Abstract

The spectroscopic, lasing, and thermal properties of chromium- and neodymium-doped gadolinium scandium aluminum garnet (Cr:Nd:GSAG) are reported. The Judd–Ofelt parameters, radiative lifetime, and branching ratios were determined, and an effective emission cross-section value of 0.92 × 10−19 cm2 was derived at 1.06 μm from our spectroscopic measurements. The temporal behavior of the Cr3+ fluorescence intensity agreed with the Inokuti–Hirayama model for the chromium–neodymium energy-transfer mechanism, which invokes a static dipole-dipole interaction and no migrational energy transfer. Under identical flash-lamp-pumping conditions the measured pumping efficiency of Cr:Nd:GSAG for threshold lasing is nearly equal to the pumping efficiency of codoped gadolinium scandium gallium garnet (Cr:Nd:GSGG). From the threshold-lasing data, an effective emission cross section of 0.7 × 10−19 cm2 for Cr:Nd:GSAG was independently determined, as well as a value of 1.3 × 10−19 cm 2 for Cr:Nd:GSGG. The normalized heating parameter χ, defined as the heat deposited per unit stored energy, experimentally ranges from 2.1 to 2.7, depending on the effective emission cross-section value. Our calculated value of χ is 1.9 ± 0.3. Based on our heating-efficiency measurements, calculated Cr:Nd:GSAG thermal lensing values are ~2.1–2.6 D/kW, which indicates a thermally induced focal length that is weaker than that of Nd:YAG by approximately a factor of 2 at the same output power. Finally, the benefits and trade-offs of laser-diode pumping are discussed.

© 1994 Optical Society of America

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