343 research outputs found
Microcavity resonance condition, quality factor, and mode volume are determined by different penetration depths
The penetration depth in a Distributed Bragg Reflector (DBR) co-determines
the resonance condition, quality factor, and mode volume of DBR-based
microcavities. Recent studies have used an incomplete description of the
penetration depth and incorrect equations. We present a complete analysis that
involves three different penetration depths. We also present a series of
experiments on microcavities to accurately determine the frequency and modal
penetration depth of our DBRs and compare these results with theoretical
predictions. The obtained results are relevant for anyone who models a DBR as
an effective hard mirror if lengths of the order of the wavelength are
relevant, as is the case for microcavities.Comment: 16 pages, 7 figure
Optical cavities and quantum emitters
Optical cavities are useful tools to enhance the interaction between light and matter, which is important to make good quantum emitters. However, it turns out that the cavities themselves (without any quantum emitters) are already interesting objects to study. When these cavities become very small, non-paraxial effects become important to describe the eigenmodes of the cavity. This thesis describes both the theoretical predictions of the cavity and shows the corresponding experiments.Biological and Soft Matter Physic
Observation of mode-mixing in the spatial eigenmodes of an optical microcavity
Quantum Matter and Optic
Nonparaxial corrections for short cavities and fibers
This paper describes optical propagation beyond the paraxial limit in rotational symmetric short Fabry-Perot cavities and long fibers with parabolic-index profiles. Frequency shifts due to paraxial and nonparaxial effects, the so-called spectral fine structure and vector corrections, are calculated with perturbation theory and expressed in a single dimensionless expansion parameter. The results obtained for short cavities and fibers have similar functional forms but are surprisingly different. These similarities and differences are pointed out and discussed, including their consequences for mode multiplexing in fibers.Quantum Matter and Optic
Thermal Particle Creation in Cosmological Spacetimes: A Stochastic Approach
The stochastic method based on the influence functional formalism introduced
in an earlier paper to treat particle creation in near-uniformly accelerated
detectors and collapsing masses is applied here to treat thermal and
near-thermal radiance in certain types of cosmological expansions. It is
indicated how the appearance of thermal radiance in different cosmological
spacetimes and in the two apparently distinct classes of black hole and
cosmological spacetimes can be understood under a unifying conceptual and
methodological framework.Comment: 17 pages, revtex (aps, eqsecnum), submitted to PRD, April 199
Sphagnum bleaching:Bicarbonate ‘toxicity’ and tolerance for seven Sphagnum species
Growth and functioning of Sphagnum mosses are closely linked to water level and chemistry. Sphagnum mosses occur in wet, generally acidic conditions, and when buffered, alkaline water is known to negatively impact Sphagnum. The effects of time, dose and species-specific responses of buffered, alkaline water on Sphagnum are largely unknown. We investigated the effects of bicarbonate and calcium on the survival, growth and physiological functioning of seven Sphagnum species occurring in contrasting environments, from raised bogs to (rich) fens. Mosses were submerged in different concentrations of bicarbonate and calcium solutions for 10 weeks under climate-controlled circumstances. After 2 weeks, all species exposed to the high bicarbonate treatment (2.0 mM) showed severe potassium leakage and swift discoloration. In contrast, species showed differential responses to the intermediate bicarbonate treatment (0.8 mM), some with a later onset of potassium leakage. S. squarrosum, S. teres & S. contortum generally persisted the longest, with all species dying after 6 to 10 weeks. Calcium alone, in contrast, negatively affected S. squarrosum, S. teres & S. contortum, causing discoloration and potassium leakage. Our study shows enrichment with bicarbonate, but not calcium, is detrimental for most Sphagnum species tested. A mechanistic model was developed that is consistent with dose and duration dependence and the species specificity. Future conservation and restoration measures for Sphagnum-dominated habitats and Sphagnum farming (cultivation, production and harvest of Sphagnum moss biomass) should limit flooding with bicarbonate-rich waters while investigating new management options, like acidifying surface waters to lower bicarbonate levels
BEC Collapse and Dynamical Squeezing of Vacuum Fluctuations
We analyze the phenomena of Bose Novae, as described by Donley et al [Nature
412, 295 (2001)], by focusing on the behavior of excitations or fluctuations
above the condensate, as driven by the dynamics of the condensate (rather than
the dynamics of the condensate alone or the kinetics of the atoms). The
dynamics of the condensate squeezes and amplifies the quantum excitations,
mixing the positive and negative frequency components of their wave functions
thereby creating particles which appear as bursts and jets. By analyzing the
changing amplitude and particle content of these excitations, our simple
physical picture (based on a test field approximation) explains well the
overall features of the Bose Novae phenomena and provide excellent quantitative
fits with experimental data on several aspects, such as the scaling behavior of
the collapse time and the amount of particles in the jet. The predictions of
the bursts at this level of approximation is less than satisfactory but may be
improved on by including the backreaction of the excitations on the condensate.
The mechanism behind the dominant effect -- parametric amplification of vacuum
fluctuations and freezing of modes outside of horizon -- is similar to that of
cosmological particle creation and structure formation in a rapid quench (which
is fundamentally different from Hawking radiation in black holes). This shows
that BEC dynamics is a promising venue for doing `laboratory cosmology'.Comment: Latex 36 pages, 6 figure
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