Filter Coating Technology: Stabilife® Thin Fim Coatings
Newport's patented Stabilife® coating technology, involves depositing many layers of refractory metal oxide film under vacuum in a precise sequence, defining the spectral signature of the filter. This allows coatings without tensile and bending stress which in turn promotes a near-indefinite life. The dielectric layers are extremely durable, temperature-stable and resistant to different environmental influences.
With Stabilife the steepest spectral band filters and edge filters are manufactured. Filters show no spectral shift due to high ambient humidity. The patented Stabilife® method allows combinations of dielectric layers with absorption materials (multi-substrates approach). This combination allows for example the production of fluorescence filters with significantly improved blocking (spectrally wider and steeper slopes) between transmission and reflection.
Patented Coating Deposition Processes
Stabilife® optical filters are manufactured using two patented processes for the deposition of metal oxide thin film optical coatings. These are reactive ion plating (RIP) and hybrid plasma deposition (HPD). Both processes yield highly dense, thin film coatings with extraordinary hardness, abrasion resistance, and adhesion to the substrate. Newport’s Stabilife® processes were developed at their Corion coating facility in Franklin, Massachusetts, where these products are manufactured.
Optical components which directly affect the spectral performance of an optical system, must be able to deliver repeatable and accurate wavelength vs. transmission response, regardless of the operating conditions. In some applications, un-stabilised metal oxide optical coatings or laminated soft-film coatings are adequate to meet the required performance parameters. However, for some of the more demanding applications such as fluorescence detection, wavelength stability is absolutely critical to ensure dependable results. Stabilife® optical filters and coatings provide the solution for these high accuracy applications.
Film Density & Spectral Stability
Film density is a critical factor affecting the spectral stability of an optical coating. Un-stabilised metal oxide thin film coatings typically exhibit a significantly lower packing density than Stabilife® coatings. This occurs as a result of the intrinsic growth properties of the coating materials when deposited using methods which do not enhance film densification. The film structure of un-stabilised metal oxide film tends to be columnar with a significant number of voids. The presence of these voids contributes to the occurrence of environmentally induced spectral shift in un-stabilised external coatings. Changes in wavelength, which are influenced by the presence of voids, tend to be elastic in nature and depend upon the ambient relative humidity in which the coating is being used. The permeability of the film will determine the degree to which this phenomena will occur. Spectral shifts in the range of 2-5% of wavelength are typical of un-stabilised metal oxide coatings. Stabilife® coatings have a higher packing density and lower void ratio than un-stabilised metal oxide coatings and are therefore less affected by water absorption. They typically exhibit total wet-to-dry shifts of less than 0.02% of wavelength. The graph that follows contains measured transmittance scans of a Stabilife® filter at 0% and 100% relative humidity. The scans are exactly overlaid as no shift is discernible at the standard scan speed for a 30nm bandwidth filter.
Thermal Properties & Spectral Stability
Stabilife® films are typically 5 to 10 times less sensitive to thermal variation than un-stabilised metal oxide films as a result of film densification. Temperature change functions as a catalyst for moisture migration in thin films having a significant volume of voids. When un-stabilised films are exposed to high temperatures, moisture migrates out of film voids contributing to the wavelength change discussed earlier. The high film density and reduced permeability resulting from the Stabilife® processes reduces this effect providing the maximum spectral stability available for all types of precision coatings including bandpass, dichroic, edge, notch and polariser coatings. The graphs that follow illustrate measured temperature-induced wavelength shift of an unstabilised metal oxide ultra-narrow bandpass filter compared to a Stabilife® ultra-narrow bandpass filter.
Stabilife® thin-film optical coatings have demonstrated excellent resistance to damage due to handling, extreme nuclear and optical radiation, and severe environmental conditions. In the most severe applications, such as autoclave immersed nuclear reactor monitoring, Stabilife® filters have demonstrated spectrally stable performance lifetimes exceeding 8,000 hours. Stabilife® filters have been qualified for telecommunications applications per the requirements of Telcordia GR-2883. While most applications are much less demanding than these, the same robust coatings as are required for extreme applications, are routinely supplied for all Stabilife® products. In the course of normal production, Stabilife® films are tested for adhesion using the snap tape test specified in MIL-C-48497, for abrasion resistance using the eraser test specified in MIL-C-675, and for humidity resistance using the aggravated test specified in MIL-STD-810E. Stabilife® thin-film optical coatings require no additional protection such as hermetic sealing using lamination or other processes, to achieve their exceptional durability.
Applications for Stabilife® Thin Films
Stabilife® films are produced over the wavelength range from 200nm in the UV to 3 microns in the IR and have been utilised in a variety of applications including:
Stabilife® Coating Designs: Standard Designs
Stabilife® Coating Designs: Specialty Designs
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