Optical and laser damage properties of HfO₂/Al₂O₃ thin films deposited by atomic layer deposition

Previous research on laser damage resistance of thin film deposited by atomic layer deposition (ALD) is rare. In this paper, ALD has been used to deposit Al₂O₃, and HfO₂ single layer films with organic and inorganic precursors at 100, 200 and 300 °C, respectively. Optical properties such as film absorption, refractive index and microstructure were investigated. Especially, laser damage properties as a key property for thin films used as laser system components were analyzed under S-on-1 measurement method. Laser damage morphologies were analyzed by scan electron microscope (SEM). For the Al₂O₃ thin films deposited with different process parameter, damaged was mainly caused by film absorption. When the AlCl₃ precursor was used at 100 °C, films have the least absorption and the best laser induced damage threshold (LIDT, ∼40 J/cm², 1064 nm, 3 ns). For the HfO₂ thin films deposited with different process parameter, damaged was mainly caused by film absorption and crystallization. When the HfCl₄ precursor was used at 100 °C, HfO₂ films have the least absorption and the best LIDT (∼31.8 J/cm², 1064 nm, 3 ns). According to the results of single layer, anti-reflectors were deposited at 100 °C to get higher LIDT. Finally, the LIDT of the anti-reflector can reach to ∼30 J/cm² (1064 nm, 3 ns), which was the best result as reported. In addition, film uniformity and transmission spectrum were also investigated. All the results show ALD is a promising coating technology for high power laser system.