Diving Into the Unknown: An Interview with Andrei Faraon

This fall, Andrei Faraon (BS '04) returned to his alma mater to take a position as an assistant professor of applied physics and materials science. Faraon, originally from Falticeni, Romania, came to the United States in 2001 to study at Caltech and earned his BS in physics in 2004, then moved to Stanford University, where he received a master's degree in electrical engineering and a PhD in applied physics. Faraon recently answered some questions about his work and returning to Caltech. 

First of all, how does it feel to be back at Caltech?

It feels great—something like a homecoming.

What is the focus of your research?

I build devices that are based on the fundamentals of light–matter interaction. What we're trying to do is manipulate single quantum systems in solids—systems like single atoms or single quantum dots—using light. Light is great for this purpose because it allows us to address these systems without destroying their fragile quantum states, and because it can easily interconnect quantum systems over large distances.

This work has applications in quantum and classical information technologies, and also for the development of sensors with very high spatial resolution and very high sensitivity. These sensors are used to probe other quantum systems and also have applications in biotechnology.

Does this have anything to do with the development of quantum computers?

The quantum computer is something of a Holy Grail, but down the road there is hope that other applications, like quantum repeaters that could enable very secure communications, will come out of these new technologies. In general, the field is just trying to get an understanding of how to better control and manipulate quantum systems in order to develop devices based on these quantum concepts.

What has been your most recent development in this line of work?

In my postdoctoral work, I was able to combine some impurities in diamond, called nitrogen vacancy centers, with optical structures known as nanoscale optical resonators. Nitrogen vacancy centers are defects in the atomic lattice that makes up diamond in which nitrogen atoms have basically replaced carbon atoms. They are interesting because they have very good quantum-coherence properties—meaning that you can actually store information in the quantum state of the impurities and keep it preserved for a relatively long time. These impurities can be used for the sensing of electromagnetic fields with high resolution, or to store and process quantum information. By combining the impurities with optical structures we are actually able to better control and modify their properties.

In general, light interacts weakly with these impurities. By embedding the nitrogen-vacancy centers in resonators, we can create a stronger interaction between them and the light field. The resonators can be further integrated in an on-chip optical network. Since the impurities are coupled to the resonators, we actually interconnect multiple nitrogen-vacancy centers on a chip, thus creating a quantum network that forms the basis of future devices for quantum information processing.

What do you find most exciting about your research?

It is really at the forefront of experimental research and it allows me to really dive into the unknown. I love the fact that we often discover unexpected things and that there is also great potential that this work will result in revolutionary technologies.

What brought you back to Caltech?

Caltech provides the best environment in which to do my research in terms of facilities, the quality of students, and the faculty that I can interact with. Caltech has a very strong effort both in photonics, which is my field of study, and also in quantum information. I think that the people are actually the greatest resource that Caltech has. 

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Caltech Mourns the Passing of David G. Goodwin

1957–2012

David G. Goodwin, professor of mechanical engineering and applied physics, emeritus, passed away at his home in Pasadena on Sunday, November 11, after a five-year battle with brain cancer and a struggle with Parkinson's disease that began in 1998. He was 55 years old. Born on October 15, 1957, Goodwin grew up in Rancho Cordova, a suburb of Sacramento, near the Aerojet plant where his father worked as an engineer. He came to Caltech in 1988 as an assistant professor of mechanical engineering, was promoted to associate professor of mechanical engineering and applied physics in 1993 and professor in 2000, and retired in 2011.

Goodwin was best known for developing ways to grow thin films of high-purity diamond. Diamond films—transparent, scratch-resistant, and efficient dissipaters of the heat generated by high-powered computer chips—are now routinely used to protect electronic and optical components, and diamond-coated drill bits can be found at any hardware store.

But the diamond work was just one facet of Goodwin's research. According to longtime collaborator David Boyd, once a postdoc of Goodwin's and now a Caltech staff member, "Dave's real passion was modeling. He felt that he never fully understood something unless he could model it. He had a keen insight into how things work. He would proffer an oftentimes very simple explanation that captured the essential physics, and was able to see how that applied in engineering terms. It's really unusual for an engineer to know that much physics, or a physicist to have that much engineering."

