Search results for "M squared"
showing 7 items of 7 documents
"Table 2" of "First measurement of the ${\mathbf{|\textit t|}}$-dependence of coherent $\mathbf{\rm{J/\psi}}$ photonuclear production"
2021
pT**2-dependence of coherent J/psi photoproduction cross section in Pb-Pb UPC.
Laser beam scattering effects in non-absorbent inhomogenous polymers
2007
Ilie, Mariana Kneip, Jean-Christophe Mattei, Simone Nichici, Alexandru Roze, Claude Girasole, Thierry; In this paper a numerical model for laser beam scattering in the semi-transparent polymers is presented, using a Monte Carlo algorithm and the Mie theory. The algorithm correctly accounts for the independent multiply-scattered light. We describe the algorithm, present a number of important parameters that account in the welding process, and explicitly show how the algorithm can be used to estimate the laser beam intensity both inside the semi-transparent component and at the welding interface and the beam widening. For the model validation an experimental bench test has been realized and s…
Manipulation of fast light using photorefractive beam fanning
2014
Light pulse group velocity manipulations due to the specific dispersion of a medium (so-called “slow” and “fast” light phenomena) can be obtained on the basis of several mechanisms. One of these techniques is two-wave mixing in a photorefractive crystal. This work presents a modification of this method, exploiting the strong beam fanning in Sb-doped Sn2P2S6 crystals. Our experimental results demonstrate a “fast light” behavior of Gaussian pulses transmitted through a Sn2P2S6:Sb sample. The phenomenon is due to the beam fanning (i.e., the self-diffraction of the incident beam on self-induced noisy photorefractive gratings) that ensures a significant depletion of the input beam. Due to the re…
Improved active fiber-based retroreflector with intensity stabilization and a polarization monitor for the near UV.
2021
We present an improved active fiber-based retroreflector (AFR) providing high-quality wavefront-retracing anti-parallel laser beams in the near UV. We use our improved AFR for first-order Doppler-shift suppression in precision spectroscopy of atomic hydrogen, but our setup can be adapted to other applications where wavefront-retracing beams with defined laser polarization are important. We demonstrate how weak aberrations produced by the fiber collimator may remain unobserved in the intensity of the collimated beam but limit the performance of the AFR. Our general results on characterizing these aberrations with a caustic measurement can be applied to any system where a collimated high-qual…
Angular shift of an electromagnetic beam reflected by a planar dielectric interface
1989
A mathematical procedure for obtaining theoretically an expression for the fields of a beam reflected by a planar interface separating two lossless, linear, isotropic, homogeneous media is presented. Comparison of this expression with that obtained when the beam undergoes reflection from a perfect conductor leads to the expression for the angular shift of the beam reflected by a planar dielectric interface. The cases of normal and parallel polarization of a microwave beam are considered. In the last case, a complete study for angles of incidence far and near the Brewster angle is made.
Free-motion beam propagation factor measurement by means of a liquid crystal SLM
2011
We propose a compact and robust method to measure beam propagation factor (M2) of continuous wave (cw) laser beams. In contrast to the conventional scanning procedure described in the ISO/DIS 11146 standard, our proposal takes advantage of the features of programmable liquid crystal spatial light modulators (SLMs) where a lens is codified. Then, by using a CCD at a fixed position, the beam width according to the second order moment of the irradiance is determined for each focal length of the codified lenses. After adjusting the measured data to the theoretical focusing behavior of a real laser beam, the beam propagation factor is obtained. The proposed method was successfully validated in t…
Analytical Evaluation of the Temporal Focal Shift for Arbitrary Pulse Shapes
2004
In this letter, we analyze the propagation of linearly chirped arbitrary-shaped light pulses through a parabolic dispersive medium to derive an analytical formula of assessing the location of the transverse plane where the pulse root-mean-square width is minimum. Closed form expressions for compressed pulses, which are independent of the input pulse shape, are demonstrated. In this way, we demonstrate that both the relative temporal focal shift and the minimum pulsewidth are solely determined by two factors, the temporal equivalent of the Fresnel number of the geometry and the pulse quality factor, i.e., the temporal analogue of the spatial M/sup 2/ beam quality factor. Some examples are di…