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Actual Coating Absorption of < 1ppm!

Photothermal Common-Path Interferometry (PCI)

Advanced Thin Films (ATF) is now using in-house PCI for absorption measurements of substrate surfaces, coatings, and bulk materials at 1070nm. This new system is a key piece of metrology for applications with critical requirements for very low absorption coatings, such as the high power continuous wave (CW) lasers used in materials processing and directed energy. ATF is also utilizing these measurements to monitor the batch-to-batch quality of our ion-beam-sputtered (IBS) optics and coatings.

Photothermal Common-Path Interferometry (PCI) is a metrology method that creates and measures a tiny, localized thermal lens with sensitivity of less than 1 part-per-million (ppm) for fractional absorption. It uses a strong pump beam to create the thermal lens effect in conjunction with a weak probe beam to detect the resulting aberration. The technique is insensitive to scatter, non-destructive, and can measure bare or coated surfaces as well as bulk material absorption of a substrate.

Actual Coating Absorption < 1 PPM

(Measured at 1070 nm using ATF's in-house PCI system)

PCI Coating Absorption Graphs
  • Total absorption at coated surface is ~1.5 ppm
  • Bulk absorption corresponds to ~0.8 ppm
    • Probed region is ~0.5mm long
    • Bulk value corresponds to ~16 ppm/cm, reasonable for Corning 7980
  • Uncoated surface absorption is ~1.0 ppm
  • Actual AR coating absorption is < 1 ppm

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PPC High Power Lenses

Custom low absorption AR coatings now available for high power lenses

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