The Mideast oil crises of Goodwin's teenage years sparked a lifelong interest in energy issues, and much of his work revolved around the intricacies of combustion. He fluently translated the complex interplay of heat flow and atomic behavior within swirling mixtures of turbulent gases into detailed mathematical models that accurately predicted how real-world, industrial-scale chemical processors would operate.

After earning his BS in engineering from Harvey Mudd College in 1979, Goodwin joined the Stanford University High Temperature Gasdynamics Laboratory, which was working on an ultraefficient method for generating electricity by burning coal at very high temperatures to create an electrically charged plasma. The process proved too expensive to be practical, but the mastery Goodwin acquired of chemical kinetics—the mathematical descriptions of how reactions proceed—set the course of his career. He earned his MS and PhD in 1980 and 1986 respectively, both in mechanical engineering.

Goodwin arrived at Caltech amid an explosion of interest in growing diamond coatings via chemical vapor deposition. The process is high-tech, but the basic idea is simple. Playing a methane flame over an object deposits carbon atoms on its surface, and under the right conditions these atoms will organize themselves into a sheen of high-purity diamond instead of the usual smudge of soot. "People had found a process that worked," says Boyd, "but really did not know how or why it did." Goodwin's models explained it all, and the set of papers he published beginning in 1990 "really turned artificial diamond into an engineering material," says Harry Atwater, the Hughes Professor and professor of applied physics and materials science, and director of the Resnick Sustainability Institute.

But far beyond that, "Dave was one of these people whose impact you measure by the codes he wrote for others to use," Atwater says. Goodwin began writing code in earnest in the 1990s, when he led the Virtual Integrated Prototyping project for the Defense Advanced Research Projects Agency. This sprawling endeavor, on which Atwater was a collaborator, created a set of simulations that began at the atomic level and went up to encompass an entire chemical reactor in order to figure out how to grow superconducting metal oxides and other thin films with demanding atomic arrangements. Atwater and Goodwin then built the reactor, which is still in use at Caltech and whose design has been widely copied.

Along the way, Goodwin wrote an extensive overhaul of CHEMKIN (for "chemical kinetics"), a collection of programs that had been developed at Sandia National Laboratories in the 1970s and had quickly gone into worldwide use. He then wrote—from scratch—his own software toolkit for modeling basic thermodynamics and chemical kinetics, which he dubbed Cantera. Breaking with the usual practice of creating a convoluted descriptor to yield a clever acronym, Cantera doesn't stand for anything, says Professor of Mechanical Engineering Tim Colonius. "He just wanted to give it a nice soothing, relaxing name, like pharmaceutical companies do. That was typical of his sense of humor." The open-source code is available pro bono and has been downloaded 120,000 times since 2004, according to Sandia's Harry Moffat, one of Cantera's current developers and the manager of the website. Says Moffat, "We have ventured into areas that CHEMKIN cannot go, including liquid-solid interactions and electrochemical applications such as batteries."

Goodwin also found time to court Frances Teng, an obstetrician-gynecologist at nearby Huntington Hospital, whose own parents had gotten married while postdocs at Caltech in the 1960s. Dave and Frances were married at the Athenaeum, Caltech's faculty club, in April 1993.

Goodwin eventually returned to the energy issues that had motivated him to become an engineer in the first place. "He really pushed us to start teaching some energy-related courses in the early 2000s," says Vice Provost Melany Hunt, the Kenan Professor of Mechanical Engineering, and the executive officer for mechanical engineering at the time. This led to ME 122, Sustainable Energy Engineering, which Goodwin inaugurated in 2008. ME 122 lives on as the centerpiece of the Energy Science and Technology option, now renumbered EST/EE/ME 109 and renamed Energy: Supply and Demand.

During that time Goodwin also collaborated on three major fuel-cell projects with Sossina Haile, professor of materials science and chemical engineering, in which he modeled the processes by which fuel molecules reacted with oxygen ions to produce electricity. "Dave was looking at it from a computational perspective, and we were looking at it from an experimental perspective," says Haile. "He pulled together all that we know from fundamental physics and chemistry to say, 'This is how the fuel cell works, and this is how to configure it so that it will actually deliver the power that you want.' Most people do a lot of parameter fitting and approximations, but he treated the problem in a very physics-based, solid way."

