The 1.5 μm spectroscopic properties of Yb,Er:GSAG crystal: A promising 1.5 μm laser gain medium

The 1.5 μm lasers exhibit excellent eye safety characteristics that make them crucial for laser ranging, radar and optical communication. In this work, the 1.5 μm spectroscopic properties of a mixed garnet crystal, Yb,Er:GSAG, were investigated. The strongest absorption at 940 nm overlaps well with the currently mature InGaAs laser diodes. Under 940 nm excitation, a strong emission band with peak wavelength at 1534 nm was detected. The Judd-Ofelt calculation was performed based on the measured absorption spectrum, and the three intensity parameters Ωt (t = 2,4,6) were fitted as 0.974 × 10−20 cm2, 0.477 × 10−20 cm2 and 0.352 × 10−20 cm2, respectively. The absorption cross-section at 940 nm and emission cross-section at 1534 nm were calculated as 0.59 and 0.81 × 10−20 cm−1, respectively. Lastly, a positive gain cross-section can be achieved at 1534 nm when the population inversion ratio β is only higher than 0.2. The results imply that this crystal is a promising 1.5 μm near infrared laser gain medium.