Optical Coatings

Acree Technologies designs and deposits optical coatings to customer specifications. We use sophisticated computer simulation software to design the coating to satisfy our customer’s needs and perform the depositions using in situ feedback and computer control to produce high quality, reproducible films. Our proprietary deposition technologies allow innovative solutions to optical coating requirements. Using highly ionized deposition techniques creates dense, highly adherent films that excel in optical applications. They also allow low temperature deposition due to the increased reactivity in the vapor phase and during the condensation process which allows the coatings to be applied to low temperature materials, such as plastics. Materials deposited include:

1.  dielectrics - DLC, TiO2, Al2O3, SiO2, Si3N4, Ta2O5;
2.  metals – Ag, Pt, Au, Al; an
3.  transparent conductors – ITO, IZO, AZO


Some examples of optical coatings developed to customer requirements are:

    • Coatings for HID lamps to reduce UV transmission and increase IR reflection. This increases internal temperature to improve efficiency (more visible light emitted for less electrical power).
    • Hard AR coatings for safety lenses and visors.
    • Transparent, conductive coatings for aircraft canopies and windows. 
To give some background on optical coatings, the transmission or reflection of light from a surface can be modified through the appropriate application of a coating. For example, the application of dielectric layers to a glass surface can be designed to decrease the reflection, without absorption, therefore increasing the transmission. This is the commonly used antireflection coating found on everything from eyeglasses to lenses in laser systems. This change is accomplished by controlling the phase of the additive multiple reflections from interfaces. If the reflected phases are 180° to each other they are out of phase and interfere destructively. For a low index dielectric on glass (material index between that of glass and air), a minimum in reflection for a given wavelength will occur at the quarter wave optical thickness given by:

where n is the index of the thin film, d is the film thickness, and _ is the wavelength of interest. The term nd is often referred to as the optical thickness. The performance of the coating is improved by adding additional layers of specified index and thickness. For example, the width of the antireflecting region and minimum reflectance can both be improved by the addition of multiple layers. The inclusion of absorbing layers and also metallic/conductive layers permits great flexibility in the design of coatings.