Goodwin was as active in the greater life of the Institute as he was in his lab. He served on the faculty board from 1996 to 1999 and from 2001 to 2005, the last two years as faculty chair. During that time, he successfully lobbied to extend the timetable for granting junior faculty tenure in cases of childbirth or adoption, Hunt says. "Dave was always concerned about diversity issues. He would say, 'Are there women coming in? Are there minority students coming in? We should make sure that we are doing things to ensure that we have a diverse group coming in to Caltech.'" Hunt recalls that when two young women wanted to take a class that wasn't offered that year, "Dave met with them in his office three times a week. He wanted to be helpful. He just felt a responsibility to do it."

"The thing that was remarkable about David Goodwin," says Haile, "was that when he was diagnosed with this rare form of cancer for which there is no rhyme or reason, he said, 'I'm so glad that I lived my life in a healthy way and that I didn't do anything that caused this,' not 'I can't believe I lived my life in such a healthy way, and it's so unfair that I got struck by this.' It was stunning. He had an incredibly optimistic view."

"Dave made you happy whenever you ran into him," says Kaushik Bhattacharya, the Howell N. Tyson, Sr., Professor of Mechanics and professor of materials science, and executive officer for mechanical and civil engineering. "You could go into his office and have a wonderful conversation about any topic in the world. He had an easy smile and a wicked sense of humor."

Goodwin's honors include five years as a National Science Foundation Presidential Young Investigator and two NASA Certificates of Recognition for his diamond-film work. He was a member of the Electrochemical Society, the American Chemical Society, the Combustion Institute, the American Physical Society, the American Society of Mechanical Engineers, and the Materials Research Society. He wrote or coauthored more than 60 papers.

In his spare time, Goodwin was an accomplished guitarist, a skilled woodworker who made several pieces of furniture for the family's Craftsman house, and a prolific painter in oils.

Goodwin is survived by his parents, George and Verma Goodwin, of Cameron Park, California; his sisters, Ellen Goodwin Levy of Sacramento and Jennifer Goodwin Smith of Elk Grove; his wife, Frances Teng; and his children, Tim, 18, and Erica, 15.

A memorial service will be held on January 12, 2013, at 1:00 p.m. at the Caltech Athenaeum, and an annual speakership in mechanical engineering is being established in his honor; contributions to the David Goodwin Memorial Lectureship can be made here

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Julia Greer Receives NASA Research Grant and Early Career Awards

Julia Greer is going to need to find space in her office for all of the awards, medals, and grant acceptance letters she has been receiving lately.

While celebrating her recent Breakthrough Award from Popular Mechanics magazine, Greer—a Caltech assistant professor of materials science and mechanics—received notice from NASA that she is among a select group of 10 recipients of the agency's inaugural Space Technology Research Opportunities Early Career Faculty grants.

Greer also recently learned that she has received the 2013 Early Career Faculty Fellow award from the Minerals, Metals & Materials Society (TMS) and the Young Investigator's Medal from the Society of Engineering Science (SES).

NASA's Space Technology Research Opportunities (STRO) program was established to identify and develop technologies that advance the agency's space-exploration priorities. For future space missions, NASA needs spacecraft and equipment to be made of strong, light, and durable materials. Through the STRO Early Career Faculty program, Greer's materials-science laboratory at Caltech—which recently helped develop the world's lightest solid material, a lattice composed of tiny, metallic tubes with a density of just 0.9 milligrams per cubic centimeter—will have access to as much as $200,000 per year for three years to develop structures made of lightweight, radiation- and damage-tolerant materials.

"In addition to being proud at having been chosen by NASA for this grant, I speak for my whole lab group when I say we are excited to be working to create the next generation of materials to be used in space exploration," says Greer.

"I am also very pleased to have been recognized by TMS as an early career fellow and the SES as a young investigator medal winner," Greer adds. "It is nice to see that the innovations that are happening here at Caltech are getting recognition from the broader community of materials scientists."

According to TMS, the Early Career Faculty Award recognizes assistant professors for accomplishments that have advanced their academic institutions and that broaden the technological profile of TMS. Formal presentation of Greer's TMS early career award will take place at the 142nd TMS annual meeting in San Antonio, Texas, on March 5.

