To: atm{at}shore.net
From: Stan Truitt 
Cc: Guy Brandenburg 
Reply-To: Stan Truitt 


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In test plate measuring, to have good fringe contrast it is ideal to match
the reflectances of the reference surface and the surface being tested. 
When using common glasses with indexes around 1.5 the surface reflectances
of both surfaces are near 0.04 (4%), and the intensity of the reflected
light from each surface is fairly well matched. These are the splendid
Newton's fringes we see in the majority of photographs taken of this
testing.  Without this matching, the fringes are typically *very* hard to
see.

In practice, it is more important to have these intensities matched than to
have pure monochromatic light.  With interferometers, using a high
reflectance reference surface to measure high reflectance (aluminized)
mirrors is the norm.

Interferometer set-up time became a barrier to timely measurement of nickel
plated aluminum mirrors.  To alleviate this bottleneck, a reference flat
was coated with a semi-transparent layer of inconel alloy.  In the green
wavelengths, both the nickel and inconel reflectances were fairly well
matched at about 0.6 (60%), and the resultant fringe contrast was superb! 
A benefit of these higher reflectances is fringe narrowing and finesse,
resulting in easier fringe data reduction.

See:
http://wyant.optics.arizona.edu/MultipleBeamInterference/MultipleBeamInterfe=
renceNotes.html

Section 1.6 to see graphs of the fringe intensity profiles for reflectances
of 0.04, 0.18, and 0.8.  The effect is striking, especially for
polychromatic fluroescent phosphors.



Cheerio,

Stan Truitt               20=B0 51'  N,  156=B0 22'  W,   511 Meters MSL
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Re: ATM testing aluminized
flats
In test plate measuring, to have good fringe contrast it is ideal
to match the reflectances of the reference surface and the surface being
tested.  When using common glasses with indexes around 1.5 the
surface reflectances of both surfaces are near 0.04 (4%), and the intensity
of the reflected light from each surface is fairly well matched. These are
the splendid Newton's fringes we see in the majority of photographs taken
of this testing.  Without this matching, the fringes are typically
*very* hard to see.

In practice, it is more important to have these intensities
matched than to have pure monochromatic light.  With
interferometers, using a high reflectance reference surface to measure high
reflectance (aluminized) mirrors is the norm.

Interferometer set-up time became a barrier to timely measurement
of nickel plated aluminum mirrors.  To alleviate this bottleneck,
a reference flat was coated with a semi-transparent layer of inconel
alloy.  In the green wavelengths, both the nickel and inconel
reflectances were fairly well matched at about 0.6 (60%), and the resultant
fringe contrast was superb!  A benefit of these higher
reflectances is fringe narrowing and finesse, resulting in easier fringe
data reduction.

See: 
http://wyant.optics.arizona.edu/MultipleBeamInterference/MultipleBeam
>InterferenceNotes.html

Section 1.6 to see graphs of the fringe intensity profiles for
reflectances of 0.04, 0.18, and 0.8.  The effect is striking,
especially for polychromatic fluroescent phosphors.



Cheerio,

Stan
Truitt               20=B0
51'  N,  156=B0 22' 
W,   511 Meters MSL


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