Optical features of Ca 4NdO(BO 3) 3:Yb single crystals under CW laser illumination

Abstract

Optical treatment of Ca 4NdO(BO 3) 3:Yb under continuous laser illumination at different wavelengths led to substantial changes of optical absorption and optical second harmonic generation. The treatment was performed successively by infrared (780 nm), red (650 nm), green (532 nm) and blue (405 nm) laser wavelengths with powers varying within the 200–400 mW range. We demonstrated enhancement of the optical second harmonic generation in the Ca 4NdO(BO 3) 3:Yb (1.9% in weighting unit) crystals under the influence of the green cw laser at 532 nm. The principal changes were observed after 15 min of the treatment. A correlation between the occurrence of the hyperfine structure in the absorption spectra and the enhancement of the optical second harmonic generation was found. The additional treatment by the blue laser led to disappearance of appeared photo-induced changes of absorption and decrease of the optical second harmonic generation. It is principal that the effect is non-reversible in time and it does not depend on the photo-inducing light polarization. The principal origin of the observed photo-induced optical second harmonic generation is photo-polarization of the particular rare earth localized levels and formation of the stable polarized states due to the presence of Yb ions, playing crucial role. No such effects were observed in pure Ca 4NdO(BO 3) 3.