Nonlinear optical dynamics and Eu³⁺ spectral holeburning in strontium barium niobate thin film grown by pulsed laser deposition

Optical quality Sr_xBa_1-xNb₂O₆ (SBN) thin films, both undoped and Eu³⁺-doped, of thickness less than 0.5 μm have been successfully grown on fused quartz substrates using a pulsed laser deposition technique. Optical properties of these films were characterized in high-resolution spectroscopic experiments in time and frequency domains. For undoped SBN thin films, broadband emission in the UV region extending to the visible was observed following excitation at 355 nm. This emission is attributed to exciton luminescence of the SBN film. Nonlinear optical response in the picosecond regime and the third-order nonlinear susceptibility, χ⁽³⁾, were studied using degenerate four-wave-mixing methods. In transverse alignment, χ⁽³⁾ is enhanced by two orders of magnitude in comparison with its bulk counterpart. A thermal annealing process, monitored via changes in spectral properties of Eu³⁺, was employed to convert the as-grown amorphous film into a polycrystalline film. High-resolution spectroscopic measurements in the frequency domain were conducted on a 200-nm-thick film of Eu³⁺-doped SBN. Our spectroscopic results suggest that Eu³⁺ ions may substitute for Nb, thereby occupying a normally six-fold coordinated lattice site. At liquid helium temperature, spectral holes in the ⁷F₀–⁵D₀ optical transition were burned in the thermally annealed films. Typical observed hole widths were 70–100 MHz and hole depths were as large as 30% of the pe- ak fluorescence intensity. © 2002 American Institute of Physics.