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Q&A: A Few Minutes With Willie Padilla

Associate Professor of Physics Willie Padilla (Photo by Lee Pellegrini)

By Ed Hayward | Chronicle Staff

Published: Dec. 1, 2011

Associate Professor of Physics Willie Padilla is at the forefront of research into metamaterials, a relatively new class of materials engineered to produce tailored responses to light. Metamaterials have produced stunning experimental results – bending light backwards with negative refractive index, perfectly absorbing all light and creating space-hiding wave patterns dubbed “invisibility cloaking.” In 2010, President Obama honored Padilla and a select group of his colleagues with a Presidential Early Career Award for Scientists and Engineers. Recently, he spoke with Ed Hayward of the Chronicle.

What led you into the field of physics?

My father steered me and was always urging me to pursue science in high school. I took as many science classes as I could, including physics. Luckily, my father’s ideas and my own were completely compatible and it was a natural fit for me. I was always inquisitive and asking questions and wanted to know how things worked -- not just on a superficial level, but deep down how things really worked. So I constantly asked questions until people would tell me to get lost. Also, my uncle was an engineer at General Atomics in San Diego and I was always asking him lots of technical questions and his ability to answer my questions really impressed me and further fueled my interest in physics.

After earning your doctorate at the University of California San Diego, you were selected for a Director’s Fellowship for post-doctoral study at Los Alamos National Laboratory. How did that experience influence your work?

The Director’s Fellowship allows you not only to do post-doctoral work with Los Alamos scientists, but also gives you the chance to conduct independent research. I took that opportunity to work on what was then the emerging field of metamaterials. At Los Alamos, I pushed the state of the art of metamaterials at terahertz frequencies, which lie between microwaves and infrared rays. There is a great need for devices capable of working in the terahertz regime and I thought metamaterials could make great advances in this area.

What are metamaterials?

Metamaterials are artificial composite materials that are designed and engineered to give them new properties that exceed the performance limits of their actual physical components in order to allow them to produce tailored responses to radiation. These materials – which are created at the nanoscale – have unique geometric shapes and can deliver instructions to manipulate light waves. Metamaterials have exhibited effects such as negative index of refraction, which bends light backwards – a feat not possible with natural materials. Researchers have combined metamaterials with general relativity concepts – also known as transformational optics – to demonstrate the “invisibility cloak” effect, essentially directing light around a space and effectively masking its existence.

What types of advances in metamaterials are you working on in your lab?

We continue to push to create state-of-the-art terahertz metamaterials. I think it’s an area that’s rich in potential applications. We’ve also had another advance that grew out of my work at Los Alamos -- the perfect absorber, which can absorb all of the light that strikes it. We’re working on infrared applications of these perfect absorbers, which could lead to the ability to make high performance infrared cameras for thermal imaging. We are working through a Department of Energy grant to take perfect absorbers and use them as emitters, which could lead to materials capable of absorbing waste heat from industrial processes, converting it to electrons and storing it as energy. There are some devices that have demonstrated these abilities, but they are not commercially feasible. We hope to change that.

Why focus on the terahertz frequency?

If you think about all the technologically advanced devices we have, you realize there are two fundamental ways in which to make devices. There are devices that use electrons, which are at one end of the electromagnetic spectrum, and those that use photons, which are at the other end. Once you try to push these devices into other frequencies, either higher or lower, they don’t work as efficiently. In between them is the terahertz frequency range. The cruel trick of nature is that we want applications in this frequency regime, but we don’t have the fundamental natural materials to make devices to control it. I always thought that metamaterials would be a good alternative to fill this terahertz gap. Since you are building artificial materials, you can design them from the bottom up to try to create the response you want.

There are a number of potential applications for terahertz radiation. It could be used for dermatological imaging to detect skin cancer. That will require a terahertz camera and we’re hoping our work can lead to that. Terahertz could also assist with security screening, since it does not “see” dry materials. So it passes through clothing, but becomes highly reflective when it strikes the skin due to the water content. That reflection would allow you to see hidden items or paraphernalia. But the current technology required for this use is not economically feasible at this point.

What is your prediction for the role metamaterials will play in our lives 20 years from now?

I think that metamaterials will lead to devices that will make our lives better, like any technology should. They will have applications and while I don’t know if they will be world changing, I think they will have a positive impact. It is a burgeoning field with thousands of researchers working in it, so I think over the next two decades we’ll see improved devices that will have real-world applications.

You were awarded a Presidential Early Career Award for Scientists and Engineers last year by President Obama. What was it like to meet the president and the other honorees?

It was better than I could have imagined. We were in a room, lined up and before you knew it he was there. He popped in and started shaking hands and greeting people. He seemed very genuine and he spoke about science and how important it is and how it is a driver of our economy. He argued funding for scientific research should not be cut. It was a great experience and I was very humbled to be in the room with him and so many accomplished scientists.

Hispanics are underrepresented in many scientific fields. How important is it to you to encourage young people of color to pursue scientific study or careers and what does it take to encourage them?

It’s important to tell them it’s possible. I think my own story speaks to that. It is a lot of hard work, but it is well worth it in the end. In my teaching, I am glad to share my passion for science and physics. I try to lead by example and I am always glad to help out students who want to pursue graduate study or careers. For students who express interest, I steer them toward opportunities, such as internships, fellowships and scholarships that are designed to increase the representation of minorities in the sciences. I received a McNair Scholarship as an undergraduate and it was a huge help to me.

People can follow you on Twitter at @metamaterialist. What led you to pick that name?

I wanted to be able to use Twitter because I wanted to be able to identify works I thought were important in the metamaterials field and make them somewhat more accessible to the public. I picked the name because one who works with metamaterials can be considered a metamaterialist.