1,109 research outputs found
Photonic quasicrystals for general purpose nonlinear optical frequency conversion
We present a general method for the design of 2-dimensional nonlinear
photonic quasicrystals that can be utilized for the simultaneous phase-matching
of arbitrary optical frequency-conversion processes. The proposed scheme--based
on the generalized dual-grid method that is used for constructing tiling models
of quasicrystals--gives complete design flexibility, removing any constraints
imposed by previous approaches. As an example we demonstrate the design of a
color fan--a nonlinear photonic quasicrystal whose input is a single wave at
frequency and whose output consists of the second, third, and fourth
harmonics of , each in a different spatial direction
Multistep cascading and fourth-harmonic generation
We apply the concept of multistep cascading to the problem of fourth-harmonic
generation in a single quadratic crystal. We analyze a new model of parametric
wave mixing and describe its stationary solutions for two- and three-color
plane waves and spatial solitons. Some applications to the optical frequency
division as well as the realization of the double-phase-matching processes in
engineered QPM structures with phase reversal sequences are also discussed.Comment: 3 pages, 3 figure
Lipid raft microdomain compartmentalization of TC10 is required for insulin signaling and GLUT4 translocation.
Recent studies indicate that insulin stimulation of glucose transporter (GLUT)4 translocation requires at least two distinct insulin receptor-mediated signals: one leading to the activation of phosphatidylinositol 3 (PI-3) kinase and the other to the activation of the small GTP binding protein TC10. We now demonstrate that TC10 is processed through the secretory membrane trafficking system and localizes to caveolin-enriched lipid raft microdomains. Although insulin activated the wild-type TC10 protein and a TC10/H-Ras chimera that were targeted to lipid raft microdomains, it was unable to activate a TC10/K-Ras chimera that was directed to the nonlipid raft domains. Similarly, only the lipid raft-localized TC10/ H-Ras chimera inhibited GLUT4 translocation, whereas the TC10/K-Ras chimera showed no significant inhibitory activity. Furthermore, disruption of lipid raft microdomains by expression of a dominant-interfering caveolin 3 mutant (Cav3/DGV) inhibited the insulin stimulation of GLUT4 translocation and TC10 lipid raft localization and activation without affecting PI-3 kinase signaling. These data demonstrate that the insulin stimulation of GLUT4 translocation in adipocytes requires the spatial separation and distinct compartmentalization of the PI-3 kinase and TC10 signaling pathways
Spatial Optical Solitons due to Multistep Cascading
We introduce a novel class of parametric optical solitons supported
simultaneously by two second-order nonlinear cascading processes,
second-harmonic generation and sum-frequency mixing. We obtain, analytically
and numerically, the solutions for three-wave spatial solitons and show that
the presence of an additional cascading mechanism can change dramatically the
properties and stability of two-wave quadratic solitary waves.Comment: 6 pages, 4 figure
Generation of the second-harmonic Bessel beams via nonlinear Bragg diffraction
We generate conical second-harmonic radiation by transverse excitation of a
two-dimensional annular periodically-poled nonlinear photonic structure with a
fundamental Gaussian beam. We show that these conical waves are the far-field
images of the Bessel beams generated in a crystal by parametric frequency
conversion assisted by nonlinear Bragg diffraction.Comment: 4 pages, 5 figures. submitte
Dicke Coherent Narrowing in Two-Photon and Raman Spectroscopy of Thin Vapour Cells
The principle of coherent Dicke narrowing in a thin vapour cell, in which
sub-Doppler spectral lineshapes are observed under a normal irradiation for a
l/2 thickness, is generalized to two-photon spectroscopy. Only the sum of the
two wave vectors must be normal to the cell, making the two-photon scheme
highly versatile. A comparison is provided between the Dicke narrowing with
copropagating fields, and the residual Doppler-broadening occurring with
counterpropagating geometries. The experimental feasibility is discussed on the
basis of a first observation of a two-photon resonance in a 300 nm-thick Cs
cell. Extension to the Raman situation is finally considered
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Improving plan quality and consistency by standardization of dose constraints in prostate cancer patients treated with CyberKnife.
Treatment plans for prostate cancer patients undergoing stereotactic body radiation therapy (SBRT) are often challenging due to the proximity of organs at risk. Today, there are no objective criteria to determine whether an optimal treatment plan has been achieved, and physicians rely on their personal experience to evaluate the plan's quality. In this study, we propose a method for determining rectal and bladder dose constraints achievable for a given patient's anatomy. We expect that this method will improve the overall plan quality and consistency, and facilitate comparison of clinical outcomes across different institutions. The 3D proximity of the organs at risk to the target is quantified by means of the expansion-intersection volume (EIV), which is defined as the intersection volume between the target and the organ at risk expanded by 5 mm. We determine a relationship between EIV and relevant dosimetric parameters, such as the volume of bladder and rectum receiving 75% of the prescription dose (V75%). This relationship can be used to establish institution-specific criteria to guide the treatment planning and evaluation process. A database of 25 prostate patients treated with CyberKnife SBRT is used to validate this approach. There is a linear correlation between EIV and V75% of bladder and rectum, confirming that the dose delivered to rectum and bladder increases with increasing extension and proximity of these organs to the target. This information can be used during the planning stage to facilitate the plan optimization process, and to standardize plan quality and consistency. We have developed a method for determining customized dose constraints for prostate patients treated with robotic SBRT. Although the results are technology specific and based on the experience of a single institution, we expect that the application of this method by other institutions will result in improved standardization of clinical practice
Turning light into a liquid via atomic coherence
We study a four level atomic system with electromagnetically induced
transparency with giant and susceptibilities of
opposite signs. This system would allow to obtain multidimensional solitons and
light condensates with surface tension properties analogous to those of usual
liquids
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