The SES Young Investigator Medal is awarded each year to researchers within 10 years of earning their doctoral degree and is given for work that has made a significant impact on their field within engineering science. The medal comes with a $1,000 prize and an invitation to give an address at the annual meeting of the SES.

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Progress for Paraplegics

Caltech investigators expand project to restore functions to people with spinal-cord injuries

In May 2011, a new therapy created in part by Caltech engineers enabled a paraplegic man to stand and move his legs voluntarily. Now those same researchers are working on a way to automate their system, which provides epidural electrical stimulation to the lower spinal cord. Their goal is for the system to soon be made available to rehab clinics—and thousands of patients—worldwide.

That first patient—former athlete Rob Summers, who had been completely paralyzed below the chest following a 2006 accident—performed remarkably well with the electromechanical system. Although it wasn't initially part of the testing protocol established by the Food and Drug Administration, the FDA allowed Summers to take the entire system with him when he left the Frazier Rehab Institute in Louisville—where his postsurgical physical therapy was done—provided he returns every three months for a checkup.

Joel Burdick, the Richard L. and Dorothy M. Hayman Professor of Mechanical Engineering and Bioengineering at Caltech, and Yu-Chong Tai, a Caltech professor of electrical engineering and mechanical engineering, helped create the therapy, which involves the use of a sheetlike array of electrodes that stimulate Summers' neurons and thus activate the circuits in his lower spinal cord that control standing and stepping. The approach has subsequently been successfully tested on a second paraplegic, and therapists are about to finish testing a third subject, who has shown positive results.

But Tai and Burdick want to keep the technology, as well as the subjects, moving forward. To that end, Tai is developing new versions of the electrode array currently approved for human implantation; these will improve patients' stepping motions, among other advances, and they will be easier to implant. Burdick is also working on a way to let a computer control the pattern of electrical stimulation applied to the spinal cord.

"We need to go further," Burdick says. "And for that, we need new technology."

Because spinal-cord injuries vary from patient to patient, deploying the system has required constant individualized adjustments by clinicians and researchers at the Frazier Institute, a leading center for spinal-cord rehabilitation. "Right now there are 16 electrodes in the array, and for each individual electrode, we send a pulse, which can be varied for amplitude and frequency to cause a response in the patient," Burdick says. Using the current method, he notes, "it takes substantial effort to test all the variables to find the optimum setting for a patient for each of the different functions we want to activate."

The team of investigators, which also includes researchers from UCLA and the University of Louisville, has until now used intelligent guesswork to determine which stimuli might work best. But soon, using a new algorithm developed by Burdick, they will be able to rely on a computer to determine the optimum stimulation levels, based on the patient's response to previous stimuli. This would allow patients to go home after the extensive rehab process with a system that could be continually adjusted by computer—saving Summers and the other patients many of those inconvenient trips back to Louisville. Doctors and technicians could monitor patients' progress remotely.

In addition to providing the subjects with continued benefits from the use of the device, there are other practical reasons for wanting to automate the system. An automated system would be easier to share with other hospitals and clinics around the world, Burdick says, and without a need for intensive training, it could lower the cost.

The FDA has approved testing the system in five spinal-cord injury patients, including the three already enrolled in the trial; Burdick is planning to test the new computerized version in the fourth patient, as well as in Rob Summers during 2013. Once the investigators have completed testing on all five patients, Burdick says, the team will spend time analyzing the data before deciding how to improve the system and expand its use.

The strategy is not a cure for paraplegics, but a tool that can be used to help improve the quality of their health, Burdick says. The technology could also complement stem-cell therapies or other methods that biologists are working on to repair or circumvent the damage to nervous systems that results from spinal-cord injury.

"There's not going to be one silver bullet for treating spinal-cord injuries," Burdick says. "We think that our technique will play a role in the rehabilitation of spinal-cord injury patients, but a more permanent cure will likely come from biological solutions."

Even with the limitations of the current system, Burdick says, the results have exceeded his expectations.

"All three subjects stood up within 48 hours of turning on the array," Burdick says. "This shows that the first patient wasn't a fluke, and that many aspects of the process are repeatable." In some ways, the second and third patients are performing even better than Summers, though it will be some time before the team can fully analyze those results. "We were expecting variations because of the distinct differences in the patients' injuries. Rob gave us a starting point, and now we've learned how to tune the array for each patient and to make adjustments as each patient changes over time.

