Older colloquia

Colloquium of Wednesday, 3 Oct. 2012

Speaker: Dr. Regine Frank

Topic: Onsager’s consequence: the lasing mode volume of random lasers

Abstract: In any quantum or wave system dissipation leads to decoherence. Therefore, it was surprising in first instance when experiments on strongly lossy random lasers showed unambiguously by measurements of the photon statistics and of the lasing mode volume that coherent feedback is possible in such systems. In coherent-feedback lasers the photons form a far-from-equilibrium condensate in the sense that a single quantum state is occupied by a macroscopic number of photons. We demonstrate that the lossy dynamics of random lasers alone imply a three dimensional finite lasing mode extent, thus resolving the puzzle about coherent feedback without resonator. Our theory of random lasing including nonlinear gain and gain saturation predicts a characteristic dependence of this lasing mode volume on the pump intensity, which can be tested experimentally.

Colloquium of Friday, 20 July 2012

Speaker: Yaron Silberberg (Weizmann Institute)

Topic: Tight-binding in a new light: Quantum random walks in photonic lattices

Abstract: Quantum walks describe the random walk behavior of a quantum particle. When a single photon propagates in an array of coupled optical waveguides, it actually performs a quantum random walk. Photons propagating in such systems evolve in close analogy with electron transport in crystals: Both are modeled by the same tight-binding approximation. This enabled in recent years the direct observations and detailed study of basic condense matter phenomena, from Bloch Oscillations to Anderson Localization. The simultaneous quantum walk of several indistinguishable photons show unique and interesting quantum features in their correlation functions. I will discuss the evolving correlations in periodic and disordered lattices, and I will report the recent observation of topological states in photonic quasi-crystals.

Further information:

Realization of Quantum Walks with Negligible Decoherence in Waveguide Lattices, H.B. Perets et al, Phys. Rev. Lett. 100, 170506 (2008).

Anderson Localization and Nonlinearity in One-Dimensional Disordered Photonic Lattices, Y. Lahini et al, Phys. Rev. Lett. 100, 013906 (2008).

Quantum and Classical Correlations in Waveguide Lattices, Y. Bromberg et al, Phys. Rev. Lett. 102, 253904 (2009).

Quantum Correlations in Anderson Localization of Indistinguishable Particles, Y. Lahini et al, Phys. Rev. Lett. 105, 163905 (2010).

Colloquium of Friday, 20 Apr. 2012

Speaker: Villy Sundström

Topic: Time resolved X-ray spectroscopy for molecular structure dynamics - two paths

Abstract: Our work to develop a table top system for sub-ps X-ray spectroscopy is described, as well as such spectroscopy based on synchrotron and free electron laser ultra short X-ray pulses. Using these techniques, dynamics associated with changes of electronic and geometrical structure of photocatalytic systems are studied.

Bio: Villy Sundström obtained his Ph.D. in 1977 from Umeå University, Sweden, after studies at Bell Labs under the guidance of Prof. Peter Renzepis. Now he is professor of Chemical Physics at Lund University. Research interests include light harvesting processes in natural and artificial photosynthesis, carotenoid photophysics, photochemistry of melanin pigments, photophysics of novel solar cell materials such as organic semiconductors and dye sensitized semiconductors, molecular structural dynamics studied by ultrafast X-ray spectroscopy.

Colloquium of Friday, 18 Nov. 2011

Speaker: Yonatan Sivan, Imperial College London

Topic: Time-reversal of short optical pulses using switchable mirrors

Abstract: We show that short pulses propagating in zero-gap periodic systems can be reversed with 100% efficiency by using weak nonadiabatic tuning of the wave velocity at time scales that can be much slower than the period. Unlike previous schemes, we demonstrate reversal of broadband (few cycle) pulses with simple structures. Our scheme may thus open the way to time reversal in a variety of systems for which it was not accessible before. [Sivan and Pendry, Phys. Rev. Lett. 2011 106, 193902.]

Colloquium of Friday, 28 Oct. 2011

Speaker: Prof. Vahid Sandoghdar

Director, Max-Planck-Institute for the Science of Light, Erlangen, Germany.

