Our conversation with Federico Capasso, laser pioneer and CLEO/IQEC speaker.
Federico Capasso of Harvard University is best known for his co-invention of the quantum cascade laser in 1994 with his colleagues at Bell Laboratories. He began his career as a post-doc at Bell Labs in 1976 and worked his way up to vice president of physical research by 2000. In 2003, he left Bell Labs to join the faculty in the School of Engineering and Applied Sciences at Harvard, where he currently leads a group that studies nanophotonics, metamaterials, quantum electrodynamics and related areas. In 2005, Capasso won the King Faisal International Prize for Science. At that time, he was cited as “one of the most creative and influential physicists in the world.”
What will you cover in your CLEO plenary talk?
I will review the state of the art of quantum cascade lasers (QCLs), from the underlying basic physics through device design and eventually all the interesting applications that have spawned from its invention. The QCL is considered an enabler of mid-infrared photonics, in particular due to its compact size and its ability to cover almost the entire infrared spectrum—from a few microns to hundreds of microns—by tailoring the thickness of its layers.
What is your greatest achievement so far?
The demonstration and invention of the QCL is most important. This research falls into the broad category of nanotechnology and, in particular, the quantum design of manmade structures. Of my more recent work at Harvard, I am particularly proud of our first measurement of the repulsive Casimir force—an elusive force due to quantum fluctuations of the electromagnetic field that could one day be harnessed to achieve quantum levitation and suppress friction in nanomachines.
Can you describe the process that led to the invention of the QCL?
The process was a gradual one. Ideas like this do not occur like a light bulb suddenly turning on. Rather, it was the culmination of a number of innovations that led to the final invention. My collaborator Jerome Faist and I started off knowing that the QCL would have to be based on resonant tunneling, due to some previous significant research that proposed a way to use this phenomenon to emit photons.
The image we had in mind was of an electron tumbling down an energy staircase made of a particular nanostructured material, designed in a certain way. As the electron tumbles down the stairs, it emits a laser photon at each step. The whole idea of this staircase was to find a way to design a structure that would make a new laser using state-of-the-art quantum well materials made by molecular beam epitaxy (MBE). The QCL would not have happened without the 15-year collaboration between Alfred Cho, who pioneered MBE, and me.
Have any of the QCL’s current uses surprised you?
In the early 1990s, this was blue sky research. We had absolutely no clue that this could have had the impact that it is having. Once we developed the QCL at Bell Labs, we gave the lasers away in droves to researchers at other institutions, so they could tell us what the potential applications could be.
It turns out the applications are wide-ranging. For example, chemists found they could use it for ultrasensitive spectroscopy of gases, since they were looking for a broadly and continuously tunable compact laser that could work at room temperature. In addition, scientists have routinely flown QCLs in the atmosphere to detect trace gases that affect climate. The QCL is currently being developed for chemical sensing and trace gas analysis, such as environmental monitoring, combustion diagnostics and homeland security applications, to name a few. In the future, we’ll see it used for breath analysis as a non-invasive, real-time, highly sensitive and selective medical diagnostics technique.
What’s next for photonics research?
It is difficult to predict where technologies developed out of optics research will go because there are economic, social and political factors that affect which technologies will ultimately make it to the market. I see nanophotonics as an area that is extremely rich for applications.
Not long ago, you switched from industry to academia. What prompted the change?
I was at Bell Labs for 27 years. I realized at some point that I couldn’t stay at one place my whole life. The opportunity to work at Harvard is exciting in that it allows me to do broader work in a larger group and to work with bright students—which I find energizing. I do seek out ties with industry because these collaborations provide access to interesting new problems of which one is often not aware in an academic environment. Fewer companies today are doing long-term research, but they still have problems that need to be solved through that research; universities can fill that gap so that everybody wins.
For students studying physics, what area of research has the greatest need for young minds?
I do not think there is one field that is more important for young researchers to enter than any other. There are so many interesting problems to solve without putting a label on the various fields of research. The divisions between fields are crumbling down, with basic and applied research becoming less distinct from one another, and interdisciplinary research across all fields of science becoming more important. It doesn’t matter if a student is an engineer, physicist, biologist or chemist; what we need are bright young minds who can solve important problems in any field.
What inspired you to study physics?
When I was 7 or 8 years old, my father gave me a book about physics written by a famous science writer in the 1950s. After I read that book, I became hooked on physics and never changed my mind about my career path. I don’t think I even had a particular talent in science; I just fell in love with the ideas of physics.
Federico Capasso will be a featured plenary session speaker at CLEO/IQEC 2009 in Baltimore, Md., U.S.A., from May 31 to June 5.
Angela Stark is OSA’s public and government relations specialist.