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Dr Christian Wolff

Biography

Dr. Christian Wolff is a post-doc in the Department of Mathematical Sciences. His current scientific focus is on the theory of the interaction between light and sound in matter, in particular stimulated Brillouin scattering.

Dr. Wolff received his PhD in 2011 from the Karlsruhe Institute of Technology (KIT), Germany for contributions to the theory and numerical treatment of photonic crystals. Afterwards, he joined the Max-Born-Institute for Nonlinear Optics and Short-Pulse Spectroscopy in Berlin for a first post-doc. There, he worked on advanced numerical tools in the context of metal optics.

Postdoctoral Research Associate, School of Mathematical and Physical Sciences
Dip. Physics, Ph D
 
Phone
+61 2 9514 2535
Can supervise: Yes

Conferences

Wolff, C. & Smith, M.J.A. 2016, 'Suppression of Stimulated Brillouin Scattering in composite media', 16th International Conference on Numerical Simulation of Optoelectronic Devices, Sydney.
Wolff, C. & Smith, M.J.A. 2016, 'Optomechanics using COMSOL (invited 3.5 hour workshop)', 16th International Conference on Numerical Simulation of Optoelectronic Devices, Sydney.
Wolff, C., Steel, M.J., Eggleton, B.J. & Poulton, C.G. 2015, 'Geometry-induced inhomogeneous broadening of the stimulated Brillouin resonance and its relation to radiation pressure', 2015 Conference on Lasers and Electro-Optics/Europe, Munich.
Wolff, C. & Busch, K. 2015, 'A generalized Drude model for time-domain simulations of ferromagnetic metals in plasmonics', 36th Progress in Electromagnetics Research Symposium, Prague.
Wolff, C., Steel, M.J., Eggleton, B.J. & Poulton, C.G. 2015, 'Impact of nonlinear loss on Stimulated Brillouin Scattering in silicon waveguides', 36th Progress in Electromagnetics Research Symposium, Prague.
Werra, J.F.M., Wolff, C., Matyssek, C. & Busch, K. 2015, 'Current sheets in the Discontinuous Galerkin Time-Domain method: An application to graphene', Proceedings of SPIE - The International Society for Optical Engineering.
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© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. © 2015 SPIE. We describe the treatment of thin conductive sheets within the Discontinuous Galerkin Time-Domain (DGTD) method for solving the Maxwell equations and apply this approach to the efficient computation of the optical properties of graphene-based systems. In particular, we show that a thin conductive sheet can be handled by incorporating the associated jump conditions of the electromagnetic field into the numerical flux of the DGTD approach. This results in a flexible and efficient numerical scheme that can be applied to a number of systems. Specifically, we show how to treat individual graphene sheets on substrates as well as finite stacks of alternating graphene and dielectric layers by modeling the dispersive and dissipative properties of graphene via a two-term critical-point model for its electrostatically doped conductivity.
Wolff, C. 2015, 'Waves and forces in optics and mechanics', Workshop on OptoMechanics and Brillouin scattering: fundamentals, Applicaitons and Technologies, Sydney.
Wolff, C., Gutsche, P., Steel, M.J., Eggleton, B.J. & Poulton, C.G. 2015, 'Performance limits of stimulated brillouin scattering due to nonlinear loss', Proceedings of SPIE, SPIE Micro+Nano Materials, Devices, and Applications 2015, Society of Photo-optical Instrumentation Engineers (SPIE), Sydney, pp. 194-194.
Wolff, C., Kuhlmey, B., de Sterke, C.M., Smith, M.J., Lapine, M. & Poulton, C.G. 2015, 'Artificial electrostriction in metamaterials', Proceedings of SPIE, SPIE Micro+Nano Materials, Devices, and Applications 2015, Society of Photo-optical Instrumentation Engineers (SPIE), Sydney, pp. 20-20.
Wolff, C., Steel, M.J., Eggleton, B.J. & Poulton, C.G. 2014, 'Stimulated brillouin scattering in high index-contrast optical waveguides: Energy, forces and symmetries', Frontiers in Optics, FiO 2014.
