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The Max Planck Research Group "Ultrafast Quantum Optics" was founded in April 2008. We are associated with T. W. Hänsch's Laser Spectroscopy Department, but are directly funded from Max Planck Headquarters.
Our research focuses on quantum optics in the wider sense, i.e. the investigation of the wave properties of matter and light and their quantum properties. Currently, we concentrate on electrons.
Our goal is to gain control over free electrons to a hitherto unmatched degree. Therefore, we investigate laser-matter interaction on the (sub-) femtosecond time scale, conceive and realize new concepts to trap, guide and steer the electrons, and develop laser sources and laser amplifiers.
In one experiment we investigate how electrons are emitted from sharp metal tips with the help of femtosecond laser pulses. In another we develop novel techniques to guide free electrons solely with electrical microwave fields. In a third experiment we aim at controlling electrons with photonic structures and lasers. Please have a look at each project by clicking on the link "projects" on the left.
The following shows news as they pop up. Please do not hesitate to contact us if you are interested in learning more about our work or if you are interested in joining us.
Heraeus School on Quantum Superposition
Profs. Markus Arndt and Klaus Hornberger are organizing a Heraeus School on Quantum Superposition in Physikzentrum Bad Honnef (near Bonn) in May 2013. Application ends on March 24. We will present our experiments on matter wave interference on attosecond time scales and discuss in depth what we can learn from these results.
- Heraeus School "Exploring the limits of the quantum superposition principle: From matter waves to nanomechanical oscillators"
Quantum electron microscope project
The Gordon and Betty Moore Foundation, Palo Alto, has made it possible that an international group of physicists carries out research towards a new kind of electron microscopy. The groups of Fatih Yanik, Karl Berggren (both MIT), Mark Kasevich (Stanford), Pieter Kruit (TU Delft) and our group will join forces to exploit quantum effects to realize an electron microscope in which the electrons interact much less with the sample than in ordinary electron microscopes. With such a device one may take movies of what's going on in living cells. With current technology, the cell dies almost instantly. Quantum mechanics offers this possibility, but it's hard to realize. We will try anyway.
Special issue out
Annals of Physics' special issue on "Ultrafast Phenomena on the Nanoscale" is out (see announcement of Feb. 2012 below; guest editors: Matthias Kling, Mark Stockman and Peter Hommelhoff). It comprises a collection of more than 25 articles and gives a comprehensive overview over the current status of this still young field of research. The special issue is freely available!
Also the second Dr. u.q.o. has defended his dissertation with distinction -- congratulations, Dr. Hoffrogge! Title of the thesis: A surface-electrode quadrupole guide for electrons.
Theory and experiment go hand in hand -- twice
Together with our theory collaborators Georg Wachter, Christoph Lemell and Joachim Burgdörfer of TU Vienna, we could show that photo-emission from nanotips can be described with models well known from atomic physics, mainly the famous three-step model. For the first time, we, i.e., our friends from Vienna, employed a model able to describe metals to demonstrate the rescattering process. We compared data extracted from theory calculations with experimental data and found very good agreement. Furthermore, in a second publication, besides from a couple of neat experimental details, we could show that strong-field photo-emission from a nanotip can serve as an ideal toy laboratory to investigate strong-field effects. Because of the broken symmetry of the tip, a number of trajectory classes does not exist that exist in atoms, which makes the interpretation of data easier as compared to atoms.
- Physical Review B 2012: Rescattering in Theory and Experiment
- New Journal of Physics 2012: An ideal toy-laboratory for strong-field physics
MPG annual report contribution
Our recent results are summarized in a contribution to the 2011/12 annual report of the Max Planck Society. Dr. Olivia Meyer-Streng kindly contributed to writing this contribution -- thanks!
Markus Schenk has defended his doctoral dissertation with highest honors -- congratulations! Title of his thesis is: Strong field effects and attoseond dynamics in photoemission from metal tips.
