Electroless nickel for optical applications

Electroless nickel (EN) is a nickel-phosphorus alloy which is currently used in the precision optics industry as a polishable surface layer on difficult-to-finish mirror substrate materials, such as beryllium. High performance applications for such reflective components range from commercial laboratory instruments to large spacebome telescopes to cryogenically cooled optical sensor systems. This paper presents a discussion of the fundamental processing parameters and control methodologies for the electrochemical growth process as well as the performance of the resulting EN coating. The coating performance evaluation will focus specifically on the influence of processing parameters on the EN composition and microstructure and the correlation between composition and critical material properties, such as thermal expansion, elastic modulus, density and hardness.