M. Sudzius

Parabolic polarization splitting of Tamm states in a metal-organic microcavity

We observe hybrid states of cavity photons and Tamm plasmons in an organic microcavity with an incorporated thin silver layer of increasing thickness up to 40 nm. Via μ-photoluminescence spectroscopy, we investigate their angular dependence. At oblique angles, we observe a TE-TM polarization splitting of more than 40 meV for each mode. An analytical model is developed to describe the coupling of Tamm plasmons and cavity photons and to account for the splitting of the orthogonally polarized resonances.

Continuously tunable laser emission from a wedge-shaped organic microcavity

We present an organic microcavity laser with wide tunability in the range of 595–650nm, having a threshold as low as 2nJ/pulse. The active medium consists of the organic composite tris(8-hydroxy quinoline) aluminum (Alq3) and 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) embedded in between two distributed Bragg reflectors. The inhomogeneously broadened emission from DCM is exploited for lasing by means of a tunable Fabry–Perot-type interferometer. Continuous tuning is achieved by varying the thickness of the active layer. The device shows a high photostability under direct excitation in the absorption band of the guest molecule, thus, allowing to monitor the optical gain spectrum of the active medium.

Photonic confinement in laterally structured metal-organic microcavities

We investigate the formation of optical modes in organic microcavities with an incorporated perforated silver layer. The metal leads to a formation of Tamm-plasmon-polaritons and thus separates the sample into metal-free or metal-containing areas, supporting different resonances. This mode splitting is exploited to confine photons in elliptic holes and triangular cuts, forming distinctive standing wave patterns showing the strong lateral confinement. A comparison with a Maxwell-Bloch based rate equation model clearly shows the nonlinear transition into the lasing regime. The concentration of the electric field density and inhibition of lateral loss channels in turn decreases the lasing threshold by up to one order of magnitude, to 0.1 nJ. By spectroscopic investigation of such a triangular wedge, we observe the transition from the unperturbed cavity state to a strongly confined complex transversal mode. Such a structured silver layer can be utilized in future for charge carrier injection in an electrically driven organic solid state laser.

Selective excitation of laser modes in an organic photonic dot microcavity

We experimentally investigate variable laser mode excitation in an organic photonic dot microcavity by shifting the excitation beam position. The sample comprises two highly reflective dielectric mirrors (R>99.9%) and a square-shaped organic dye mesa of a DCM doped (2 wt %) Alq3-matrix. Its wavelength-size (≈5×5 μm2) transforms the cavity mode dispersion to a set of discrete states, each with a different intensity distribution of the electromagnetic field in space. Numerical simulations, including absorption and gain, confirm the experimentally observed relation between mode distribution and progression on the excitation condition.

Multimode laser emission from laterally confined organic microcavities

Room-temperature multimode laser emission is observed in a microcavity consisting of dielectric mirrors and small-molecular-weight organic photonic dots as a cavity layer. The structure shows simultaneous lasing of a wide variety of transverse modes. A comparison of the laser operating characteristics with those of unpatterned structures shows an enhancement in the spontaneous emission coupling factor by more than two orders of magnitude due to the lateral confinement. The spectral features are in quantitative agreement with calculations of quantized photonic states in three-dimensional optical cavities.

Polarization splitting and terahertz oscillations from a single planar Fabry-Perot microcavity

We report the experimental observation of polarization splitting at normal incidence and terahertz oscillations of transmitted light from a single planar microcavity. Optical anisotropy in the SiO2∕TiO2-dielectric mirrors leads to two perpendicularly polarized transmission modes. We ascribe the anisotropy to oblique columnar structures in the dielectrics resulting from off-axial growth of the microcavity structure. We apply an up-conversion setup for temporally and spectrally resolved measurements and obtain a corresponding beating of 1.25THz. Time resolved measurements yield a cavity photon lifetime of 0.65ps, corresponding to a Q value of 1600. To explain our observations we introduce a Fourier-transform based analytical model.

Mode discretization in an organic microcavity including a perforated silver layer

Two optical Tamm plasmons and a discretized microcavity state are observed simultaneously in an organic microcavity by angle-resolved photoluminescence spectroscopy. The Tamm plasmons form as a result of a 40 nm silver layer placed between the bottom distributed Bragg reflector and the λ/2 cavity layer. This silver layer is perforated by round holes of a few microns size, generating optical mesas from which discretized microcavity states are observed concurrently. The discretization and the intensity of the different states are studied as a function of angle and hole diameter and compared to analytical calculations.

Bloch Wave Packets in Semiconductor Superlattices: Composition and Spatial Displacement

We investigate the temporal and spatial displacement dynamics of optically excited wave packets in a semiconductor superlattice. We present an experimental technique which measures directly the displacement of the wave packet center-of-mass: the oscillating Bloch wave packets create a microscopic dipole moment which can be detected using the shift of the Wannier-Stark ladder transition energy as a sensitive field detector. A true spatial oscillation of the photo-excited wave packet identifies quantum beats of the Wannier-Stark states as Bloch oscillations. We show that the Bloch wave packet undergoes harmonic spatial motion in accordance with the predictions of Bloch and Zener. The influence of initial experimental conditions on evolution and composition of the wave packet is discussed.

Threshold reduction by multidimensional photonic confinement in metal-organic microcavities

Due to their geometry, optical microcavities allow strong confinement of light between the mirrors and promise single mode operation at lowest possible lasing thresholds. Nevertheless, such devices suffer from losses not only due to parasitic absorption of the active or mirror layers, but especially via outcoupling of leaky and waveguided modes within the active layer. In this work, we present an organic microcavity sandwiched between high quality dielectric distributed Bragg reflectors. A highly conductive silver layer of 40nm thickness is added next to the active layer, leading to the formation of Tamm-Plasmon-Polaritons (TPP), one replacing the original cavity mode and shifting its resonance to the red, another one emerging from the long-wavelength sideband and moving to the blue. To avoid parasitic absorption introduced by such contacts, the silver layer is structured on the micrometer-scale using photolithography, yielding separated areas supporting either original cavity mode or red shifted TPP-resonances. This separation leads to a strong spatial trapping of the modes to only their resonant regions on the sample and can in turn be exploited to achieve complete three-dimensional confinement of photons. In elliptic holes produced in the metal layer, we observe the formation of Mathieu-Modes, leading to a reduction of the lasing threshold by six times. Facilitating triangular cuts in the silver layer, highly confined standing modes develop in the system, allowing a precise optimization of the spatial mode extension and reducing the threshold even further down to one order of magnitude below the threshold of an unstructured organic cavity. These results show that the introduction of absorptive metals, needed for the realization of an electrically driven laser, can in turn be harnessed to improve the characteristics of the device.

Polarization splitting of discrete states in square shaped organic photonic dots

We analyze the polarization dependence of the discrete photonic states in an organic microcavity system that is laterally confined on the micron scale. Via microscopic photoluminescence measurements on square shaped photonic dots, we demonstrate a polarization splitting that increases up to 10 meV for higher order modes. These experimental results are evaluated using a vectorial waveguide approach and the splitting is attributed to phase shifts, which occur as a result of reflection at the side walls of the mesa structures.