10. Anniversary of attosecond physics: Special issue of J. Phys. B
It's hard to believe, but attosecond physics has already turned 10. Journal of Physics B celebrates this anniversary with a special issue. Even though attosecond physics at sharp tips is less than one year old, we were invited to write a review abut this fast paced field. The result, together with the other anniversary contributions, have been published now.
- 10th anniversary of attosecond physics: special issue
- Our contribution in simple words
- Our contribution
Special issue on Ultrafast Phenomena at the nanoscale
In summer of 2012, a special issue of Annals of Physics will be closed that will give an overview of the whole, fast paced field of ultrafast phenomena at the nanoscale. We, Matthias Kling, Mark Stockman and Peter Hommelhoff, cordially invite contributions. Please follow the link if you are interested.
Rescattering physics at metal tip
Together with our colleagues of Technical University of Vienna, we have investigated what exactly happens at the surface of our sharp metal tips if they are exposed to few cycle laser pulses. We investigate both theoretically and experimentally the process and observe that a part of the electrons that is emitted from the tip is driven back towards the metal surface. There electrons are scattered back and matter wave intereference effects arise (see image). The rescattering effect has so far not been observed off a metal surface. It might lead to a new method that allows measuring ultrafast surface dynamics.
UQO in October 2011
Two years after the previous group picture, it was time for another on: This is the UQOs as of October 2011 -- again with an honorary member.
NJP article with details and new ideas on microwave guiding of electrons
In this article we consider in detail microwave fields needed to confine electrons in linear Paul traps. We find that propagation effects in long structures can have adverse effects on the trapping potential, to the extent that trapping is fully lost. We have found a solution to this problem and discuss it here. Enjoy reading!
The article is part of a nice NJP focus issue on matter wave optics and interferometry.
Even though he couldn't start working full-time right away, Trey has apparently already inherited the hands-on approach of his dad's, John.
Nature article: Tip-based control of electrons on attosecond time scale
Attosecond science is based on steering of electrons with the electric field of well-controlled femtosecond laser pulses. It has led to, for example, the generation of XUV light pulses with a duration in the sub-100-attosecond regime, to the measurement of intra-molecular dynamics by diffraction of an electron taken from the molecule under scrutiny, and to novel ultrafast electron holography. All these effects have been observed with atoms or molecules in the gas phase. Although predicted to occur, a strong light-phase sensitivity of electrons liberated by few-cycle laser pulses from solids has hitherto been elusive. Here we show a carrier-envelope (C-E) phase-dependent current modulation of up to 100% recorded in spectra of electrons laseremitted from a nanometric tungsten tip. Controlled by the C-E phase, electrons originate from either one or two sub-500 as long instances within the 6-fs laser pulse, leading to the presence or absence of spectral interference. We also show that coherent elastic re-scattering of liberated electrons takes place at the metal surface. Due to field enhancement at the tip, a simple laser oscillator suffices to reach the required peak electric field strengths, allowing attosecond science experiments to be performed at the 100-Megahertz repetition rate level.
This is how our article starts that has been published in the July 7, 2011 issue of Nature. Please find additional information by following the links below. Feel free to contact us if you would like to hear more or obtain high resolution images.
Phys. Rev. Lett. with results of Jakob's diploma thesis
The results of Jakob Hammer's diploma thesis, which he did in Orsay, France, have been published in Physical Review Letters: Microwave cooling of Josephson plasma oscillations -- congratulations!
Frankfurter Allgemeine reports
Germany's top newspaper "Frankfurter Allgemeine Zeitung" reported on our electron guiding results (see below) -- electrons seem to be appealing.
Electron guiding on PRL cover
What a nice surprise! One of our figures made it on the PRL cover. Have a look on the right how great the picture looks if PRL's graphics editors get a hand on it. Below: our original.
Article on microwave guiding of electrons published in PRL
Our manuscript on the guiding of electrons in microwave fields just appeared in PRL (see also below: Electrons in microwave Paul trap). PRL selected it as "editor's choice for reading across fields" and recommends it scientists from other fields -- which we happily agree with.
