Hollow-core infrared fiber incorporating metal-wire metamaterial (2009)
Yan, Min, Mortensen, Niels Asger
Infrared (IR) light is considered important for short-range wireless communication, thermal sensing, spectroscopy, material processing, medical surgery, astronomy etc. However, IR light is in general...
Electronic properties of graphene antidot lattices (2009)
Fuerst, Joachim A., Pedersen, Jesper G., Flindt, Christian, Mortensen, Niels Asger, Brandbyge, Mads, Pedersen, Thomas G., ...
Graphene antidot lattices constitute a novel class of nano-engineered graphene devices with controllable electronic and optical properties. An antidot lattice consists of a periodic array of holes...
Material Limitations on the Detection Limit in Refractometry (2009)
Peder Skafte-Pedersen, Pedro S. Nunes, Sanshui Xiao, Niels Asger Mortensen
We discuss the detection limit for refractometric sensors relying on high-Q optical cavities and show that the ultimate classical detection limit is given by min {Δn} ≳ η with n + iη being the...
Resonant-tunnelling-assisted crossing for subwavelength plasmonic slot waveguides (2008)
Xiao, Sanshui, Mortensen, Niels Asger
We theoretically investigate the properties of crossing for two perpendicular subwavelength plasmonic slot waveguides. We show that, when encountering nano intersection, the crosstalk for the direct...
Limits of slow-light in photonic crystals (2008)
Pedersen, Jesper Goor, Xiao, Sanshui, Mortensen, Niels Asger
While ideal photonic crystals would support modes with a vanishing group velocity, state-of-the art structures have still only provided a slow-down by roughly two orders of magnitude. We find that...
Nanostructure design for surface-enhanced Raman spectroscopy - prospects and limits (2008)
Xiao, Sanshui, Mortensen, Niels Asger, Jauho, Antti-Pekka
Surface-enhanced Raman spectroscopy (SERS) allows single-molecule detection due to the strong field localization occurring at sharp bends or kinks of the metal-vacuum interface. An important question...
Optical properties of graphene antidot lattices (2008)
Pedersen, Thomas G., Flindt, Christian, Pedersen, Jesper, Jauho, Antti-Pekka, Mortensen, Niels Asger, Pedersen, Kjeld
Undoped graphene is semi-metallic and thus not suitable for many electronic and optoelectronic applications requiring gapped semiconductor materials. However, a periodic array of holes (antidot...
Graphene Antidot Lattices - Designed Defects and Spin Qubits (2008)
Pedersen, Thomas G., Flindt, Christian, Pedersen, Jesper, Mortensen, Niels Asger, Jauho, Antti-Pekka, Pedersen, Kjeld
Antidot lattices, defined on a two-dimensional electron gas at a semiconductor heterostructure, are a well-studied class of man-made structures with intriguing physical properties. We point out that...
Electro-viscous effects in capillary filling of nanochannels (2008)
Mortensen, Niels Asger, Kristensen, Anders
We theoretically examine the widespread hypothesis of an electro-viscous origin of the increase in apparent viscosity observed in recent experiments on capillary filling of nanochannels. Including...
Pedersen, Jesper, Xiao, Sanshui, Mortensen, Niels Asger
Slow-light enhanced absorption in liquid-infiltrated photonic crystals has recently been proposed as a route to compensate for the reduced optical path in typical lab-on-a-chip systems for...
In a recent paper, Subbaraman et al report a theoretical and numerical study of highly dispersive pure silica photonic crystal fiber supporting group-velocity dispersion exceeding -2*10^4 ps/nm/km....
Designed defects in 2D antidot lattices for quantum information processing (2008)
Pedersen, Jesper, Flindt, Christian, Mortensen, Niels Asger, Jauho, Antti-Pekka
We propose a new physical implementation of spin qubits for quantum information processing, namely defect states in antidot lattices defined in the two-dimensional electron gas at a semiconductor...
Spin qubits in antidot lattices (2008)
Pedersen, Jesper, Flindt, Christian, Mortensen, Niels Asger, Jauho, Antti-Pekka
We suggest and study designed defects in an otherwise periodic potential modulation of a two-dimensional electron gas as an alternative approach to electron spin based quantum information processing...
Enhanced circular dichroism via slow-light in dispersive structured media (2007)
Pedersen, Jesper, Mortensen, Niels Asger
Circular dichroism (CD) is in widespread use as a means of determining enantiomeric excess. We show how slow-light phenomena in dispersive structured media allow for a reduction in the required...
[First paragraph] In a recent paper Yamada et al. propose the novel concept of "pinched flow fractionation" (PFF) for the continuous size separation and analysis of particles in microfabricated...