© 2014 Optical Society of America. We theoretically investigate the important physical processes for Stimulated Brillouin Scattering in high-contrast optical waveguides. We explore the relevant forces and scattering mechanisms, their symmetry properties and their relationships based on the conservation of energy.
Poulton, C.G., Aryanfar, I., Wolff, C., Casas-Bedoya, A., Steel, M.J. & Eggleton, B.J. 2014, 'Stimulated Brillouin Scattering, hybrid acoustic modes and nonreciprocal mode-conversion in nanophotonic waveguides', Optics InfoBase Conference Papers.
We theoretically investigate non-reciprocal mode-conversion arising from Stimulated Brillouin Scattering (SBS) in sub-micron nanophotonic waveguides. We find that hybrid acoustic modes can be efficiently generated via radiation pressure, leading to enhancement of SBS-based mode conversion. © 2014 OSA.
Wolff, C., Küchenmeister, J., Busch, K., Peschel, U. & Romanov, S.G. 2014, 'Transformation of light polarization in thin-film opal photonic crystals', Proceedings of the SPIE, Photonic Crystal Materials and Devices XI, p. 91270I.
Poulton, C.G., Aryanfar, I., Wolff, C., Casas-Bedoya, A., Steel, M.J. & Eggleton, B.J. 2014, 'Stimulated Brillouin Scattering, hybrid acoustic modes and nonreciprocal mode-conversion in nanophotonic waveguides', Conference on Lasers and Electro-Optics Europe - Technical Digest.
© 2014 Optical Society of America. We theoretically investigate non-reciprocal mode-conversion arising from Stimulated Brillouin Scattering (SBS) in sub-micron nanophotonic waveguides. We find that hybrid acoustic modes can be efficiently generated via radiation pressure, leading to enhancement of SBS-based mode conversion.
Wolff, C. & Busch, K. 2013, 'Non-markovian radiation dynamics in photonic band gap materials', Lasers and Electro-Optics (CLEO), 2013 Conference on.
Hoeppe, U., Wolff, C., Benner, H. & Busch, K. 2013, 'Modeling spontaneous emission control in photonic crystals by ferromagneticresonance', IEEE Transactions on Magnetics, IEEE TRansactions on Magnetics, pp. 1013-1019.
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Wolff, C., Hoeppe, U., Benner, H. & Busch, K. 2012, 'Radiation dynamics of a spin system in a photonic band gap material', AIP Conference Proceedings, TaCoNa-Photonics 2012, American Institute of Physics, Bad Honneff, Germany, pp. 95-97.
Wolff, C., Romanov, S., Küchenmeister, J., Peschel, U. & Busch, K. 2011, 'Polarization change in face-centered cubic opal films', AIP Conference Proceedings, TaCoNa-Photonics 2011, American Institute of Physics, Bad Honneff, Germany, pp. 112-114.
Wolff, C., Küchenmeister, J., Busch, K., Romanov, S.G. & Peschel, U. 2011, 'Cross-polarization breakdown in 3-dimensional opal photonic crystals', Conference on Lasers and Electro-Optics Europe, Conference on Lasers and Electro-Optics Europe 2011.
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Schuler, C.J., Wolff, C., Busch, K. & Florescu, M. 2010, 'Thermal emission from finite photonic crystals', Proceedings of SPIE, Active Photonic Materials III, Society of Photo-optical Instrumentation Engineers, p. 77560B.
Staude, I., Thiel, M., Essig, S., Wolff, C., Busch, K., von Freymann, G. & Wegener, M. 2010, 'Woodpile photonic crystals with a complete bandgap reaching telecomwavelengths', Conference on Lasers and Electro-Optics (CLEO) and Quantum Electronics and Laser Science Conference (QELS), 2010, CLEO/QELS 2010.
Wolff, C. & Busch, K. 2009, 'Generation of 3D wannier functions', AIP Conference Proceedings, TaCoNa-Photonics, American Institute of Physics, Bad Honneff, Germany, pp. 166-168.

