Growth, structural, spectral and high-power continuous-wave laser operation of Yb 0.11 Gd 0.89 COB crystal

Abstract A Yb 0.11 Gd 0.89 Ca 4 O(BO 3 ) 3 crystal with new composition was grown by the Czochralski method. The crystal structure was measured and analyzed. The unit-cell parameters of the Yb 0.11 Gd 0.89 COB were calculated to be a =0.8089(7) nm, b =1.5987(6) nm, c =0.3545(8) nm, β =101.22°. The absorption and fluorescence spectra were measured. The maximum absorption cross-section of Yb 0.11 Gd 0.89 COB crystal was 0.79×10 −20 cm 2 , which occurred at 976 nm with Y polarization. The emission cross-section at 1027 nm was calculated to be 0.33×10 −20 cm 2 . The radiative lifetime τ rad was calculated to be 2.74 ms. The Stark energy-level diagram of Yb 3+ in the Yb 0.11 Gd 0.89 COB crystal field at room temperature was determined. The ground-state energy level 2 F 7/2 splitting was calculated to be as large as 1004 cm −1 and the zero-line energy was 10246 cm −1 . A maximum output power of 9.35 W was achieved in continuous-wave (CW) mode, with the slope efficiency being 42.1%. Chemical etching experiment revealed that the dominating imperfections in the studied Yb 0.11 Gd 0.89 COB crystal were dislocations and sub-grain boundaries. The existence of crystal defects could cause light scattering, and degrade laser output efficiency. The influence of crystal defects on laser properties was discussed.