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Laser experiments expand spectrum of physics knowledge


Associate Professor Derek Kimball, from left, leads students Trinity Pradhananga, Christopher Palm and Khoa Nguyen '07 in conducting experiments using a laser spectrometer. (Photo Jesse Cantley)

  • April 5, 2012

Ever sat in on a lecture where an instructor used a glowing red laser pointer to direct your attention to a particular spot on the white board? Then you’ve seen a continuous wave laser in action.

A common technology, it’s a laser any shopper can pick up at an office supply store for as little as $25. A far more sophisticated relative of the humble laser pointer called a frequency comb laser spectrometer – and that produces a pulsing wave that “flashes” on and off at the rate of about 1 billion times per second – is at the center of leading-edge experiments happening at Cal State East Bay’s College of Science.

Funded through a National Science Foundation grant as a result of the American Recovery and Reinvestment Act, it’s one of a handful of laser spectrometers of its kind at undergraduate universities nationwide. The others are found at large research universities and institutions. At Cal State East Bay, the device – also known simply as a spectrometer – is giving undergraduates, graduate students and faculty a rare opportunity to study aspects of physics that were technologically impossible until a few years ago, said Associate Professor Derek Kimball of the physics department.

Kimball’s research, which started when the spectrometer came to Cal State East Bay in fall 2010, has begun yielding data that will allow scientists to confirm – or call into question – long held basic physics principles.

Involvement with the research project also has catapulted one undergraduate, senior Trinity Pradhananga, on her way toward a promising physics career. Pradhananga received the 2011 Steven Chu Award for Best Undergraduate Research from the California American Physical Society for her frequency comb spectroscopy work under Kimball’s tutelage.

“This is the first time I’ve ever done undergraduate experiments,” said Pradhananga, a native of Nepal. “I was really excited.”

She credits Kimball’s patience and encouragement for keeping her motivation and morale up throughout the experiment, which she said often felt like taking “one step forward and 10 steps back.”

“Professor Kimball is the greatest professor I’ve ever come across,” Pradhananga said. “He thinks so positive. You can ask the same thing of him 100 times, and he would not hesitate to explain, which is really nice.”

When a beam of white light is broken down into its component wavelengths, an ordered array of colors known as a spectrum is revealed. Traditional lasers give off long pulses of light that span a narrow part of the spectrum, Kimball explained. The laser spectrometer CSUEB owns, however, emits short pulses of light that cover a far broader part of the spectrum, allowing scientists using it to study light at a more fundamental level than possible 10 years ago.

“It’s new territory in terms of accuracy and precision,” Kimball says.

In the past, he says, scientists had no way of measuring light at its most basic level.

“There was no yardstick for light,” he said. “You could reference blue to red on the spectrum, but you couldn’t measure the vibrations of light in terms of oscillations per second."  

Scientists precisely measure the color of light in terms of its frequency, Kimball pointed out. “Light is a vibrating electromagnetic field,” he added. “And rate, or frequency, at which the vibrations occur determines the color of the light and the energy of the photons of which the light is made."

(For comparison’s sake, he said: Suppose drivers wanted to know how long it takes to travel from City A to City B but had no speedometers to measure speed and no clocks to measure time. “All they could do is compare the trip from A to B to other trips: It will take longer than it takes to get to City C, but less time than it takes to get to City D. The frequency comb is like providing clocks and speedometers to these people.")

With laser spectroscopy, “now we can come up with concrete measurements” for light, Kimball said. “Anything measured before can now be measured 1,000 times better or more accurately.”

For the first time, scientists who want to measure visible light can use a clock to help them; and not just any clock, the most accurate one available, the atomic clock.

“It’s very exciting,” Kimball said. “What we’re doing in our experiment … is looking at different properties of atoms. We’re going to look at one at a time and look at different energies that electrons take on in the atom.

By studying which wavelength of light an atom emits or absorbs it tells you a lot or properties about the atom. The more you study it, the more you find out about the way forces hold it together.”

Khoa Nguyen ’07 earned his B.S. in physics at CSUEB. He credits the opportunities he received to work in the lab and contribute to a published article during his undergrad days to helping him gain admittance to graduate school at San Jose State University. He’s also returned to the CSUEB laser spectrometer lab to conduct dissertation research probing “the finest atomic detail of rubidium.”

“I really enjoyed it, because I got a chance to interact with new technology and a new research direction that can give way to something else,” Nguyen said. “The research itself is pioneering new ways of probing materials down to their atomic structure.”

Kimball agreed that the state-of-the-art equipment is opening doors into new areas of knowledge for students and scholars.

“We’re looking at discovering new aspects of physics,” he said.

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