We present our experiments on refractometric sensing with ultrahigh-Q, crystalline, birefringent magnesium fluoride (MgF2) whispering gallery mode resonators. The difference to fused silica which is most commonly used for sensing experiments is the small refractive index of MgF2 which is very close to that of water. Compared to fused silica this leads to more than 50% longer evanescent fields and a 4:25 times larger sensitivity. Moreover the birefringence amplifies the sensitivity difference between TM and TE type modes which will enhance sensing experiments based on difference frequency measurements. We estimate the performance of our resonators and compare them with fused silica theoretically and present experimental data showing the interferometrically measured evanescent field decay and the sensitivity of mm-sized MgF2 whispering gallery mode resonators immersed in water. These data show reasonable agreement with the developed theory. Furthermore, we observe stable Q factors in water well above 1 x 10(8). (C) 2014 Optical Society of America
Crystalline MgF2 whispering gallery mode resonators for enhanced bulk
index sensitivity
R. Zeltner,
F. Sedlmeir,
G. Leuchs,
H. G. L. Schwefel
EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS
223
(10)
1989-1994
(2014)
| Journal
We report on experiments on refractrometric sensing with crystalline Whispering Gallery Mode (WGM) resonators made of magnesium fluoride, which has a refractive index that is only slightly larger than that of water (Delta n approximate to 0.05). The resulting evanescent field of a WGM resonator placed in an aqueous environment penetrates therefore deep into the surrounding medium, which makes it a promising candidate for sensing applications. We measured a bulk index sensitivity of 1.09 nm/RIU (refractive index unit) in a resonator with a radius of R = 2.91mm and intrinsic Q-factors of more than 10(8) in aqueous environments. Furthermore, we describe the fabrication process of crystalline WGM resonators.
Ultrabroadband Airy light bullets
P. Piksarv,
A. Valdmann,
H. Valtna-Lukner,
P. Saari
We present the measurements of the spatiotemporal impulse responses of two optical systems for launching ultrashort Airy pulses, including ultrabroadband nonspreading Airy beams whose main lobe size remains invariantly small over propagation. First, a spatial light modulator and, second, a custom refractive element with continuous surface profile were used to impose the required cubic phase on the input field. A white-light spectral interferometry setup based on the SEA TADPOLE technique was applied for full spatio-temporal characterization of the impulse response with ultrahigh temporal resolution approaching a single cycle of the light wave. The results were compared to the theoretical model.
Atomic mercury vapor inside a hollow-core photonic crystal fiber
Ulrich Vogl,
Christian Peuntinger,
Nicolas Y. Joly,
Philip St. J. Russell,
Christoph Marquardt,
Gerd Leuchs
We demonstrate high atomic mercury vapor pressure in a kagome-style hollow-core photonic crystal fiber at room temperature. After a few days of exposure to mercury vapor the fiber is homogeneously filled and the optical depth achieved remains constant. With incoherent optical pumping from the ground state we achieve an optical depth of 114 at the 6(3)P(2) - 6(3)D(3) transition, corresponding to an atomic mercury number density of 6 x 10(10) cm(-3). The use of mercury vapor in quasi one-dimensional confinement may be advantageous compared to chemically more active alkali vapor, while offering strong optical nonlinearities in the ultraviolet region of the optical spectrum. (C) 2014 Optical Society of America
Dynamic operation of optical fibres beyond the single-mode regime
facilitates the orientation of biological cells
Moritz Kreysing,
Dino Ott,
Michael J. Schmidberger,
Oliver Otto,
Mirjam Schuermann,
Estela Martin-Badosa,
Graeme Whyte,
Jochen Guck
The classical purpose of optical fibres is delivery of either optical power, as for welding, or temporal information, as for telecommunication. Maximum performance in both cases is provided by the use of single-mode optical fibres. However, transmitting spatial information, which necessitates higher-order modes, is difficult because their dispersion relation leads to dephasing and a deterioration of the intensity distribution with propagation distance. Here we consciously exploit the fundamental cause of the beam deterioration-the dispersion relation of the underlying vectorial electromagnetic modes-by their selective excitation using adaptive optics. This allows us to produce output beams of high modal purity, which are well defined in three dimensions. The output beam distribution is even robust against significant bending of the fibre. The utility of this approach is exemplified by the controlled rotational manipulation of live cells in a dual-beam fibre-optical trap integrated into a modular lab-on-chip system.
