Emersons procedure is used to determine true absolute contours of optical flats. Absolute contours of standard flats are determined and a comparison is then made between standard and unknown flats. Contour differences are determined by deviation of Fizeau fringe

Primak, W.

English

NASA Technical Reports Server

July 1969
	
Brief 69-10209 
•	 vicy C.
AEC-NASA TECH BRIEF 
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
of the U.S. AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial 
application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Determination of the Absolute Contours of Optical Flats 
.
The problem: 
Development of a procedure for determination of 
the true absolute contours of optical flats. Other tech-
niques entail the scanning of coated plates, the ex-
amination frequently utilizing different parts of the 
auxiliary optical system; aberrations in the optical 
system and the coating itself then introduce optical 
errors. Emerson's procedure (the one in use at the 
National Bureau of Standards) avoids these problems, 
but mapping of a whole plate by this procedure is 
laborious, and higher precision may be desired. A 
more precise method would permit reliable examina-
tion toward the end of the figuring process and would 
decrease the labor in determination of a standard flat. 
The solution: 
Emerson's procedure for determination of the 
absolute contours of highly precise optical flats was 
preferred for its greater precision and for the speed 
with which readings were taken. The precision 
achieved in determination of a set of differences 
between two plates was approximately 1/600 of a 
Fizeau fringe; in determination of the absolute con-
tour, 0.005 of a Fizeau fringe (estimated). The fringes 
were scanned over a photoelectric detector and the 
intensity profile was presented on an oscilloscope. 
Setting was accurate within a fraction of 100th of a 
fringe. A complete set of data was gathered on a data 
logger in about 5 minutes. 
How it's done: 
By Emerson's method the absolute contours of the 
standard flats are determined by intercomparison of 
three sets of flats and solution of the three sets of 
differences to yield the absolute contour of each flat. 
Comparisons are then made between the standard
flats and unknown flats whose contours are calculated 
from the differences and the known contour of the 
standard flat. The contour differences are determined 
by measurement of the deviation of a Fizeau fringe 
from straightness when the plates are transported 
parallel to the fringe system under a Fizeau-fringe 
viewer; the position of the flat, the spacing of the 
fringes, and the deviation of the fringe from straight-
ness must all be measured. The fringe position is read 
visually by setting oF a cross hair on the fringe. 
In this new method the plates are transported per-
pendicular to the fringe systems, and only one set of 
readings is required—the fringe positions: and, for 
increased speed of reading, the positions are re-
corded on an automatic data logger. 
In order to increase the precision of setting on the 
fringes, a photoelectric procedure is adapted for 
reading of the fringes. The image of the fringe is 
swept across a slit in front of a photoelectric cell, and 
a signal, proportional to the light intensity, is placed 
on the vertical plates of an oscilloscope. The same 
sweeping device is used to develop an increasing and 
a decreasing ramp alternately on the horizontal plates 
of the oscilloscope. Thus two representations of the 
light intensity of the fringe pattern are formed: one 
plotted from left to right; the other, from right to left. 
When the fringe is centered on the slit, the two 
patterns are superimposed. The slit is thus the 
fiduciary mark for the fringe position. In principle 
the precision can be controlled over many orders of 
magnitude by alteration of the amplification at the 
oscilloscope, but in practice the mechanical stability 
of the sweep system and electrical noise in the photo-
electric system and the light source limit the precision. 
-	 (ct,iiliiiticd ''c rlc;iI 
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https://ntrs.nasa.gov/search.jsp?R=19690000209 2020-03-16T17:42:42+00:00Z
Notes: 
I. For details see W. Primak, App!. Optics 6(11), 1917 
(Nov. 1967). 
2. This information may interest the optical industry, 
particularly manufacturers of optical flats for inter-
ferometers. 
3. Inquiries may be directed to: 
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B69-10209 
Source: William Primak
Solid State Science Division 
(ARG-10352)
Patent status: 
Inquiries concerning rights for commercial use of 
this innovation may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439 
ra 
Brief 69-10209	 Category 05


Determination of the absolute contours of optical flats

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