Laser Life

Bedford scientist a laser pioneer

New Hampshire Union Leader
August 16. 2014 10:44PM
Bedford scientist Paul Hoff shows the latest laser component he is working on in his Nashua laboratory. (MARK HAYWARD/UNION LEADER)

Although the space race between the United States and Soviet Union concluded when Americans put men on the moon in 1969, it didn't end the scientific rivalry between the Cold War adversaries.

Four decades ago, superpower scientists were in a frenzied race to perfect the laser. The invention had been around since 1960, but the first lasers produced weak beams, and many scientists derided the laser as a solution looking for a problem, recalled J. Gary Eden, a professor of engineering at the University of Illinois and editor-in-chief of Progress in Quantum Electronics.

Both countries wanted more.

Theoretically at least, a strong laser would be used to fuse atoms, creating a nearly limitless source of power that would mimic the way the sun creates energy.

Edward Teller, the father of the hydrogen bomb, tasked MIT-trained physicist Paul Hoff with making a laser worthy of its hype.

"My instructions were, 'Don't lose out to the Russians,'?" recalled Hoff, who now lives in Bedford.

Earlier this year, Hoff was recognized in Washington for his work, during an event following last year's 40-year anniversary of the excimer laser's creation.

Today's variations of Hoff's discovery are used on everything from the sketching of tiny integrated circuits to the correcting of eyesight with LASIK surgery.

If you use a cell phone, Eden said, you're using chip circuitry patterned by excimer lasers.

"Paul has been one of my heroes," Eden said. "He was the forerunner; he was the father of these excimer lasers."

Now 70, Hoff is a relic of the post-war era, when science offered the promise of space travel and technological advancement, along with the threat of world destruction. He earned a doctorate in quantum electronics from Massachusetts Institute of Technology in 1970, and within a few years, joined the famed Lawrence Livermore National Laboratory.

"It was an incredibly exciting time," Hoff said. "Everything was burgeoning; there was lots of support."

Lasers were part of it.

Hoff and much of the scientific community knew that the rare gas xenon was the answer to a stronger laser. The challenge was the nature of the element. The xenon atom is a loner; it won't bond to other atoms, even other xenon atoms.

Hoff used an electron beam to knock the electron of a xenon atom into a higher orbit, or excite it (hence the term excimer). Pressurized to the level of five atmospheres, the excited atoms coupled, only to break apart almost instantly.

The breakup created energy in the form of ultraviolet light waves. Those waves bounced off mirrors in a separate chamber, which magnified them into the excimer laser beam.

Eden said Hoff was the first to use molecules not found in nature to create a laser."He recognized, 'I can make these on demand. They do what I like, they fall apart, they do it again,'?" Eden said.

Hoff said it took a year to reach the breakthrough. Often the problems were technical, such as designing proper mirrors, which had to be made and installed in an oxygen-free environment.

The breakthrough came on a Friday afternoon. The next day, the Oakland Tribune ran a front-page photograph of Hoff, topping a story that Watergate special prosecutor Archibald Cox had subpoenaed Richard Nixon.

The development of the excimer laser quickly led to other breakthroughs.

Next up were halide lasers, created by rare gas excimers and halogens such as chlorine and fluorine. By 1975, scientists at IBM realized that halide lasers could cut patterns in plastic, giving birth to the shrinking of the computer chip.

Life after Livermore

In 1978, Soviet physicist and Nobel laureate Nikolay Basov presented Hoff with the Order of Lenin, an award the USSR usually reserved for its own scientists. The following year, Hoff left government work for New Hampshire and Sanders Associates, now part of BAE Systems. He married Selma Naccach, the current chairman of the English Department at Manchester High School Central.

Hoff left BAE in 2006. He now heads TransEtch Manufacturing, a Nashua startup technology company that works on the development of advanced ablation lasers. Those lasers emit beams in incredibly short bursts - one-10,000th of a billionth of a second, or in mathematical terms 1 second to the -13th power of 10.

Through his career, Hoff has worked on robotics, wireless communication, micro-electronic machines, ground sensors and defense systems.

Although he holds several patents - one on the detection of nuclear weapons in shipping containers - Hoff never received a proprietary share from the excimer laser. Had he received a patent, his fortune would be enormous.

"You can't think about that," Hoff said with a shrug. Times were different. Researchers went to work either for big government or big industry, such as Bell Labs and IBM. Venture capitalists and patent attorneys weren't part of the picture.

"At the time," Hoff said, "I understood I was getting paid by the government to make things better for the country."

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