Professor Federico Capasso

Q. Tell us a little bit about your current research activities. A. My research on QCLs centres on develop- ing new broadband sources, and in particular broadband mid-infrared spectrometers on a chip; high power/high power efficiency continuous-wave QCLs, beam engineered QCLs, as well new terahertz sources based on intracavity difference frequency generation. A significant portion of my QCL research is industry driven through collaborations with major industrial players. I also have a fairly large effort in plasmonics and metamaterials where we are exploring both novel pheno­ mena, device applications and new fabrication techniques based on soft lithography and colloidal chemistry. In particular, we have recently shown that by structuring the facet of a terahertz QCL as a metamaterial, the normally highly divergent terahertz radiation can be highly collimated. Finally, we are Federico Capasso is the Robert Wallace putting unreasonable obstacles in the career Professor Federico Capasso investigating optical forces that arise between Professor of Applied Physics in the School of of ambitious and talented young people. So (centre), Dr Nanfang Yu (right) waveguides and other photonic components and graduate student Mikhail Engineering and Applied Sciences at Harvard I decided to spend two years in a telecom Kats (left) in the Capasso in close proximity, as well as quantum University, Cambridge, MA. He is a member government laboratory; I gained experience in Laboratory in the School electrodynamical forces generated by of the US National Academy of Sciences and fibre optics, and then, at the first opportunity, of Engineering and Applied quantum fluctuations of vacuum and matter, Science at Harvard University of the National Academy of Engineering, and I landed in United States at in 1976. such as the . a Fellow of: the American Academy of Arts This was then the ‘Mecca’ of industrial and Sciences; the Institute of Physics (UK); research spanning the whole range from basic Q. Within your research in the terahertz area, of America; the Institute science to applications. I had an exciting what are the key challenges? of Electrical and Electronic Engineers; and career there but when the call came from A. The biggest challenge remains achieving the American Physical Society. He won the Harvard University in 2002 I could not resist, operation at thermoelectric cooler tempera- 2010 Berthold Leibinger Zukunft Prize knowing the wonderful research environment ture, and then at room temperature in both (Future); the 2005 King Faisal International there. It has also been a great change working pulsed and continuous-wave mode. Prize for Science; the 2005 Gold Medal of the with students and teaching. President of for meritorious achievement Q. It has often been said that ‘terahertz is a in science; the 2004 Edison Medal, Institute Q. When did you start working in the solution looking for a problem’ - do you of Electrical and Electronic Engineers terahertz field? agree? (IEEE); and the 2004 Arhur Schawlow Prize A. In the late nineties a new frontier of A. Largely yes: I don’t yet see compelling in Laser Science of the American Physical (QCL) research was applications that can drive new markets. Society. to make a terahertz laser. The top QCL groups then started to push hard in that Q. What do you see as the prospects for Q. What inspired you to become a researcher? direction. I was brilliantly scooped by the team exploiting terahertz techno­logy, and what are A. My dad, when I was six years old, gave led by Alessandro Tredicucci (in Pisa, Italy), the key barriers? What one key thing would me a book entitled Our friend the Atom, by and Edmund Linfield. transform the terahertz field? What are the Heinz Haber, a gifted science writer. I got potential applications that you find the most hooked and though I never showed an early Q. Has the terahertz field developed as you exciting? talent in science, I decided on the spot that I might have expected? What have been the A. These are all connected questions. Until a would be a physicist; that was it: I never had a biggest surprises? compact solid-state laser with excellent doubt that there could be anything more A. To be honest, though a lot of excellent performance, at least operating under thermo- exciting than the thrill of discovery. Yes, the research has been done by many groups, the electric cooling in pulsed and continuous-wave fun part was a key driver. impact of terahertz QCLs has been far less is achieved, I don’t see prospects for real than mid-infrared QCLs. The latter have applications except basically in small niches. Q. How did you get started in your academic far better performance in terms of optical If these barriers can be overcome then security career? power, tunability and broadband operation, applications such as the search for concealed A. After completing my doctorate I decided I and most importantly, can operate continu- weapons and explosives, and other applications did not want to work in academia as in Italy ous-wave and pulsed at room temperature such as materials diagnostics could become politics and bureaucracy was (and still is) with high power. important. doi: 10.1049/el.2010.3356 Electronics Letters Dec. 2010 – Special Supplement: Terahertz Technology S51