Near-infrared spectroscopy for monitoring water permeability of optical coatings on plastics

Near-infrared spectroscopy has been applied to determine the water content of plastic lenses. An analytical method is presented for monitoring the water permeability of thin layers on plastic optics by utilizing the reversible moisture absorption of organic polymers. As an example, scratch-restistant and antireflective layers on poly((diehylenglycol-bis(allylcarbonate)) lenses are investigated. The measurements demonstrate the relatively high water barrier of coatings deposited by plasma-ion assisted deposition compared with classical physical vapor deposition coatings and polysiloxane dip coatings.