Topic: On Single Photons and Single Atoms

More info: http://www.mpl.mpg.de/people/nano-optics-group/director.html

Colloquium of Thursday Sept. 15th 2011

Speaker: Dr. Jose Pozo (TNO)

Topic: Photonic Sensing @TNO

Abstract: Recent advances in the fabrication technology of photonic integrated circuits has made it possible to use the CMOS technology, which has a strong track record in the electronics integrated circuits (ICs) industry, for photonic integrated circuit fabrication. This makes low-cost photonic ICs available for applications. TNO has started a Photonic Sensing activity, which exploits these latest technology trends to design low-cost and disposable photonic sensors. In this talk, an overview of the state of the art technology, the applications, the industry and the latest trends of the Photonic Sensing industry will be presented.

Bio: Dr. Jose Pozo is working at TNO since 2010. In the last 10 years he has worked in 4 different countries in the field of nanophotonics gaining experience on integration and material characterization. He graduated from the Universidad Publica de Navarra (Spain) and Vrije Universiteit Brussel (Belgium) as an Electrical Engineer with MsC in Telecommunications. He did his PhD at the University of Bristol (United Kingdom) on the study of GaInNAs/GaAs lasers towards uncooled operation. Consequently he joined the COBRA Research Institute (Eindhoven, The Netherlands) when he worked on the study of chaotic semiconductor lasers as emitter and receivers of a chaos-encrypted communication link; and on the development of a novel concept for an integrated tunable laser based on filtered feedback. He joined TNO in 2010 as a scientist specialist in integrated nanophotonics.

Colloquium of Monday August 29th, 2011

Speaker: Dr. Henri Thyrrestrup Nielsen, Technical University of Denmark

Topic: Mode Distributions and Cavity QED in the Anderson Localized Regime

Abstract: The talk will review the latest results from the leading DTU group on (Anderson) localizing light as a result of (intentional) disorder in photonic crystal waveguides.

Bio: Henri Thyrrestrup Nielsen received his masters degree at DTU on cavity QED in photonic crystals. He obtained his PhD in 2011 from the group of prof. Peter Lodahl at DTU.

Colloquium of Friday 29th of July, 2011

Speaker: Dr. Gleb Vdovin from Flexible Optical BV

Topic: Smart optics - an old new technology

Bio: Gleb Vdovin received his masters degree in Optical Engineering in 1986 from the Leningrad Institute of Fine Mechanics and Optics (USSR), and his PhD in 1996 from Delft University of Technology in the Netherlands, with thesis "Adaptive mirror micromachined in silicon".

In 2009 he decided to terminate his UHD employment at TU Delft, to have more freedom for business development. He is a founder of OKO Technologies, a company that since 1997 develops and produces adaptive optical components and systems. In 1997 he received Rudolph Kingslake Medal and Prize from SPIE. A number of papers published by Dr. G. Vdovin received citation index of higher than 100. Company website: http://www.okotech.com/

Abstract: Adaptive optics was suggested in the 5-th decade of the 20th century by H. Babcock (USA) and by V Linnik (USSR) for the compensation of atmospheric turbulence. In more than 50 years of development the technology found its way into industrial, medical, scientific and military applications.

The talk will give an overview of latest achievements in the field of adaptive and smart optics, with a reference to the products and systems developed by Flexible optical BV (OKO).

Colloquium of Friday May 20th, 2011

Speaker: Thomas Volz from the ETH in Zurich, Switzerland

Topic: Mesoscopic cavity QED with a single quantum dot

Abstract: In this talk, I will review our recent experimental efforts in understanding the physics of a single quantum dot strongly coupled to a photonic crystal defect cavity. In particular, I will discuss the effect of far-off resonant cavity feeding, i.e. the efficient emission of cavity light upon excitation of the quantum dot in the case of large quantum dot-cavity detuning. This effect has no counterpart in an atomic-physics cavity-QED setting. The second part of the talk is devoted to our most recent experimental results on the observation of strongly-correlated photons from the quantum-dot cavity system. Here, using resonant scattering spectroscopy, we were able to demonstrate both strong photon anti-bunching due to photon blockade and photon bunching due to a two-photon transition to the second manifold of the Jaynes-Cummings ladder. The observed photon correlations directly demonstrate for the first time the non-linearity of the Jaynes-Cummings ladder in an integrated photonic device in the solid state. Moreover, they open up the possibility to realize more complex photonic devices on a chip, such as a single-photon transistor or a quantum-optical Josephson interferometer.

