Titanium gem (Ti: sapphire, Ti³⁺: Al₂O₃) is today's excellent tunable laser crystal, tuning bandwidth: 660nm~1100nm, absorption band is located in 400~600nm, peak absorption near 490nm. In addition to the optical crystal requirements, an important indicator is the crystal quality factor (figure of merit, referred to as FOM). FOM is defined as: FOM=α490 PI /α800 PI, α490 PI and α800 PI represent the absorption coefficients of polarized light at 490nm and 800nm, respectively. Ti:Upper energy lifetime of sapphire laser transition 3us.