40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  PSL  Not logged in ELOG logo
Entry  Fri Nov 9 18:56:49 2012, tara, HowTo, RefCav, Howto optically contact mirrors IMG_1964.jpgIMG_1955.jpgfixture_assem.PDF
    Reply  Wed Nov 28 20:37:57 2012, tara, HowTo, RefCav, assembling short ref cav IMG_2029.jpgIMG_2034.jpg
       Reply  Wed Apr 13 16:45:18 2016, tara, HowTo, RefCav, Optical Contact Tutorial IMG_2705.JPG
Message ID: 1072     Entry time: Fri Nov 9 18:56:49 2012     Reply to this: 1085
Author: tara 
Type: HowTo 
Category: RefCav 
Subject: Howto optically contact mirrors 

I have been practicing to optically contact two flat mirrors together. I think now I get it.

   Since I need to build my refcav by optically contacting mirrors to a spacer. I tried the procedure by contacting two flat blank mirrors together. I bought blank fused silica mirrors from Thorlabs, pf10-03. Here are the instructions:

  1. Clean your space.
  2. Wear lab gown, mask, gloves to prevent dust from your clothes
  3. Use a can duster to blow away any obvious dust/dirt from the mirrors. Clean the whole mirror if possible. Any dust on the mirror back or side might fall on the surface anytime.
  4. Wipe the mirror with acetone (I wiped the back and the edge first, before wiping the front face). Then switch to isopropanol. I tried drag wipe first, but it did not remove one of a particle right in front of the surface, so I had to wipe it with more pressure.
  5. Contact to surfaces together. I put one on top of another. You will see a fringe pattern changes as the surfaces become close together under gravity. Press it to make it contact properly. ( I pressed with my finger for ~ a minute with ~10-20 Newton). If the surfaces are clean, there should be no fringe pattern (see fig2).  There should be no change when you remove the applied pressure.



fig1: On the right, fringe patter can be seen when two surfaces are put close together. On the left, after applying pressure the fringe should go away. The fringe pattern(purple-yellowing) on the left side indicates that these surface are not properly contacted.


 fig2:  These mirrors are optically contacted somehow, except the center. I don't know what happen here that cause white area in the center. I might be that the mirrors are not flat enough. But the rim seems to have a nice optical contact. I tried to remove the mirrors by hands but they are well stuck. I'll ask peter for more about what causes the white area here.


As I tried to do this, I got an idea of a fixture for optical contacting the spacer to mirrors. It will be a cap with a center hole for the mirror position. Here is a solidwork drawing. The part can be aluminum. I have to think about the tolerance of the piece, but from the calculation it can be an order of a  cm (to keep the beam to go through the window). So the hole can be ~ .01 inch larger than the spacer and the mirror.


ELOG V3.1.3-