Teensy extremes at the speed of light
In Naomi Ginsberg's realm of lasers and photosynthesis, a picosecond dawdles like a snail in slow-mo
She'll join us in a picosecond—a trillionth of a second. She's quick, but curiosity makes her linger. In just a laser's flicker Naomi Ginsberg will finish her calculation: a few more femtoseconds—quadrillionths of a second.
For Ginsberg, every atom counts on her way to finding out how plants capture sunlight so quickly. Ordinary plants—miraculous green transformers—zip solar energy from photon to molecule, from light particle to organic compound.
Every farmer and cultivator of orchids knows how marvelously efficient plants are at gathering solar energy. Yet we know little about how they do it, Ginsberg says. Photosynthesis remains a mostly unexplored frontier of science. She aims to dash into this frontier. The potential payoff could be vast: abundant clean energy.
Smart and pretty, Ginsberg forges confidently into science realms that until recent years had been largely the province of men. At UC Berkeley she teaches undergraduate physical chemistry and biophysical chemistry, including topics such as thermodynamics. "It's the hard chemistry course," she says. More thrilling, she conducts research through Lawrence Berkeley National Laboratory. "That lab brings together scientists from all different backgrounds," she says.
The science job market is changing fast. "In the sciences, women have been underrepresented," Ginsberg says. "As an undergraduate, I remember walking into the computer lab and being the only woman there. Our department is pretty good. We have a number of senior women who are pioneers." She started teaching there in 2010. By the time Julia finishes college, science careers will be populated by plenty of women, she says. "There's absolutely no reason women shouldn't choose a career like this. Do what you want. Have the self-confidence to know that you are in the right place."
"There's absolutely no reason women shouldn't choose a career like this. Do what you want. Have the self-confidence to know that you are in the right place."
"One of the reasons I took a job here is because people study photosynthesis from many angles," Ginsberg says. She earned a Ph.D. in physics from Harvard University. Before starting her own laboratory she did post-doctoral study at UC Berkeley with Dr. Graham Fleming, considered a pioneer in photosynthesis research. "Before that I didn't study anything alive," Ginsberg says. She studied atoms in vacuum chambers, always focused on light.
She's especially intrigued by the first phase of photosynthesis when light hits a leaf then energy is transported to a location where biochemistry occurs. She points to a straggly philodendron that drapes down from the ceiling in her office. "They don't look very happy because we have no windows," she says, laughing. "Inside the plant leaves are chloroplasts, where chlorophyll is. Chlorophyll molecules absorb light. That gives electrons more energy, which sits on one chlorophyll molecule then hops to another." Energy moves among clusters of chlorophyll molecules on its way to other molecules that transform excited electrons into glucose—sugar. "That's how they store energy." Food is stored solar energy.
"Nobody understands why the energy absorbed gets to the right spot," Ginsberg says. "All the photons get used. Somehow they're guided, but the guiding principles are completely unknown. That's a frontier research topic right now. It's still a secret. What is it about the architecture of these protein and chlorophyll molecules, the way they're arranged, that ensures that all the light energy gets to the right spot?"
A poignant question such as that can define entire careers in science. In summer 2011 Ginsberg was developing her million-dollar laboratory, where a forest of tabletop lasers and mirrors put light through carefully calculated paces. She points to blue and red dots that appear on tiny white screens. "These are actually pulses of light," she says. Two red pulses add together to create a blue dot, which indicates that lasers are aligned.
A crystal helps measure the duration of pulses. She will replace the crystal with a photosynthetic sample and send laser pulses into the sample to measure how the sample is changed or how the laser pulses are changed by the sample. "We excite a chlorophyll molecule with one laser pulse then wait some number of femtoseconds later and send in another pulse," she says. Computers capture data from the experiments. Ginsberg and her team of three graduate students and post-doctorate scholars will soon direct laser pulses into a potent microscope to measure photosynthesis in action. "It's awesome," she says. "I like coming in here!"
On bright sunny days a plant will not use all the light energy absorbed. On cloudy days the plant adapts to use nearly all the light. Some of these adjustments happen in billionths or trillionths of a second.
