvard University, Cambridge, USA
Subject
"Quantum Cascade Lasers"
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| Prof. Dr. Federico Capasso |
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| | Quantum cascade lasers are the first to emit laser light in a large region of the invisible light spectrum, with wavelengths from 3 to 300 micrometers. This results in enormous commercial and scientific opportunities. Quantum Cascade Lasers (QCL) cover the region of wavelengths known as mid-infrared where most molecules have their telltale absorption fingerprints. |
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QCLs are applied in local sensing of trace gases in tiny concentrations – from parts per billion to parts per trillion in volume – as well as in remote sensing of chemicals. Some examples are detection of greenhouse gases, pollution monitoring, breath analysis and combustion diagnostics. Other implementations include freespace communication and high-power security and military applications.
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Federico Capasso, in collaboration with Jerome Faist, Deborah Sivco, Carlo Sirtori, Albert Hutchinson and Alfred Y. Cho, first demonstrated the QCL at Bell Labs in 1994 and played a crucial role in its invention, in many subsequent scientific and technological innovations and in commercialization from its inception to the present day. | |
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| Federico Capasso with his students. Any wall is a white board. |
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First as Department Head and then Vice President of Physical Research at Bell Labs, he promoted the technology transfer and licensing of QCL patents to startups and established companies. He has been Robert Wallace Professor of Applied Physics at the School of Engineering and Applied Sciences at Harvard University in Boston, USA, since 2003.
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| The Capasso group at Harvard does intensive research on new concepts. |
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| | Conventional semiconductor lasers generate light depending on the so-called bandgap that depends on the material. To change the color, it is necessary to find a new material, which requires hard work. It is also difficult to generate very long wavelengths; good materials are available only for wavelengths from 0.3 to 3 micrometers. The properties of the light generated by QCLs depend on the design. They are made of materials widely used commercially, but are the ultimate in nanotechnology. The energy levels determining the emitted wavelength of a QCL can be quantum mechanically tailored by adjusting the thickness of the nanometer scale layers of the composed material. The name derives from the path of electrons that move from one quantum well to another, dropping down energy levels like a cascaded waterfall. On its way through the active region an electron emits a photon at each “drop”, making this type of laser highly efficient. |
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| The tiny quantum cascade laser can hardly be recognized in the center of the picture. |
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| | The Capasso group at Harvard does extensive research and development on the design and application of QCLs. One example is a spectrometer on the chip based on an array of 32 QCLs, fabricated monolithically on the same chip. Each individual laser is designed to emit at a different wavelength that can be tuned in a small range so that it can cover the entire region between the emission wavelengths of its neighbors. |
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| The single device can be used to target all the molecular absorption lines in the range of 8.73 to 9.43 micrometers for sensing. Other fields of work include terahertz generation through difference frequency generation in QCLs, growth of high-power QCLs, high-temperature operation as well as optical mode and far-field manipulations. |
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