Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2001-05-04
2004-02-03
Porta, David (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S201300, C382S280000
Reexamination Certificate
active
06686587
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the methods of precision calibration of magnification of scanning microscopes with the use of a test diffraction grate.
Methods of precision calibration of a magnification of synthetic microscopes with the use of a test diffraction gratings are known. In the existing methods test object is positioned and oriented on a microscope table, and corresponding part of the test objects is scanned, with subsequent processing of the thusly obtained data. It is believed that the existing methods can be further improved.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method of precision calibration of magnification of a scanning microscopes with the use of a test diffraction grating.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a method of precision calibration of magnification of scanning microscopes with the use of a test diffraction grating, comprising the steps of positioning and orientation of a test object on a table of microscope so that strips of a test diffraction grate are perpendicular to a direction along which a calibration is performed; scanning of a selected portion of the test object along axes X and Y; measuring values of a signal S versus coordinates X and Y in a plane of scanning and storing of said values S (x, y) in a digital form as a two-dimensional digital array; transforming the two-dimensional array of signals S(x, y) into a two-dimensional array S (u, v) by turning of the axes so that a direction of a new axis u is perpendicular to the strips of the grating and a direction of a new axis v coincides with the strips of the grating; line-by-line mathematical processing of the array S(u,v) for each line S(u) by calculating of a Fourier spectrum of the line SP(&ohgr;) in correspondence with the formula
SP
(
ω
)
=
1
2
-
∫
-
∞
∞
S
(
u
)
·
exp
(
ⅈu
ω
)
ⅆ
u
,
wherein &ohgr; is a coordinate in a reciprocal space which represents a space frequency; SP(&ohgr;) is a complex spectrum density which corresponds to the space frequency &ohgr;; S(u) is a function which describes a one-dimensional profile of the signal; and i={square root over ( )}−1 is an imaginary unit; converting of the one dimensional complex function SP (&ohgr;) into a one-dimensional spectrum of real values of a module |SP(&ohgr;)| by multiplying of each value SP(&ohgr;) by a complex-conjugate value; finding from the spectrum of the real values T the greatest spectral maximum and determining its characteristic frequency &ohgr;
h
as an abscissa of a point with the maximum value |SP|; calculating an average value of a pitch T
h
of the diffraction grate in accordance with the formula:
T
h
=
1
W
h
performing the mathematical processing, the conversion, the determination and the calculation for subsequent lines S(u) with a new value of a coordinate v; statistically processing the thusly obtained set of values T
h
for all lines and determining an average value T and a standard deviation &Dgr;T over a whole frame; and determining a magnification M
u
in accordance with the selected direction u in accordance with the formula:
M
u
=
T
·
L
T
0
·
N
,
where L is a width of a medium of image in direction of the calibration, T
0
is an independently obtained value of the pitch of the same test object, and N is a number of pixels in the line along the direction u.
When the method is performed in accordance with the present invention, it reliably provides a precision calibration of magnification of scanning microscopes, and achieves a very high accuracy of calibration.
REFERENCES:
patent: 5714832 (1998-02-01), Shirrod et al.
patent: 6384408 (2002-05-01), Yee et al.
Nikitin Arkady
Yeremin Dmitriy
General Phosphorix LLC
Porta David
Yam Stephen
Zborovsky I.
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