Like many researchers who specialize in lasers, Jeff Squier was excited to hear this week that three scientists had won the 2018 Nobel Prize in Physics for their pioneering work with the intense beams of light.
For the Colorado School of Mines physics professor, the news took on a slightly more personal significance, too.
One of the three laureates, Gérard Mourou now of École Polytechnique in Paris, was Squier’s PhD advisor at the University of Rochester. Mourou's co-laureate, Donna Strickland of University of Waterloo, Canada, was the senior graduate student during Squier’s time there.
Squier joined Mourou’s lab in 1986, the year after Strickland and Mourou’s revolutionary article on chirped pulse amplification was published. The discovery, which permitted the creation of ultrashort high-intensity laser pulses without destroying the amplifying materials, “paved the way towards the shortest and most intense laser pulses ever created by mankind,” in the words of the Nobel announcement.
“It had just happened,” Squier said. “I still remember my first day – one of the lasers actually caught on fire and it shut down the whole facility.”
Squier sat down with Mines Newsroom to talk about the Nobel Prize-winning discovery and how his time in Mourou’s lab continues to influence his research today at Mines.
Q: What’s your connection to the Nobel laureates?
A: After getting my master’s in physics here at Mines, I applied and got into the PhD program at the Institute of Optics at the University of Rochester. I interviewed with Gérard and he took me on a PhD student in his research group. I was totally intrigued by femtosecond lasers, picosecond lasers. It was a good match from a research point of view. I knew I wanted to do ultrafast optics.
Gérard was super engaging. From him, I really learned to push the limits of things. And Donna was awesome – she was senior graduate student to me. The most important thing I remember from working with her in the lab was she had such amazing confidence in the lab and solving problems that happen every day in a lab. It was great to work side by side with someone like that—to see, OK, it’s broken, it's not working, we can fix it, that can-do attitude.
Q: What kind of research did you do during your time in Dr. Mourou’s lab?
A: What Donna and Gérard did is chirped pulse amplification. The original work by Donna showed you can amplify picosecond pulses to the millijoule level and then they would extend it to higher energy levels. Part of my job was then to go into the next regime. I helped push it into femtoseconds – even higher intensity, shorter pulse durations and higher average powers, too.
With lasers, you have to watch the peak power – their instantaneous power – and their average power. Power is just energy divided by time and in this case when you’re using picosecond or femtosecond pulses, that’s essentially dividing by zero so your power goes through the roof – that’s your peak power. Even just going from picoseconds to 100 femtoseconds, for the same amount of energy you get 10 times the peak power.
We worked on really pushing the limits on these systems. We were able to push the pulse duration down into the femtosecond regime and the average power when I started was at 10 milliwatts. We had them over 1 watt by the time my work with Gérard was done. It was a prolific time. In my PhD time with Gérard, Gérard and I conspired on around 40 research articles and over 40 conference presentations.
Q: What has been the long-term impact of their discovery?
A: Chirped pulse amplification systems have proliferated worldwide – they’re pushing the limits in terms of high intensities, in large facilities. There’s also been this outgrowth of smaller systems, which are finding lots of industrial applications. Where they found their first major niche was in eye surgery. That was a continuation of my thesis as well – once we developed these high-power systems that were compact, real-world applications started to sprout up. All laser LASIK employs a femtosecond component.
They’re also used for a lot of rapid 3D prototyping. Femtosecond lasers can do additive 3D printing but they can also do subtractive manufacturing. My PhD student Nathan Worts has just finished writing and publishing a paper where we took a laser 3D printer and printed a part and then we were able to show with the femtosecond laser we could reduce the surface as printed surface roughness. Another challenge of 3D printing metal parts is how you authenticate it as a part from a given system – it’s going to be easy to produce knockoffs. Nathan was able to use a femtosecond laser to write a code on the surface of the part that’s invisible. Only the manufacturer will know where it is, and when you shine a light on it, the special code lights up in rainbow colors. It went from an initial discovery to real-world applications in advanced manufacturing.
Q: What was your reaction when you heard the news?
A: It was always in the back of many of our minds, all of the students who worked for him, that this was that big of a discovery. I started getting emails from friends and all of us who worked together that morning. A lot of us always wondered if it would receive a Nobel because it was a technology achievement, not basic science. For those of us that work in the technology areas, it’s super exciting to see that technology is being held up to the level of basic science.
Q: How has the work you did with Dr. Mourou influenced the research you are conducting today here at Mines?
A: It still influences what I do today. Both Physics Professor Chip Durfee and I here at Mines work on advancing the source development – there are still ways to make the lasers better, more compact, more efficient, higher average power. We’re both actively engaged in that. Chip really derives a lot of the basic science applications with these new sources and I drive the technology end. It’s super synergistic.
We’ve got this great new advanced manufacturing initiative here on campus, so I’m involved with Aaron Stebner, in Mechanical Engineering, now in using our techniques both as a metrology in advanced manufacturing and a way to process parts in advanced manufacturing. For me, it’s really fun. We keep pushing the technology but also having this almost immediate impact on what we can do in industry. We’re also working with Geology, with Alexis Navarre-Sitchler. We’ve worked with Mike Kaufman in Metallurgical and Materials Engineering, David Marr in Chemical and Biological Engineering, folks in Chemistry. It’s getting broader and broader, all the things we can do.
Designing and building femtosecond lasers from scratch is becoming a lost art. There are so many companies now – it’s become a nice economic business for companies to produce them and universities now buy them versus having faculty build them from scratch. But our students here at Mines still have to develop them from scratch. They get that unique experience and now they’ve got multiple pathways in their career – they can go work for these companies who are finding it harder and harder to find students who have actually built these systems or they can go into academia or industry and apply them.
Editor’s note: This interview has been condensed and edited for clarity.
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