[ATM] Polishing and a red laser

["Francis J. O'Reilly" <foreilly@verizon.net>]

I've completed fine grinding and now have put the optical flat project aside for a few days. 

I am now polishing out my 12.5 inch f~7 mirror. I ground the mirror starting with a pre-generated curve and fine ground in 45 minute to one hour sessions per grade from 120, 220, 320, 500 SiC then 25 micron, 15 micron, 9 micron, 5 micron and finally three micron AlO. I am using cerium oxide on a Gugolz 73 pitch lap in a basement that is around 65 degrees F. A little hard, but not too bad. I have been polishing for about five hours now, alternating tool and mirror on top for equal half hour sessions. Generally one in the morning and one in the evening, about twelve hours apart. The tool and the mirror are in great contact from every angle. I'm pretty pleased so far.

I am past the faux polish and am now pretty much to a stage where all of the white light from my American Optical microscope light source passes through the first surface of the mirror. Generally this is considered to be done. I'd like to put in about another five hours before I'm satisfied. I should be there by Sunday noght as I tend to double things up over the weekend.

I looked at the surface with a red laser this evening. I was dismayed to find that a substantial amount of the light was reflected by the first surface rather than passing through. It seems to illuminate very small pits. I looked at other surfaces that I have made and found the same to be true with them, although they aluminized very well (I had subsequently removed the aluminum as it had become quite dirty from sitting around and I wanted to recoat them).

Does anyone have any experience with using a laser to ascertain the state of polish on a mirror substrate? I'd like to hear your thoughts.

Thank you.

Francis J. O'Reilly 
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