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Electric field induced second harmonic (EFISH) generation typically increases with laser intensity. Therefore, EFISH signals generated at the rear S i / S i O 2 interface by a laser beam transmitted through a thin silicon membrane should be much weaker than the signals generated in reflection at the front surface. The counter-intuitive finding that the signal generated at the rear surface is stronger than the front surface signal [Appl. Phys. B 104, 735 (2011)APBOEM0946-217110.1007/s00340-011-4682-1] is now confirmed by detailed experiments applying 10 to 30 µm thin membranes. Using, in addition, the local laser beam intensity [Appl. Phys. B 123, 253 (2017)APBOEM0946-217110.1007/s00340-017-6824-6] leads to the hypothesis that the quasi-static electric field at the rear interface consists of two counteracting components.

The transmission of a Ti:sapphire laser beam (c.w. and fs pulsed operation at 800 nm) through a 10 µm thin oxidized silicon membrane at 45 • angle of incidence at first increases with the incident laser power, then shows a maximum, and finally decreases considerably. This nonlinear transmission behavior is the same for c. w. and pulsed laser operation and mainly attributed to free charge carrier (FCA) absorption in Si. A simple FCA model is developed and tested.

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Abstract:We present measurements of the slope efficiency and the pump power at threshold of a Tm 3+ -doped silica triple clad fiber laser emitting at 2.02 µm using different cooling techniques. The slope efficiency of 53.6 % was obtained at a temperature of 25 o C with a maximum output power of 5 W for 19 W of absorbed power at the pump wavelength of 800 nm and 9.9 W threshold. In a slightly different setup, the output power could be increased to 10 W for an absorbed pump power of 32 W.