Journal articles

Hille, A., Moeferdt, M., Wolff, C., Matyssek, C., Rodríguez-Oliveros, R., Prohm, C., Niegemann, J., Grafström, S., Eng, L.M. & Busch, K. 2016, 'Second Harmonic Generation from Metal Nano-Particle Resonators: Numerical Analysis on the Basis of the Hydrodynamic Drude Model', Journal of Physical Chemistry C, vol. 120, no. 2, pp. 1163-1169.
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© 2015 American Chemical Society. A detailed computational study of the wavelength-dependent efficiency of optical second-harmonic generation in plasmonic nanostructures is presented. The computations are based on a discontinuous Galerkin Maxwell solver that utilizes a hydrodynamic material model to calculate the free-electron dynamics in metals without any further approximations. Besides wave-mixing effects, the material model thus contains the full nonlocal characteristics of the electromagnetic response, as well as intensity-dependent phenomena such as the Kerr effect. To be specific, two prototypical nanostructures are studied in depth with the help of two independent computer codes. For an infinitely long metal cylinder, it is found that the spectral position of linear particle plasmon modes (dipolar modes, higher-order modes, and, for frequencies above the plasma frequency also bulk plasmon modes) and their associated relative strengths for scattering and absorption both at the fundamental and second-harmonic wavelengths largely control the conversion efficiency. Notably, Fabry-Perot resonances associated with longitudinal bulk plasmons may be detectable via background-free second-harmonic spectroscopy. For a more complex V-groove nanostructure, it becomes possible to engineer a doubly resonant scenario at the fundamental and the second-harmonic wavelength. This leads to an efficient enhancement of second-harmonic emission. Our work thus demonstrates that the careful design of nanostructures on the nonlocal linear level facilitates highly efficient nanoantennas for second-harmonic emission with applications in background-free imaging and frequency conversion systems.
Wolff, C., Van Laer, R., Steel, M.J., Eggleton, B.J. & Poulton, C.G. 2016, 'Brillouin resonance broadening due to structural variations in nanoscale waveguides', New Journal of Physics, vol. 18, no. 2.
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© 2016 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. We study the impact of structural variations (that is slowly varying geometry aberrations and internal strain fields) on the width and shape of the stimulated Brillouin scattering (SBS) resonance in nanoscale waveguides. We find that they lead to an inhomogeneous resonance broadening through two distinct mechanisms: firstly, the acoustic frequency is directly influenced via mechanical nonlinearities; secondly, the optical wave numbers are influenced via the opto-mechanical nonlinearity leading to an additional acoustic frequency shift via the phase-matching condition. We find that this second mechanism is proportional to the opto-mechanical coupling and, hence, related to the SBS-gain itself. It is absent in intra-mode forward SBS, while it plays a significant role in backward scattering. In backward SBS increasing the opto-acoustic overlap beyond a threshold defined by the fabrication tolerances will therefore no longer yield the expected quadratic increase in overall Stokes amplification. Finally, we illustrate in a numerical example that in backward SBS and inter-mode forward SBS the existence of two broadening mechanisms with opposite sign also opens the possibility to compensate the effect of geometry-induced broadening. Our results can be transferred to other micro- and nano-structured waveguide geometries such as photonic crystal fibres.
Mirnaziry, S.R., Wolff, C., Steel, M.J., Eggleton, B.J. & Poulton, C.G. 2016, 'Stimulated Brillouin scattering in silicon/chalcogenide slot waveguides', Optics Express, vol. 24, no. 5, pp. 4786-4800.
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© 2016 Optical Society of America. We study slot waveguide geometries, comprising a combination of soft glasses and high-index guiding structures, for enhancing stimulated Brillouin scattering (SBS). We show that strong optical and acoustic mode confinement in these waveguides can lead to a substantial increase in SBS gain, comparable to or greater than recently proposed suspended silicon nanowire structures. We compute the optimal parameters of the structure and examine the physics of optical and acoustic confinement within slot waveguides. Finally, we compute the effects of linear and nonlinear loss mechanisms on optimum pump/Stokes powers and waveguide lengths.
