Interferometers/Mapping

[jetstream]

A question about interferometers. They can measure the wavefront of an optic. When many multiples of IF pictures across the optic are taken they then give an accurate "map" of the surface? If so then the more fringe pictures taken across the optic, the more accurate the map.

So if an interferometer is tested in red light vs green does this affect the actual accuracy of the map? If so how much? I'm not talking Strehl ratio here just the visual optic map seen with reports that is most likely computer generated from (hopefully) a very high number of fringe pictures.

If IF mapping can be used to map, can it be used to give an accurate indication of smoothness of the optic? Should other tests such as Focault shadowgrams be used as well?

Thank, Gerry

Edited March 27, 2023 by jetstream

[jetstream]

                                                                                               

[andrew s]

There are many types of interferometer.  If you mean the Zygo type used by OO then they have some info on there site.

In general the shorter wave length gives a more detailed picture so green is better than red. There are some subtle issues in their use for example how any off axis illumination is accounted for but they should give a fair picture of an optics quantity if not deliberately played. 

Other methods tend to be more subjective and depend more on the skill of the observer (and their prejudice).

Regards Andrew 

 

[skybadger]

You could look up the dtfringe software by Dale Easton and its use with a home made Bath interferometer. There's lots of info on the web. 

I have one in bits waiting to be assembled on the bench right now, behind a long list of other projects. 

 

[jetstream]

7 hours ago, skybadger said:

You could look up the dtfringe software by Dale Easton and its use with a home made Bath interferometer. There's lots of info on the web. 

I have one in bits waiting to be assembled on the bench right now, behind a long list of other projects. 

 

Thank you , I have an interest in optical testing and the fringe analysis programs. It is my understanding that there are vg ones out there and some that are deadly expensive. I'm trying to evolve a plan to keep my data as good or "hard" as I can to feed the program (s).

Please keep us updated on the progress of your IF.

Thank you , Gerry