Orbital-angular-momentum-preserving helical Bloch modes in twisted photonic crystal fiber
X. M. Xi,
G. K. L. Wong,
M. H. Frosz,
F. Babic,
G. Ahmed,
X. Jiang,
T. G. Euser,
P. St. J. Russell
In optical fiber telecommunications, there is much current work on the use of orbital angular momentum (OAM) modes for increasing channel capacity. Here we study the properties of a helically twisted photonic crystal fiber (PCF) that preserves the chirality of OAM modes of the same order, i.e., it inhibits scattering between an order +1 mode to an order -1 mode. This is achieved by thermally inducing a helical twist in a PCF with a novel three-bladed Y-shaped core. The effect is seen for twist periods of a few millimeters or less. We develop a novel scalar theory to analyze the properties of the twisted fiber, based on a helicoidal extension to Bloch wave theory. It yields results that are in excellent agreement with full finite element simulations. Since twisted PCFs with complex core structures can be produced in long lengths from a fiber drawing tower, they are of potential interest for increasing channel capacity in optical telecommunications, but the result is also of interest to the photonic crystal community, where a new kind of guided helical Bloch mode is sure to excite interest, and among the spin-orbit coupling community. (C) 2014 Optical Society of America
As2S3-silica double-nanospike waveguide for mid-infrared supercontinuum
generation
Shangran Xie,
Francesco Tani,
John C. Travers,
Patrick Uebel,
Celine Caillaud,
Johann Troles,
Markus A. Schmidt,
Philip St J. Russell
A double-nanospike As2S3-silica hybrid waveguide structure is reported. The structure comprises nanotapers at input and output ends of a step-index waveguide with a subwavelength core (1 mu m in diameter), with the aim of increasing the in-coupling and out-coupling efficiency. The design of the input nanospike is numerically optimized to match both the diameter and divergence of the input beam, resulting in efficient excitation of the fundamental mode of the waveguide. The output nanospike is introduced to reduce the output beam divergence and the strong endface Fresnel reflection. The insertion loss of the waveguide is measured to be similar to 2 dB at 1550 nm in the case of free-space in-coupling, which is similar to 7 dB lower than the previously reported single-nanospike waveguide. By pumping a 3-mm-long waveguide at 1550 nm using a 60-fs fiber laser, an octave-spanning supercontinuum (from 0.8 to beyond 2.5 mu m) is generated at 38 pJ input energy. (C) 2014 Optical Society of America
In Situ Heterogeneous Catalysis Monitoring in a Hollow-Core Photonic
Crystal Fiber Microflow Reactor
Ana M. Cubillas,
Matthias Schmidt,
Tijmen G. Euser,
Nicola Taccardi,
Sarah Unterkofler,
Philip St. J. Russell,
Peter Wasserscheid,
Bastian J. M. Etzold
We propose a general technique to retrieve the information of dipole-forbidden resonances in the autoionizing region. In the simulation, a helium atom is pumped by an isolated attosecond pulse in the extreme ultraviolet (EUV) combined with a few-femtosecond laser pulse. The excited wave packet consists of the S-1, P-1, and D-1 states, including the background continua, near the 2s2p(P-1) doubly excited state. The resultant electron spectra with various laser intensities and time delays between the EUV and laser pulses are obtained by a multilevel model and an ab initio time-dependent Schrodinger equation calculation. By taking the ab initio calculation as a "virtual measurement," the dipole-forbidden resonances are characterized by the multilevel model. We found that in contrast to the common assumption, the nonresonant coupling between the continua plays a significant role in the time-delayed electron spectra, which shows the correlation effect between photoelectrons before they leave the core. This technique takes the advantages of ultrashort pulses uniquely and would be a timely test for the current attosecond technology.
