Femtosecond-laser-fabricated periodic tapered structures on a silicon substrate for terahertz antireflection.

In this research, terahertz (THz) antireflective structures tapered with several profiles (linear, exponential, Klopfenstein) were modeled for high-resistivity silicon and theoretically evaluated using a high-frequency electromagnetic field simulation (HFSS). Their antireflective characteristics are greatly affected by the profiles. One-dimensional periodic tapered THz antireflective structures with different profiles were also fabricated on high-resistivity silicon using femtosecond laser processing. Their antireflective characteristics were experimentally evaluated by standard THz time-domain spectroscopy and modeled by HFSS for reference. The experimental results are in good agreement with the simulations, which showed that the Fresnel reflection reduces to almost zero over a band broader than 1 THz.

Ytterbium-doped all glass leakage channel fibers with highly fluorine-doped silica pump cladding.

All glass leakage channel fibers have been demonstrated to be a potential practical solution for power scaling in fiber lasers beyond the nonlinear limits in conventional large mode area fibers. The all glass nature with absence of any air holes is especially useful for allowing the fibers to be used and fabricated much like conventional fibers. Previously, double clad active all glass leakage channel fibers used low index polymer as a pump guide with the drawbacks of being less reliable at high pump powers and not being able to change fiber outer diameter independent of pump guide dimension. In this work, we demonstrate, for the first time, ytterbium-doped double clad all glass leakage channel fibers with highly fluorine-doped silica as pump cladding. The new all glass leakage channel fibers have no polymer in the pump path and have independent control of fiber outer diameters and pump cladding dimension, and, therefore, enable designs with smaller pump guide for high pump absorption and, at the same time, with large fiber diameters to minimize micro and macro bending effects, a much desired features for large core fibers where intermodal coupling can be an issue due to a much increased mode density. An ytterbium-doped double clad PM fiber with core diameter of 80 microm is also reported, which can be coiled in 76 cm diameter coils.

Chemical effects in high-resolution nickel Kalpha X-ray fluorescence spectra.

The nickel Kalpha spectra of oxides, halides (NiF2, K2NiF6, NiCl2, NiBr2), complex compounds, and metal are measured with two different double-crystal X-ray fluorescence spectrometers. The peak shifts and line width changes due to the changes in the chemical states are reported. High reproducibility has been shown for the chemical shift and line width measurements. The DV-Xalpha molecular orbital calculation at the ground and the 1s(-1) hole states was performed to prove that the chemical effect originats from the charge-transfer mechanism.