Search results for "polarization."
showing 10 items of 1842 documents
Actively mode-locked fiber ring laser by intermodal acousto-optic modulation
2010
We report an actively mode-locked fiber ring laser. A simple and low-insertion-loss acousto-optic modulator driven by standing flexural waves, which couples core-to-cladding modes in a standard single-mode optical fiber, is used as an active mechanism for mode locking. Among the remarkable features of the modulator, we mention its high modulation depth (72%), broad bandwidth (187 GHz), easy tunability in the optical wavelength, and low insertion losses (0.7 dB). The narrowest optical pulses obtained were of 95 ps time width, 21 mW peak power, repetition rate of 4.758 MHz, and 110 mW of pump power.
Excitation and interrogation of whispering-gallery modes in optical microresonators using a single fused-tapered fiber tip
2011
We show that whispering-gallery modes (WGMs) in optical microresonators can be excited and detected using a fused-tapered fiber tip (FTFT). The fabrication of FTFTs is simple and inexpensive; they are robust and allow the excitation and interrogation of the resonances with a single fiber. Excitation of high-Q WGMs in silica microcylinders and microspheres is demonstrated.
Characterization of fiber nonuniformities with ppm resolution using time-resolved in-fiber acousto-optics
2014
Time-resolved acousto-optic interaction using flexural waves enables the characterization of fiber nonuniformities along sections of about 1-2 m. A resolution better than 10 ppm of fiber diameter and core refractive index is demonstrated.
Design and optimization of broadband tapered optical fibers with a nanofiber waist
2010
The control over the transmission properties of tapered optical fibers (TOFs) is an important requirement for a whole range of applications. Using a carefully designed flame pulling process that allows us to realize preset fiber radius profiles, we fabricate TOFs with a nanofiber waist. We study the spectral transmission properties of these TOFs as a function of the taper profile and the waist length and show how the transmission band of the TOF can be tuned via different fiber profile parameters. Based on these results, we have designed a nanofiber-waist TOF with broadband transmission for surface spectroscopy of organic molecules. Moreover, our method allows us to analyze the loss mechani…
Endlessly single-mode heat-sink waveguide
1998
Recently, a new form of optical fiber, the photonic crystal fiber, has been reported. This fiber has a hexagonal array of submicrometer air holes running along its length and a lattice site without a hole (a line defect) in its center. The defect acts as a core, confining light that travels along the fiber as a guided mode. This structure can be endlessly single mode, never supporting more than one confined mode no matter what the diameter of the core or the wavelength of the light. Having discovered this effect experimentally and provided a qualitative explanation for the observed behavior, we present here a planar version of this fiber. Periodic arrays of parallel planar fins are placed o…
Influence of Whole-Body Dynamics on 15N PISEMA NMR Spectra of Membrane Proteins: A Theoretical Analysis
2009
AbstractMembrane proteins and peptides exhibit a preferred orientation in the lipid bilayer while fluctuating in an anisotropic manner. Both the orientation and the dynamics have direct functional implications, but motions are usually not accessible, and structural descriptions are generally static. Using simulated data, we analyze systematically the impact of whole-body motions on the peptide orientations calculated from two-dimensional polarization inversion spin exchange at the magic angle (PISEMA) NMR. Fluctuations are found to have a significant effect on the observed spectra. Nevertheless, wheel-like patterns are still preserved, and it is possible to determine the average peptide til…
Hyperpolarized 1H long lived states originating from parahydrogen accessed by rf irradiation
2013
Hyperpolarization has found many applications in Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI). However, its usage is still limited to the observation of relatively fast processes because of its short lifetimes. This issue can be circumvented by storing the hyperpolarization in a slowly relaxing singlet state. Symmetrical molecules hyperpolarized by Parahydrogen Induced Hyperpolarization (PHIP) provide a straightforward access to hyperpolarized singlet states because the initial parahydrogen singlet state is preserved at almost any magnetic field strength. In these systems, which show a remarkably long 1H singlet state lifetime of several minutes, the conversion of t…
Carbon nanorings: A challenge to theoretical chemistry
2006
High-level quantum-chemical methods show that the binding in the inclusion complex of hexamethylbenzene (HMB) in 6-cycloparaphenilacetylene (6-CPPA) cannot be explained only in terms of electrostatic interactions - caused by the polarization associated to curved Ï-conjugated systems - and the inclusion of dispersion forces is definitely needed. The theoretical description of van der Waals interactions is notoriously complicated and in fact some DFT methods cannot even predict the existence of the relatively small supramolecular nanoring studied here. However, ab initio MP2 calculations agree with experimental data and show that, in the considered complex, the HMB fragment is placed at the …
Rapid hyperpolarization and purification of the metabolite fumarate in aqueous solution
2020
Significance Magnetic resonance imaging is hindered by inherently low sensitivity, which limits the method for the most part to observing water molecules in the body. Hyperpolarized molecules exhibit strongly enhanced MRI signals which opens the door for imaging low-concentration species in vivo. Biomolecules can be hyperpolarized and injected into a patient allowing for metabolism to be tracked in real time, greatly expanding the information available to the radiologist. Parahydrogen-induced polarization (PHIP) is a hyperpolarization method renowned for its low cost and accessibility, but is generally limited by low polarization levels, modest molecular concentrations, and contamination by…