Absorption spectra and selective excitation of Y3Al5O12 : Tm3+ and YLiF4 :Tm3+ laser systems

The absorption spectrum and the Stark structure are measured for the first time at the temperature T = 300 K for high-lying F-3(4), F-3(3), F-3(2), (1 )G(4), D-1(2), I-1(6), P-3(0), P-3(1), P-3(2) multiplets of Tm3+ ions in th e YAG : Tm-3 laser system with a concentration of 2, 5, 10, 15, and 80% and for I-1(6), P-3(0), P-3(1), and P-3(2) multiplets in the YLiF4 : Tm3+ matr ix with a concentration of 1%. It is demonstrated that, in the pulse-period ic regime of excitation, transmission and absorption coefficients of laser crystals depend on the relation of the time interval between the pulses (De lta T) and the lifetime tau of the metastable activator level if Delta T mu ch less than tau. The investigation of absorption spectra of crystals with different concentrations of Tm3+ has shown that, for excitation rates of ac tive centers equal to 10(7) and 10(5) s(-1), two photons are sequentially a bsorbed through the H-3(6) --> F-3(3) --> D-1(2) and H-3(6) --> (1)G(4) --> P-3(2) schemes. Analysis of the transmission coefficient I/I-0 of the YAG : Tm3+ (2%) crystal as a function of the laser intensity of a free-running ruby laser reveals the appearance of induced emission from the D-1(2) level in the process of excitation.