Caltech Mourns the Death of William Bridges (1934–2024)

William B. Bridges, Carl F Braun Professor of Engineering, Emeritus, died on November 1, 2024, at the age of 89. Bridges was best known for his invention of the argon ion laser, which is still used today to treat diabetic retinopathy, in DNA sequencing, and to help increase the power of other lasers, for example.

Bridges was born on Thanksgiving Day, November 29, 1934, in Inglewood, California, to a working-class family. He was influenced by his grandfather, John Brown, and great-uncle Milo Tupper, who had garages filled with tools and allowed Bridges to use them. As a teenager, he became a ham (amateur) radio enthusiast, a passion that remained with him his entire life.

After graduating near the top of his class from Inglewood High School in 1952, Bridges attended UC Berkeley to study electrical engineering. During the summers following his junior and senior years, he worked at Varian Associates, a scientific instrument business in the Palo Alto area, and became interested in microwaves and microwave tubes. Late in his career, Bridges would say, "I still enjoy working with my hands—I'm an experimentalist, really."

After graduating in 1956, Bridges stayed at Berkeley to pursue doctoral studies. He earned his master's degree in 1957. As a graduate student, Bridges was given the opportunity to teach a lecture class. It was then that he discovered his love for teaching. More significantly for his future research, he also uncovered a basic phenomenon during his graduate studies that helped explain noise processes in microwave vacuum tubes.

Although Bridges officially earned his doctorate in 1962, he started working in June 1961 at Hughes Research Laboratories of the Hughes Aircraft Company (which later became HRL Laboratories) in Malibu, California. The laser had recently been invented there by Theodore Maiman. Bridges started working on microwave tubes for Hughes but quickly became interested in figuring out the internal mechanisms that make lasers work. In 1964, while experimenting with a self-built mercury-ion laser, he discovered that ionized argon gas could produce laser light of shorter (blue) wavelengths. Thus was born the argon ion laser.

In 1977, Bridges, who remained a consultant at HRL for many years, joined the Caltech faculty as a professor of electrical engineering and applied physics. He was a Sherman Fairchild Distinguished Scholar at Caltech during the 1974–75 academic year and was named Braun Professor in 1983.

Although he commented that he was happiest in the laboratory, "puttering around, getting something to work, or trying to figure out how it works," he was a dedicated and engaging teacher.

Kerry Vahala (BS '80, MS '81, PhD '85), Caltech's Ted and Ginger Jenkins Professor of Information Science and Technology and Applied Physics and executive officer for applied physics and materials science, recalled meeting Bridges on his own first day as an undergraduate student at Caltech. "His love of optics and dedication to students and teaching were all immediately obvious," says Vahala. "And his classes were interesting and fun because he combined the lecture material with so many firsthand accounts of laser development and applications."

Beyond that, Vahala says, Bridges had an extraordinarily detailed knowledge of optics, lasers, atomic clocks, microwave tube technology, and even everyday things. "Conversations with Bill were rich and enlightening, such that the information warranted many retellings to my own students, family, and friends," Vahala says.

Lee Burrows (BS '88, MS '93) recalls that when he was a first-year student at Caltech, he was advised by fellow students to take anything Bridges taught, so he took all of Bridges' courses in applied physics and electrical engineering. "Bill was an amazing teacher who wanted his students to learn and thrive. Whether it was a lecture or a lab, Bill put every effort into creating the highest quality product possible," Burrows says.

Later, Burrows was a TA for Bridges' classes, "I did my best to emulate his energy, thoroughness, and focus," he says. Eventually, Burrows joined Bridges' group, and Bridges helped him start a company based on their research.

Bridges's deep experience with laser technology proved beneficial on campus in many ways. In the mid-1980s, when Vahala was a new faculty member at Caltech, his group was given an old krypton-ion laser. At that time, such ion lasers were widespread in labs despite their enormous size, price, and power consumption. Vahala and his team "desperately needed" for the laser to work, he says, but when it turned out to not be operational, he turned to Bridges.

"How lucky for me to have the inventor of ion lasers in the applied physics department," Vahala says. "Bill showed up with transformers and other pieces of hardware to perform a laser tube recovery process. Controlling a Variac (transformer for voltage adjustments) in one hand while monitoring a glowing and sparking laser tube cathode, Bill commented, 'It is now incandescent. … A little higher should work.' And the laser came back to life. Both the graduate student and I thought we had certainly witnessed a miracle."

Bridges became quite involved in the operations of the department and the Institute, serving as executive officer for electrical engineering from 1978 to 1981. He is also credited with establishing electrical engineering as a major for undergraduates at Caltech. Bridges helped reactivate the Caltech chapter of the Society for Women Engineers and served on many faculty committees, including the Health Committee, what was then the Freshman Admissions Committee (which he chaired for two years), and the Undergraduate Academic Standards and Honors committee (which he also chaired for two years). And, naturally, he was an active member of the Caltech Amateur Radio Club, W6UE.

In 1984, Bridges agreed to serve as the faculty director of the Program in Advanced Technologies, a Caltech program designed to use corporate funding to enable the work of young faculty members or innovative new avenues of research. It was in that role that he met his second wife, Linda McManus, who was an events coordinator in corporate relations for Caltech's development office at the time. The two were married at the Athenaeum on November 15, 1986, which turned out to be the same day as Caltech's traditional interhouse party. Bridges later wrote, "Our guests enjoyed the explosions and flames that occasionally broke out during our reception."

Bridges retired in 2002. Among other honors, Bridges was a member of the National Academy of Engineering, the National Academy of Sciences, and a fellow of the American Academy of Arts and Sciences. He received the Arthur L. Schawlow Medal from the Laser Institute of America in 1988 and was a fellow of the IEEE as well as the Optical Society of America (now Optica), for which he served as president in 1988. He received the Distinguished Teaching Award from the Associated Students of Caltech in 1980 and 1982, and the organization's Lifetime Excellence in Teaching Award in 2000.

Bridges is survived by McManus; his children from a previous marriage: Ann Bridges, Judy Bridges, and Bruce Bridges; and his grandchildren: Connor, Mika, Rowan, and Max.