Search results for " Polarization"
showing 10 items of 668 documents
Demonstration of Stimulated-Raman-scattering suppression in optical fibers in a multifrequency pumping configuration
1999
International audience; We analyze the stimulated-Raman-scattering-(SRS) process induced by a linearly polarized multifrequency pump field in a normally dispersive single-mode fiber. We show, by theoretical analysis and numerical simulations, that the SRS process may be either controlled by switching all the generated Stokes radiations to the lowest-frequency pump or suppressed for all the frequency components of the pump field. The suppression process is achieved by an appropriate choice of the frequency separation between the pumps and a particular power distribution among the frequency components of the pump field. We present experimental spectra showing the effectiveness of this suppres…
Simultaneous achievement of polarization attraction and Raman amplification in optical fibers
2004
We present a theoretical analysis and experimental demonstration of the combined effects of polarization attraction and Raman amplification in isotropic optical fibers. The polarization attraction is based on four-wave mixing interaction of counterpropagating waves.
Strong reduction of optimum pump power for efficient wave conversion in optical fibers with dual-frequency circularly polarized pump waves.
2002
We present experiments that show achievement of highly efficient generation of parametric sidebands in an optical fiber with dual-frequency, circularly polarized pump waves. An appropriate choice of the separation between the pump frequencies permits a strong reduction of the optimum power for highly efficient frequency conversion.
Broadband tuning of polarization modulation instability in microstructured optical fibers
2020
The wideband tuning of strong bands generated through polarization modulation instability (PMI) in microstructured optical fibers (MOFs) is reported. Tunability is achieved by exploiting the dependence of the phase-matching condition on the fiber’s chromatic dispersion and birefringence, which is particularly sensitive when the fiber is pumped near the zero-dispersion wavelength. MOFs designed to accomplish PMI phase-matching when they are infiltrated with ethanol and pumped at 1064 nm were designed and fabricated. Taking advantage of the large thermo-optic coefficient of ethanol, both chromatic dispersion and birefringence were varied through temperature. Wavelength shifts from 937 nm to 8…
Nonlinear repolarization dynamics in optical fibers: transient polarization attraction
2011
International audience; In this work, we present a theoretical and experimental study of the response of a lossless polarizer to a signal beam with a time-varying state of polarization (SOP). By lossless polarizer, we mean a nonlinear conservative medium (e.g., an optical fiber) that is counterpumped by an intense and fully polarized pump beam. Such a medium transforms input uniform or random distributions of the SOP of an intense signal beam into output distributions that are tightly localized around a well-defined SOP. We introduce and characterize an important parameter of a lossless polarizer--its response time. Whenever the fluctuations of the SOP of the input signal beam are slower th…
Novel spectra in the supercontinuum generation with applications in the biodiversity conservation
2014
This paper presents some spectra of the supercontinuum generation obtained with microstructured fibers and tapered fiber devices excited with quasi-continuous pumps. These spectra are part of a group (collection) of multiple configurations that were studied and evaluated by our working group, and that could be very useful in LIDAR as well as bio-imaging applications. This work is limited to present some spectra that could be useful in applications of biodiversity conservation. The prototypes for specific applications will be evaluated in future research.
MRI of the lungs using hyperpolarized noble gases
2002
The nuclear spin polarization of the noble gas isotopes (3)He and (129)Xe can be increased using optical pumping methods by four to five orders of magnitude. This extraordinary gain in polarization translates directly into a gain in signal strength for MRI. The new technology of hyperpolarized (HP) gas MRI holds enormous potential for enhancing sensitivity and contrast in pulmonary imaging. This review outlines the physics underlying the optical pumping process, imaging strategies coping with the nonequilibrium polarization, and effects of the alveolar microstructure on relaxation and diffusion of the noble gases. It presents recent progress in HP gas MRI and applications ranging from MR mi…
Realization of a broad band neutron spin filter with compressed, polarized 3He gas
1997
The strongly spin dependent absorption of neutrons in nuclear spin polarized 3He opens the possibility to polarize beams of thermal and epithermal neutrons. An effective 3He neutron spin filter (NSF) requires high 3He nuclear polarization as well as a filter thickness corresponding to a gas amount of the order of 1 barl. We realized such a filter using direct optical pumping of metastable 3He∗ atoms in a 3He plasma at 1 mbar. Metastable exchange scattering transfers the angular momentum to the whole ensemble of 3He atoms. At present 3 × 1018 3He-atoms/s are polarized up to 64%. Subsequent polarization preserving compression by a two stage compressor system enables to prepare NSF cells of ab…
Optimization of a polarization imaging system for 3D measurements of transparent objects
2009
This paper presents a multispectral imaging system for 3D reconstruction of transparent objects based on "shape from polarization" technique. The originality of this work relies on a multispectral active lighting system which enables to cope with the two ambiguities on the zenith angle and azimuth angle. A calibration step allows optimising the polarimetric measurements. Example of a reconstructed transparent object is presented.
<title>Spin-polarized electron kinetics under high-intensity picosecond excitation</title>
2003
ABSTRACT Spin-polarized electron kinetics is studied by time-resolved polarized photoemission with picosecond resolution. The re-sponse time of strained layer photocathodes is found to be in a range of a few picosecond offering an ultrafast response andhigh spin-polarization of emitted electrons. The studies of the sub-picosecond spin dynamics are facilitated in high-intensityexcitation regime when the length of the emission pulse is enlarged due to the dispersion of acceleration time and Coulombrepulsion ofthe electrons in their flight in the vacuum.Keywords: optical orientation, spin kinetics, strained semiconductor layer, time-resolved emission. 1. INTRODUCTION GaAs, layers are known to …