"What is it about the architecture of these protein and chlorophyll molecules . . . that ensures that all the light energy gets to the right spot?"
Time and length measurements of photosynthesis are in fractions of a second or inch, Ginsberg says. Distances are measured in nanometers; time is measured in femtoseconds or picoseconds. "Energy is moving through the chloroplasts on those time scales."
Light travels at 186,282 miles per second; it needs about a nanosecond—a billionth of a second—to travel a foot. A nanometer is a billionth of a meter. Some processes in photosynthesis happen in picoseconds or femtoseconds, a thousandth or millionth of a nanosecond. "That's how long it takes for a molecule to absorb a photon," she says. "It's really fast. There's a lot of stuff that happens really fast. We need to make light pulses that short to measure them. We have super-powerful lasers."
"Photosynthesis is so efficient, especially this first step," which can capture up to 95 percent of solar energy input. "If we knew how to do that with manmade materials, that would be great," Ginsberg says. The knowledge could be used to develop better photovoltaic cells or generate fuel. Later stages of photosynthesis are much less efficient; overall, the plant may capture about 1 percent of the energy.
As a graduate student Ginsberg studied Bose-Einstein condensates, where identical atoms clump together. "In order to make a Bose-Einstein condensate you need to manipulate a bunch of atoms with light. You can actually push atoms around with lasers," Ginsberg says. "It's really cool."
Cool is right. Some of these experiments take place a few billionths of a degree above absolute zero, which is minus 459.67 degrees Fahrenheit. At this temperature atoms come to near standstill and ice cream doesn't drip. "Atoms behave like a fluid that has no friction," she says. "You can spin it and it keeps on spinning forever—or until you need to graduate. I learned how to manipulate matter with light, and how to manipulate light with matter. That put me in a good place to try something new, to use those skills to study photosynthesis, which is alive and very important."
Algae and some bacteria also are photosynthetic. One project at Lawrence Berkeley Laboratory explores how photosynthetic bacteria produce electrons and how to use these electrons as a source of energy. Energy could be captured as hydrogen or ethanol. "How can we engineer microorganisms?" she says. "I'm providing optics experience to measure these processes." The lab thrives as a locus where thousands of brilliant minds from around the globe cross-pollinate. "I'm surrounded by people who are curious. The spirit of curiosity is infectious and invigorating," she says. Some of the scientists work well into their seventies, still vibrant with ideas. "That's inspiring."
Other studies examine use of plastics or polymers in photovoltaics, much cheaper than silicon. "Can organic materials be robust enough to work in this capacity? That's something we're really excited about," she says.
"I'm surrounded by people who are curious. The spirit of curiosity is infectious and invigorating."
As an undergraduate in Canada, Ginsberg studied engineering. "It was like arts and crafts for scientists. You tinker with things," she says. Her parents were non-technical: both worked in retail; her father also worked as a French language professor.
Aside from research and mentoring students, Ginsberg writes grant proposals to obtain funding. She also organizes seminars with guest speakers. "Somebody has to plan that," she says. "These jobs are behind the scenes related to science. You get to interact with other scientists. What I most appreciate about my job—I do a lot of interacting with people. I enjoy teaching the undergrads. That's what I'm paid for. It's so much fun. I get to perform."
Scientists at her level also get to travel frequently. Ginsberg did one project in Italy, and attended a photosynthesis conference in China. "There are a lot of perks," she says. Her office, though ensconced in a labyrinthine basement, sits two stories below a tranquil redwood grove on campus.
"People don't choose this job because of the pay," Ginsberg says. "You definitely don't starve. If you want to be a millionaire, find something else to do."
Ginsberg feeds on unanswered questions that spawn intensive research. "What I do is hard. You can only do it if you love it. It's not instant gratification. It takes a long time to get results. We toil away in the dark for many years before we understand what our data means."
"It can be a slog," she says, "but there's day-to-day problem-solving: a leak in the chiller that cools my laser. There's a lot of tinkering, funky ways to build, quick-fixes, creative solutions to how to arrange mirrors on our laser table so we can send the beams all the way to the microscope. You have little opportunities to be resourceful. You end up with a big toolbox," she says. "It's intellectually challenging, but I really love it."
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