Comparison of ALD and IBS HfO2/Al2O3 anti-reflection coatings for the harmonics of the Nd: YAG laser

Abstract

Atomic layer deposition (ALD) has been widely used in Micro-electronics due to its self-terminating process. The ALD films have precise thickness and nodular-free structure, which are desirable properties for high power laser applications. ALD Al2O3 and HfO2 single layers were prepared through ALD process. The layer properties relevant to high power laser industry were studied and compared with IBS Al2O3 and HfO2 single layers, respectively. Anti-reflection coatings for different harmonics of Nd: YAG laser were prepared through ALD and IBS respectively. ALD single layer films show comparable refractive indices and band gap energies with IBS films. ALD films have tensile stress, in contrast to the compressive stress of IBS films. ALD single layer films have absorption as small as several ppm at fundamental wavelength of Nd: YAG laser, and higher LIDT than IBS films. The spectra of anti-reflection coatings indicate precise thickness control of ALD by counting the cycles. ALD coatings show better laser resistance than IBS anti-reflection coatings at 1ω-4ω harmonics of Nd: YAG lasers. The LIDT of both ALD and IBS coatings are limited by the HfO2 layers. Also in ALD films, defects are the main cause for ns laser damage. The study in this text indicates the high versatility of ALD films for applications in high-power coatings.