[ATM] No fringes

["Christopher Dalla Piazza" <dalchri@hotmail.com>]

I can't get fringes to appear on the interference test.

I am using a green LED which I assume is monochromatic enough.  There are a 
few little specks of shellac which I left on my convex lens on purpose to 
act as the shim and to also prevent glass on glass contact.

I have the concave reference R=185" facing me.  In front of that, I place 
the convex, matching surface against it.  I know that the surfaces must be 
getting close together because I have to overcome that vacuum force when I 
try to separate them.

Next I just hold the LED next to my eye just like in the spit test and find 
the effective radius of curvature when the light fills the lens.  This is 
much close than 185" since the convex R=43" alters the focus, perhaps about 
60" away from the test stand.

Light fills the lens but no fringes.  I tried increasing the wedge to the 
point that I could see a double image of the LED inside focus with no 
change.

Do I need to create a pinhole or a slit for the LED?  Texereau just shows a 
Neon lamp and a prism at the radius of curvature.  Is the orientation of the 
air wedge important relative to my eye-source axis?  For example, if I place 
the source to the right of my eye, does the thick part of the air wedge need 
to be on the right and not the top or bottom?

Am I completely misinterpreting the illustration?  I wanted to avoid making 
a diffuser but is that what needs to be done instead of being at the radius 
of curvature?

Thanks again!

_________________________________________________________________
Exercise your brain! Try Flexicon. 
http://games.msn.com/en/flexicon/default.htm?icid=flexicon_hmemailtaglineapril07

_______________________________________________
ATM mailing list http://www.atmlist.net/