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Viscosity of fluorine-doped silica glasses
The viscous behavior of fluorine-doped synthetic silica is studied using collapsing experiments with different fluorine-doped tubes on a modified chemical vapor deposition (MCVD) lathe. The principles, techniques, and evaluations of this method are the same as the ones demonstrated previously in detail with pure and doped silica. The present investigations provide information about the influence of fluorine doping up to a concentration of about 10 mol% F (3.4 wt% F) in a temperature range between 1600°C and 2000°C. Fluorine doping leads to a systematic decrease in the viscosity, combined with a decrease of the activation energy of the viscous flow and a certain increase of the pre-exponential factor. In summary, this demonstrates the weakening influence of fluorine on the glass network, similar to the incorporation of hydroxyl or chlorine.
Yb-doped large mode area fiber for beam quality improvement using local adiabatic tapers with reduced dopant diffusion
A newly designed all-solid step-index Yb-doped aluminosilicate large mode area fiber for achieving high peak power at near diffraction limited beam quality with local adiabatic tapering is presented. The 45µm diameter fiber core and pump cladding consist of active/passively doped aluminosilicate glass produced by powder sinter technology (REPUSIL). A deliberate combination of innovative cladding and core materials was aspired to achieve low processing temperature reducing dopant diffusion during fiber fabrication, tapering and splicing. By developing a short adiabatic taper, robust seed coupling is achieved by using this Yb-doped LMA fiber as final stage of a nanosecond fiber Master Oscillator Power Amplifier (MOPA) system while maintaining near diffraction limited beam quality by preferential excitation of the fundamental mode. After application of a fiber-based endcap, the peak power could be scaled up to 375 kW with high beam quality and a measured M2 value of 1.3~1.7.A newly designed all-solid step-index Yb-doped aluminosilicate large mode area fiber for achieving high peak power at near diffraction limited beam quality with local adiabatic tapering is presented. The 45µm diameter fiber core and pump cladding consist of active/passively doped aluminosilicate glass produced by powder sinter technology (REPUSIL). A deliberate combination of innovative cladding and core materials was aspired to achieve low processing temperature reducing dopant diffusion during fiber fabrication, tapering and splicing. By developing a short adiabatic taper, robust seed coupling is achieved by using this Yb-doped LMA fiber as final stage of a nanosecond fiber Master Oscillator Power Amplifier (MOPA) system while maintaining near diffraction limited beam quality by preferential excitation of the fundamental mode. After application of a fiber-based endcap, the peak power could be scaled up to 375 kW with high beam quality and a measured M2 value of 1.3~1.7.