Photoinduced non-linear optical effects in lanthanum calcium borate single crystals

We have revealed that lanthanum calcium borate (La2CaB10O19) crystals show two-photon absorption (TPA) favored by UV laser field. UV-induced TPA measurements were performed under illumination of a Xe-F laser (λ = 217nm) as a photoinducing (pumping) beam. This pumping laser beam created a thin surface layer (about 85 nm) that was a source of the observed photoinduced TPA. Use of the longer photoinducing wavelength leads to a substantial decrease of the photoinduced TPA. The performed DFT calculations of the band energy dispersion clearly show that the effect observed is due to specific band energy dispersion between the sub-bands. The Raman shifted Nd-YAG laser radiation (λ = 1.9 μm) as well as its second and fourth harmonics (λ = 950 and λ = 475 nm, respectively) were used as fundamental (probing) beams of the TPA. The highest values of the TPA β coefficient were achieved for polarization of the pumping light directed along the second-order crystallographic axis. The obtained values of TPA coefficients are higher than for BiBO crystals that were also investigated by us.