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.

Ultra high power single mode fiber laser system with non-uniformly configured fiber-to fiber rod multimode amplifier

Abstract: A high power fiber laser system includes a booster which is configured as a fiber amplifier extending over free space, pump source and laser head including a reflective element which receives pump light and. reflects toward the output end of the booster in a counter signal- propagating direction. The booster is configured with concentric and coextending frustoconically shaped multimode ("MM") core and cladding around the core. The core includes a mode transition region expanding between small diameter SM input and large diameter MM output core ends and configured so that amplification of high order modes is substantially suppressed as a single mode ("SM") signal light propagates from the input to output core ends. The laser head receives output, ends of respective pump light delivery fibers and signal fiber, respectively. The pump source is structured with a plurality of independent sub-pumps arranged around the booster. The laser head supports a segmented mirror configured to reflect pump lights from respective pump sub-sources to the output end of the booster in a counter propagating direction, wherein the booster is configured to emit the amplified signal light reaching up to MW power levels substantially in the SM.

Sediment Transport in a Microscale Braided Stream: From Grain Size to Reach Scale

Abstract: This paper explores the influence of grain size and flood plain length on trans- port equations in a micro-scale braided stream. 159 experiments were conducted with varying slope, water discharge, input sediment discharge, grain size and flood- plain length. The experiments complement previous results (Metivier and Meunier (2003)). Bed load transport at the outlet is correlated with both stream power index and input flux for all the grain sizes. A general dimensionless transport equation can be derived that relates transport ecency of a braided river to its eective stream power. Experiments have been run to evaluate the critical stream power index for motion inception and include it in this relationship. We further explore the influence of dierent characteristic length scales (flow depth, floodplain length) on the transport dynamics. We show that bed load is probably related to the ratio of water depth to grain size as suggested by Bagnold (1973). In our runs, the input flux tends to reduce the bed load rate by forcing the river to braid. This reduction increases with grain size and decreases with flood plain length. This suggests that braiding process is highly improved with coarse material but that dispersion of the sediment wave occurs to counteract this influence.

Seismic anisotropy and its precursory change before eruptions at Piton de la Fournaise volcano, La Réunion

Abstract: The Piton de la Fournaise volcano exhibits frequent eruptions preceded by seismic swarms and is a good target to test hypotheses about magmatically induced variations in seismic wave properties. We use a permanent station network and a portable broadband network to compare seismic anisotropy measured via shear wave splitting with geodetic displacements, ratios of compressional to shear velocity (Vp/Vs), earthquake focal mechanisms, and ambient noise correlation analysis of surface wave velocities and to examine velocity and stress changes from 2000 through 2012. Fast directions align radially to the central cone and parallel to surface cracks and fissures, suggesting stress-controlled cracks. High Vp/Vs ratios under the summit compared with low ratios under the flank suggest spatial variations in the proportion of fluid-filled versus gas-filled cracks. Secular variations of fast directions (ϕ) and delay times (dt) between split shear waves are interpreted to sense changing crack densities and pressure. Delay times tend to increase while surface wave velocity decreases before eruptions. Rotations of ϕ may be caused by changes in either stress direction or fluid pressure. These changes usually correlate with GPS baseline changes. Changes in shear wave splitting measurements made on multiplets yield several populations with characteristic delay times, measured incoming polarizations, and fast directions, which change their proportion as a function of time. An eruption sequence on 14 October 2010 yielded over 2000 shear wave splitting measurements in a 14 h period, allowing high time resolution measurements to characterize the sequence. Stress directions from a propagating dike model qualitatively fit the temporal change in splitting.

High power raman-based fiber laser system and method of operating the same

Abstract: A fiber Raman laser is configured with a microstructured double clad passive fiber whic has an inner cladding receiving and guiding a high intensity pump light. The double-cla passive fiber further has a core surrounded by the inner cladding and an outer cladding. An arrangement of air holes is configured to define the inner, waveguiding cladding so that an NA of the latter varies between about 0.25 - 0.9 allowing this to reduce the diameter of the inner cladding. The passive fiber is characterized by a substantial overla between the pump light and 1st stokes in the core and further includes an absorber operative to substantially suppress the signal light at the 2 nd stokes so that the Ge-doped fiber outputs a SM, bright radiation at up to kW levels.