Huynh, D.N., Moeferdt, M., Matyssek, C., Wolff, C. & Busch, K. 2016, 'Ultrafast three-wave-mixing in plasmonic nanostructures', Applied Physics B: Lasers and Optics, vol. 122, no. 5.
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© 2016, Springer-Verlag Berlin Heidelberg. We present a perturbative approach to the time-domain computation of three-wave-mixing signals from plasmonic nanostructures. Based on a hydrodynamic material model which features nonlinear as well as nonlocal characteristics, we compute the ultrafast response of electrons in metals in a perturbative manner, where fundamental waves and second-order response are evaluated separately. This allows us to examine the source distribution of the second-order nonlinear response originating from the fundamental waves in a consistent manner that takes the nonlocal characteristics of the system into account. We validate this framework by comparing with the results of the fully nonlinear model and apply it to the study of three-wave-mixing enhancements from nanoplasmonic antennas.
Smith, M.J.A., Kuhlmey, B.T., De Sterke, C.M., Wolff, C., Lapine, M. & Poulton, C.G. 2016, 'Metamaterial control of stimulated Brillouin scattering', Optics Letters, vol. 41, no. 10, pp. 2338-2341.
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© 2016 Optical Society of America.Using full opto-acoustic numerical simulations, we demonstrate enhancement and suppression of the SBS gain in a metamaterial comprising a subwavelength cubic array of dielectric spheres suspended in a dielectric background material. We develop a general theoretical framework and present several numerical examples using technologically important materials. For As2 S3 spheres in silicon, we achieve a gain enhancement of more than an order of magnitude compared to pure silicon and for GaAs spheres in silicon, full suppression is obtained. The gain for As2 S3 glass can also be strongly suppressed by embedding silica spheres. The constituent terms of the gain coefficient are shown to depend in a complex way on the filling fraction. We find that electrostriction is the dominant effect behind the control of SBS in bulk media.
Wolff, C., Steel, M.J., Eggleton, B.J. & Poulton, C.G. 2015, 'Stimulated Brillouin scattering in integrated photonic waveguides: Forces, scattering mechanisms, and coupled-mode analysis', Physical Review A: Atomic, Molecular and Optical Physics, vol. 92, no. 1.
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Recent theoretical studies of stimulated Brillouin scattering (SBS) in nanoscale devices have led to intense research effort dedicated to the demonstration and application of this nonlinearity in on-chip systems. The key feature of SBS in integrated photonic waveguides is that small, high-contrast waveguides are predicted to experience powerful optical forces on the waveguide boundaries, which are predicted to further boost the SBS gain that is already expected to grow dramatically in such structures because of the higher mode confinement alone. In all recent treatments, the effect of radiation pressure is included separately from the scattering action that the acoustic field exerts on the optical field. In contrast to this, we show here that the effects of radiation pressure and motion of the waveguide boundaries are inextricably linked. Central to this insight is a new formulation of the SBS interaction that unifies the treatment of light and sound, incorporating all relevant interaction mechanisms—radiation pressure, waveguide boundary motion, electrostriction, and photoelasticity— from a rigorous thermodynamic perspective. Our approach also clarifies important points of ambiguity in the literature, such as the nature of edge effects with regard to electrostriction and of body forces with respect to radiation pressure. This new perspective on Brillouin processes leads to physical insight with implications for the design and fabrication of SBS-based nanoscale devices.
Smith, M.J.A., Kuhlmey, B.T., De Sterke, C.M., Wolff, C., Lapine, M. & Poulton, C.G. 2015, 'Electrostriction enhancement in metamaterials', Physical Review B - Condensed Matter and Materials Physics, vol. 91, no. 21.
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© 2015 American Physical Society. We demonstrate a controllable enhancement in the electrostrictive properties of a medium using dilute composite artificial materials. Analytical expressions for the composite electrostriction are derived and used to show that enhancement, tunability, and suppression can be achieved through a careful choice of constituent materials. Numerical examples with Ag, As2S3, Si, and SiO2 demonstrate that even in a nonresonant regime, artificial materials can bring more than a threefold enhancement in the electrostriction.
