Energy transfer efficiency from Cr3+ to Nd3+ in Cr, Nd YAG ceramics laser media in a solar-pumped laser in operation outdoors

Abstract Energy transfer efficiencies from Cr3+ to Nd3+: ηCr→Nd in Cr (0, 0.4, 0.7, and 1.0 at %), Nd (1.0 at%):YAG ceramic laser mediums were assessed for the first time in solar-pumped laser (SPL) in operation under the natural sunlight. In addition to this stimulated emission (StE) conditions, assessment of ηCr→Nd in solar pumped spontaneous emission (SpE) conditions was performed using the same SPL system but without the optical cavity eliminating the output coupler. In SpE at the incident solar power at the solar concentrator: IOAP of 1.12 W, ηCr→Nd were measured to be 0.803γ for 0.4 at%, 0.726γ for 0.7 at%, 0.766γ for 1 at %, where γ ≾ 1. When IOAP was increased to 3.07 W, ηCr→Nd in SpE decreased to 0.675γ, 0.623γ, 0.625γ, respectively. In StE, ηCr→Nd further decreased to 0.448 γ, 0.213 γ, 0.166 γ. These values are lower than those previously reported values measured by the laboratory experiments such as luminescent decay analyses. Both in SpE and StE, the highest values of ηCr→Nd were given at the Cr content of 0.4 at% at which the output laser power also took the maximum value. The decrease in ηCr→Nd in the increased IOAP in SpE can be attributed to the fact that formation of excited Nd3+ ions by the energy transfer from Cr3+ ions became difficult because Nd3+ ions had been already excited directly by the sunlight.