Viewports - Introduction
Viewport is the designation given by MDC to to all of its ISI™ hermetically sealed optical components. Viewports provide a means for visual, optical or broad-band energy transmission in and out of vacuum systems.
We use state of the art hermetic brazing and joining technologies to produce seals of unsurpassed quality and reliability. Window materials include Single Crystal Sapphire and Fused Silica. Standard viewports are uncoated plano/plano windows of ultraviolet (UV) grade. All ceramic to metal seal products are manufactured to ISO 9001:2008 standard. Custom engineering and special order AR coatings are available on ISI™ viewports.
Sapphire is a synthetic, hexagonal single crystal anisotropic material which displays substantially different physical, thermal, dielectric and optical characteristics when measured along different axes. ISI™ standard Sapphire Viewports use material with 90° crystal orientation, i.e. crystal orientation parallel to window surface. Viewports with crystal orientation parallel to optical axis, or 0° orientation, are available on request at additional cost. Most material grades are available up to 1.94 inch view diameters.
Quartz and synthetic Fused Silica are polycrystalline, isotropic materials with no crystal orientation. Fused Quartz is suitable for all but the most demanding optical applications. Impurities in Fused Quartz cause a blue-violet fluorescence when exposed to ultraviolet radiation at 253.7µm. This fluorescence is not evident in synthetic Fused Silica, which is manufactured by flame hydrolysis of silicon tetrachloride.
ISI™ Fused Silica Viewports offer three grades of synthetic fused silica to meet the growing demand for high performance optical vacuum windows. A base or general purpose fused silica replaces the previously offered fused quartz windows. For deep UV applications in the region of 200nm a DUV-200 grade is available. In addition to this, EUV-185, an extreme UV or excimer grade fused silica material is available and suitable for transmission down to 185nm. ISI™ Viewports can also be provided with special order, low "OH" infrared fused silica windows with useful transmission up to 3600nm. This material is not stock and will be quoted on request. All material grades are available up to 7.78 inch view diameters.
Special order Anti-Reflection coatings can be applied to windows with view diameters greater than or equal to 1 inch. Note that one window surface is recessed within the viewport’s tubular metal mount, which will produce shadowing on that side of the window. MDC guarantees uniform AR coating over 80% of the window’s clear aperture or view diameter. High temperature braze cycles (800°C) require that all coatings be applied after brazing.
Single Layer (Narrow Band) Anti-Reflection (SLAR) coating is available for ISI™ Sapphire or Fused Silica window substrates. This coating may be tailored and optimized for specific wavelengths between 200nm and 2200nm, with reflection losses less than or equal to 0.5% per surface for either substrate material.
Multi-Layer (Broad Band) Anti-Reflection (MLAR) coating is available for ISI™ Sapphire or Fused Silica window substrates. This coating is optimized for transmission over the entire range of wavelengths from 450nm to 800nm, with reflective losses at less than or equal to 1.0% per surface for either substrate material.