Wolff, C., Steel, M.J., Eggleton, B.J. & Poulton, C.G. 2015, 'Stimulated Brillouin scattering in integrated photonic waveguides: Forces, scattering mechanisms, and coupled-mode analysis', Physical Review A: Atomic, Molecular and Optical Physics, vol. 92, no. 1.
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Recent theoretical studies of stimulated Brillouin scattering (SBS) in nanoscale devices have led to intense research effort dedicated to the demonstration and application of this nonlinearity in on-chip systems. The key feature of SBS in integrated photonic waveguides is that small, high-contrast waveguides are predicted to experience powerful optical forces on the waveguide boundaries, which are predicted to further boost the SBS gain that is already expected to grow dramatically in such structures because of the higher mode confinement alone. In all recent treatments, the effect of radiation pressure is included separately from the scattering action that the acoustic field exerts on the optical field. In contrast to this, we show here that the effects of radiation pressure and motion of the waveguide boundaries are inextricably linked. Central to this insight is a new formulation of the SBS interaction that unifies the treatment of light and sound, incorporating all relevant interaction mechanisms—radiation pressure, waveguide boundary motion, electrostriction, and photoelasticity— from a rigorous thermodynamic perspective. Our approach also clarifies important points of ambiguity in the literature, such as the nature of edge effects with regard to electrostriction and of body forces with respect to radiation pressure. This new perspective on Brillouin processes leads to physical insight with implications for the design and fabrication of SBS-based nanoscale devices.
Wolff, C., Gutsche, P., Steel, M.J., Eggleton, B.J. & Poulton, C.G. 2015, 'Impact of nonlinear loss on stimulated Brillouin scattering', Journal of the Optical Society of America B, vol. 32, pp. 1968-1978.
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Wolff, C., Steel, M.J., Eggleton, B.J. & Poulton, C.G. 2015, 'Acoustic build-up in on-chip stimulated Brillouin scattering', Scientific Reports, vol. 5.
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Wolff, C., Gutsche, P., Steel, M.J., Eggleton, B.J. & Poulton, C. 2015, 'Power limits and a figure of merit for stimulated Brillouin scattering in the presence of third and fifth order loss', Optics Express, vol. 23, no. 20, pp. 26628-26638.
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Wolff, C., Steel, M.J. & Poulton, C.G. 2014, 'Formal selection rules for Brillouin scattering in integrated waveguides and structured fibers', Optics Express, vol. 22, no. 26, pp. 32489-32501.
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We derive formal selection rules for Stimulated Brillouin Scattering (SBS) in structured waveguides. Using a group-theoretical approach, we show how the waveguide symmetry determines which optical and acoustic modes interact for both forward and backward SBS. We present a general framework for determining this interaction and give important examples for SBS in waveguides with rectangular, triangular and hexagonal symmetry. The important role played by degeneracy of the optical modes is illustrated. These selection rules are important for SBS-based device design and for a full understanding the physics of SBS in structured waveguides.
Aryanfar, I., Wolff, C., Steel, M.J., Eggleton, B.J. & Poulton, C.G. 2014, 'Mode conversion using stimulated Brillouin scattering in nanophotonic silicon waveguides.', Optics express, vol. 22, no. 23, pp. 29270-29282.
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We theoretically and numerically investigate Stimulated Brillouin Scattering generated mode conversion in high-contrast suspended silicon nanophotonic waveguides. We predict significantly enhanced mode conversion when the linked effects of radiation pressure and motion of the waveguide boundaries are taken into account. The mode conversion is more than 10 times larger than would be predicted if the effect of radiation pressure is not taken into account: we find a waveguide length of 740 m is required for 20dB of mode conversion, assuming a total pump power of 1W. This is sufficient to bring the effect into the realm of chip-scale photonic waveguides. We explore the interaction between the different types of acoustic modes that can exist within these waveguides, and show how the presence of these modes leads to enhanced conversion between the different possible optical modes.
Wolff, C., Soref, R., Poulton, C.G. & Eggleton, B.J. 2014, 'Germanium as a material for stimulated Brillouin scattering in the mid-infrared', Optics Express, vol. 22, no. 25, pp. 30735-30747.
