Harald Georg Leonhard Schwefel

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Recent experiments on similarly shaped polymer microcavity lasers show a dramatic difference in the far-field emission patterns. We show, for different deformations of the ellipse, quadrupole and hexadecapole, that the large differences in the far-field emission patterns are explained by the differing ray dynamics corresponding to each shape. Analyzing the(More)
We study lasing emission from asymmetric resonant cavity GaN microlasers. By comparing far-field intensity patterns with images of the microlaser we find that the lasing modes are concentrated on three-bounce unstable periodic ray orbits; i.e., the modes are scarred. The high-intensity emission directions of these scarred modes are completely different from(More)
We study level crossing in the optical whispering-gallery (WG) modes by using toroidal microcavities. Experimentally, we image the stationary envelope patterns of the composite optical modes that arise when WG modes of different wavelengths coincide in frequency. Numerically, we calculate crossings of levels that correspond with the observed degenerate(More)
We report on progress in developing optical microresonators and mi-crolasers based on deformations of dielectric spheres and cylinders. We review the different semiconductor and polymer dye microlasers which have been developed and demonstrated using this approach. All the lasers exhibit highly directional emission despite the presence of ray chaos in the(More)
The quasi-bound modes localized on stable periodic ray orbits of dielectric micro-cavities are constructed in the short-wavelength limit using the parabolic equation method. These modes are shown to coexist with irregularly spaced ???chaotic??? modes for the generic case. The wavevector quantization rule for the quasi-bound modes is derived and given a(More)
We report a precise direct measurement of the Goos-Hänchen shift after one reflection off a dielectric interface coated with periodic metal stripes. The spatial displacement of the shift is determined by image analysis. A maximal absolute shift of 5.18 and 23.39 mum for TE and TM polarized light, respectively, is determined. This technique is simple to(More)
We predict and investigate the emission of high-order harmonics by atoms that cross intense laser hot spots that last for a nanosecond or longer. An atom that moves through a nanometer-scale hot spot at characteristic thermal velocity can emit high-order harmonics in a similar fashion to an atom that is irradiated by a short-duration (picosecond-scale)(More)
It has been predicted and experimentally demonstrated that by injecting squeezed light into an optomechanical device, it is possible to enhance the precision of a position measurement. Here, we present a fundamentally different approach where the squeezing is created directly inside the cavity by a nonlinear medium. Counterintuitively, the enhancement of(More)