Laser stimulated third harmonic generation studies in ZnO-Ta2O5-B2O3 glass ceramics entrenched with Zn3Ta2O8 crystal phases

In this study zinc borate glasses doped with different concentrations Ta₂O₅ were synthesized and were crystallized by heat treatment for prolonged times. The samples were characterized by XRD, SEM, IR and Raman spectroscopy techniques. The SEM images of the crystallized samples have indicated that the samples contain randomly distributed crystal grains with size ∼1 μm entrenched in the residual amorphous phase. XRD studies have exhibited diffraction peaks identified as being due to the reflections from (1 1 1) planes of monoclinic Zn₃Ta₂O₈ crystal phase that contains intertwined tetrahedral zinc and octahedral tantalate structural units. The concentration of such crystal phases in the bulk samples is observed to increase with increase of Ta₂O₅ up to 3.0 mol%. The IR and Raman spectroscopy studies have confirmed the presence of ZnO₄ and TaO₆ structural units in the glass network in addition to the conventional borate structural units. For measuring third harmonic generation (THG) in the samples, the samples were irradiated with 532 nm laser beam and the intensity of THG of probing beam (Nd:YAG λ = 1064 nm 20 ns pulsed laser (ω)) is measured as a function of fundamental beam power varying up to 200 J/m². The intensity of THG is found to be increasing with increase of fundamental beam power and found to be the maximal for the glass crystallized with 3.0 mol% of Ta₂O₅. The intensity of THG of the ceramicized samples is found to be nearly 5 times higher with respect to that of pre-crystallized samples. The generation of 3ω is attributed to the perturbation/interaction between Zn₃Ta₂O₈ anisotropic crystal grains and the incident probing beam.