"I do this work because I love it," Burdick says. "When you work with these people and get to know them and see how they are improving, it's personally inspiring."

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Reconsidering the Global Thermostat

Caltech researcher and colleagues show outcome of geoengineering can be tunable

PASADENA, Calif.—From making clouds whiter and injecting aerosols into the stratosphere, to building enormous sunshades in space, people have floated many ideas about how the planet's climate could be manipulated to counteract the effects of global warming—a concept known as geoengineering. Many of the ideas involve deflecting incoming sunlight before it has a chance to further warm the earth. Because this could affect areas of the planet inequitably, geoengineering has often raised an ethical question: Whose hand would control the global thermostat?

Now a team of researchers from the California Institute of Technology (Caltech), Harvard University, and the Carnegie Institution says there doesn't have to be just a single global control. Using computer modeling, they have shown that varying the amount of sunlight deflected away from the earth by season and by region can significantly improve the parity of the situation. The results appear in an advance online publication of the journal Nature Climate Change.

Previous geoengineering studies have typically assumed uniform deflection of sunlight everywhere on the planet. But the pattern of temperature and precipitation effects that would result from such efforts would never compensate perfectly for the complex pattern of changes that have resulted from global warming. Some areas would end up better off than others, and the climate effects are complex. For example, as the planet warms, the poles are heating up more than the tropics. However, in models where sunlight is deflected uniformly, when enough sunlight is redirected to compensate for this polar warming, the tropics end up colder than they were before man-made activities pumped excess carbon dioxide into the atmosphere.

In the new study, the researchers worked with a climate model of relatively coarse resolution. Rather than selecting one geoengineering strategy, they mimicked the desired effect of many projects by simply "turning down the sun"—decreasing the amount of sunlight reaching the planet. Instead of turning down the sun uniformly, they tailored when and where they reduced incoming sunlight, looking at 15 different combinations. In one, for example, they turned down the sun between January and March while also turning it down more at the poles than at the tropics.

"That essentially gives us 15 knobs that we can tune in order to try to minimize effects at the worst-off regions on the planet," says Doug MacMartin, a senior research associate at Caltech and lead author of the new paper. "In our model, we were able to reduce the residual climate changes (after geoengineering) in the worst-off regions by about 30 percent relative to what could be achieved using a uniform reduction in sunlight."

The group also found that by varying where and when sunlight was reduced, they needed to turn down the sun just 70 percent as much as they would in uniform reflectance to get a similar result. "Based on this work, it's at least plausible that there are ways that you could implement a geoengineering solution that would have less severe consequences, such as a reduced impact on ozone," MacMartin says.

The researchers also used the tuning approach to focus on recovering Arctic sea ice. In their model, it took five times less solar reduction than in the uniform reflectance models to recover the Arctic sea ice to the extent typical of pre-Industrial years.

"These results indicate that varying geoengineering efforts by region and over different periods of time could potentially improve the effectiveness of solar geoengineering and reduce climate impacts in at-risk areas," says Ken Caldeira of the Carnegie Institution. "For example, these approaches may be able to reverse long-term changes in the Arctic sea ice."

The group acknowledges that geoengineering ideas are untested and could come with serious consequences, such as making the skies whiter and depleting the ozone layer, not to mention the unintended consequences that tend to arise when dealing with such a complicated system as the planet. They also say that the best solution would be to reduce greenhouse gas emissions. "I'm approaching it as an engineering problem," MacMartin says. "I'm interested in whether we can come up with a better way of doing the geoengineering that minimizes the negative consequences."  

In addition to MacMartin and Caldeira, David Keith of Harvard University and Ben Kravitz, formerly of the Carnegie Institution but now at the DOE's Pacific Northwest National Lab, are also coauthors on the paper, "Management of trade-offs in geoengineering through optimal choice of non-uniform radiative forcing."

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Engineering with Impact

Watson Lecture Preview

Guruswami (Ravi) Ravichandran is an expert on breakups—of ceramics and metals, not relationships. The John E. Goode, Jr., Professor of Aerospace and professor of mechanical engineering and the director of the Graduate Aerospace Laboratories at Caltech, Ravichandran will talk about his work at the leading edge of impact mechanics on Wednesday, October 24, at 8:00 p.m. in Caltech's Beckman Auditorium. Admission is free.