Colloquium of Friday April 29th, 2011

Speaker: Robert Moerland from the Aalto University, Optics & Photonics and Quantym Dynamics groups, Espoo Finland

Topic: Vacuum Rabi splitting and strong coupling dynamics for surface plasmon polaritons and Rhodamine 6G molecules

Abstract: Coherent phenomena in Surface Plasmon Polariton (SPP)/emitter systems, where strong coupling dominates, are an intensly studied subject for lasing and coherent energy transfer applications. Also a coherent phenomenon is vacuum Rabi splitting; we report on strong coupling between surface-plasmon polaritons (SPP) and Rhodamine 6G (R6G) molecules, with double vacuum Rabi splitting energies up to 230 and 110 meV. In addition, we demonstrate the emission of all three energy branches of the strongly coupled SPP-exciton hybrid system, revealing features of system dynamics that are not visible in conventional reflectometry. Finally, in analogy to tunable-Q microcavities, we show that the Rabi splitting can be controlled by adjusting the interaction time between waveguided SPPs and R6G deposited on top of the waveguide. The interaction time can be controlled with sub-fs precision by adjusting the length of the R6G area with standard lithography methods.

Colloquium of Thursday April 28th, 2011

Speaker: Hui Cao from Yale (More info on the speaker: http://www.eng.yale.edu/caolab/)

Topic: Random laser, bio-inspired laser and time-reversed laser

Abstract: In this talk, I will review our studies of photonic nanostructures of random morphology. First, I show how we can trap light in such structures to make random lasers. Next, learning from the non-iridescent color generation by isotropic nanostructures in bird feathers, we use short-range order to enhance light confinement and improve lasing efficiency in artificial nanostructures. Finally I will introduce our recent work on time-reversed laser – coherent perfect absorber.

Colloquium of Tuesday April 5th, 2011

Speaker: Dr. Sebastian Slama from the university of Tübingen, Germany

Topic: Surface Quantum Optics - Ultracold atoms in plasmonically tailored optical near-fields

Abstract: Surface Quantum Optics is an emerging field in physics which connects ultracold atoms with solid surfaces with the perspective to generate surface nanotraps for cold atoms and hybrid atom – solid state systems [1]. Such surface traps can be tailored with sub-wavelength resolution by plasmonic structures which are integrated on the substrate. We investigate such systems with the goal to build ultra-steep dipole traps close to plasmonic nanowires for strong coupling between single atoms and single plasmons. Along this way physical effects have to be faced like Casimir Polder forces which are typically strongly attractive and can lead to a loss of atoms from the trap.

In my talk I will report on our work on cold atoms in evanescent light fields close to a dielectric prism. The first part deals with our measurement of the Casimir-Polder force with cold atoms [2]. The second part is on the interaction of ultracold atoms with the optical near-fields above integrated micro- and nanostructures. In this context, we used clouds of ultracold atoms as optical near-field probes and measured surface plasmon resonance above various gold structures. Furthermore, I will show matter-wave diffraction of Bose-Einstein condensates from such tailored near-fields, demonstrating the possible application of such devices for matter-wave optics.

[1] H. Bender, Ph. Courteille, C. Zimmermann, and S. Slama, Appl. Phys. B 96, 275 (2009).

[2] H. Bender, Ph.W. Courteille, C. Marzok, C. Zimmermann, and S. Slama, Phys. Rev. Lett. 104, 083201 (2010).

Colloquium of Friday March 25th, 2011

Speaker: Dr. Karla de Bruin & Dr. Arian van Asten (National Forensic Institute (NFI))

Topic: Possible applications of optical techniques on the crime scene

Colloquium of March 7th, 2011

Speaker: Wolfgang Langbein (http://langsrv.astro.cf.ac.uk/)

Topic: Novel Multiphoton Microscopy Techniques for Cell Imaging: CARS Microscopy and Resonant Four-Wave Mixing

Abstract: This talk will discuss two novel multiphoton microscopy techniques. Firstly, frequency-differential CARS (D-CARS) using linearly chirped femtosecond laser pulses derived from a single source.

By replicating the Pump-Stokes pair into a pulse train at twice the laser repetition rate and adjusting the Raman frequency probed by each pair, CARS at two vibrational frequencies is detected simultaneously by a single photomultiplier.

