Robert Hellwarth, pioneer in laser technology, dies at 90
Physicist Robert Hellwarth, pictured circa 1986, once noted that “a really outstanding scientist is one who resists the temptation to adore his own work and instead concentrates on the search for his errors.” (Photo: Courtesy of USC University Archives/USC Trojan Family.)

Robert Hellwarth, pioneer in laser technology, dies at 90

A professor of physics, astronomy and electrical engineering at USC for nearly 50 years, Hellwarth was a laser innovator and a beloved mentor, universally appreciated for his kindness, good humor and humility. [7 min read]
Susan Bell

University Professor Emeritus of Electrical Engineering-Electrophysics and Physics and Astronomy Robert Hellwarth, who held appointments at USC Dornsife College of Letters, Arts and Sciences and USC Viterbi School of Engineering, has died. He was 90.

Hellwarth — a Renaissance man who pioneered laser technology, sat in on accordion with Irish punk band The Pogues at a Los Angeles party and once asked Andy Warhol to sign a can of Campbell’s tomato soup — died on Jan. 20 at Providence St. John’s Health Center in Santa Monica, California, of complications from COVID-19.

His eldest child, Ben Hellwarth, remembers his father as “an archetypical absent-minded professor, with requisite sartorial quirks, but taller, athletic and handsome — a fun-loving mashup of Indiana Jones and ‘Doc’ Emmett Brown, with an easy-going kindness and an optimistic, self-effacing manner that Mr. Rogers would have admired.”

But despite his modest nature, Hellwarth advanced world-altering scientific frontiers, including optics and quantum electronics, making an early mark during Southern California’s aerospace boom by inventing and demonstrating “Q-switching.” This breakthrough supercharged the usefulness of the laser by boosting its power a millionfold, opening the gates to the field of high-power lasers.

Hellwarth joined USC in 1971, helping to build its physics and electrical engineering departments for the next half century.

“Bob’s co-invention of the Q-switch made possible a transformation for the field of chemical physics and molecular spectroscopy — to be able to capture transient species by using the short pulses of light the Q-switched laser delivered,” said Stephen Bradforth, divisional dean for physical sciences and mathematics and professor of chemistry. “USC Dornsife’s physical chemistry grouping on the upper floors of Seaver Science Center, where Bob also had his labs, has exploited the pulsed laser in more than 50 years of applications to understand molecular behavior.”

Hellwarth’s research focused on understanding and developing materials for nonlinear optical devices. At USC, he developed a new and now widely employed method for generating the time-reversed version of a light wave, a process often called “optical beam phase conjugation.” He also invented widely used laser-spectroscopic techniques, which he named Raman-induced Kerr effect and Raman-induced phase-conjugation.

“Bob was an inventor in the fullest sense of what that means,” said Hans Bozler, professor of physics and astronomy at USC Dornsife. “I recall him as a spirited and engaged faculty member, unpretentious, but with lots of questions.”

A.F.J. Levi, professor of physics and astronomy at USC Dornsife and professor and chair of electrical and computer engineering at USC Viterbi, said Hellwarth was a highly respected and distinguished colleague whose life positively influenced many senior and junior faculty at USC.

“His enthusiastic and often unique approach to pursuit of knowledge was inspirational, often stimulating exchange of ideas that would not have happened otherwise,” Levi said.

Stephan Haas, professor and chair of physics and astronomy at USC Dornsife, paid tribute to Hellwarth’s enthusiasm for understanding new concepts in physics and his encouragement to fellow faculty members and graduate students.

“His sunny presence in our community created a lightness that will be missed,” Haas said.

Jack Feinberg, professor of physics and astronomy at USC Dornsife and professor of electrical engineering-electrophysics at USC Viterbi, a colleague and friend of Hellwarth’s for more than 40 years, said people were struck by just how open, friendly and collaborative he was.

“All he cared about was the science. He wasn’t at all concerned with making sure he got credit,” Feinberg said. “He was the kindest, smartest man I’ve ever known. I will miss him terribly.”

From basement tinkerer to Princeton valedictorian

Born in Ann Arbor, Michigan, on Dec. 10, 1930, the son of a farm-boy-turned-engineer and a college-educated homemaker, Hellwarth was the oldest of four boys. Growing up in Detroit, he attended neighborhood public schools, spending summers on family farms in Ohio.

