At the Lawrence Livermore National Laboratory (LLNL) we have engineered a silicon prototype sample that can be used to reflect focused hard x-ray photons at high intensities in back-scattering geometry.1 Our work is motivated by the need for an all-x-ray pump-and-probe capability at X-ray Free Electron Lasers (XFELs) such as the Linac Coherent Light Source (LCSL) at SLAC. In the first phase of our project, we exposed silicon single crystal to the LCLS beam, and quantitatively studied the x-ray induced damage as a function of x-ray fluence. The damage we observed is extensive at fluences typical of pump-and-probe experiments. The conclusions drawn from our data allowed us to design and manufacture a silicon mirror that can limit the local damage, and reflect the incident beam before its single crystal structure is destroyed. In the second phase of this project we tested this prototype back-reflector at the LCLS. Preliminary results suggest that the new mirror geometry yields reproducible Bragg reflectivity at high x-ray fluences, promising a path forward for silicon single crystals as x-ray back-reflectors.
Focused femtosecond laser pulses from a 1 MHz fiber laser were used to create modifications in Er-
Yb doped zinc phosphate glass. Two glasses with similar phosphate glass networks but different
network modifiers were investigated. To understand the resulting changes caused by the
femtosecond laser pulses various characterization techniques were employed: glass structural
changes were investigated with confocal Raman spectroscopy, defect generation as well as local Er
and Yb environment were investigated with confocal fluorescence spectroscopy, and elemental
segregation resulting from heat accumulation effects was ascertained by scanning electron
We have systematically studied femtosecond-laser fabrication of optical waveguides in an Er-Yb doped phosphate glass.
Waveguides were written using the IMRA America FCPA μJewel D-400 femtosecond fiber laser system with pulse
repetition rates ranging from 250 kHz to 2.2 MHz. At every pulse repetition rate a series of waveguides was written
while varying scan speeds from 50 μm/s to 100 mm/s and pulse energies from 80 nJ to 320 nJ. The optical quality of the
waveguides was evaluated by measuring the waveguide mode profile as well as the optical loss. Laser-induced defects
and structural changes in the glass were characterized using confocal fluorescence and Raman microscopy.