ENERGY-TRANSFER UP-CONVERSION AND EXCITED-STATE ABSORPTION OF LASER-RADIATION IN ND-YLF LASER CRYSTALS

Experiments at room temperature were carried out to study the higher o rder processes that produced the yellow and blue fluorescence observed in Nd:YLF laser crystals, which were pumped by lasers with wavelength s between 785 nm and 811 nm, and with the pump power density ranging f rom 10 to 30 kW/cm(2), or the stored energy density, 15-45 J/cm(3), Th e analysis of the experimental results provided an explanation for the performance degradation of a Q-switched laser with increasing pump in tensity, These higher order processes were energy transfer up-conversi on and excited state absorption of both pump and laser radiation, A mo del was also developed based upon rate equations to describe these hig her order processes, This model allowed us to discriminate between the se processes and to determine which one played the most important role , The experimental results agreed well with the predictions of the mod el, It is concluded that the energy transfer up-conversion process is the dominant mechanism for the population of the G7/2 multiplet, It is also concluded that excited state absorption of the 1.05 mu m or 1.3 mu m radiation from the (4)G(7/2) multiplet play a significant role in populating the P-2(3/2), D-2(1)(5/2), and P-2(1/2) manifolds, and in the performance of Nd:YLF lasers operating in the pulsed mode, The eff ect of excited state absorption of the pump radiation from the F-4(1/2 ) multiplet is much less important.