Broadband single-photon-level memory in a hollow-core photonic crystal
fibre
M. R. Sprague,
P. S. Michelberger,
T. F. M. Champion,
D. G. England,
J. Nunn,
X. -M. Jin,
W. S. Kolthammer,
A. Abdolvand,
P. St J. Russell, et al.
Storing information encoded in light is critical for realizing optical buffers for all-optical signal processing(1,2) and quantum memories for quantum information processing(3,4). These proposals require efficient interaction between atoms and a well-defined optical mode. Photonic crystal fibres can enhance light-matter interactions and have engendered a broad range of nonlinear effects(5); however, the storage of light has proven elusive. Here, we report the first demonstration of an optical memory in a hollow-core photonic crystal fibre. We store gigahertz-bandwidth light in the hyperfine coherence of caesium atoms at room temperature using a far-detuned Raman interaction. We demonstrate a signal-to-noise ratio of 2.6:1 at the single-photon level and a memory efficiency of 27 +/- 1%. Our results demonstrate the potential of a room-temperature fibre-integrated optical memory for implementing local nodes of quantum information networks.
Optimized photonic gauge of extreme high vacuum with Petawatt lasers
Angel Paredes,
David Novoa,
Daniele Tommasini,
Hector Mas
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS
47
(6)
065601
(2014)
| Journal
One of the latest proposed applications of ultra-intense laser pulses is their possible use to gauge extreme high vacuum by measuring the photon radiation resulting from nonlinear Thomson scattering within a vacuum tube. Here, we provide a complete analysis of the process, computing the expected rates and spectra, both for linear and circular polarizations of the laser pulses, taking into account the effect of the time envelope in a slowly varying envelope approximation. We also design a realistic experimental configuration allowing for the implementation of the idea and compute the corresponding geometric efficiencies. Finally, we develop an optimization procedure for this photonic gauge of extreme high vacuum at high repetition rate Petawatt and multi-Petawatt laser facilities, such as VEGA, JuSPARC and ELI.
Multimode ultrafast nonlinear optics in optical waveguides: numerical
modeling and experiments in kagome photonic-crystal fiber
Francesco Tani,
John C. Travers,
Philip St. J. Russell
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS
31
(2)
311-320
(2014)
| Journal
We introduce a general full-field propagation equation for optical waveguides, including both fundamental and higher order modes, and apply it to the investigation of spatial nonlinear effects of ultrafast and extremely broad-band nonlinear processes in hollow-core optical fibers. The model is used to describe pulse propagation in gas-filled hollow-core waveguides including the full dispersion, Kerr, and ionization effects. We study third-harmonic generation into higher order modes, soliton emission of resonant dispersive waves into higher order modes, intermodal four-wave mixing, and Kerr-driven transverse self-focusing and plasma-defocusing, all in a gas-filled kagome photonic crystal fiber system. In the latter case a form of waveguide-based filamentation is numerically predicted. (C) 2014 Optical Society of America
Selective excitation of higher order modes in hollow-core PCF via
prism-coupling
Barbara M. Trabold,
David Novoa,
Amir Abdolvand,
Philip St. J. Russell
Prism-coupling through the microstructured cladding is used to selectively excite individual higher order modes in hollow-core photonic crystal fibers (PCFs). Mode selection is achieved by varying the angle between the incoming beam and the fiber axis, in order to match the axial wavevector component to that of the desired mode. The technique allows accurate measurement of the effective indices and transmission losses of modes of arbitrary order, even those with highly complex transverse field distributions that would be extremely difficult to excite by conventional endfire coupling. (C) 2014 Optical Society of America
Realization of laterally nondispersing ultrabroadband Airy pulses
Andreas Valdmann,
Peeter Piksarv,
Heli Valtna-Lukner,
Peeter Saari
We present the measurements of the spatiotemporal impulse response of a system creating nondispersing Airy pulses, i.e., ultrabroadband Airy beams whose main lobe size remains constant over propagation. A custom refractive element with a continuous surface profile was used to impose the cubic phase on the input beam. The impulse response of the Airy pulse generator was spatiotemporally characterized by applying a white-light spatial-spectral interferometry setup based on the SEA TADPOLE technique. The results were compared with the theoretical model and previously spatiotemporally characterized Airy pulses generated by a spatial light modulator. (C) 2014 Optical Society of America
Hollow-core photonic crystal fibres for gas-based nonlinear optics
P. St J. Russell,
P. Hoelzer,
W. Chang,
A. Abdolvand,
J. C. Travers
Unlike the capillaries conventionally used for gas-based spectral broadening of ultrashort (<100 fs) multi-millijoule pulses, which produce only normal dispersion at usable pressure levels, hollow-core photonic crystal fibres provide pressure-adjustable normal or anomalous dispersion. They also permit low-loss guidance in a hollow channel that is about ten times narrower and has a 100-fold-higher effective nonlinearity than capillary-based systems. This has led to several dramatic results, including soliton compression to few-cycle pulses, widely tunable deep-ultraviolet light sources, novel soliton-plasma interactions and multi-octave Raman frequency combs. A new generation of versatile and efficient gas-based light sources, which are tunable from the vacuum ultraviolet to the near infrared, and of versatile and efficient pulse compression devices is emerging.
