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Thread: ARC Photo Mechanics

  1. #1
    Master OptiBoarder sandeepgoodbole's Avatar
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    ARC Photo Mechanics

    I have read some where that for a lens to be anti reflective,it need to have coating from both the sides. Front side Puts the light in systematic Order and Back side helps by adjusting the "Phase" ie. Crests and troughs of the Light waves so that they nutralise each other.
    1.How far this is true ?
    2. How it can be verified?
    3. How does the Single sided Coating work?
    :hammer:

  2. #2
    Master OptiBoarder Darryl Meister's Avatar
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    Reflectance and anti-reflectance apply to each individual lens surface, so it is not necessary to coat both surfaces to render only one anti-reflective. All that is needed to reduce the reflections at a lens surface (or any boundary between two optical media) is a single thin coating (or film).

    While you do not need two lens surfaces to produce an anti-reflective effect, you do need at least two optical boundaries for each surface. These two optical boundaries can be provided by a thin coating of finite thickness on the lens surface, which creates a boundary between air and the front of the coating (1st) and a boundary between the lens surface and the back of the coating (2nd).

    Basically, the coating eliminates reflections (for at least one color of light) using the principle of destructive interference. A small fraction of light is first reflected at the first boundary (between air and the coating) as the light passes through. When the remaining light strikes the second boundary (between the coating and the lens), another small fraction of light is reflected -- in the same direction of the initial reflection. The light from the second reflection will then interact (or interfere) with the light from the first reflection. If the thickness of the coating happens to be equal to 1/4th the wave length of incident light, the second reflection will travel roughly half its wave length as it passes through the coating (1/4th) and then bounces back (1/4th) from the second boundary. This will put the second reflection out of step (or phase) with the first reflection by half its wave length. This aligns the trough of one light wave with the crest of the second one. The net combination of these two light waves will be equal to zero, and the reflections are thereby cancelled.

    There are some other restrictions concerning the index of the coating (i.e., path condition), ideal thickness (i.e., amplitude condition and coherence), and so on. You can also apply multiple thin films, creating a stack to improve the performance of the anti-reflective coating by improving adhesion, eliminating more reflections, controlling reflex color appearance, etc.

    Best regards,
    Darryl

  3. #3
    Master OptiBoarder Joann Raytar's Avatar
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    Darryl,
    You can also apply multiple thin films, creating a stack to improve the performance of the anti-reflective coating by improving adhesion, eliminating more reflections, controlling reflex color appearance, etc
    Is this why coatings with more bands are considered higher quality?

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