Secondly, we demonstrate multiphoton microscopy exploiting four-wave mixing (FWM) of gold nanoparticles (GNPs) triply resonant to their surface plasmon. The coherent, transient and resonant nature of this signal allows its detection free from the background limiting other contrast methods for GNPs. We show high-contrast high-resolution imaging of gold-labels down to 5nm size in Golgi structures of HepG2 cells. By detecting the transient nonlinearity of single GNPs with 100fs pulses, furthermore we gain fundamental insights into the physical processes creating FWM.

Colloquium of Wednesday December 15th, 2010

Speaker: Prof. dr. Jean-Jacques Greffet

Topic: Tailoring local density of states with surface waves: application to nanoantennas and enhanced radiative heat transfer.

Biography: Prof. Greffet graduated in 1988 at the University of Orsay. In 1995 he became full professor at the Ecole Centrale de Paris. He was invited professor at the Institute of Optics in Rochester (USA) in 2001-2002. Recently, he has started a research group at the well-known Institut d'Optique in Palaiseau, France.

Colloquium of Thursday December 9th, 2010

Speaker: Bill Barnes

Topic: Plasmonics with Particles

Biography: Professor William Barnes received his BSc and PhD in Physics from Exeter in 1983 and 1986 respectively. His PhD work was on the optical properties of organic thin films. From 1986 to 1992, he was a research fellow in the Optoelectronics Research Centre at Southampton University, where he worked on fibre lasers and amplifiers. In 1992, he was appointed to a staff position at the University of Exeter. Since then, he has built up a research group working on light-matter interactions in general and plasmonics in particular.

For more information: http://newton.ex.ac.uk/research/emag/wlb/

Colloquium of Friday Nov. 12th, 2010

Speaker: Zhipei Sun from the Nanomaterials and Spectroscopy group

Topic: Ultrafast Fiber Lasers Mode-Locked by Nanotubes and Graphene

Abstract: Carbon nanotubes (CNTs) are excellent saturable absorbers, i.e. they become transparent under sufficiently intense light. This has great potential for applications in photonics. By tuning the nanotube diameter it is easy to cover a broad optical range of interest for telecommunications, medicine and military applications. The performance of CNTs based saturable absorbers strongly depends on their concentration, bundle size, and transparency of the polymer matrix. CNT saturable absorbers can be produced by cheap wet chemistry and can be easily integrated into polymer photonic systems. Here, we review the fabrication and characterization of saturable absorbers based on CNT-polymer composites. These are successfully used to mode-lock lasers in a broad spectral range. We report the realization of a mode-locked tuneable fiber laser. This is achieved through the control of amplification at the transitions of an Er3+ gain medium by placing a band pass filter in the cavity. This gives 2.4 ps pulses continuously tuneable between 1518 and 1558 nm, the widest to date. We also present a stretched-pulse fibre laser generating ~115 fs pulses. This allows us achieve high power outputs, exceeding 1.6 W, orders of magnitude higher than previous nanotube-based fibre lasers. We will then extend our investigation to graphene. Single and few layer graphene also have strong nonlinear optical properties with ultrafast response over a broad spectral range. We will report the linear and nonlinear optical characterization of graphene-polymer composites prepared using wet chemistry techniques. The composites are then integrated in a fiber laser cavity, to generate ultrafast pulses. We obtain pulse duration of sub-200fs at 1560nm with a 15.6nm spectral bandwidth. Tuneable mode-locked and Q-switched pulses using graphene based saturable absorbers also are demonstrated. These graphene composites are expected to mode-lock from visible to IR due to its broad absorption range, with the potential to overcome the wide tunability of nanotubes.

Colloquium of Friday March 12th, 2010

Speaker: Prof. Eberhard Riedle, BioMolecular Optics, Ludwig-Maximilians-Universität München

Topic: From chemical to optical control of complex reactions

Abstract: The talk will focus on the optical aspects of "real chemical" time-resolved spectroscopy to the generation of sub-20 fs shaped UV pulses.

Colloquium of Friday August 28th, 2009

Speaker: Rana Biswas

Topic: Sub wavelength hole arrays and photonic crystals- new applications

Biography: Dr. Biswas is one of the pioneers in the field of photonic crystals, and works with the leading Ames Laboratory Photonics group. He has performed seminal work, notably on (theory of) 3D photonic crystals, and has also done prime theoretical work on condensed matter physics, sensors, and physics at the nanoscale. See also his personal website at www.mrc.iastate.edu/NewStaff/RanaBiswas.htm