Self-induced mode mixing of ultraintense lasers in vacuum
We study the effects of the quantum vacuum on the propagation of a Gaussian laser beam in vacuum. By means of a double perturbative expansion in paraxiality and quantum vacuum terms, we provide analytical expressions for the self-induced transverse mode mixing, rotation of polarization, and third harmonic generarion. We discuss the possibility of searching for the self-induced, spatially dependent phase shift of a multipetawatt laser pulse, which may allow the testing of quantum electrodynamics and new physics models, such as Born-Infeld theory and models involving new minicharged or axion-like particles, in parametric regions that have not yet been explored in laboratory experiments.
The key role of off-axis singularities in free-space vortex
transmutation
David Novoa,
Inigo J. Sola,
Miguel Angel Garcia-March,
Albert Ferrando
We experimentally demonstrate the generation of off-axis phase singularities in a vortex transmutation process induced by the breaking of rotational symmetry. The process takes place in free space by launching a highly charged vortex, owning full rotational symmetry, into a linear thin diffractive element presenting discrete rotational symmetry. It is shown that off-axis phase singularities follow straight dark rays bifurcating from the symmetry axis. This phenomenon may provide new routes toward the spatial control of multiple phase singularities for applications in atom trapping and particle manipulation.
Supercontinuum up-conversion via molecular modulation in gas-filled
hollow-core PCF
S. T. Bauerschmidt,
D. Novoa,
B. M. Trabold,
A. Abdolvand,
P. St J. Russell
We report on the efficient, tunable, and selective frequency up-conversion of a supercontinuum spectrum via molecular modulation in a hydrogen-filled hollow-core photonic crystal fiber. The vibrational Q(1) Raman transition of hydrogen is excited in the fiber by a pump pre-pulse, enabling the excitation of a synchronous, collective oscillation of the molecules. This coherence wave is then used to up-shift the frequency of an arbitrarily weak, delayed probe pulse. Perfect phase-matching for this process is achieved by using higher order fiber modes and adjusting the pressure of the filling gas. Conversion efficiencies of similar to 50% are obtained within a tuning range of 25 THz. (C)2014 Optical Society of America
Plasmonic kinks and walking solitons in nonlinear lattices of metal
nanoparticles
Roman E. Noskov,
Daria A. Smirnova,
Yuri S. Kivshar
We study nonlinear effects in one-dimensional (1D) arrays and two-dimensional (2D) lattices composed of metallic nanoparticles with the nonlinear Kerr-like response and an external driving field. We demonstrate the existence of families of moving solitons in 1D arrays and characterize their properties such as an average drifting velocity. We also analyse the impact of varying external field intensity and frequency on the structure and dynamics of kinks in 2D lattices. In particular, we identify the kinks with positive, negative and zero velocity as well as breathing kinks with a self-oscillating profile.
