Double V-Coats, also called W-coat, are generally multi-layer dielectric coatings specifically engineered for critical anti-reflective applications at two distinct wavelengths.

These coatings achieve exceptionally low reflectance, with typical absolute reflectance levels below 0.2% at both bands. Additionally, they are highly durable and can withstand multiple GW/cm² of laser power fluence.

The Double-V-coat is a straightforward enhancement to the single quarter-wave layer that significantly expands its antireflection zone while reducing reflectance at the edges.

This modification involves inserting a half-wave layer of high, but not excessively high, refractive index between the quarter-wave layer and the substrate.

The reflectance at the reference wavelength remains similar to that of the single quarter-wave layer, but it decreases on either side. For example, with crown glass, the reflectance is approximately 1.25% at the center.

However, when using a higher-index glass, such as BaSF 1, the center reflectance can be much lower. As a result, the W-coat is primarily used with flint glasses rather than crown glasses.