Characterization of absorption bands in Ti:sapphire crystals

We have measured and characterized, over a wide range of doping levels, the UV-near-IR (190-2000-nm) absorption properties of Ti:sapphire crystals. We find that the strengths of absorption centered around 400-450 and 268 nm depend on the square of the Ti3+ doping level, suggesting an origin from pairs of Ti3+ ions. In addition, we have identified an absorption feature below 210 nm due to Ti3+, rather than Ti4+ charge-transfer transitions. Finally, our data on 800-nm-peak, near-IR absorption shows a complex lineshape, with a lower limit set by Ti3+ pair absorption. Thus the maximum possible Figure-of-Merit for Ti:sapphire reduces as the doping level increases.