 

Q: What do you do?

A: I study the dynamic behavior of materials. How they deform on impact. How they break up, how they absorb energy and disperse momentum. We subject materials to millions of atmospheres of pressure by shooting projectiles at them, or dropping weights on them, or jabbing them with a bar like a medieval battering ram. You cannot simulate the pressure at the core of the earth, for example, in a normal laboratory. But impact provides a means for creating those conditions, and lets you explore properties of these materials at these extreme conditions.

 

Q: Why is this cool?

A: It is cool because we look at things that you cannot ordinarily look at—not only extremes of temperature and pressure, but time. We have very high-speed optical and thermal infrared cameras that can go up to one hundred million frames per second. That's one frame every 10 nanoseconds, and it lets us visualize phenomena that you normally won't be able to see. We can watch a crack tear through a metal plate in real time, for example, and we can map the shear stresses and temperature fields across the plate as it stretches before giving way.

We are motivated by the big questions. Where did we come from? The extinction of the dinosaurs, how did that occur? And what's our relationship to that period of the earth's history? But we also explore real-life problems, such as how to build protective structures such as armor. If you think of the crash-worthiness of a car, how do you make a better cage to strengthen the passenger compartment?

And we can even create new materials. A few years back, for example, we made some titanium / silicon carbide composites that could not have been made otherwise. They're more ductile than usual, which could be a useful property for aerospace applications.

 

Q: How did you get into this line of work?

A: When I started graduate school at Brown I was already working on impact-related problems. I enjoyed them, so I've kept up with the thing ever since. It just happened to fall into place. But I did always wonder about those Road Runner cartoons—you see a rock or something break apart after an impact, and you think, "Are those crack patterns for real?"

 

Named for the late Caltech professor Earnest C. Watson, who founded the series in 1922, the Watson Lectures present Caltech and JPL researchers describing their work to the public. Many past Watson Lectures are available online at Caltech's iTunes U site.

 

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Developing the Next Generation of Microsensors

Caltech researchers engineer microscale optical accelerometer

PASADENA, Calif.—Imagine navigating through a grocery store with your cell phone. As you turn down the bread aisle, ads and coupons for hot dog buns and English muffins pop up on your screen. The electronics industry would like to make such personal navigators a reality, but, to do so, they need the next generation of microsensors.

Thanks to an ultrasensitive accelerometer—a type of motion detector—developed by researchers at the California Institute of Technology (Caltech) and the University of Rochester, this new class of microsensors is a step closer to reality. Beyond consumer electronics, such sensors could help with oil and gas exploration deep within the earth, could improve the stabilization systems of fighter jets, and could even be used in some biomedical applications where more traditional sensors cannot operate.

Caltech professor of applied physics Oskar Painter and his team describe the new device and its capabilities in an advance online publication of the journal Nature Photonics.

Rather than using an electrical circuit to gauge movements, their accelerometer uses laser light. And despite the device's tiny size, it is an extremely sensitive probe of motion. Thanks to its low mass, it can also operate at a large range of frequencies, meaning that it is sensitive to motions that occur in tens of microseconds, thousands of times faster than the motions that the most sensitive sensors used today can detect.

"The new engineered structures we made show that optical sensors of very high performance are possible, and one can miniaturize them and integrate them so that they could one day be commercialized," says Painter, who is also codirector of Caltech's Kavli Nanoscience Institute.

Although the average person may not notice them, microchip accelerometers are quite common in our daily lives. They are used in vehicle airbag deployment systems, in navigation systems, and in conjunction with other types of sensors in cameras and cell phones. They have successfully moved into commercial use because they can be made very small and at low cost.

Accelerometers work by using a sensitive displacement detector to measure the motion of a flexibly mounted mass, called a proof mass. Most commonly, that detector is an electrical circuit. But because laser light is one of the most sensitive ways to measure position, there has been interest in making such a device with an optical readout. For example, projects such as the Laser Interferometer Gravitational-Wave Observatory (LIGO) rely on optical interferometers, which use laser light reflecting off mirrors separated by kilometers of distance to sensitively measure relative motion of the end mirrors. Lasers can have very little intrinsic noise—meaning that their intensity fluctuates little—and are typically limited by the quantum properties of light itself, so they make it much easier to detect very small movements.

