Growth, structural, spectral and high-power continuous-wave laser operation of Yb0.11Gd0.89COB crystal

Abstract

A Yb0.11Gd0.89Ca4O(BO3)3 crystal with new composition was grown by the Czochralski method. The crystal structure was measured and analyzed. The unit-cell parameters of the Yb0.11Gd0.89COB 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 Yb0.11Gd0.89COB crystal was 0.79×10−20 cm2, which occurred at 976 nm with Y polarization. The emission cross-section at 1027 nm was calculated to be 0.33×10−20 cm2. The radiative lifetime τrad was calculated to be 2.74 ms. The Stark energy-level diagram of Yb3+ in the Yb0.11Gd0.89COB crystal field at room temperature was determined. The ground-state energy level 2F7/2 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 Yb0.11Gd0.89COB 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.