Screening model for nanowire surface-charge sensors in liquid (2007)
Sorensen, Martin H., Mortensen, Niels Asger, Brandbyge, Mads
The conductance change of nanowire field-effect transistors is considered a highly sensitive probe for surface charge. However, Debye screening of relevant physiological liquid environments challenge...
Air-clad fibers: pump absorption assisted by chaotic wave dynamics? (2007)
Wave chaos is a concept which has already proved its practical usefulness in design of double-clad fibers for cladding-pumped fiber lasers and fiber amplifiers. In general, classically chaotic...
Mortensen, Niels Asger, Xiao, Sanshui, Pedersen, Jesper
Optical techniques are finding widespread use in analytical chemistry for chemical and bio-chemical analysis. During the past decade, there has been an increasing emphasis on miniaturization of...
Failure of standard approximations of the exchange coupling in nanostructures (2007)
Pedersen, Jesper, Flindt, Christian, Mortensen, Niels Asger, Jauho, Antti-Pekka
We calculate the exchange coupling for a double dot system using a novel, numerically exact yet efficient technique, based on finite-element methods. Specifically, we evaluate the exchange coupling...
Xiao, Sanshui, Mortensen, Niels Asger, Qiu, Min
Enhanced transmissions through a gold film with arrays of subwavelength holes are theoretically studied, employing the rigid full vectorial three dimensional finite difference time domain method....
Slow-light enhancement of Beer-Lambert-Bouguer absorption (2007)
Mortensen, Niels Asger, Xiao, Sanshui
We theoretically show how slow light in an optofluidic environment facilitates enhanced light-matter interactions, by orders of magnitude. The proposed concept provides strong opportunities for...
Xiao, Sanshui, Mortensen, Niels Asger
Optofluidic sensors based on highly dispersive two-dimensional photonic crystal waveguides are theoretically studied. Results show that these structures are strongly sensitive to the refractive index...
Liquid-infiltrated photonic crystals: Ohmic dissipation and broadening of modes (2007)
Mortensen, Niels Asger, Ejsing, Simon, Xiao, Sanshui
The pronounced light-matter interactions in photonic crystals make them interesting as opto-fludic "building blocks" for lab-on-a-chip applications. We show how conducting electrolytes cause...
Mass and charge transport in micro and nanofluidic channels (2007)
Mortensen, Niels Asger, Olesen, Laurits H., Okkels, Fridolin, Bruus, Henrik
We consider laminar flow of incompressible electrolytes in long, straight channels driven by pressure and electroosmosis. We use a Hilbert space eigenfunction expansion to address the general problem...
Highly dispersive photonic band-gap-edge optofluidic biosensors (2006)
Xiao, Sanshui, Mortensen, Niels Asger
Highly dispersive photonic band-gap-edge optofluidic biosensors are studied theoretically. We demonstrate that these structures are strongly sensitive to the refractive index of the liquid, which is...
Mortensen, Niels Asger, Xiao, Sanshui, Felbacq, Didier
We consider meta materials made from a two-dimensional dielectric rod-type photonic crystal. The magnetic response is studied within the recently developed homogenization theory and we in particular...
Nonlinear photonic crystal fibres: pushing the zero-dispersion towards the visible (2006)
Saitoh, Kunimasa, Koshiba, Masanori, Mortensen, Niels Asger
The strong waveguide dispersion in photonic crystal fibres (PCFs) provides unique opportunities for nonlinear optics with a zero-dispersion wavelength λ0 far below the limit of ~1.3 μm set by the...
Nonlinear photonic crystal fibres: pushing the zero-dispersion towards the visible (2006)
Saitoh, Kunimasa, Koshiba, Masanori, Mortensen, Niels Asger
The strong waveguide dispersion in photonic crystal fibres (PCFs) provides unique opportunities for nonlinear optics with a zero-dispersion wavelength λ0 far below the limit of ~1.3 μm set by the...
Nonlinear photonic crystal fibres: pushing the zero-dispersion towards the visible (2006)
Saitoh, Kunimasa, Koshiba, Masanori, Mortensen, Niels Asger
The strong waveguide dispersion in photonic crystal fibres (PCFs) provides unique opportunities for nonlinear optics with a zero-dispersion wavelength λ0 far below the limit of ~1.3 μm set by the...
Nonlinear photonic crystal fibres: pushing the zero-dispersion toward the visible (2006)
Saitoh, Kunimasa, Koshiba, Masanori, Mortensen, Niels Asger
The strong waveguide dispersion in photonic crystal fibres provides unique opportunities for nonlinear optics with a zero-dispersion wavelength $\lambda_0$ far below the limit of ~1.3 micron set by...
We consider photonic crystal fibres (PCFs) made from arbitrary base materials and introduce a short-wavelength approximation which allows for a mapping of the Maxwell's equations onto a dimensionless...