He was a sharp student with a genuine interest in science and math. The family basement contained a treasure trove of left-over electronic parts and tools, enabling him to gain rudimentary knowledge of electrical engineering. As a teenager, Hellwarth struck a deal with his father: If he could successfully rebuild a junker, then he could drive it. They found an old car and Hellwarth quickly got it running — far sooner than his father had bargained for.

Offered a scholarship to Princeton University, Hellwarth at first turned it down, content to attend the University of Michigan, closer to home, before finally accepting the offer. At Princeton, he was valedictorian of his class, earning a dual undergraduate degree in physics and electrical engineering in 1952. He was selected as a Rhodes Scholar and spent the next three years at the University of Oxford, earning his doctorate in physics in 1955 and becoming a lifelong Anglophile.

An innovative approach

He spent a year as a postdoctoral researcher at Caltech in Pasadena, California, working with eminent physicist and future Nobel Prize-winner Richard Feynman, who became Hellwarth’s lifelong friend and mentor.

From 1956 to ’70, Hellwarth divided his time between Hughes Research Laboratories and his position as a senior research fellow at Caltech.

In 1960, he witnessed the demonstration of the first laser at Hughes Research Laboratories, remarking that this ruby laser, while obviously revolutionary, produced a red beam that flickered, coming out in fits and starts known as “spikes,” rather than as a smooth, continuous beam.

Instead of trying to figure out how to eliminate the spikes, Hellwarth took a different approach: Why not find a way to make them much bigger? That would generate light pulses more than a million times more powerful than the beam itself, and those giant pulses could ultimately be more useful.

Hellwarth devised a method to make the spikes much stronger by “Q-switching” the laser cavity’s inherent light-bouncing quality to create an ultra-powerful light pulse — a technique roughly akin to holding a thumb on a garden hose to produce a burst of water when the thumb is lifted.

Aided by this power-boosting effect, lasers soon proved valuable for the Hughes Aircraft Company, notably in the development of advanced radar systems for the U.S. Air Force.

Q-switched lasers have since found applications in everything from tattoo removal to surgical procedures to metal cutting to the quest for laser-induced nuclear fusion, the latter of which was long a favorite puzzle for Hellwarth. Major attempts at realizing laser fusion continue at specialized facilities such as the Lawrence Livermore National Laboratory, where Hellwarth’s input as a consultant was frequently sought. He also collaborated regularly with the Clarendon Laboratory in Oxford, the Max Planck Institute in Munich and the Institut d’Optique in Paris.

Before joining USC, Hellwarth returned to Oxford in 1970 on a National Science Foundation fellowship. He returned to the city many times over his lifetime, eventually buying an apartment there.

A fellow of the U.S. National Academies of Sciences and Engineering, the American Association for the Advancement of Science, the American Physical Society, the Institute of Electrical and Electronics Engineers and the Optical Society of America (OSA), Hellwarth was also the recipient of the OSA’s Charles Hard Townes Award.

Hellwarth wrote or co-authored more than 200 papers and articles, the last published in 2018, shortly before his 88th birthday.

Renaissance man

Hellwarth, a keen pianist blessed with perfect pitch, could play virtually anything by ear. He skied well into his 60s, enjoyed biking and roller skating with his kids along the Venice Boardwalk and loved playing the harmonica and a good chess game. His vehicle of choice was a VW bus.

He was also interested in art. While driving along Sunset Boulevard one day, Hellwarth, a fan of Andy Warhol, spotted a book signing event with the famed pop artist. Making an impromptu pit stop at a nearby market, Hellwarth bought a can of Campbell’s tomato soup, then asked Warhol to sign it.

In 1957, Hellwarth married Abigail Gurfein. The couple had three children before divorcing in the late 1970s. In 1985, Hellwarth married Theresia de Vroom ’87, a USC Dornsife graduate student in English, accomplished pianist and later an English professor at Loyola Marymount University. Feynman was their best man.

Hellwarth is survived by his brother, Jim; de Vroom, and their son, William; his children from his first marriage, Ben, Margaret and Tom ’94; and four grandchildren, Sutter, Camryn, Grace and Evan.