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Federico Capasso is the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow at Harvard University, which he joined in 2003 after a 26-year career at Bell Labs where he rose from postdoc to Vice President of Physical Research. He holds a doctorate in Physics from the University of Rome, Italy (1973) and an honorary doctorate in Electronic Engineering from the University of Bologna (2003).
Capasso’s research has cut across several disciplines, bridging basic and applied physics and engineering. These include photonics, laser physics and nonlinear optics, electronics, nanotechnology, mesoscopic physics, and most recently MEMS applied to basic studies of quantum electrodynamics and its applications to nanomechanics. A unifying theme of his research has been the quantum design and study of artificial materials, nanostructures and new devices with man-made electronic and optical properties, an approach that Capasso pioneered and dubbed bandstructure engineering. These structures were grown by thin-film deposition techniques such as Molecular Beam Epitaxy (MBE), pioneered by Al Cho. An excellent example of this research is his invention and first demonstration in 1994 with Jerome Faist, Al Cho and other collaborators at Bell Laboratories of the Quantum Cascade (QC) laser, a fundamentally new light source whose emission wavelength can be designed to cover the entire spectrum from the mid-infrared to the THz region by tailoring the active region layer thickness. QC lasers are now commercially available and have wide ranging applications to molecular spectroscopy, chemical sensing and trace gas analysis (such as atmospheric chemistry, combustion diagnostics, breath analyzers in medicine, pollution monitoring and industrial process control, homeland security) and optical wireless.
Among Capasso’s other important contributions to photonics one should mention multilayer low-noise avalanche photodiodes with artificially enhanced ratio of ionization coefficients and the concept of the solid-state photomultiplier, new photoconductors based on the different tunneling rates of electrons and holes (effective mass filtering) and the demonstration of a new class of giant optical nonlinearities in the mid-infrared, associated with intraband transitions, that have found applications in the modelocking of QC lasers.
In recent years Capasso’s photonics research has branched off to new microlasers based on concepts of chaos and on photonic crystals. His group and Douglas Stone’s at Yale demonstrated deformed (noncircular) whispering gallery microlasers, capable of supporting chaotic rays, which led to a major enhancement of their optical power through the use of “bow-tie” modes. This year Capasso’s group and Oskar Paynter’s groups at Caltech demonstrated the first electrically pumped photonic crystal semiconductor microlaser.
Capasso’s contributions to high-speed electronic devices such as heterostructure transistors and related investigations of electronic transport have also had a major impact. In the early eighties he and his collaborators initiated a new line of research on graded bandgap semiconductors which led them to the direct demonstration that “quasi electric fields” in these materials, a concept pioneered by Nobel Prize winner Herbert Kroemer, can impart electron velocities in excess of 2x107 cm/s, and to the first realization of Kroemer’s graded-gap base transistor concept. This device, in its Silicon Germanium implementation, is now commercial and has found many applications in electronics such as lightwave communication systems.
Capasso then moved on to the investigation of resonant tunneling (RT) in heterostructures and to its exploitation in novel devices. He proposed and first demonstrated RT bipolar transistors, pioneering their use in a new class of circuits with greatly reduced number of components per function. This opened up a new direction of research in quantum devices and related circuit architectures, which continues to be actively pursued world-wide and broadly applied to materials ranging from semiconductors to carbon nanotubes and other molecular structures.
Capasso’s current research activity also focuses on the investigation of quantum electrodynamical phenomena such as the Casimir effect, i.e. the attractive force between uncharged metallic surfaces, which is the manifestation of quantum mechanical vacuum fluctuations, and its dependence on the boundary conditions of the electromagnetic fields. The goal is to tailor vacuum fluctuations and to investigate nanomechanical devices based on the Casimir effect. For this new line of research Capasso is using MEMS technology and has demonstrated new actuators and nonlinear oscillators based on the Casimir effect, which have been widely cited.
He is the author of over 300 articles and coeditor of six volumes. He holds over 45 US patents. Capasso has been widely honored for his work. He is a member of the National Academy of Sciences, the National Academy of Engineering, the American Academy of Arts and Sciences and an Honorary Member of The Franklin Institute. His awards include the American Physical Society Arthur Schawlow Prize for Laser Science, the Wetherill Medal of the Franklin Institute, the Optical Society of America Wood Prize, the Rank Prize in Optoelectronics (UK), the IEEE David Sarnoff Award in Electronics, the IEEE LEOS W. Streifer Award, the Duddell Medal of the Institute of Physics (UK), the Materials Research Society Medal, the Willis Lamb Medal for Laser Physics and Quantum Optics, the “Vinci of Excellence” Prize (France), the Welker Memorial Medal (Germany), the International Symposium on Compound Semiconductor Award, the New York Academy of Sciences Award, the Newcomb Cleveland Prize of AAAS, the NASA Group Achievement Award, the Bell Labs Distinguished Member of Technical Staff and the Bell Labs Fellow Award. He is a Fellow of IEEE, the American Physical Society, the Optical Society of America, SPIE and the American Association for the Advancement of Science.

“ I am very grateful for these honors (the IEEE Edison Medal and the American Physical Society Schawlow Prize in Laser Science). I was fortunate to join Bell Labs at the dawn of a new Golden Age in materials science and solid-state physics, made possible by the advent of Molecular Beam Epitaxy. MBE enabled the synthesis of semiconductor “designer” materials in which the electrical and optical properties can be tailored at will for new device applications and for the observation of new physics. When I realized this tremendous potential shortly after coming to Bell Labs in the early eighties, I all of a sudden felt like a kid in the candy store! Almost anything is possible, I thought, the possibilities are limitless! I can have fun for the rest of my life! And indeed the impact of heterostructure materials on science and technology has been remarkable, ranging form basic physics discoveries like the fractional quantum Hall effect and an extremely rich variety of new quantum phenomena to a host of useful devices that are widely used in fields such as communications. I am deeply grateful to Bell Labs for its fantastic interdisciplinary research atmosphere and the many great colleagues, in particular Al Cho, inventor of MBE, with whom I have had the privilege to collaborate for so many years and sharing so many scientific adventures.”

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