Ultrafast dynamics of femtosecond laser ablation on lithium niobate crystals

Lithium niobate crystals are a multifunctional material, exhibiting numerous excellent properties such as photoelectric, acousto-optic, and ferroelectric characteristics. They are widely used in various applications including optical communication technology, photonic integrated circuit, and high-frequency filters. Femtosecond lasers are a means of processing with extremely high peak power, a very small heat-affected zone, and the ability to process in three dimensions in a flexible and controllable manner. To date, femtosecond lasers have successfully fabricated a variety of structures in lithium niobate crystals, including photonic crystals, nanogratings, waveguides, and surface periodic stripes. Therefore, investigating the interaction mechanism between femtosecond lasers and lithium niobate is essential. This paper mainly employs time-resolved reflective pump-probe techniques to obtain transient reflectivity evolution images within femtosecond-picosecond-nanosecond time scales. It analyzes ultrafast processes such as photon-electron, electron-phonon coupling, and phase transitions induced by femtosecond laser irradiation on material surfaces, revealing the ultrafast dynamics of near-infrared femtosecond laser interactions with lithium niobate single crystals of different orientations. Our research results are of significant importance for promoting the fabrication of various photonic devices such as electro-optic modulators, frequency converters, and beam splitters on lithium niobate materials using femtosecond lasers.