IPG Photonics

About: IPG Photonics is a based out in . It is known for research contribution in the topics: Laser & Fiber laser. The organization has 903 authors who have published 1241 publications receiving 63339 citations.

Adiabatic approximation, Gell-Mann and Low theorem, and degeneracies: A pedagogical example

Abstract: We study a simple system described by a $2\ifmmode\times\else\texttimes\fi{}2$ Hamiltonian and the evolution of its quantum states under the influence of a perturbation. More precisely, when the initial Hamiltonian is not degenerate, we check analytically the validity of the adiabatic approximation and verify that, even if the evolution operator has no limit for adiabatic switchings, the Gell-Mann and Low formula allows the evolution of eigenstates to be followed. In the degenerate case, for generic initial eigenstates, the adiabatic approximation (obtained by two different limiting procedures) is either useless or wrong, and the Gell-Mann and Low formula does not hold. We show how to select initial states in order to avoid such failures.

In situ High-Temperature Experiments

Abstract: When Frank Hawthorne (1988) edited the Reviews in Mineralogy volume on “Spectroscopic Methods in Mineralogy and Geology,” all the experiments presented had been performed at room pressure and room temperature because, at that time, vibrational and X-ray techniques were already quite difficult at ambient conditions so more sophisticated sample environments were not a priority. However, it has now become somewhat easier to perform experiments in situ at high temperatures (HT), high pressures (HP) or under combined high temperature and pressure (HP-HT). These types of experiments are becoming routine on crystals, glasses and liquids (see Shen and Wang 2014, this volume). High-temperature experiments are important because most of the physical properties of high-temperature liquids, such as magmas and melts, are related to their atomic structure. Consequently, it is important to probe the local environment of the atoms in the sample under the conditions noted above (e.g., HT). However, at very high temperatures (~≥ 1200 °C) it is difficult to use conventional furnaces because of a number of experimental difficulties associated with their use: temperature regulation, thermal inertia and spatial obstruction of the sample. Due to the progress made in the development of lasers and X-ray, neutron and magnetic sources it is now possible to perform experiments in situ at HT, HP and HT-HP on samples of millimeter or micron size. In this chapter, we discuss some of these noncommercial methods used in performing experiments at HT, and outline the best choices for heating systems with regard to the experimental requirements. Different commercial heating systems are available such as the systems available from Linkam® ( http://www.linkam.co.uk/ ) or Leica® ( http://www.leica-microsystems.com/ ) for example. These two systems are well adapted to performing experiments at HT including Raman (Neuville et al. 2014, this volume) and IR spectroscopy (Della Ventura et al. 2014, this volume) …

Low-mode high power fiber combiner

Abstract: A high power fiber laser system is configured with a combiner end fiber spliced to a combiner output fiber. The system further includes a light stripper extending along the combiner end and output fibers and configured with sequentially located zones 'which are provided with respective refractive indices. In a forward propagating direction of light signal, the upstream zone includes polymeric material with the refractive index higher than that of the cladding of the combiner end fiber. This zone is configured to remove the backreflected core guided light bled into the cladding of the combiner through a splice between combiner end and output fibers. The intermediate zone includes polymeric material configured with a refractive index lower than that of the cladding of the combiner output fiber so it can prevent clad guided signal light from decoupling the cladding under the material. The downstream zone is configured with polymeric material having a refractive index lower than that of the cladding of the combiner output fiber. The polymeric material of the downstream zone is impregnated with a plurality of light diffusers scattering high numerical aperture rays of the clad-guided signal light.