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Silicon wafers? Spectralon?

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#1 Squidink

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Posted 25 October 2020 - 10:46 PM

Digging through my attic, I came across two circa 1997 AMD 150mm wafers and a few big pieces of Spectralon sintered teflon- used in integrating spheres.

 

Are either of these useful? I could envision the Si wafers being a decent flat mirror, at least in terms of smoothness. I am not sure the spectralon is useful unless it could be used for AP somehow.

 

Any thoughts?



#2 Benach

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Posted 26 October 2020 - 02:55 AM

I have considered to use a wafer myself another day. In ATM a flat mirror can be used approximately for three purposes:
1) Autocollimation flat. Problems to be solved: reflection is rather low (about 40%) and aluminium does not adhere well to silicon without an intermediate layer. This will require some experiments. Apart from that: because the wafers are very thin, they need a very special cell. This requires FEA knowledge as well or you have to glue the wafer to a more thicker piece of material underneath it. But note that this may create peeling problems.
2) Elliptical flat mirror. Approximately similar problems as 1.
3) A spherometer nulling plate. Does not have the problems above. But this can be done with a normal slab of glass as well.

2) Spectralon can be used in a few ways. How big are the chunks anyway?



#3 Squidink

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Posted 26 October 2020 - 11:32 AM

I have 8" diameter slabs of spectralon. It was extras from a 6(edit) foot diameter integrating sphere for NIST from the late 1990s.

 

I was wondering about the wafers for mirror test.

 

For autocollimation, I imagine, I can just use more illumination? and adhere it to a slab of thicker glass, or given the CTE mismatch, use low modulus  foam tape

 

I am curious to see if the mirror on the Starfinder is good, and I need to take it apart anyway, so this would be an interesting way to learn about testing.


Edited by Squidink, 26 October 2020 - 07:53 PM.


#4 Benach

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Posted 26 October 2020 - 12:53 PM

Squidlink: If you want to go for autocollimation, I'd check for flatness of the wafer after bonding it. The CTE is not a problem if you keep the setup indoors and as long as you keep the temperature more or less constant. If you take a bright source, probably 40% reflection is no problem either. But I would definitely bond it to a piece of material to increase stiffness.

 

You can consider to make a flat panel from the spectralon.


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#5 Pinbout

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Posted 26 October 2020 - 01:16 PM

 

I'd check for flatness of the wafer after bonding it.

waytogo.gif



#6 Squidink

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Posted 26 October 2020 - 07:52 PM

Yeah, I was wondering about that.I have 1" thick slabs of aluminum I can "float" it on. I can check them for flatness at work first. Smooth won't matter much if I make a silicon funhouse mirror.



#7 gregj888

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Posted 26 October 2020 - 09:51 PM

float it, bonding would need to have matching CTE or temp control.



#8 Benach

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Posted 27 October 2020 - 02:06 AM

Gregj888: Only relevant if you want to change the temperatures. Indoors the temperature barely changes.

#9 Spectral Joe

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Posted 27 October 2020 - 01:22 PM

Wafers have a somewhat arcane set of "flatness" specifications. Flatness in wafer spec space refers to total thickness variation, and a really good wafer has a flatness spec of a micron. More meaningful are warp and bow numbers, referring to 1 or 2 dimensional curvature. Those are typically in the 10-50 micron range. So, wafers are far from flat, as compared to optical surfaces.


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#10 Squidink

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Posted 28 October 2020 - 08:56 PM

Wafers have a somewhat arcane set of "flatness" specifications. Flatness in wafer spec space refers to total thickness variation, and a really good wafer has a flatness spec of a micron. More meaningful are warp and bow numbers, referring to 1 or 2 dimensional curvature. Those are typically in the 10-50 micron range. So, wafers are far from flat, as compared to optical surfaces.

I was suspecting that it was too good to be true. Oh well, I will keep them filed with the Christmas tree ornaments and disco ball.




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