Rindorf, Lars, Mortensen, Niels Asger
We present a method for calculating the transmission spectra, dispersion, and time delay characteristics of optical-waveguide gratings based on Green's functions and Dyson's equation. Starting from...
Quantum computing via defect states in two-dimensional anti-dot lattices (2005)
Flindt, Christian, Mortensen, Niels Asger, Jauho, Antti-Pekka
We propose a new structure suitable for quantum computing in a solid state environment: designed defect states in antidot lattices superimposed on a two-dimensional electron gas at a semiconductor...
Endlessly single-mode holey fibers: the influence of core design (2005)
Saitoh, Kunimasa, Tsuchida, Yukihiro, Koshiba, Masanori, Mortensen, Niels Asger
In this paper we evaluate the cut-off properties of holey fibers (HFs) with a triangular lattice of air holes and the core formed by the removal of a single (HF1) or more air holes (HF3 and HF7)....
Non-perturbative approach to high-index-contrast variations in electromagnetic systems (2005)
Rindorf, Lars, Mortensen, Niels Asger
We present a method that formally calculates \emph{exact} frequency shifts of an electromagnetic field for arbitrary changes in the refractive index. The possible refractive index changes include...
Universal dynamics in the onset of a Hagen-Poiseuille flow (2005)
Mortensen, Niels Asger, Bruus, Henrik
The dynamics in the onset of a Hagen-Poiseuille flow of an incompressible liquid in a channel of circular cross section is well-studied theoretically. We use an eigenfunction expansion in a Hilbert...
Propagation of Light in Photonic Crystal Fibre Devices (2005)
Dabirian, Ali, Akbari, Mahmood, Mortensen, Niels Asger
We describe a semi-analytical approach for three-dimensional analysis of photonic crystal fibre devices. The approach relies on modal transmission-line theory. We offer two examples illustrating the...
The radiated fields of the fundamental mode of photonic crystal fibers (2005)
Dabirian, Ali, Akbari, Mahmood, Mortensen, Niels Asger
The six-fold rotational symmetry of photonic crystal fibers has important manifestations in the radiated fields in terms of i) a focusing phenomena at a finite distance from the end-facet and ii) the...
We consider photonic crystal fibers made from arbitrary base materials and derive a unified semi-analytical approach for the dispersion and modal properties which applies to the short-wavelength...
Mortensen, Niels Asger, Okkels, Fridolin, Bruus, Henrik
We consider pressure-driven, steady state Poiseuille flow in straight channels with various cross-sectional shapes: elliptic, rectangular, triangular, and harmonic-perturbed circles. A given shape is...
Nielsen, Martin Dybendal, Folkenberg, Jabob Riis, Mortensen, Niels Asger
A single-mode all-silica photonic crystal fiber with an effective area of 600 square-micron and low bending loss is demonstrated. The fiber is characterized in terms of attenuation, chromatic...
Modeling of realistic cladding structures for air-core photonic band-gap fibers (2003)
Mortensen, Niels Asger, Nielsen, Martin Dybendal
Cladding structures of photonic band-gap fibers often have air-holes of non-circular shape and, typically, close-to-hexagonal air holes with curved corners are observed. We study photonic band-gaps...
Photonic crystal fiber design based on the V-parameter (2003)
Nielsen, Martin Dybendal, Mortensen, Niels Asger
Based on a recent formulation of the V-parameter of a photonic crystal fiber we provide numerically based empirical expressions for this quantity only dependent on the two structural parameters - the...
Mode areas and field energy distribution in honeycomb photonic bandgap fibers (2003)
Laegsgaard, Jesper, Mortensen, Niels Asger, Bjarklev, Anders
The field energy distributions and effective mode areas of silica-based photonic bandgap fibers with a honeycomb airhole structure in the cladding and an extra airhole defining the core are...
Material effects in airguiding photonic bandgap fibers (2003)
Laegsgaard, Jesper, Mortensen, Niels Asger, Riishede, Jesper, Bjarklev, Anders
The waveguiding properties of two silica-based airguiding photonic bandgap fiber designs are investigated with special emphasis on material effects. The nonlinear coefficients are found to be 1-2...
A "poor man's approach" to modelling of micro-structured optical fibres (2003)
Riishede, Jesper, Mortensen, Niels Asger, Laegsgaard, Jesper
Based on the scalar Helmholtz equation and the finite-difference approximation, we formulate a matrix eigenvalue problem for the calculation of propagation constants, beta(omega), in micro-structured...
Low-loss criterion and effective area considerations for photonic crystal fibers (2003)
Mortensen, Niels Asger, Folkenberg, Jacob Riis
We study the class of endlessly single-mode all-silica photonic crystal fibers with a triangular air-hole cladding. We consider the sensibility to longitudinal nonuniformities and the consequences...
