Comment on: Jun Dong and Peizhen Deng, 'Ti:sapphire crystal used in ultrafast lasers and amplifiers', Journal of Crystal Growth 261 (2004) 514-519

摘要

As background for those not familiar with Ti:sapphire, this material (Ti-doped sapphire) is used for several tunable solid state laser applications including continuous wave (cw), pulsed and ultra-short (femtosecond) lasers. As a general rule, low-doped, large size crystals are used for cw and highly doped, very thin (path length of ～2 mm) crystals are used for femtosecond lasers. The lasing action is due to Ti~(3+) and any Ti~(4+) ions cause a broad parasitic absorption in the lasing wavelengths; therefore, figure of merit (FOM) was developed to maximize the Ti~(3+) and minimize the Ti~(4+) in a crystal. The segregation coefficient of Ti in sapphire is less than 0.2; hence low-doped crystals are obtained from initial growth and higher doped crystals are obtained from material towards the end of growth. Several boules containing varying amounts of Ti in the initial charge are grown to cover the spectrum of laser applications, e.g., for femtosecond lasers (α_(514) of 6-10 cm~(-1)), the initial grown material of that boule may be higher doped than required for cw laser application.