Markus Pollnau, Chair of the Integrated Optical MicroSystems Group, MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands, is visiting the Faculty of Physics and Astronomy as ASP Visiting Professor in September, October and November 2013. During his stay he will give a series of lectures.
Markus Pollnau received the M.Sc. degree from the University of Hamburg, Germany, in 1992, and the Ph.D. degree for work performed at the University of Bern, Switzerland, in 1996, both in physics. After postdoctoral positions with the University of Southampton, UK and the University of Bern, he was a Project and Research Group Leader with the Swiss Federal Institute of Technology, Lausanne, Switzerland. In 2004, he became a Full Professor and Chair of the Integrated Optical MicroSystems Group, MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands. He has contributed to more than 500 reviewed journal and international conference papers and ten book chapters in the fields of crystal and thin-film growth, rare-earth-ion spectroscopy, solid-state and fiber lasers, as well as waveguide fabrication, devices, and applications. He has presented ~70 invited talks at international conferences and ~30 lectures at international summer schools.
Dr. Pollnau has held European, Swiss, and Dutch personal Fellowships and has obtained numerous National and European Research Grants. In 2013 he was awarded an ERC Advanced Grant from the European Research Council. He has been involved in the organization of major international conferences, e.g., as a Program and General Co-chair of the Conference on Lasers and Electro-Optics (2006/2008) and the Conference on Lasers and Electro-Optics Europe (2009/2011), as founding General Chair and Steering Committee Chair of the Europhoton Conference (2004/2008), and served as Topical Editor for the Journal of the Optical Society of America B (2007-2010) and on the Editorial Board of the journal Laser Physics Letters (2008-2011). In 2013 he was elected to the rank of Fellow by the Optical Society of America for "for seminal contributions to rare-earth-ion spectroscopy and highly efficient dielectric waveguide amplifiers and lasers".
In 2004 I started my work as a full professor. Colleagues asked me about my future research direction. When I replied "rare-earth-ion-doped waveguide amplifiers and lasers", they had the typical I-can't-believe-this-is-true look on their face. One or the other uttered "But we have semiconductor amplifiers and lasers! These have much higher gain and can be directly electrically pumped. Your approach is not competitive!" True - however, only to a certain extent, as we learned by doing. In this first lecture I will discuss rare-earth-ion-doped channel waveguide amplifiers and lasers based on a family of monoclinic crystalline materials, potassium double tungstates. By liquid-phase epitaxy we grow thin layers co-doped with Gd, Lu, and Y to simultaneously achieve lattice matching and high refractive-index contrast with the Y-containing substrate, as well as high doping concentrations of active rare-earth ions such as Yb or Tm. The breath-taking performance of these micro-structured channel waveguides includes a small-signal gain per unit length of ~1000 dB/cm, which is two orders of magnitude higher than previously reported in the literature for any rare-earth-ion-doped material and very well comparable with semiconductor optical amplifiers, as well as lasers with slope efficiencies clearly exceeding 80% and reaching the absolute theoretical limit for the involved transitions.
Tuesday, September 17, 10:00 am, Fraunhofer IOF Jena, Carl-Zeiss-Saal
Keynote at DoKDoK
This lecture describes the operation principle of a continuous-wave (cw) laser. In order to keep the photon rate equation and its solution simple, usually the spontaneous-emission rate is neglected with the argument that it is so much smaller than the stimulated-emission rate. The direct consequence is that in a cw laser the gain would equal the losses. Yet, additional implications are that the light emitted by such a laser would be a pure sine wave with an infinite coherence length, its linewidth would become a delta function, its Q-factor would assume an infinite value, the coherent photon number would build up and coherence would manifest itself inside the resonator only when pumping above the laser threshold, and the threshold inversion would depend only on the total resonator losses. None of these implications holds true for any laser that mankind has ever created. Starting from vacuum fluctuations, we consider spontaneous emission directly in the photon rate equation, thereby a priori avoiding all these inconsistencies. It is then straight-forward to see that in a cw laser the gain is smaller than the losses, a cw laser does not only have a finite linewidth that can be derived in a very simple manner, but also a finite Q-factor, as well as two laser thresholds which are both different from the commonly assumed "threshold inversion". This work was performed in collaboration with Dr. Marc Eichhorn from the French-German Research Institute of St. Louis, France.
Wednesday, October 09, 9:00 am, Ringberg Hotel Suhl, Please note, if you would like to attend this talk at DoKDoK only, you have to register at the conference and pay the visitors fee.
Pre-dinner talk at DoKDoK
Before asking yourself the question how to become a professor, as a potential candidate you should ask yourself the question whether it is desirable to become a professor. If the answer to this initial question is "no", let this pre-dinner talk convince you that your choice is right. If against all rational evidence the answer is "yes", your choice may nevertheless be right. You are welcome to participate in a lecture about the many Do's and Don't Do's and what prey to look out for when hunting along the stony route towards academic independence and, moreover, what to expect when entering the academic "paradise".
Wednesday, October 09, 4:20 pm, Ringberg Hotel Suhl, Please note, if you would like to attend this talk at DoKDoK only, you have to register at the conference and pay the visitors fee.
Amorphous dielectric materials can be deposited on a silicon chip, making them compatible with silicon photonics and electronics. However, rare-earth ions doped into such amorphous materials exhibit inhomogeneous broadening of their transition lines, resulting in small transition cross-sections. Consequently, such materials produce only a small gain per unit length. Nevertheless, if this gain is large enough to compensate the round-trip losses of a micro-resonator, these materials can generate efficient laser oscillation on a silicon chip. Since the refractive-index changes accompanied with the excitation of rare-earth ions in a dielectric material are orders of magnitude smaller and temporally significantly more stable than those induced by electron-hole-pair excitation in a semiconductor, rare-earth-ion-activated distributed-feedback (DFB) lasers produce laser line widths which are several orders of magnitude narrower than those obtained in their semiconductor counterparts. I will discuss our recent work on amorphous Al2O3:Er3+ and Al2O3:Yb3+ DFB lasers with free-running linewidths down to 1.7 kHz, dual-wavelength operation, microwave beat-frequency generation, and intra-laser-cavity nano-particle sensing on a silicon chip.
Friday October 11, 10:00 am, Fraunhofer IOF Jena, Carl-Zeiss-Saal
During the second half of the past century integration and miniaturization have led to significant performance improvement and cost reduction of electronic devices. During the present half century, photonics will follow the same path. In this lecture I will show two examples. Firstly, in an optofluidic chip, we demonstrate electrophoretic separation of DNA molecules with sub-base-pair resolution and ultra-low limit of detection down to a few molecules in the detection volume. Different sets of exclusively color-labeled DNA fragments from independent human genomic segments, associated with genetic predispositions to breast cancer and anemia, are traced back to their origin by modulation-frequency-encoded multi-wavelength laser excitation, fluorescence detection with a single ultrasensitive photomultiplier, and Fourier analysis decoding. Secondly, optical coherence tomography (OCT) has enabled clinical applications that revolutionized in vivo medical diagnostics. Exploiting integrated optics, we assemble the central components of a spectral-domain OCT system on a silicon chip. The spectrometer comprises an arrayed-waveguide grating, while the beam splitter is realized by a non-uniform adiabatic coupler. With this device whose overall volume is 0.36 cm3 we demonstrate high-quality in vivo imaging in human skin with 1.4-mm penetration depth, 7.5-μm axial resolution, and a signal-to-noise ratio of 74 dB.
Thursday, November 21, 10:00 am, Institute of Applied Physics, Seminar room, Albert-Einstein-Strasse 15, Jena