Optical Coatings

Plasma Assisted Reactive Magnetron Sputtering or PARMS is the technique in Omega's coating portfolio which provides the greatest spectral complexity.

The resulting thin-film layers are very dense and durable. State-of-the-art programmable logic enables in-process corrections to layer thicknesses. Such control of the coating process yields exceptionally precise spectral performance, high batch-to-batch repeatability and environmental durability.

Unlike traditional PVD that typically uses refractory oxide starting materials, PARMS bombards an elemental target (usually Si or Nb) using a magnetically accelerated Argon/Oxygen plasma. The accelerated atoms transfer momentum to the target material which in turn ejects the element from the surface onto the substrates, forming a very thin (sub-monolayer) layer. In a different part of the chamber, an oxygen plasma oxidizes this layer, creating an oxide. 

Ion assist, or Ion Assisted Deposition (IAD), is used to densify films prepared by PVD. While in the gas phase, molecules are accelerated by a beam of energetic ions (typically Argon and Oxygen) directed towards the substrate. The IAD-prepared filters are denser and demonstrate greater environmental stability than traditional PVD deposited films.

Using a beam of electrons as a heat source, the PVD process is carefully controlled in temperature and rate, and augmented by specific chamber geometry. The physical thickness of each alternating layer of high and low refractive index material is precisely measured as it grows on the substrate. A single optical filter may contain upwards of several hundred layers to achieve the desired spectral response. 

Physical vapor deposition (PVD) is the process in which a solid material is heated and passes directly from a solid to a gas (sublimation) and then back again to a solid state as it condenses on a given substrate, usually while under vacuum. The traditional approach has been to use a resistive heating element to evaporate the materials. The thermally-prepared coatings were Omega’s bread and butter business for over 25 years.  To protect and preserve these filters for long-term stability, they are typically laminated with a coverslip after preparation.  Although they have fallen out of favor recently, they still offer several advantages over surface coatings.  Because the range in refractive index is much higher amongst these materials when compared to oxides, a much thinner coating stack can achieve similar results.  This reduces stress on the substrate, and can minimize wavefront distortions.  This becomes particularly important as the wavelengths of interest move into the infrared, where thicker layers are required.  These optical filters offer deep out-of-band blocking with low residual stress and stable spectral performance.

Plasma Enhanced Chemical Vapor Deposition (PECVD) is a technique used to deposit thin films, including diamond-like carbon (DLC) coatings, onto various substrates. PECVD leverages plasma to enhance the chemical reactions required to deposit the coating material, resulting in high-quality, uniform films at relatively low temperatures.

PECVD produces high-quality, uniform DLC films with excellent adhesion and customizable properties, making it ideal for a wide range of industrial, biomedical, optical, and electronic applications.