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The
Model 2GRP LAZER GRAZER is
a non-contacting Grazing Incidence Interferometer. . . the first modestly
priced Interferometer for measuring flatness of semi-matte or matte-finished
surfaces. The Model 2GRP also permits the measurement of parts which are
much larger than its 2-inch aperture because is measures flatness across
a 2 inch by 8 inch elliptical beam path as illustrated below.
Principle
of Operation
When
a rough surface is examined at a low grazing angle, it appears to be highly
reflective.
The
LAZER
GRAZER utilizes this principle to produce high contrast interferograms
of unpolished surfaces. A grazing angle of 14.48 degrees was selected
since at that angle, each interference fringe equals one wavelength.
With a normal incidence Fizeau Interferometer, each fringe equals one half
wavelength. Clicking on the link below will provide further information
on the subject of
Grazing
Incidence Interferometers |
With a
normal incidence interferometer, 1 fringe = 0.5 wave = 0.3164 micron
With a grazing Incidence
interferometer (grazing angle of 14.48 degrees) 1 fringe = 1 wave. = 0.6328
micron
WHAT IS A GRAZING ANGLE? |
Note
that the live image shows interference fringes on the surface of the test
sample while providing a "3-D" image of the part. This unique display
will only be found as a feature available with GRAHAM's LAZER GRAZER Interferometers!
This capability is of enormous value in the interpretation of test pieces
with complex geometry. |
 Comparison
of Normal Incidence Interferogram
(1
fringe = 0.5 wave)
and
Grazing Incidence Interferograms
(
1 fringe = 1 wave)
Upper Drawing shows the interferogram
of a part using a normal incidence interferometer. 8 circular fringes
which implies part is concave or convex by:
8 X 0.3164 microns = 2.53
microns
The Lower Drawing shows the
interferogram of the same part using a grazing incidence interferometer..
The interferogram shows 4 circular fringes which implies the part is concave
or convex by:
4 X .6328 micron = 2.53
microns |
Note
that the live image shows interference fringes on the surface of the test
sample while providing a 3-D image of the part. This is a unique display
is a feature available only with GRAHAM's unique Grazing Incidence Interferometers!
This capability is of enormous value in the interpretation of test pieces
with complex geometry. |
Red
arrows show light coming in from the left at a "Grazing Angle" of 14.48
degrees
|
 This
drawing illustrates the ray path shown in the photograph. The collimated
beam passes through the interferometer's reference surface, strikes the
test sample, bounces up to the right and reflects from the return mirror,
again bounces off the sample and reenters the interferometer, and
interferes with the reference beam. |
Measure
flatness
...before polishing!
The
ability to measure flatness of unpolished parts opens the door to examining
surfaces which would be difficult if not impossible for a normal incidence
interferometer. This permits the operator to check parts for flatness
while still in the grinding stage. For some operations, this is all that
is needed since the finished parts do not require polishing. GRAHAM's
LAZER GRAZER puts an end to all of those “tricks” using wax and
china markers to increase reflectivity of the surface.
Difficult
substrates easily tested
With
the LAZER GRAZER, matte, semi-matte, or polished surfaces can be
checked for flatness of virtually any material. Very difficult substrates
such as ceramics, graphite, tungsten carbide and silicon carbide can be
evaluated with ease. Even machined metal surfaces can be tested.
The high contrast fringes produced by the LAZER GRAZER will assist
in fine-tuning the production process and increasing both quality and through-put.
Because
of the wide variation in sample thickness encountered, it is essential
to make provision for the sample surface to be totally covered by the incident
laser beam. By providing a height adjustment for the tilt table, samples
of various thickness can be examined. After the appropriate tip-tilt
adjustment has been made, the tilt-table may be raised or lowered as required
for the sample to fully encounter the beam. |
 |
Because
of the low grazing angle of the incident light, the illuminated area of
the tilt-table is much elongated with the result that a long ellipse of
light, in this case 4 times the interferometer's aperture is available
for evaluating long narrow parts. It can also be used to look
at parts substantially larger than the interferometer's aperture by examining
a narrow swath across the substrate and then rotating the sample to look
at another swath.
Special
advantages offered by LAZER GRAZER Interferometers
-
Ability to measure flatness
of semi-matte and matte surfaces
-
Measure narrow swaths across
surfaces much larger than the interferometer aperture
-
Simultaneous oblique view
of test piece and interferogram of surface.
|
GRAHAM
OPTICAL SYSTEMS, 9530 Topanga Canyon Blvd., Chatsworth, CA 91311
Phone
(818) 700-1263 FAX (818) 700-1627 E-mail:
techinfo@grahamoptical.com
Copyright
© 2008 Graham Optical Systems All Rights Reserved
This
page last updated JUly 7, 2008
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