Abstract

We observed a reduction in the absorption of 532-nm laser radiation by Ti:sapphire with increased laser fluence up to 3.5 J/cm². This effect was observed for all Ti:sapphire samples studied, six crystals as of now, and is attributed to saturation of the optical transition of the Ti³⁺ ions. Since 532-nm radiation is used to pump Ti:sapphire lasers, it is important to know its absorption characteristics to understand completely the laser performance. However, this saturation effect is more important as an accurate method of measuring dopant ion density and absorption cross section independently. The transmittances of Ti:sapphire at 532-nm were measured with respect to incident laser fluence and fitted to a numerical saturation model using a nonsteady-state rate equation analysis based on the Franz-Nodvick approach. Upper-state fluorescence was ignored since absorption occurred on a time scale (≈10 ns) short compared to the fluorescence lifetime (≈3.2 μs). The fitted parameters were the weak-signal transmittance T₀ and the saturation flux E_sat (hν/σ) from which the absorption cross section and dopant ion density can be determined. For example, using a 2.1-cm Ti:sapphire sample having a weak-signal absorption coefficient of 1.58 cm⁻¹ at 532 ran, the E_sat was 7.7 J/cm² which gave a cross section of 4.8 × 10⁻²⁰ cm² and a Ti³⁺ density of 3.3 × 10¹⁹ cm⁻³, consistent with estimates of the total Ti density.

© 1986 Optical Society of America