Abstract

Site-selective spectroscopy of Nd:Ba₂MgGe₂O₇ (BMAG) reveals fifteen crystal field sites for the Nd³⁺ ion. The ⁴F_3/2 to ⁴I_11/2 peak transition wavelength varies from 1050 to 1080 nm at 10 K, depending on the site. Energy transfer between sites is thermally activated and time independent for excitation into the ²P_1/2 and ⁴G_5/2 + ²G_7/2 manifolds. Selectively pumping any site at room temperature results in complete energy transfer to a single site that has a laser wavelength of 1054 nm. Laser slope efficiency measurements were performed at room temperature on a BMAG sample using 1-J, 60-µs pulses from an alexandrite laser. The slope efficiency (laser output power vs absorbed power) is linear at low pump power, saturates and curves downward at high power. The slope efficiencies were found to be pump wavelength dependent and ranged from 0.7 to 3.5%. Excited state absorption (ESA) of the pump photons is thought to be responsible for the differences in slope efficiencies and the blue-green fluorescence observed while lasing at 1054 nm. Several ESA transitions are used to model the results, and excited state absorption cross sections are given.

© 1989 Optical Society of America