CW-pumped single-pass frequency comb generation by resonant
optomechanical nonlinearity in dual-nanoweb fiber
A. Butsch,
J. R. Koehler,
R. E. Noskov,
P. St. J. Russell
Recent experiments in the field of strong optomechanical interactions have focused on either structures that are simultaneously optically and mechanically resonant, or photonic crystal fibers pumped by a laser intensity modulated at a mechanical resonant frequency of the glass core. Here, we report continuous-wave (CW) pumped self-oscillations of a fiber nanostructure that is only mechanically resonant. Since the mechanism has close similarities to stimulated Raman scattering by molecules, it has been named stimulated Raman-like scattering. The structure consists of two submicrometer thick glass membranes (nanowebs), spaced by a few hundred nanometers and supported inside a 12-cm-long capillary fiber. It is driven into oscillation by a CW pump laser at powers as low as a few milliwatts. As the pump power is increased above threshold, a comb of Stokes and anti-Stokes lines is generated, spaced by the oscillator frequency of similar to 6 MHz. An unprecedentedly high Raman-like gain of similar to 4 x 10(6) m(-1) W-1 is inferred after analysis of the experimental data. Resonant frequencies as high as a few hundred megahertz are possible through the use of thicker and less-wide webs, suggesting that the structure can find application in passive mode-locking of fiber lasers, optical frequency metrology, and spectroscopy. (C) 2014 Optical Society of America
Taking Two-Photon Excitation to Exceptional Path-Lengths in Photonic
Crystal Fiber
Gareth O. S. Williams,
Tijmen G. Euser,
Jochen Arlt,
Philip St. J. Russell,
Anita C. Jones
The well-known, defining feature of two-photon excitation (TPE) is the tight, three-dimensional confinement of excitation at the intense focus of a laser beam. The extremely small excitation volume, on the order of 1 mu m(3) (1 femtoliter), is the basis of far-reaching applications of TPE in fluorescence imaging, photodynamic therapy, nanofabrication, and three-dimensional optical memory. Paradoxically, the difficulty of detecting photochemical events in such a small volume is a barrier to the development of the two-photon-activated molecular systems that are essential to the realization of such applications. We show, using two-photon-excited fluorescence to directly visualize the excitation path, that confinement of both laser beam and sample solution within the 20 mu m hollow core of a photonic crystal fiber permits TPE to be sustained over an extraordinary path-length of more than 10 cm, presenting a new experimental paradigm for ultrasensitive studies of two-photon-induced processes in solution.
Real-time Doppler-assisted tomography of microstructured fibers by side-scattering
Alessio Stefani,
Michael H. Frosz,
Tijmen G. Euser,
Gordon K. L. Wong,
Philip St. J. Russell
We introduce the concept of Doppler-assisted tomography (DAT) and show that it can be applied successfully to non-invasive imaging of the internal microstructure of a photonic crystal fiber. The fiber is spun at similar to 10 Hz around its axis and laterally illuminated with a laser beam. Monitoring the time-dependent Doppler shift of the light scattered by the hollow channels permits the azimuthal angle and radial position of individual channels to be measured. An inverse Radon transform is used to construct an image of the microstructure from the frequency-modulated scattered signal. We also show that DAT can image sub-wavelength features and monitor the structure along a tapered fiber, which is not possible using other techniques without cutting up the taper into several short pieces or filling it with index-matching oil. The non-destructive nature of DAT means that it could potentially be applied to image the fiber microstructure as it emerges from the drawing tower, or indeed to carry out tomography on any transparent microstructured cylindrical object. (C) 2014 Optical Society of America
Midinfrared frequency combs from coherent supercontinuum in chalcogenide
and optical parametric oscillation
Kevin F. Lee,
N. Granzow,
M. A. Schmidt,
W. Chang,
L. Wang,
Q. Coulombier,
J. Troles,
Nick Leindecker,
Konstantin L. Vodopyanov, et al.
We observe the coherence of the supercontinuum generated in a nanospike chalcogenide-silica hybrid waveguide pumped at 2 mu m. The supercontinuum is shown to be coherent with the pump by interfering it with a doubly resonant optical parametric oscillator (OPO) that is itself coherent with the shared pump laser. This enables coherent locking of the OPO to the optically referenced pump frequency comb, resulting in a composite frequency comb with wavelengths from 1 to 6 mu m. (C) 2014 Optical Society of America
Damage-free single-mode transmission of deep-UV light in hollow-core PCF
F. Gebert,
M. H. Frosz,
T. Weiss,
Y. Wan,
A. Ermolov,
N. Y. Joly,
P. O. Schmidt,
P. St. J. Russell
Transmission of UV light with high beam quality and pointing stability is desirable for many experiments in atomic, molecular and optical physics. In particular, laser cooling and coherent manipulation of trapped ions with transitions in the UV require stable, single-mode light delivery. Transmitting even similar to 2 mW CW light at 280 nm through silica solid-core fibers has previously been found to cause transmission degradation after just a few hours due to optical damage. We show that photonic crystal fiber of the kagome type can be used for effectively single-mode transmission with acceptable loss and bending sensitivity. No transmission degradation was observed even after >100 hours of operation with 15 mW CW input power. In addition it is shown that implementation of the fiber in a trapped ion experiment increases the coherence time of the internal state transfer due to an increase in beam pointing stability. (C) 2014 Optical Society of America
Rydberg atoms in hollow-core photonic crystal fibres
G. Epple,
K. S. Kleinbach,
T. G. Euser,
N. Y. Joly,
T. Pfau,
P. St J. Russell,
R. Loew
The exceptionally large polarizability of highly excited Rydberg atoms-six orders of magnitude higher than ground-state atoms-makes them of great interest in fields such as quantum optics, quantum computing, quantum simulation and metrology. However, if they are to be used routinely in applications, a major requirement is their integration into technically feasible, miniaturized devices. Here we show that a Rydberg medium based on room temperature caesium vapour can be confined in broadband-guiding kagome-style hollow-core photonic crystal fibres. Three-photon spectroscopy performed on a caesium-filled fibre detects Rydberg states up to a principal quantum number of n = 40. Besides small energy-level shifts we observe narrow lines confirming the coherence of the Rydberg excitation. Using different Rydberg states and core diameters we study the influence of confinement within the fibre core after different exposure times. Understanding these effects is essential for the successful future development of novel applications based on integrated room temperature Rydberg systems.
