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.

Phonon surface mapping of graphite: Disentangling quasi-degenerate phonon dispersions

Abstract: The two-dimensional mapping of the phonon dispersions around the $K$ point of graphite by inelastic x-ray scattering is provided. The present work resolves the longstanding issue related to the correct assignment of transverse and longitudinal phonon branches at $K$. We observe an almost degeneracy of the three TO-, LA-, and LO-derived phonon branches and a strong phonon trigonal warping. Correlation effects renormalize the Kohn anomaly of the TO mode, which exhibits a trigonal warping effect opposite to that of the electronic band structure. We determined the electron-phonon coupling constant to be $166\text{ }{(\text{eV}/\text{\AA{}})}^{2}$ in excellent agreement to GW calculations. These results are fundamental for understanding angle-resolved photoemission, double-resonance Raman and transport measurements of graphene-based systems.

Preservation of protein globules and peptidoglycan in the mineralized cell wall of nitrate‐reducing, iron(II)‐oxidizing bacteria: a cryo‐electron microscopy study

Abstract: Iron-oxidizing bacteria are important actors of the geochemical cycle of iron in modern environments and may have played a key role all over Earth's history. However, in order to better assess that role on the modern and the past Earth, there is a need for better understanding the mechanisms of bacterial iron oxidation and for defining potential biosignatures to be looked for in the geologic record. In this study, we investigated experimentally and at the nanometre scale the mineralization of iron-oxidizing bacteria with a combination of synchrotron-based scanning transmission X-ray microscopy (STXM), scanning transmission electron microscopy (STEM) and cryo-transmission electron microscopy (cryo-TEM). We show that the use of cryo-TEM instead of conventional microscopy provides detailed information of the successive iron biomineralization stages in anaerobic nitrate-reducing iron-oxidizing bacteria. These results suggest the existence of preferential Fe-binding and Fe-oxidizing sites on the outer face of the plasma membrane leading to the nucleation and growth of Fe minerals within the periplasm of these cells that eventually become completely encrusted. In contrast, the septa of dividing cells remain nonmineralized. In addition, the use of cryo-TEM offers a detailed view of the exceptional preservation of protein globules and the peptidoglycan within the Fe-mineralized cell walls of these bacteria. These organic molecules and ultrastructural details might be protected from further degradation by entrapment in the mineral matrix down to the nanometre scale. This is discussed in the light of previous studies on the properties of Fe-organic interactions and more generally on the fossilization of mineral-organic assemblies.

Multi-Watt mid-IR femtosecond polycrystalline Cr(2+):ZnS and Cr(2+):ZnSe laser amplifiers with the spectrum spanning 2.0-2.6 µm.

Abstract: We demonstrate efficient amplification of few-optical-cycle mid-IR pulses in single-pass continuously pumped laser amplifiers based on polycrystalline Cr(2+):ZnS and Cr(2+):ZnSe. The 1.7 W output of a Kerr-lens mode-locked master oscillator at 2.4 µm central wavelength, 79 MHz repetition rate was amplified to 7.1 W and 2.7 W in Cr(2+):ZnS and Cr(2+):ZnSe, respectively. High peak power of the input pulses (0.5 MW) and high nonlinearity of the amplifiers' gain media resulted in a significant shortening of the output pulses and in spectral broadening. Transform-limited 40 fs pulses of the master oscillator were compressed to about 27-30 fs. The spectrum of the pulses was broadened from 136 nm to 450 nm (at -3 dB level); the span of the spectra exceeds 600 nm at -10 dB level.

An attempt to constrain the age, duration, and eruptive history of the Karoo flood basalt: Naude's Nek section (South Africa)

Abstract: We have carried out paleomagnetic sampling of a similar to 750 m sequence of the Karoo large igneous province (Naude's Nek Pass, South Africa). K-Ar dating (Cassignol-Gillot) has been performed on four samples from the 650 m upper unit (mean age 179.2 +/- 1.8 Ma) and a sample from the lower unit (184.8 +/- 2.6 Ma). A succession of two phases of volcanism is suggested. The lower 25 flows (115 m thick) have recorded a reversed polarity; the next 23 flows (135 m thick) are transitional and contribute a detailed record of the "Van Zijl" (1962) Jurassic reversal. The upper 38 flows (500 m thick) have normal polarity. Directional groups (DGs) of lava flows with quasi-identical remanence directions indicate eruption durations too short to have recorded geomagnetic secular variation and hence are interpreted as single eruptive events. Altogether, 19 DGs and 10 sheet lobes yield a sequence of 29 distinct directions. This could correspond to a total eruptive activity shorter than 3000 years, less than one per mil of the total duration over which the section was emplaced. We obtain a new paleomagnetic pole for South Africa at similar to 180 Ma (lambda = 75.2 degrees N, phi = 276.4 degrees E, A(95) = 5.8 degrees, N = 19), which is consistent with earlier reports.