Interview with Francesca Calegari about the Physics Nobel Prize for Donna Strickland

11 December 2018, by Ingeborg Adler

Photo: The Royal Swedish Academy of Sciences/Johan Jarnestad

Illustration of the CPA technique.

Photo: UHH/CUI/Calegari

Francesca Calegari in the lab.

Yesterday, the Nobel Committees presented the 2018 Laureates at the Nobel Prize Award Ceremony in Stockholm, Sweden. Donna Strickland shares the distinction of being one of only three women to ever win the Nobel Prize for physics. Strickland, along with Arthur Ashkin from the US and Gérard Mourou from France, were awarded this year’s prize “for groundbreaking inventions in the field of laser physics” – and it is exactly the technique the canadian scientists developed which lies at the heart of modern laser research, that is precisely the research at the cluster of excellence "The Hamburg Centre for Ultrafast Imaging" (CUI). And still: Donna Strickland won the Nobel Prize before she even had a wiki page. We talked to Francesca Calegari, who is a professor at Universität Hamburg and a leading scientist at DESY, about Strickland, her work, and her publicity. As a board member of the new cluster “Advanced Imaging of Matter”, Calegari will be responsible for Equal Opportunity.

Ms. Calegari, could you please explain the research Donna Strickland won the Nobel Prize for in a few words?

Calegari: The research Strickland won the Prize for was done in 1985, while she was a PhD student with Gérard Mourou (with whom she shares the Nobel Prize) experimenting with laser technology. Their work paved the way for the generation of the brightest and the shortest laser pulses. “Compression of amplified chirped optical pulses”, as the article which was key to the Nobel decision is called, is still one of the really important papers in the laser community. It is one of the first papers you read as a student in laser physics.

What makes her invention so special to you and your colleagues?

Calegari: It had lasting effects in various directions. The technique she invented is called Chirped Pulse Amplification (CPA). It is the basis for the generation of bright laser pulses with lot of energy in a very short time duration, which are very useful not only for fundamental science but also for industry and medicine. Ultrahigh intensity pulses are currently used for instance for material processing, for eye surgery, to generate electron-positron pairs, for advanced ignition schemes for fusion energy and to accelerate protons for proton therapy for cancer. Many of the groups here at CFEL are using or even developing CPA-based laser sources, it is a prerequisite for our basic research. Without CPA, my research field of attosecond science would not exist. We use intense pulses to drive the generation of attosecond light pulses (1as = 10^-18 s), the shortest pulses generated so far. With this light transients we can image the electronic motion in matter in realtime.

Donna Strickland won the Prize before she was accepted by Wikipedia. Do you have an explanation for what seems like lacking publicity?

Calegari: No, I really don’t know why she didn’t get the publicity. But I was really surprised to see, that she is an associated professor rather than a professor. Maybe it shows once more that women do not dare to apply for top positions. But applying is really important and I would like to use the opportunity to suggest to all the early career women: apply, try it!

Have you ever met Donna Strickland?

Calegari: No, but I heard about her as a young student. I knew her paper and her name. As far as I know, many colleagues here at CFEL don’t know her personally. But we are thinking about organizing a workshop on the topic of the Nobel Prize next year.

In an interview for Nature, reporter Elizabeth Gibney apologizes for asking Donna Strickland about the fact that she is a woman. How do you deal with gender questions?

Calegari: Donna Strickland was a bit surprised by the focus on the gender issue, she said “I see myself as a scientist, not a woman in science”. I think that’s the way we should deal with gender questions, we should put the science and our achievements first. However, I must say that I am working hard for the next generations of female scientists so that they won’t have to deal with gender questions anymore because at that point a woman in science will be simply a scientist.

You will be responsible for Equal Opportunity in the new cluster “Advanced Imaging of Matter”. What are your priorities in that position?

Calegari: As a priority I will continue some of the excellent initiatives we had in “The Hamburg Center for Ultrafast Imaging” including the Mildred Dresselhaus Guest Professorship, established to bring two internationally recognized female top researchers to Hamburg and the Louise Johnson Fellowship, which will be offered to excellent female scientists who already show a distinctly high potential for early independence. We will work to keep the gender balance a priority in the recruiting process of the cluster and we will support female PhD students and postdocs with a mentoring program to develop a successful career. Hopefully, we will have many more female Nobel laureates in the future!

Thank you very much.

Interview: Ingeborg Adler