From: "CSC" 
To: "Atm" 
Reply-To: "CSC" 


I use any size grating, from 50 to 200.  The finer grating is trouble in
white light because of the overlapping diffraction images.  With
monochromatic light, the internal diffraction bands are sharp and useful.
50, 100, 150 are all excellent.

-----Original Message-----
From: J-Engineering [mailto:Ray{at}J-Engineering.com]
Sent: Thursday, February 13, 2003 11:47 AM To: CSC
Subject: Ronchi, was ATM Tesing a spheriod?


I posted this to the list with little luck.

I should get my laser diodes very soon.

> I did use the laser source with a 200 lpi Ronchi and it is WILD!  The
> diffraction with a monochromatic source creates bands WITHIN the dark
Ronchi
> bands, (let's call them internal diffraction bands) and by expanding the
> image of one Ronchi line to nearly cover the mirror, it becomes a most
> elegant test for straightness of the bands and hooks and crooks at the
edge.
> The internal diffraction bands are superbly sharp as opposed to blurry
with
> monochromatic light. Also, while regular white light Ronchi creates
> diffraction effects which make reading the edge difficult due to the
> overlapping images, this Monochromatic Ronchi test uses this diffraction
to
> advantage. Internal diffraction bands are sharp and clear to the edge.
Any
> TDE or zone shows much more clearly.
>
> I don't know who else uses it. Let's call it the Monochromatic Ronchi
test.
> Perhaps it's an illusion, but it appears to reliably show very small edge
> defects.  Anyone care to analyze this effect?  Is it sort of a Shearing
> interferometer?
>
> Colin

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