In addition, our Vienna friends Jörg Schmiedmayer and Thorsten Schumm were invited by PRL to write a viewpoint on our paper. They nicely explain our work to non-experts and ponder thoughts on the future of the experiment. About 100 out of 16,000 annually published PRL articles receive this special highlighting.
Finest gold tips
Sharp tips made of gold can be useful for plenty of applications -- to make them with high quality is not so simple though. Max Eisele, who recently did his diploma thesis with us, found a simple and benign recipe. Very recently, his publication appeared. On the right you can see such a tip under an optical microscope. The shiny surface indicates the smoothness and great surface quality.
Electrons in microwave Paul trap
We have mapped out the stability region for guiding of electrons in our microwave guide. This together with the idea to directly inject electrons into the transverse ground state of the electron guide, and more we have just submitted for publication. Please go to "Publications" to follow the link to the arXiv to have a look into the manuscript.
ATP manuscript accepted at Phys. Rev. Lett.
Our manuscript on above-threshold photoemission and strong-field effects in electron emission from sharp tips has been accepted at Physical Review Letter -- great!
Our article describing a new and comparatively simple model to compute and optimize laser amplification was selected as physics highlight by the American Physical Society.
Above-threshold photoemission und strong-field effects
We did energy-resolved measurements of electrons emitted with a few-cycle laser oscillator from a sharp metal tip. We observe that the electrons are emitted with energies much higher than needed to just overcome the potential barrier. This effect is called above-threshold photoemission (ATP). We observe electrons with energies corresponding to up to six photons above the threshold in clear spectra (see figure). When we increase the laser intensity we observe that the lowest-order peak is becoming suppressed, and also that all features of the spectrum are shifted towards smaller energies. Both of these effects are a result of the interaction of the emitted electrons with the laser field: in higher laser intensities the electrons not only need to provide the energy to overcome the barrier but also the wiggle-energy in the laser electric field. This effect can be elegantly described in the so-called dressed-state picture, in which the electronic continuum state is dressed with the light field and is thus light-shifted. We have submitted a publication. A preprint can be found under "publications". Sept. 2010.
Electron guiding works in novel microwave guide
A new waveguide for electrons works! We could guide electrons through a two-dimensional trapping potential that was generated with microwave electric fields, a so-called 2d Paul trap. The 2d-trap is generated above a planar substrate with the help of coplanar waveguide structures. July 2010.
Single-pass laser amplification
We finished a series of experiments on single-pass laser amplification of pulses of a Titanium:sapphire laser in another Titanium:sapphire crystal with a couple of publications. Last we came up with a new model to calculate and numerically optimize the experimental parameters for such experiments, the Tapered-shell model. The paper just came out, see publications.
UQO group as of fall 2009
Members of the UQO group, including one honorary member.
John Breuer has joined our group. He will be working on acceleration of electrons with laser light. Aug. 2009.
Together with Akira Ozawa, Waldemar Schneider und Thomas Udem we recently set up and characterized a cryogenic single pass amplifier for ultrashort Titanium-sapphire laser pulses. This amplifier helps in reaching peak powers exceeding 2MW with sub-8-fs laser pulses at the full oscillator repetition rate of 80 MHz -- all this in a phase stable manner. The power is so high that we were able to efficiently drive a highly-nonlinear process at the full oscillator repetition rate; we demonstrated white-light generation at close to 100 MHz. The crystal was kindly provided by the Riedle group, and the results are published in New Journal of Physics. Spring / summer 2009.
Cooperation with Peter Fierlinger of Munich Universe Cluster
Due to a cooperation with Peter Fierlinger of Munich Universe Cluster we set up the first laser in our lab. Our femtosecond laser is currently running next door -- why: soon to come. November 2008.
Lab warming party
Lab warming party for all those who were part of the remodeling -- keeping fingers crossed was considered supportive action.
Lab remodeling II
Renovation took a while (and still is), but we can move in the lab now. Doesn't it look good?
First grad students -- April 08
Welcome Markus and Johannes!
The lab is anything but ready -- anyways, we are starting.