Femtosecond Laser Damage Threshold of Titanium Dioxide

We investigate titanium dioxide (TiO₂) as a material for on-chip nonlinear nanophotonic devices. Such devices use ultrashort, high-intensity light pulses to, for example, modulate lightwave signals or generate white light in miniature, highly-efficient components. One of the important properties of materials to be used in nonlinear optical applications is the laser damage threshold (LDT): the amount of laser energy that can be applied to the material before it is physically damaged. Measuring the LDT of TiO₂ is critical for understanding the limitations of the material and selecting which of its various crystalline and amorphous phases is optimal for nonlinear nanophotonic applications. In this research, we study the LDT of single-crystalline bulk rutile, polycrystalline anatase thin films, and amorphous TiO₂ thin films. We characterize the basic structural and optical properties of the samples using Raman spectroscopy, scanning electron microscopy (SEM) and spectrophotometry. Using Raman spectroscopy and SEM, we obtain information about the phase and morphology of the samples. We determine the materials’ linear optical absorption edges to be in the wavelength range of 300 nm – 420 nm by transmission and reflection spectrophotometer measurements. We measure the LDT with a femtosecond laser at a wavelength of 800 nm, one of the proposed working wavelengths for TiO₂-based optical devices. To identify their effect on the LDT of the different samples; we vary the repetition rate, power, and pulse duration of the laser. The laser-damaged films are also characterized using optical microscopy, SEM, and Raman spectroscopy.