So, shall I start now?

Yes, go ahead.

Okay. Yeah, then I have the pleasure of introducing our speaker today Pascal De Heide, who is a research group leader at the Max Planck Institute for the science of light in Erlangen.

Pascal joined us in January of this year.

He came to us from the National Physical Laboratory in England, where he was a senior and principal research scientist, leading a research group for about four years between 2015 and 2019.

Now I go maybe more towards the beginning. From the beginning, Pascal did his undergraduate studies in physics

at Aachen, essentially his fourth diploma, and then he switched to the University of Munich

to do his diploma. And he did his diploma thesis on cascaded parametric frequency conversion in monolithic micro resonators that became an important topic for a good part of his scientific career.

He did that work at the Max Planck Institute for quantum optics in the group of Tobias Kippenberg in the bigger kind of orbit of Ted Hench.

He stayed there and also did his PhD on optical frequency comb generation in monolithic micro resonators.

He finished his PhD in 2011 and then went for a four year postdoc or three and a half years or so

to the National Institute of Standards and Technology, NIST, in Boulder, the United States.

And so right after that he took on the position that I told you about already in England. Pascal has won several awards, maybe the most important award, the way I see it, or I want to mention a few of them.

He got the Helmholtz Prize for Metrology, he got the European Physical Society Thesis Prize for Fundamental Aspects, and he got the National Physical Laboratory Rady Award for his work.

And he has also received an ERC starting grant in 2018, which he still has and is using to do his research at NPL.

I'm not going to say more about what he does because that's what he's going to do himself. So the floor is yours.

Thank you very much for the detailed introduction. Yes, so it's a big pleasure here to give a talk in the in the physics colloquium at FAU.

And, yes, as I mentioned, I started here at the beginning of the year. And even in these crazy times, I felt very welcome here so far and I really enjoy already the connection with the university and actually starting to teach here and getting in touch with more and more students.

So, but let me start to share my slides.

That works.

Okay, so I hope you can all see the screen.

Yes, I will, I will talk a bit about my research topics that we're working on right now and it's mostly about frequency comms and more general nonlinear photonics in so called whispering gallery micro resonators.

And I will introduce this a bit. So, yeah, so especially these frequency comms are something that's already kind of part of my life since a long time since, since my PhD actually.

And, yes, so we moved to Max Planck here beginning of the year, and we were actually using the bit more quiet time and less conferences to start setting our labs and we're kind of getting ready to do experiments now.

But let me start a bit and and sorry for the people from Max Planck who might have seen this presentation already before, but what we are working on is on interaction of light, light, and to give a bit more of a background so usually it's very difficult

for light to interact with light, and you need a lot of optical power to make that work. And maybe as a comparison. So in order for light to interact with light in space for example so for photon to scatter off the microwave background photons in empty space.

That would require something like 80 terabyte electron or photon energy.

That's a lot of energy and so LHC at CERN reaches 13 terabyte electron volt maximum so that's roughly six times the energy that LHC can achieve right now.

And maybe a bit more easy to understand comparison is 80 terabyte electron volt is the kinetic energy of the common fly.

And that's the energy that will apply hitting your skin that's roughly 80 terabyte electron volt. And so that's usually optical powers we don't have available.

There was actually a very interesting experiment recently just a few years ago at CERN, at the Atlas experiment, which is part of LHC, where scientists have shown that it's possible to see this photon-photon scattering, at least in the vicinity of heavy lead ions.

And it is possible. That's a very interesting paper to read actually. But in our case we don't have a budget for a big large hydron collider.

But we still want to make light interact with light, because our big goal of course at some point is to have light sabers.

Make light interact with light in free space and make them work like in the movies.

So in our case we use optical micro resonators to make light interact with light. And it's a bit of a similar concept like LHC, we have a ring. But in this case we have a little so-called whispering gallery ring resonator.

These whispering gallery resonators are actually first discovered in the world of acoustics. And here on the left side you can see a few pictures of these round structures.

And so, the name whispering gallery actually comes from St. Paul's Cathedral in London and there's this dome on the cathedral. And what people realized pretty early on, is that when you whisper against the walls of this dome and the sound waves are periodically reflected along the walls, which is shown in this picture.

This leads to the very nice effect that when you kind of put your ear close to the wall,

you can hear another person whisper on the other side of the dome,

and it feels like the person is standing next to you.

So that's a quite interesting effect.

And this was first explained by Lord Rayleigh in 1912.

And Lord Rayleigh is the guy here on the right side with this nice hat,

and he's sitting here together with William Ramsey.

So the same thing that works with sound waves actually also works with light waves.

And in our case, we use these optical micro resonators to reflect light waves continuously around the circular boundary.

And there are many different types of these optical whispering galleries.

And actually the very first ones that have been fabricated was that was actually in Moscow and Russia in the 1980s by Babinsky, Gorodetsky and Olchenko.

And what they did is essentially they just melted pieces of glass fibers with a hydrogen plane.

And they got kind of these little balls of glass.