Stepwise-graded-index multilayer broadband low-reflectivity coating for AlGaAs/GaAs power lasers

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Abstract
We describe a new type of optical low-reflectivity coating and its application to GaAs/AlGaAs power lasers. The low-reflectivity region of this coating extends over a broad wavelength range, therefore making the overall reflectivity much less sensitive to thickness variations as compared to single-layer coatings. In addition, only two materials (SiO2 and a-Si:H) are required, thus making it very easy to fabricate such coatings with standard deposition techniques such as plasma-enhanced chemical vapor deposition (PECVD) or ion beam sputtering. Finally, the optical quality of coatings deposited by PECVD was confirmed by measurements on power lasers, showing optical power outputs in excess of 60 W/mm, among the highest reported value for coated mirrors.