Direct measurements of the terminal laser level lifetime in neodymium-doped crystals and glasses

We have measured the terminal level lifetime (τ11/2) for the 1-μm neodymium transition in several laser media, using a novel pump (2.41-μm) and probe (1.06-μm) technique. This method allows us to populate the 4I13/2 level directly and subsequently to monitor the terminal level 4I11/2 population as a function of time by observing the change in integrated fluoresence of the 0.88-μm emission for each time delay between the pump and the probe pulses. We developed a computer model to analyze the data and determined the upper and lower limits for the τ11/2 lifetime. The results for some of the materials investigated are 115–225 ps for Nd:Y3Al5O12, 250–450 ps for Nd:LG-750 (phosphate glass), 535–740 ps for Nd:LG-660 (silicate glass), 896–1900 ps for Nd:YAlO3, and 10.5–20 ns for Nd:YLiF4. In addition, we found the lifetimes to be independent of the neodymium doping concentration for the phosphate and silicate glass samples investigated.