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© 2014 Optical Society of America. In a theoretical design study, we propose buried waveguides made of germanium or alloys of germanium and other group-IV elements as a CMOS-compatible platform for robust, high-gain stimulated Brillouin scattering (SBS) applications in the mid-infrared regime. To this end, we present numerical calculations for backward-SBS at 4mm in germanium waveguides that are buried in silicon nitride. Due to the strong photoelastic anisotropy of germanium, we investigate two different orientations of the germanium crystal with respect to the waveguide's propagation direction and find considerable differences. The acoustic wave equation is solved including crystal anisotropy; acoustic losses are computed from the acoustic mode patterns and previously published material parameters.
Schell, A.W., Engel, P., Werra, J.F.M., Wolff, C., Busch, K. & Benson, O. 2014, 'Scanning Single Quantum Emitter Fluorescence Lifetime Imaging: Quantitative Analysis of the Local Density of Photonic States', Nano Letters, vol. 14, no. 5, pp. 2623-2627.
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Frölich, A., Fischer, J., Wolff, C., Busch, K. & Wegener, M. 2014, 'Frequency-Resolved Reciprocal-Space Mapping of Visible Spontaneous Emission from 3D Photonic Crystals', Advanced Optical Materials, vol. 2, no. 9, pp. 849-853.
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Köhl, M., Wolff, C. & Busch, K. 2014, 'Disordered photonic crystals: a cluster coherent potential approach using photonic Wannier functions', Journal of the Optical Society of America B, vol. 31, no. 10, pp. 2246-2246.
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Wolff, C., Rodriguez-Oliveros, R. & Busch, K. 2013, 'Simple magneto-optic transition metal models for time-domain simulations', OPTICS EXPRESS, vol. 21, no. 10, pp. 12022-12037.
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Wolff, C., Mack, P. & Busch, K. 2013, 'Generation of Wannier functions for photonic crystals', PHYSICAL REVIEW B, vol. 88, no. 7.
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Küchenmeister, J., Wolff, C., Busch, K., Peschel, U. & Romanov, S.G. 2013, 'Abandoned Functionality of Thin-Film Opal Photonic Crystals', Advanced Optical Materials, vol. 1, no. 12, pp. 952-962.
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Koehl, M., Wolff, C. & Busch, K. 2012, 'Cluster coherent potential approximation for disordered photonic crystals using photonic Wannier functions', OPTICS LETTERS, vol. 37, no. 4, pp. 560-562.
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Hoeppe, U., Wolff, C., Kuechenmeister, J., Niegemann, J., Drescher, M., Benner, H. & Busch, K. 2012, 'Direct Observation of Non-Markovian Radiation Dynamics in 3D Bulk Photonic Crystals', PHYSICAL REVIEW LETTERS, vol. 108, no. 4.
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Wolff, C. & Busch, K. 2012, 'Constraints in the generation of photonic Wannier functions', Physica B: Condensed Matter, vol. 407, no. 20, pp. 4051-4055.
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Blum, C., Wolff, C. & Busch, K. 2011, 'Photonic-crystal time-domain simulations using Wannier functions', OPTICS LETTERS, vol. 36, no. 2, pp. 307-309.
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Busch, K., Blum, C., Graham, A.M., Hermann, D., Koehl, M., Mack, P. & Wolff, C. 2011, 'The photonic Wannier function approach to photonic crystal simulations: status and perspectives', JOURNAL OF MODERN OPTICS, vol. 58, no. 5-6, pp. 365-383.
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Staude, I., Thiel, M., Essig, S., Wolff, C., Busch, K., von Freymann, G. & Wegener, M. 2010, 'Fabrication and characterization of silicon woodpile photonic crystals with a complete bandgap at telecom wavelengths', OPTICS LETTERS, vol. 35, no. 7, pp. 1094-1096.
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Schuler, C.J., Wolff, C., Busch, K. & Florescu, M. 2009, 'Thermal emission from finite photonic crystals', APPLIED PHYSICS LETTERS, vol. 95, no. 24.
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