People have tried, with limited success, to make miniature versions of these large-scale interferometers. One stumbling block for miniaturization has been that, in general, the larger the proof mass, the larger the resulting motion when the sensor is accelerated. So it is typically easier to detect accelerations with larger sensors. Also, when dealing with light rather than electrons—as in optical accelerometers—it is a challenge to integrate all the components (the lasers, detectors, and interferometer) into a micropackage.

"What our work really shows is that we can take a silicon microchip and scale this concept of a large-scale optical interferometer all the way down to the nanoscale," Painter says. "The key is this little optical cavity we engineered to read out the motion."

The optical cavity is only about 20 microns (millionths of a meter) long, a single micron wide, and a few tenths of a micron thick. It consists of two silicon nanobeams, situated like the two sides of a zipper, with one side attached to the proof mass. When laser light enters the system, the nanobeams act like a "light pipe," guiding the light into an area where it bounces back and forth between holes in the nanobeams. When the tethered proof mass moves, it changes the gap between the two nanobeams, resulting in a change in the intensity of the laser light being reflected out of the system. The reflected laser signal is in fact tremendously sensitive to the motion of the proof mass, with displacements as small as a few femtometers (roughly the diameter of a proton) being probed on the timescale of a second.

It turns out that because the cavity and proof mass are so small, the light bouncing back and forth in the system pushes the proof mass—and in a special way: when the proof mass moves away, the light helps push it further, and when the proof mass moves closer, the light pulls it in. In short, the laser light softens and damps the proof mass's motion.

"Most sensors are completely limited by thermal noise, or mechanical vibrations—they jiggle around at room temperature, and applied accelerations get lost in that noise," Painter says. "In our device, the light applies a force that tends to reduce the thermal motion, cooling the system." This cooling—down to a temperature of three kelvins (about –270°C) in the current devices—increases the range of accelerations that the device can measure, making it capable of measuring both extremely small and extremely large accelerations.

"We made a very sensitive sensor that, at the same time, can also measure very large accelerations, which is valuable in many applications," Painter says.

The team envisions its optical accelerometers becoming integrated with lasers and detectors in silicon microchips. Microelectronics companies have been working for the past 10 or 15 years to try to integrate lasers and optics into their silicon microelectronics. Painter says that a lot of engineering work still needs to be done to make this happen, but adds that "because of the technological advancements that have been made by these companies, it looks like one can actually start making microversions of these very sensitive optical interferometers."

"Professor Painter's research in this area nicely illustrates how the Engineering and Applied Science faculty at Caltech are working at the edges of fundamental science to invent the technologies of the future," says Ares Rosakis, chair of Caltech's Division of Engineering and Applied Science.  "It is very exciting to envision the ways this research might transform the microelectronics industry and our daily lives."

The lead authors on the paper, titled "A high-resolution microchip optomechanical accelerometer," have all worked in Painter's lab. Alexander Krause and Tim Blasius are currently graduate students at Caltech, while Martin Winger is a former postdoctoral scholar who now works for a sensor company called Sensirion in Zurich, Switzerland. This work was performed in collaboration with Qiang Lin, a former postdoctoral scholar of the Painter group, who now leads his own research group at the University of Rochester. The work is supported by the Defense Advanced Research Projects Administration QuASaR program, the National Science Foundation Graduate Research Fellowship Program, and Intellectual Ventures.

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How I Spent My Summer Vacation

A SURF Video Diary

Last summer, Caltech junior Julie Jester worked on a project that might one day partially counteract blindness caused by a deteriorating retina. Her job: to help Assistant Professor of Electrical Engineering Azita Emami and her graduate students create the communications link between a tiny camera and a novel wireless neural stimulator that can be surgically inserted into the eye.

Now in its 34th year, Caltech's Summer Undergraduate Research Fellowships (SURF) program has paired nearly 7,000 students with real-world, hands-on projects in the labs of Caltech faculty and JPL staff.

 

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A "Gifted" Professor

A Group of Caltech Alumni Come Together to Create a Professorial Chair to Honor Their Mentor, Frank Marble

Gifted teacher. Inspired researcher. Knowledgeable adviser. Personal friend. These are a few of the ways in which professor emeritus Frank Marble's former students describe him.

