Spectroscopy and Laser Properties of Nd3+-Doped CaF2, SrF2, and BaF2

The optical properties of Nd3+ in CaF2, SrF2, and BaF2 have been investigated in order to determine if these materials are useful as laser-pumped amplifier media. The CaF2:Nd crystal was found to not be useful because the impurities tend to cluster at very low concentration, leading to the formation of nonluminescent centers. On the other hand, the Nd3+ centers in BaF2 exhibit unacceptably low transition strengths. SrF2:Nd appears to have adequate absorption strength, and, in addition, to have a remarkably long emission lifetime of 1280 μs. A maximum doping of 0.20 atomic % Nd3+ can be tolerated in SrF2 without the occurrence of detrimental clustering. The peak emission cross section of SrF2:Nd is 1.7 × 10−20 cm2 at 1036.5 nm. Direct measurement of the gain spectrum of SrF2:Nd3+ reveals the presence of the 4F3/2 → 2G9/2 excited state absorption lines, although the impact on the emission cross section is minor.