Measurement of the 4F5/2 and 2H(2)9/2 manifold lifetime in Nd3+:YLiF4

We present direct measurements of the lifetime of the 4F5/2 and 2H(2)9/2 manifold in Nd3+:YLiF4, using a fluorescence pump–probe technique. The technique populates the 4F5/2 and 2H(2)9/2 manifold directly with a pump pulse. Via excited state absorption from this excited manifold, the 2F(2)5/2 manifold of Nd3+ is populated with a delayed probe pulse. The population in the 4F5/2 and 2H(2)9/2 manifold is monitored as a function of time by observing the change in integrated UV fluorescence from the 2F(2)5/2 manifold for each time delay between pump and probe pulses. The pump (∼780nm) and probe (∼390nm) beams come from the fundamental and second harmonic wavelengths of a femtosecond Ti:sapphire regenerative amplifier. The measured lifetime (230±30ps) agrees well with the energy gap law, based on other nonradiative lifetime measurements from the literature for Nd3+:YLiF4.