Mortensen, Niels Asger, Folkenberg, Jacob Riis
The transition from the near to the far field of the fundamental mode radiating out of a photonic crystal fiber is investigated experimentally and theoretically. It is observed that the hexagonal...
Effective area of photonic crystal fibers (2002)
We consider the effective area A_eff of photonic crystal fibers (PCFs) with a triangular air-hole lattice in the cladding. It is first of all an important quantity in the context of non-linearities,...
Mesoscopic Coulomb Drag (2001)
This thesis describes the merging of the two fields of Coulomb drag and mesoscopic physics. The thesis presents a theory for Coulomb drag between two mesoscopic systems based on linear-response...
Mesoscopic fluctuations of Coulomb drag between quasi-ballistic 1D-wires (2001)
Mortensen, Niels Asger, Flensberg, Karsten, Jauho, Antti-Pekka
Quasiballistic 1D quantum wires are known to have a conductance of the order of 2e^2/h, with small sample-to-sample fluctuations. We present a study of the transconductance G_12 of two...
Coulomb drag in the mesoscopic regime (2001)
Mortensen, Niels Asger, Flensberg, Karsten, Jauho, Antti-Pekka
We present a theory for Coulomb drag between two mesoscopic systems which expresses the drag in terms of scattering matrices and wave functions. The formalism can be applied to both ballistic and...
Coulomb drag in phase-coherent mesoscopic structures - Numerical study of disordered 1D-wires (2001)
Mortensen, Niels Asger, Flensberg, Karsten, Jauho, Antti-Pekka
We study Coulomb drag between two parallel disordered mesoscopic 1D-wires. By numerical ensemble averaging we calculate the statistical properties of the transconductance G_21 including its...
Diffusion equation and spin drag in spin-polarized transport (2001)
Flensberg, Karsten, Jensen, Thomas Stibius, Mortensen, Niels Asger
We study the role of electron-electron interactions for spin polarized transport using the Boltzmann equation and derive a set of coupled transport equations. For spin polarized transport the...
Coulomb Drag in Coherent Mesoscopic Systems (2000)
Mortensen, Niels Asger, Flensberg, Karsten, Jauho, Antti-Pekka
We present a theory for Coulomb drag between two mesoscopic systems. Our formalism expresses the drag in terms of scattering matrices and wave functions, and its range of validity covers both...
Side-gate modulation of critical current in mesoscopic Josephson junction (2000)
Mortensen, Niels Asger, Bastian, Georg
We study the normal state conductance and the Josephson current in a superconductor-2DEG-superconductor structure where the size/shape of the 2DEG-region can be modified by an additional side-gate...
Mortensen, Niels Asger, Ronnow, H. M., Bruus, Henrik, Hedegard, Per
The magnetic resonance at 41 meV observed in neutron scattering studies of Y Ba_2 Cu_3 O_7 holds a key position in the understanding of high-T_c superconductivity. Within the SO(5) model for...
Mortensen, Niels Asger, Jauho, Antti-Pekka, Flensberg, Karsten
An inherent difficulty in studying mesoscopic effects in semiconductor--superconductor hybrid structures is the large Schottky barrier which often forms at the interface. A large technological effort...
Dephasing in semiconductor-superconductor structures by coupling to a voltage probe (1999)
Mortensen, Niels Asger, Jauho, Antti-Pekka, Flensberg, Karsten
We study dephasing in semiconductor-superconductor structures caused by coupling to a voltage probe. We consider structures where the semiconductor consists of two scattering regions between which...
Contact resistance of quantum tubes (1999)
Mortensen, Niels Asger, Johnsen, Kristinn, Jauho, Antti-Pekka, Flensberg, Karsten
We consider the conductance of a quantum tube connected to a metallic contact. The number of angular momentum states that the tube can support depends on the strength of the radial confinement. We...
Conductance enhancement in quantum point contact-semiconductor-superconductor devices (1999)
Mortensen, Niels Asger, Jauho, Antti-Pekka, Flensberg, Karsten, Schomerus, Henning
We present numerical calculations of the conductance of an interface between a phase-coherent two-dimensional electron gas and a superconductor with a quantum point contact in the normal region....
Interfacial tension in water at solid surfaces (1999)
Mortensen, Niels Asger, Kuhle, Anders, Morch, Knud A.
A model for the formation of cavitation nuclei in liquids has recently been presented with basis in interfacial liquid tension at non-planar solid surfaces of concave form. In the present paper...
Angle dependence of Andreev scattering at semiconductor-superconductor interfaces (1998)
Mortensen, Niels Asger, Flensberg, Karsten, Jauho, Antti-Pekka
We study the angle dependence of the Andreev scattering at a semiconductor-superconductor interface, generalizing the one-dimensional theory of Blonder, Tinkham and Klapwijk. An increase of the...