Not too surprisingly, these sentiments also capture some of the many reasons why 20 of Marble's former PhD and graduate student advisees have joined together to honor and thank their mentor by creating an endowed professorship in his and his wife's names. They have also seeded the initial funds for a graduate fellowship in the Marbles' honor.

The Frank and Ora Lee Marble Endowed Professorship will benefit a faculty member in the Division of Engineering and Applied Science. The $3 million professorship was made possible with a lead gift from alumnus Laurence B. Zung (MS '63, PhD '67) and his wife, Coralie, as well as accompanying gifts from other Marble advisees, and a $1 million match from the Gordon and Betty Moore Matching Program. Another $177,000 has also been collectively pledged to begin the establishment of what will be the Frank and Ora Lee Marble Graduate Fellowship.

"I wanted to do something so that the Marbles could both witness our appreciation and participate in it," says Zung. "The things I learned from him have benefited me throughout my life and my career. He trained me to learn how to learn and to learn how to think."

Marble, the Richard L. and Dorothy M. Hayman Professor of Mechanical Engineering and Professor of Jet Propulsion, Emeritus, advised more than three dozen PhD students during his tenure of more than 40 years at Caltech (from 1948 to 1989), all the while making major fundamental, theoretical, and experimental contributions to the fields of internal aerodynamics, combustion, and propulsion—especially with respect to gas turbines and rockets. Marble is a member of both the National Academy of Engineering and the National Academy of Science, and a recipient of the Daniel Guggenheim Medal.

Ann Karagozian and Frank MarbleCALTECH ALUMNA ANN KARAGOZIAN RECONNECTS WITH HER FORMER MENTOR, FRANK MARBLE, AT A RECENT CALTECH EVENT CELEBRATING A GIFT MADE IN HIS HONOR.
Credit: Bob Paz

"It was a privilege to learn from Dr. Marble," says Ann Karagozian (MS '79, PhD '82), who helped initiate the campaign for a graduate fellowship in Marble's honor. "He always gave me excellent advice, whether it was on research or career choices or embarking in new directions."

With his wife, Ora Lee, Marble also helped create a "home away from home" for many of his students. The couple regularly invited Caltech students into their house for dinners and special gatherings at which they could mingle with one another as well as with professors.

"By their example, the Marbles gave us a lasting lesson on how to live a fulfilling life," says Gerald "Jerry" Marxman (PhD '62). "I hope this gift will serve as a permanent symbol of the Marbles' wonderful impact on so many others' lives, and as a reminder of the gratitude felt by all those graduate students who have benefited so much from knowing them."

Marble initially came to Caltech as a student himself—earning an engineer's degree in 1947 and a PhD in 1948 under the advisement of Theodore von Kármán. He credits much of his teaching and mentoring style—in which he encouraged students to pursue their passions, wherever they led them—to the lessons he learned from his own mentor.

"I will never forget what my students and friends have done," says Marble, who considers all his doctoral students to be his "academic children." "This is about as impressive an act as I can think of. It allows the administration a significant hand in choosing faculty members who represent new fields of research and new fields of teaching."

Ares Rosakis, chair of the Division of Engineering and Applied Science (EAS) at Caltech says, "Inspirational teachers and researchers like Frank Marble and his adviser Theodore von Kármán create new schools of thought which nurture generation after generation of academics.  It is this long term commitment to education and research that helps the Engineering and Applied Science Division and Caltech maintain their number one position in the recently announced world university rankings."

Several of Marble's former colleagues, students, and their families gathered at Caltech in September to celebrate the Marbles' enduring contributions and the establishment of the professorial chair. Both the chair and the eventual fellowship will be awarded to individuals with interests in aerospace and mechanical engineering, the fields in which Marble made his greatest scientific and engineering contributions.

"For the family, this is a humbling experience, without a doubt," says Marble's son, Steve Marble. "It's a very sweet validation of what my father spent so much of his life doing. The idea that his former colleagues and friends would do something of this sort to honor him, especially in his lifetime, is profoundly meaningful for him . . . and it underscores the importance of a teacher who gets such pleasure from stirring the passions of his students."

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