High-temperature strain sensing using sapphire fibers with inscribed first-order Bragg gratings

Strain sensor designs and strain measurements based on single-crystal sapphire fibers with inscribed first-order fiber Bragg gratings for applications up to 600 °C are presented. We report on all the details of two different sensor designs; for instance, we show that the resolution of multimode sapphire fiber Bragg grating (SFBG) strain sensors is about l / l = ¼ 10-5 (10 µstrain), which is comparable with state-of-the-art high-temperature sensors. We apply our sensors for the determination of the thermal expansion coefficients of high-temperature steel alloys, showing a good match to known values. Hence, we believe that SFBG sensors may represent a promising alternative to currently used non-optic-based strain-detecting devices

High performance fiber-Fabry-Perot resonator targeting quantum optics applications

Quantum optics experiments frequently require the separation of single-photon-level signals from strong classical fields. In circumstances in which the signals are spectrally close, and one cannot make use of relatively simple separation methods based around differences in polarization state, optical mode, or beam direction, it is necessary to exploit the frequency difference itself as the means for signal separation. We have constructed and characterized an efficient and robust fiber-based filter, consisting of an all-fiber Fabry-Perot resonator, to achieve this goal. Our filter shows 31dB of suppression of unwanted signals and 76% transmission of the desired signal. The transmission of the filter was stabilized to within 2% of its maximum for over 35hours through simple temperature stabilization.Jonathan P. Hedger, Tino Elsmann, Martin Becker, Tobias Tiess, Andre N. Luiten and Ben M. Sparke

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