Laser-induced damage threshold of GaN nanostructures under high-power laser irradiation

With the rapid development and widespread applications of high-power lasers, traditional bulky optical components are inadequate to meet the demands of instrument miniaturization and multi-functionalization. Micro- or nano-optical components exhibit unique advantages such as design flexibility and functional diversity, with promising applications in the fields of high-power optical systems. However, unlike bulk or thin-film optical materials, subwavelength nanostructures are inherent optical defects, where their resistance to high power lasers are generally lower than that of pristine materials. Consequently, how to improve the laser-induced damage threshold (LIDT) of nano-devices become a critical challenge. In this paper, we investigate the LIDT of GaN nanostructures related to structural geometry, surface micro-morphology, and interfacial defects. The single-crystal GaN has a low defect intensity and a wide bandgap, showing higher LIDT value than that of conventional oxide films. We design and fabricate GaN nanostructures with different shapes and periodicities. Under the irradiation of high-power pulsed laser (~9 ns@1064 nm), the measured LIDT of GaN nano-structural arrays is approximate to 3.5 J/cm². While under the irradiation of a high-repetition-rate quasi-continuous laser, the measured LIDT of GaN nanostructures decreases to ~1 J/cm². Moreover, as the geometrical size of nanostructures decreases, the LIDT of GaN nanostructures degenerates gradually. However, compared to planar wafer regions, the LIDT of 200 nm GaN nanopillar array remains over 50%, which is still better than that of common oxide laser films. GaN nanostructures are capable to design of nanophotonic devices for high-energy laser or strong-field modulation and application.