Multistability and spontaneous breaking in pulse-shape symmetry in fiber
ring cavities
M. J. Schmidberger,
D. Novoa,
F. Biancalana,
P. St J. Russell,
N. Y. Joly
We describe the spatio-temporal evolution of ultrashort pulses propagating in a fiber ring cavity using an extension of the Lugiato-Lefever model. The model predicts the appearance of multistability and spontaneous symmetry breaking in temporal pulse shape. We also use a hydrodynamical approach to explain the stability of the observed regimes of asymmetry. (C) 2014 Optical Society of America
Accuracy of the capillary approximation for gas-filled kagome-style
photonic crystal fibers
M. A. Finger,
N. Y. Joly,
T. Weiss,
P. St. J. Russell
Precise knowledge of the group velocity dispersion in gas-filled hollow-core photonic crystal fiber is essential for accurate modeling of ultrafast nonlinear dynamics. Here we study the validity of the capillary approximation commonly used to calculate the modal refractive index in kagome-style photonic crystal fibers. For area-preserving core radius alpha(AP) and core wall thickness t, measurements and finite element simulations show that the approximation has an error greater than 15% for wavelengths longer than 0.56 root(alpha(AP)t), independently of the gas-filling pressure. By introducing an empirical wavelength-dependent core radius, the range of validity of the capillary approximation is extended out to a wavelength of at least 0.98 root(alpha(AP)t). (C) 2014 Optical Society of America
Chirped pulse formation dynamics in ultra-long mode-locked fiber lasers
By modeling giant chirped pulse formation in ultra-long, normally dispersive, mode-locked fiber lasers, we verify convergence to a steady-state consisting of highly chirped and coherent, nanosecond-scale pulses, which is in good agreement with recent experimental results. Numerical investigation of the transient dynamics reveals the existence of dark soliton-like structures within the envelope of the initial noisy pulse structure. Quasi-stationary dark solitons can persist throughout a large part of the evolution from noise to a stable dissipative soliton solution of the mode-locked laser cavity. (C) 2014 Optical Society of America
Probing and Controlling Autoionization Dynamics with Attosecond Light
Pulses in a Strong Dressing Laser Field
We review the theoretical investigations of the autoionzing wave packet excited by an isolated attosecond pulse and dressed by a time-delayed intense laser pulse. The few-level model is described and the applications in photoemission and photoabsorption are given. For the three-level, resonantly coupled system, the main features are explained by the Rabi oscillation modulated in the dressing field. For such a system, by precisely controlling the intensity and the time delay of the dressing pulse, we show the shaping of the attosecond pulse when propagating in a gas medium. A more sophisticated multi-level system with coupling terms involving continuum states is also developed, in which the importance of the continuum-continuum coupling is evaluated with the help of an ab initio calculation.
Kontakt
Bitte richten Sie forschungsbezogene Anfragen an philip.russell@mpl.mpg.de und allgemeine Anfragen an Bettina Schwender:
Max-Planck-Institut für die Physik des Lichts Staudtstr. 2 91058 Erlangen
