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Interview: Donna Strickland, 2018 Nobel Prize in physics

Professor Donna Strickland has had a whirlwind two years. As a Nobel Prize winner, you can expect the spotlight, but if you are the first winner from your university and a woman in physics, you can expect a fluorescent beam of attention. On 3rd October, 2018, Canadian Professor Donna Strickland became the third woman ever to win a Nobel Prize in physics, joining the likes of Marie Curie and Maria Goeppert-Mayer, as well as the first ever winner from the University of Waterloo.

I meet Professor Strickland the day after her talk at the Oxford physics department, an inspiring talk to which we battled through Storm Ciara to attend. During her trip to Oxford – Strickland’s first – she also visited the Rutherford Appleton laboratory, who were one of the earlier adopters of her Nobel prize-winning discovery, chirped pulse amplification (CPA).

Strickland won the prize jointly with her doctoral supervisor, Gérard Mourou of Ecole Polytechnique, France, and is one of very few winners to be awarded the prize for work she completed during her PhD. In 1985, Gérard Mourou and Donna Strickland succeeded in creating ultrashort high-intensity laser pulses. They developed a technique to stretch the duration of the laser pulses to reduce their peak power, then amplified them, and finally compressed into a shorter time period to create a high intensity pulse. CPA has many uses, including corrective eye surgeries, though Strickland wears glasses. She said “I have great faith in lasers, but no one’s putting one near my eye.”

The laser group at the University of Rochester, where Strickland completed her PhD, called themselves “laser jocks”. Strickland says this is because “we were good with our hands, we could get the lasers to work, like a jock would be good with their hands to throw a ball properly. She wonders whether it was a derogatory term from the other people on the team but says they take it as a point of pride: “we’re good with our hands as well as with our heads.”

Interviews with Strickland frequently focus on her gender, and she acknowledges this, saying she “understands it because it’s what makes me special – I am the third woman to win the Nobel Prize in physics.” However, she says: “it takes away a little from my male counterparts that won with me, and also I think it does take away a little from me, as Donna, the scientist, not ‘Donna the woman scientist’.” Strickland says that throughout her career she “either didn’t notice when people didn’t take me seriously – or I just assumed they would and moved along. I’ve never felt that people didn’t take me seriously.”

She refers to her supervisor and joint-prize winner, Gérard Mourou here. “Gérard and I had our ups and downs, like any supervisor and student – it’s not always going to go swimmingly. For the most part we got on well, and I think he treated me fairly and didn’t treat me differently because I was a woman.” Strickland thinks they made a good team, “probably because I listened to him!”

“Gérard is an idea guy and he throws ideas out, but he’s not the one who’s going to go in the lab anymore. He would spit out ideas and it was up to you to make it happen, and I was the one who was able to make it happen.”

Donna Strickland in the lab | Copyright © University of Waterloo

Professor Strickland moves to discuss how she got interested in physics. Her father was an electrical engineer and her mother was an English teacher. She says her “mother always told me she wished she had stuck to her guns and gone into maths at university, but she was told that she shouldn’t as a woman and she should go into the arts instead, which she did, and regretted it. She always said to me “don’t let other people tell you what to do”.’

We go on to discuss her Nobel prize winning discovery. Strickland reflects on the day she found out she won, which she describes as “right out of the blue”. “It was 11am Swedish time so it was 5am for us – they asked for Professor Strickland and they said to wait on the line for an important call. I did know it was October 2nd and I held onto my husband and thought ‘oh my gosh I think this is the Nobel Prize!’.”

On her prize winning discovery, Strickland says: “I like to say that I built a laser hammer. With lasers, sometimes it’s energy that’s required and sometimes it’s the energy per unit time. It’s like pushing a nail in with your finger or picking up a hammer and doing a quick rap. This is what CPA allows. It’s for those applications for which it matters what the peak power is, not what the energy is. We found a way to take the energy and squeeze the length of the pulse and make it very short, and still have high intensity.”

“People had asked me if I thought I’d win the Nobel Prize but there are a lot of factors at play. It’s unusual for a grad student to win it with the supervisor, so I could have envisioned that Gérard would win it without me. I also wondered whether there was enough physics in it. It helped new physics a lot but it’s more of a technique than new physics itself. There are so many things out there that could win the Nobel Prize, so it’s hard to believe it could be yours.”

Some people draw comparisons between Strickland and Jocelyn Bell Burnell. Bell Burnell is a fellow at Mansfield College and discovered pulsars, rapidly rotating neutron stars which emit regular pulses of radio waves across the sky at up to one thousand times a second.

She was famously snubbed the Nobel Prize in favour of her supervisor, as she was also a graduate student at the time of discovery. Strickland says “I’ve always been lucky and I think times have changed quite a bit. Obviously, she was robbed and I don’t think anyone would disagree with that. I think most people would think it’s ridiculous that she didn’t win. It’s such an amazing honour to win the Nobel prize but you always have to take pride in your own work and I think she does – she knows she discovered the pulsar.”

We move on to discuss her career. Strickland’s life work has been in high-intensity lasers and non-linear optics. She reflects on why she enjoys it so much. “Optics, especially non-linear optics where we turn one colour of light into another colour of light is just a beautiful thing to see. I work on Multi-frequency Raman generation (MRG), which efficiently generates a large number of frequencies right from the infrared to the ultraviolet. It’s a beautiful rainbow.”

Professor Strickland discusses what’s next for her. “I’m still trying to make a different kind of laser, to go into the infrared. I’m still trying to make shorter pulses – single femtoseconds but having enough intensity to do non-linear optics – right now the attosecond world is shorter than what I’m talking about but they don’t have the intensity that I would like to have with the Multi-frequency raman generation.

Strickland doubts there are many limits on laser optics, “apart from possibly when you get to 1029 watts per cm you will presumably make matter out of nothing. At that point, even in a vacuum, light can’t get through. We might never get to that 1030 because all the energy is going into breaking down and making matter, so that could be the fundamental limit where we’re making matter in a vacuum.”

Strickland discusses what it takes to be a good scientist, and concludes that it’s patience. “I think for an experimentalist you need to be more patient than for a theorist because at least for a theorist their work is the same when they wake up in the morning, whereas we have to spend much of the day getting the laser to work the way it was when we turned it off before we can start making any progress. Science is a team sport; you have to listen to other people. Very few of us can figure out everything by thinking it up in our own head.”

We frequently hear about “lightbulb” moments, as well as accidental discoveries and coincidences in science. Discussing when science takes its greatest leaps, Strickland says that “there’s a lot of serendipity in what we see and what we find.”

“Science requires people to be constantly thinking about things but sometimes things will just jump out at you and it might even be something you’d seen before but it strikes you differently that time. I think that scientists have to be supportive. We have to support creative thinking and we have to give science the chance to perform. With that, it flourishes. I think people are creative and intelligent and flourish given that opportunity.”

Strickland discusses her life since she won the Nobel prize, with charming modesty. “It’s been incredible. It’s hard on your psyche because it’s work we did 35 years ago and people in the high intensity laser community have always given me a lot of credit for it, but outside of that it’s not been known. All of a sudden you have this voice and it makes you wonder what made you so special. So you want to be careful with it and before I was never very careful of what I say. On the other hand – what doors it’s opened up. Gérard and I had an audience with the Pope! It’s opened up such an incredible world for me – it’s exciting and tiring!”