Nanofiber Fabry-Perot microresonator for non-linear optics and cavity quantum electrodynamics

We experimentally realize a Fabry-Perot-type optical microresonator near the cesium D2 line wavelength based on a tapered optical fiber, equipped with two fiber Bragg gratings which enclose a sub-wavelength diameter waist. Owing to the very low taper losses, the finesse of the resonator reaches F = 86 while the on-resonance transmission is T = 11 %. The characteristics of our resonator fulfill the requirements of non-linear optics and cavity quantum electrodynamics in the strong coupling regime. In combination with its demonstrated ease of use and its advantageous mode geometry, it thus opens a realm of applications.Comment: 4 pages, 3 figure

Real-time and Sub-wavelength Ultrafast Coherent Diffraction Imaging in the Extreme Ultraviolet

Coherent Diffraction Imaging is a technique to study matter with nanometer-scale spatial resolution based on coherent illumination of the sample with hard X-ray, soft X-ray or extreme ultraviolet light delivered from synchrotrons or more recently X-ray Free-Electron Lasers. This robust technique simultaneously allows quantitative amplitude and phase contrast imaging. Laser-driven high harmonic generation XUV-sources allow table-top realizations. However, the low conversion efficiency of lab-based sources imposes either a large scale laser system or long exposure times, preventing many applications. Here we present a lensless imaging experiment combining a high numerical aperture (NA=0.8) setup with a high average power fibre laser driven high harmonic source. The high flux and narrow-band harmonic line at 33.2 nm enables either sub-wavelength spatial resolution close to the Abbe limit (Delta r=0.8 lambda) for long exposure time, or sub-70 nm imaging in less than one second. The unprecedented high spatial resolution, compactness of the setup together with the real-time capability paves the way for a plethora of applications in fundamental and life sciences

The small RNA RssR regulates myo-inositol degradation by Salmonella enterica

Small noncoding RNAs (sRNAs) with putative regulatory functions in gene expression have been identified in the enteropathogen Salmonella enterica serovar Typhimurium (S. Typhimurium). Two sRNAs are encoded by the genomic island GEI4417/4436 responsible for myo-inositol (MI) degradation, suggesting a role in the regulation of this metabolic pathway. We show that a lack of the sRNA STnc2160, termed RssR, results in a severe growth defect in minimal medium (MM) with MI. In contrast, the second sRNA STnc1740 was induced in the presence of glucose, and its overexpression slightly attenuated growth in the presence of MI. Constitutive expression of RssR led to an increased stability of the reiD mRNA, which encodes an activator of iol genes involved in MI utilization, via interaction with its 5'-UTR. SsrB, a response regulator contributing to the virulence properties of salmonellae, activated rssR transcription by binding the sRNA promoter. In addition, the absence of the RNA chaperone Hfq resulted in strongly decreased levels of RssR, attenuated S. Typhimurium growth with MI, and reduced expression of several iol genes required for MI degradation. Considered together, the extrinsic RssR allows fine regulation of cellular ReiD levels and thus of MI degradation by acting on the reiD mRNA stability

100 W average power femtosecond UV laser for ultra-high photon flux XUV sources

We present a femtosecond laser system delivering up to 100 W of average power at 343 nm. The laser system employs an Yb-based femtosecond fiber laser and subsequent secondand third harmonic generation in BBO. Thermal gradients within the BBO crystals are reduced due to sapphire heat spreaders directly bonded to the front and back surface of the crystals. Thus a nearly diffraction-limited beam quality (M2<1.5) is achieved despite the high thermal load to the nonlinear crystals. This laser source is expected to generate XUV radiation with ultra-high photon flux in the near future

Verfahren zum Fügen von Substraten

The invention relates to a method for joining substrates. The aim of the invention is to join together substrates consisting of substrate materials without having to spend added time and effort to apply a coating in coating processes to be additionally carried out and to also achieve a good joint quality. In the method according to the invention, a pretreatment of at least one joint surface of a substrate to be joined is carried out in a low-pressure oxygen plasma prior to the actual joining process. During the joining process, a pressing force ranging from 2 kPa to 5 MPa acts on the substrates to be joined, and a heat treatment is carried out at an increased temperature of at least 100 DEG C and at negative pressure conditions of maximally 10 mbar, preferably -3 mbar

Post-hydrogen-loaded draw tower fiber Bragg gratings and their thermal regeneration

The idea of Bragg gratings generated during the drawing process of a fiber dates back almost 20 years. The technical improvement of the draw tower grating (DTG) process today results in highly reliable and cost-effective Bragg gratings for versatile application in the optical fiber sensor market. Because of the single-pulse exposure of the fiber, the gratings behave typically like type I gratings with respect to their temperature stability. This means that such gratings only work up to temperatures of about 300 °C. To increase temperature stability, we combined DTG arrays with hydrogen postloading and a thermal regeneration process that enables their use in high-temperature environments. The regenerated draw tower gratings are demonstrated to be suitable for temperatures of more than 800 °C. © 2011 Optical Society of America

Arrays of regenerated fiber bragg gratings in non-hydrogen-loaded photosensitive fibers for high-temperature sensor networks

We report about the possibility of using regenerated fiber Bragg gratings generated in photosensitive fibers without applying hydrogen loading for high temperature sensor networks. We use a thermally induced regenerative process which leads to a secondary increase in grating reflectivity. This refractive index modification has shown to become more stable after the regeneration up to temperatures of 600 °C. With the use of an interferometric writing technique, it is possible also to generate arrays of regenerated fiber Bragg gratings for sensor networks. © 2009 by the authors

Thermal regenerated type IIa fiber Bragg gratings for ultra-high temperature operation

Thermally regenerated fiber Bragg gratings written in photosensitive fibers with nanosecond laser pulses without hydrogen loading have been shown to become temperature stable up to 600 °C. In this paper, we give an experimental analysis of the refractive index development for fabricating the gratings and for the thermal regeneration process. Furthermore, we identify a thermal induced type IIa (type In) behavior of the refractive index to be responsible for the regeneration. The variation of refractive index modulation and the average index in the grating region is discussed. With additional annealing it is possible to improve the temperature stability beyond 1000 °C. © 2010 Elsevier B.V. All rights reserved