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This post is the second in a series on some of the influential women in science and engineering whom I have had the pleasure of interviewing over the course of my career.
Although I earned a degree in engineering and worked in that field for eight years, I discovered my true calling when I landed a job as associate editor at the trade magazine Lasers & Applications. In 1986, another editor, Susan Lamping, and I were given the plum assignment of writing a feature article on pioneering women in the laser industry.
One of the accomplished engineers we interviewed was Mary L. Spaeth, a specialist in the field of laser optics. Spaeth graduated from Valparaiso University in Indiana and earned a master’s degree in nuclear physics at Wayne State University in Detroit. In 1962, she went to work at Hughes Aircraft Co. in Culver City, Calif.
While working with ruby lasers at Hughes, she “came to believe that dyes would make excellent lasers.”
Inventing a “tunable” laser
The year was 1966, only six years after the first laser was invented. All over the world, laboratories were involved in a mad push in laser research, and Spaeth wasn’t the only one to think of using liquid dye in a laser.
It turned out that an IBM research group led by Peter Sorokin had also happened upon the concept of dye lasers, and theirs was the first reported in the scientific literature. Sorokin went on to receive credit for inventing the dye laser.
“We had designed the equipment and were getting ready to test it when we heard about Sorokin’s work,” Spaeth told us.
However, she was undeterred. “Since there was so much difference in the [dye] molecules we proposed to use, the decision was made to proceed,” she said.
That decision was an important one, because Spaeth’s laser turned out to be tunable, unlike Sorokin’s. “Tunable” means that the laser can be adjusted, or tuned, to operate in a range of wavelengths, similar to the way that a radio can be tuned to different stations.
And so in 1966, Spaeth became the first person to design and operate a tunable laser.
“No one at Hughes believed that it was an actual laser because it was tunable and no tunable lasers had yet been seen,” she told us.
Winning with AVLIS
Her success inventing the tunable laser led Spaeth to a new project at the Department of Energy’s Lawrence Livermore National Laboratory (LLNL).
In the 1970s, scientists there proposed using Atomic Vapor Laser Isotope Separation (AVLIS) to enrich uranium. To create electricity, nuclear power plants need enriched uranium as fuel. Enriched uranium has been treated so that it contains a larger percentage of isotopes than is found in nature. Isotopes are molecules with the same number of protons, but a different number of neutrons: Uranium-235 has three fewer neutrons than uranium-238.
Tuning is the key
The key to making laser enrichment work was Spaeth’s tunable laser concept. By fine-tuning its wavelength, the laser beam is able to excite (ionize) only the uranium-235 molecules, without affecting the uranium-238 molecules. The ionized molecules become attracted to an electrical collector plate, leaving the non-ionized molecules to pass through untouched.
This AVLIS technology was predicted to cost much less, save a lot of energy, and produce less hazardous waste than the two existing enrichment methods.
In 1986, Spaeth had risen to deputy program leader of AVLIS. She became responsible for defending it in a year-long peer review process to determine which advanced enrichment technology should be chosen: laser isotope separation with AVLIS, or advanced gas centrifuge technology.
“We were pitted against four major companies in the U.S.,” she said. “Three and a half billion dollars of U.S. citizens’ money had been invested in the competing technology, but we were the winners. The judges were convinced that the process we were developing had a bigger chance for doing what the U.S. needs—a progression from something that’s just a gleam in your eye to a business worth more than a hundred million dollars a year.”
Back in 1986, Spaeth counted this as her highest achievement. “When I came to the program 12 years ago, nobody would have given two cents for the probability that we would be in the position we’re in today,” she told us.
Chief Technology Officer at NIF
In 1992, LLNL demonstrated a complete, commercially viable AVLIS system, and the AVLIS technology was leased to the U.S. Enrichment Corporation (USEC) to begin commercial operation. But in 1999, USEC abandoned laser enrichment of uranium. Laser isotope separation technology is being developed in other countries and may still prove to benefit areas such as astronomy, medicine, materials processing and power plant nuclear waste re-use.
By that time, Spaeth had moved on. In 1991, she was chosen to help Livermore start up a grand new project—the National Ignition Facility (NIF). At the NIF, scientists hope to learn whether bombarding a small target of hydrogen fuel with a gigantic laser pulse could create a sustainable nuclear fusion reaction and become a new source of energy in the future.
In addition to engineering large laser systems, Spaeth’s specialty was working with laser optics, the coated, ground and polished glass lenses and mirrors used to direct a laser beam and keep it stable over long distances.
When high-energy beams pass through the optics, they sometimes damage the pure glass structure. Any microfracture, impurity or contamination in the optics will slow down or degrade the laser beam, and reduce the power delivered to the target.
At NIF, Spaeth is known for designing a “Loop Strategy” to identify, mitigate, repair and recycle damaged optics at appropriate points, rather than throwing them away.
On being female in a “male occupation”
By the time Spaeth retired in 2012, she had become Chief Technology Officer of NIF. She left less than one year before researchers there demonstrated a ground-breaking energy positive fusion reaction. Her contributions, in laser optics and in systems engineering management, were no doubt critical to the mission’s success so far.
On the subject of being a woman engineer in a traditionally male occupation, Spaeth told us back in 1986, “I don’t think of myself as anything other than a person who is trying to accomplish a task.”
“There are always individuals that will give you a hard time,” she said. “But at Livermore, you are judged by whether or not you deliver a product.” And Mary Spaeth’s long and fruitful career as a woman engineer testifies to the truth of her statement.
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