CO₂ laser deposition of single and multilayer transparent coatings using oxide nanoparticles (Invited Paper)

This study reports the CO₂ laser-assisted deposition of transparent thin and thick films on quartz substrates using nanoparticles (NPs) of anatase-TiO₂, amorphous SiO₂, and chalcogenide As₂S₃ . The preparation process of the films involves three steps: (i) spin-coating for wet deposition, (ii) evaporation of Ethylene Glycol (EG) using either a lamp or laser, and (iii) laser sintering. A heat transfer model selects the laser processing parameters, while an Anti-Reflection Coating (ARC) model determines the optimal material selection and layer thickness to minimize reflectance and enhance transmittance. Microscopy analyses show that CO₂ laser energy induces necking and coalescence between NPs, as observed through SEM and optical microscopy. Film thickness is measured using an optical profilometer, and reflectance is assessed via UV/Vis spectrophotometry. UV/Vis/NIR spectrophotometry reveals that the sintered coatings are highly transparent, achieving transmittance above 90% in specific wavelength ranges. Single-layer (∼ 110 nm thick) and double-layer TiO₂ films of the same total thickness were analyzed to examine the interface's effect on transmittance. This study also examines the impact of TiO₂ and SiO₂ layer sequences on the optical properties of heterogeneous multilayer films. Thick films of As₂S₃ glass of high transparency were successfully deposited. XRD confirms the high purity and microstructural integrity of the sintered anatase-TiO₂ films, with no evidence of rutile transformation. These findings provide a comprehensive understanding of the AR properties and potential applications of these transparent coatings.