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Thermal expansion/contraction of lens

  1. Sep 15, 2014 #1
    to measure the thermal strain of optical lens. Due to temperature variation the lens surface is expanding / contracting in radial direction with two extreme operating temperature. (-40C to +70C )
    Optical lens is SF56A (CTE - 7.9*e-6 per Kelvin)

    What to do:
    I need to measure this expansion/contraction of lens. I think I can do that by strain gauge. But I was looking for some earlier references on internet as bonding on gauge is very tricky. Even a small scratch on lens can deteriorate its performance. So I need to very careful while bonding gauge on it.

    1. Anyone have previous exp/suggestion on how to bond the gauge & its placement.
    2. Any references on internet.
  2. jcsd
  3. Sep 15, 2014 #2


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    Staff: Mentor

    Hi deepak.midri. I see you're new here, so http://imageshack.com/a/img515/4884/welcomesign.gif [Broken]

    I can't offer advice on strain gauges. But if you could fix to the lens a tiny mirror (or simply use a reflection off the already polished surface), you might be able to use optical magnification to determine movement of the surface. Arrange it so that a laser beam bounced at an angle off the surface will make a wide sweep across the wall of the room for a tiny movement of the mirror.
    Last edited by a moderator: May 6, 2017
  4. Sep 15, 2014 #3

    Andy Resnick

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    I'm a little confused. First, since you know what the glass is and have a CTE, why do you need to measure the CTE? Are you concerned about lot-to-lot variability? Second, why do you have to use a strain gauge? I can think of a few alternate methods (for example, I expect an interferometric measurement to be much more sensitive).
  5. Sep 15, 2014 #4


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    I agree using a strain gauge is a bad idea. How are you going to allow for the thermal expansion of the gauge itself, and whatever material you use to bond it to the lens?

    A non-contact measurement method seems more appropriate.
  6. Sep 16, 2014 #5

    I need to measure the expansion/contraction of lens only. Since sometimes lens develop crack as it is holded in a Aluminium assembly. So when both expand/contract lens develop a crack in it.
    I need to measure at what expansion/contraction of lens/housing this happen.

    1. I am facing trouble regarding strain gauge method. Since pasting is problem. moreover it may develop a crack.

    2. What about interferometric method. Is there any special method for such type of application
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