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  • 1
    Electronic Resource
    Electronic Resource
    Compact InP-based ring lasers employing multimode interference couplers and combiners (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 1753-1755 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Multimode interference (MMI) 3 dB couplers and MMI power combiners have been integrated with compact InP/InGaAsP ring lasers (R=150 μm). Radiative loss from the curves is small, and MMI 3 dB couplers are shown to be more efficient than conventional Y junctions. In addition, we demonstrate improved efficiency by combining counterpropagating beams in a single output by means of a MMI combiner. Single mode spectral behavior, with 35 dB side mode suppression, has been measured and is explained as resulting from coupled cavities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111797
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    Paper (German National Licenses)
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  • 2
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    Optimization of confocal laser induced fluorescence in a plasmaa) (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-07-19
    Description: Laser Induced Fluorescence (LIF) provides measurements of flow speed, temperature, and density of ions or neutrals in a plasma. Traditionally, a LIF measurement requires two ports on a plasma device; one for laser injection and one for emission collection. Proper alignment of LIF optics is time consuming and sensitive to mechanical vibration. We describe a confocal configuration for LIF that requires a single port and requires no alignment. The measurement location is scanned radially by physically moving the entire optical structure. Confocal LIF measurements are compared to traditional LIF measurements over the same radial range.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Time-domain response of atomically thin MoS2 nanomechanical resonators (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-08-02
    Description: We measure the energy relaxation rate of single- and few-layer molybdenum disulphide (MoS 2 ) nanomechanical resonators by detecting the resonator ring-down. Recent experiments on these devices show a remarkably low quality (Q)-factor when taking spectrum measurements at room temperature. The origin of the low spectral Q-factor is an open question, and it has been proposed that besides dissipative processes, frequency fluctuations contribute significantly to the resonance line-width. The spectral measurements performed thus far however, do not allow one to distinguish these two processes. Here, we use time-domain measurements to quantify the dissipation. We compare the Q-factor obtained from the ring-down measurements to those obtained from the thermal noise spectrum and from the frequency response of the driven device. In few-layer and single-layer MoS 2 resonators, the two are in close agreement, which demonstrates that the spectral line-width in MoS 2 membranes at room temperature is limited by dissipation, and that excess spectral broadening plays a negligible role.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    A Landau-de Gennes theory for hard colloidal rods: Defects and tactoids (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-05-17
    Description: We construct a phenomenological Landau-de Gennes theory for hard colloidal rods by performing an order parameter expansion of the chemical-potential dependent grand potential. By fitting the coefficients to known results of Onsager theory, we are not only able to describe the isotropic-nematic phase transition as function of density, including the well-known density jump, but also the isotropic-nematic planar interface. The resulting theory is applied in calculations of the isotropic core size in a radial hedgehog defect, the density dependence of linear defects of hard rods in square confinement, and the formation of a nematic droplet in an isotropic background.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 5
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    Spectroscopic studies of non-thermal plasma jet at atmospheric pressure formed in low-current nonsteady-state plasmatron for biomedical applications (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-04-19
    Description: The optical and electrophysical characteristics of the nonequilibrium low-temperature plasma formed by a low-current nonsteady-state plasmatron are experimentally investigated in the present work. It is demonstrated that experimental data on the optical diagnostics of the plasma jet can provide a basis for the construction of a self-consistent physical and mathematical plasma model and for the creation of plasma sources with controllable electrophysical parameters intended for the generation of the required concentration of active particles. Results of spectroscopic diagnostics of plasma of the low-current nonsteady-state plasmatron confirm that the given source is efficient for the generation of charged particles and short-wavelength radiation—important plasma components for biomedical problems of an increase in the efficiency of treatment of biological tissues by charged particles. Measurement of the spatial distribution of the plasma jet potential by the probe method has demonstrated that a negative space charge is formed in the plasma jet possibly due to the formation of electronegative oxygen ions.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 6
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    Using standard calibrated geometries to characterize a coaxial high purity germanium gamma detector for Monte Carlo simulations (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-06-17
    Description: A detector model optimization procedure based on matching Monte Carlo simulations with measurements for two experimentally calibrated sample geometries which are frequently used in radioactivity measurement laboratories results in relative agreement within 5% between simulated and measured efficiencies for a high purity germanium detector. The optimization procedure indicated that the increase in dead layer thickness is largely responsible for a detector efficiency decrease in time. The optimized detector model allows Monte Carlo efficiency calibration for all other samples of which the geometry and bulk composition is known. The presented method is a competitive and economic alternative to more elaborate detector scanning methods and results in a comparable accuracy.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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  • 7
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    Strain-dependent damping in nanomechanical resonators from thin MoS2 crystals (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-09-02
    Description: We investigate the effect of mechanical strain on the dynamics of thin MoS 2 nanodrum resonators. Using a piezoelectric crystal, compressive and tensile biaxial strain is induced in initially flat and buckled devices. In the flat device, we observe a remarkable strain-dependence of the resonance line width, while the change in the resonance frequency is relatively small. In the buckled device, the strain-dependence of the damping is less pronounced, and a clear hysteresis is observed. The experiment suggests that geometric imperfections, such as microscopic wrinkles, could play a role in the strong dissipation observed in nanoresonators fabricated from 2-D materials.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 8
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    An early warning indicator for atmospheric blocking events using transfer operators (2015)
    American Institute of Physics (AIP)
    In: Chaos
    Details
    Publication Date: 2015-02-19
    Description: The existence of persistent midlatitude atmospheric flow regimes with time-scales larger than 5–10 days and indications of preferred transitions between them motivates to develop early warning indicators for such regime transitions. In this paper, we use a hemispheric barotropic model together with estimates of transfer operators on a reduced phase space to develop an early warning indicator of the zonal to blocked flow transition in this model. It is shown that the spectrum of the transfer operators can be used to study the slow dynamics of the flow as well as the non-Markovian character of the reduction. The slowest motions are thereby found to have time scales of three to six weeks and to be associated with meta-stable regimes (and their transitions) which can be detected as almost-invariant sets of the transfer operator. From the energy budget of the model, we are able to explain the meta-stability of the regimes and the existence of preferred transition paths. Even though the model is highly simplified, the skill of the early warning indicator is promising, suggesting that the transfer operator approach can be used in parallel to an operational deterministic model for stochastic prediction or to assess forecast uncertainty.
    Print ISSN: 1054-1500
    Electronic ISSN: 1089-7682
    Topics: Physics
    Published by American Institute of Physics (AIP)
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