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Gratings - Questions
What are OEM custom size capabilities?Thicknesses of 2mm, 3mm, 5mm, 6mm, 9.5mm, 12mm and 16mm float glass are routinely available for faster delivery. Sizes in round, rectangular or square shapes as small as 6 mm, up to 90 mm are within Optometrics capabilities, depending upon which grating you have chosen.

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What substrate materials are available?Pyrex and float glass are routinely available as standard materials. However, gratings can generally be replicated on any hard surface such as Zerodur, Fused Silica, Metals and Hard Plastics.

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Should I choose float glass or Pyrex?Your application will generally dictate. The primary advantage of Pyrex is that it has a lower coefficient of thermal expansion and has better thermal stability.

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Which way are grooves oriented on a rectangular grating?Unless otherwise specified, rectangular gratings are cut with grooves parallel to the short dimension.

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What types of surface coatings are available?Bare aluminum offers good visible and infrared performance. AlMgF2 (aluminum magnesium fluoride) is used for enhanced UV performance. Gold is used to increase reflectivity primarily in the near infrared.

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Do cosmetic blemishes affect grating performance?Scratches or other cosmetic defects do not, unless extreme, usually affect optical performance.

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Can I clean the grating surface?The surface of a diffraction grating can be easily damaged by fingerprints, aerosols, moisture or the slightest contact with any abrasive material. Gratings should only be handled when necessary and always held by the sides. Latex gloves or a similar protective coating should be worn to prevent oil from fingers from reaching the grating surface. Any attempt to clean a grating with a solvent voids the Optometrics warranty. No attempt should be made to clean a grating other than blowing off dust with clean, dry air or nitrogen.

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Are published efficiency curves based upon actual or theoretical data?Typical grating efficiency curves published by Optometrics are based upon actual measurements of the gratings Optometrics sells. Efficiency curves available at “View/Download Specific Grating Efficiency Curves” were determined using absolute efficiency criteria. Be careful when comparing the efficiency curves from different manufacturers. Some publish relative efficiency data and relative efficiency curves will always give you a higher efficiency value than an absolute reading. To better understand relative vs absolute efficiency measurements, see “What is the difference between absolute and relative efficiency?” under FAQ for Gratings.

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What is the difference between absolute and relative efficiency?Grating efficiency is typically expressed as either “absolute” efficiency or “relative” efficiency. The absolute efficiency of a grating is the percentage of incident monochromatic radiation on a grating that is diffracted into the desired order. This efficiency is determined by both the groove profile (blaze) and the reflectivity of the grating’s coating. In contrast, relative (or groove) efficiency compares the energy diffracted into the desired order with the energy reflected by a plane mirror coated with the same material as the grating. Be careful when comparing the efficiency curves from different manufacturers. Some publish relative efficiency data and relative efficiency curves will always give you a higher efficiency value than an absolute reading. Efficiency curves published by Optometrics at “View/Download Specific Grating Efficiency Curves” were determined using absolute efficiency criteria.

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Can Optometrics manufacture transmission gratings for the Visible range?Yes. Call, fax or contact Optometrics online for recommendations.

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