Latent tracks and novel infrared waveguide formation in lithium tantalate irradiated with swift heavy ions

In this work, the formation mechanisms of latent ion tracks and infrared-light waveguides in ion-irradiated LiTaO₃ single crystals were comparatively studied using 200 MeV Kr¹⁷⁺ irradiation at a fluence of 1  ×  10¹² cm⁻² and 247 MeV Ar¹²⁺ irradiation at fluences of 1  ×  10¹² cm⁻² and 3  ×  10¹² cm⁻². Because of the intense electronic energy loss, the produced lattice disorder and formed latent track were experimentally determined through complementary techniques, including the analysis of transmission electron microscopy patterns and Rutherford backscattering/channeling spectra. Corresponding to different ions with different irradiation energies and electronic energy losses, the related spatio-temporal evolutions of lattice temperatures in Kr¹⁷⁺- and Ar¹²⁺-irradiated LiTaO₃ crystals were numerically calculated using the inelastic thermal spike model. The simulation results theoretically describe the experimentally observed lattice disorder and latent track behaviors. The lattice swelling in the latent-ion-track regions was demonstrated using high-resolution x-ray diffraction patterns; the lattice swelling resulted in a decrease in the refractive index, thereby providing a path to tailor the optical properties and fabricate the waveguide structure. Optical measurements and simulations indicated that the formed LiTaO₃ waveguide could effectively support the guided modes and confine the light propagation, especially in the infrared region. (paper)