Abstract
The spectroscopy of atomic thallium 6P3/2 → 6D5/2 transition has been observed by laser-induced fluorescence (LIF). The absolute frequency of atomic thallium (205Tl) 6P3/2, F=2 → 6D5/2, F=3 transition has been measured for the first time to an uncertainty of 56 MHz using the femtosecond optical frequency comb and the measured absolute frequency of this transition is 851634646 (56) MHz .The possibility of laser cooling of atomic thallium has also been studied and the calculation shows that the velocity of atomic thallium could be deceased to 12.1 m/s .