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Characteristics

  • Low weight: Our standard mirror blank consists of a front and back plate with a thickness of 6mm (soda-lime glass) or 6,5mm (borosilicate glass) with an density of 2,5g/cm3 or 2,2g/cm3 producing a mirror blank with an areal density of around 30,0Kg/m2. Later stages of optical processing remove typically 2-3mm glass in total. The areal density of the finished mirror will be in the range of about 25,0Kg/m2. Using coarse abrasives further glass removal on the front and back plate can be achieved and will bring areal density significantly down. We do not recommend going below 17,5Kg/m2 areal density (3,5mm on the face plate) since print through can become an issue if not great care, low polishing pressure or sophisticated polishing technologies are used. It is possible to produce a mirror blank with more support elements without increasing the areal density on special request for even lower weight targets.
  • Semi closed back plate: The back plate of our standard mirror blank is flat and closed to over 70%. This sandwich design provides considerably more stiffness for the substrate than traditional web backed mirrors. The semi closed back plate facilitates support on polishing machines, it facilitates manual processing and it facilitates the axial support in common mirror cells. The semi closed back plate protects the support structure in case of rough handling. It is possible to produce a mirror blank where the back plate has a certain radius of curvature, a certain contour, or a different thickness.
  • Fire polished support structure: The light weighting structure is fire polished and free of micro cracks. This means high structural strength and tension resistance from production to use. The wavy nature of support elements reduces points of stress concentration.
  • Constant thickness front and back plate: This means equal cooling for the whole mirror.
  • 100% pure monolithic: No different materials, no bonding: STROPEK - Glastechnik guarantees that the mirror blank is 100% pure monolithic with exact one and the same material throughout. No bonding or mixing different materials. If properly supported and in thermal equilibrium our blanks will deliver the optical quality as tested in the optical shop. Today and forever.
  • 100% free of bubbles: A flawless product without bubbles, striae, impurities in the critical layer or anywhere else in the mirror blank.
  • 100% vacuum applicable: Full ventilation.
  • High degree of transparency for stringent inspection and quality control.
  • Fine annealed with only low internal stress.
  • Near net shape: On larger mirror blanks the work necessary for generating the desired radius of curvature is intense . Our mirror blanks are near net shape. Vastly reducing time, effort for generating the final ROC.
  • Material: Soda-lime glass or borosilicate glass are available. For astronomical purposes as long as the diameter of the mirror does not exceed 32 inch we recommend soda-lime glass in combination with our light weigh technology. The driving force for quality images is low deflection of the mirror under gravity and fast thermal equilibrium and not the type of glass material. The average linear thermal expansion rate of soda-lime glass is 8.5x10-6m/m/K. Density is 2.5g/cm3. For our mirror blanks in borosilicate glass we use "BOROFLOAT" (Schott). Borosilicate glass offers a lower expansion rate of 3.3x10-6m/m/K. Density is 2.2g/cm3. Please refer to the website of Schott www.schott.de for further details on "BOROFLOAT" which is a registered trademark of Schott AG, Mainz, Germany.

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