Optical: systems and elements – Lens – Multiple component lenses
Reexamination Certificate
2000-03-13
2001-10-02
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
Multiple component lenses
C359S205100, C359S206100, C359S719000
Reexamination Certificate
active
06297916
ABSTRACT:
BACKGROUND OF THE INVENTION
Grazing incidence interferometric devices which can measure the surface contours of a surface of interest by conveying a coherent light beam at grazing incidence to the surface are well-known.
FIG. 15
illustrates a typical configuration of these prior art grazing incidence interferometric devices. Such a device conveys collimated, coherent light to a diffractive beam splitter
102
that divides the wave front into two light beams. One of the two light beams, termed the “object beam”, is then conveyed at grazing incidence to a surface
2
a
and the light reflected therefrom is combined with the collimated light (termed the reference beam) which has not been reflected from the surface
2
a
. Diffractive beam combiner
104
redirects the reference beam so as to be combined with the object beam and travel along a common axis. Imaging lens
106
(in this case the lens of a television camera
108
) then forms an interference pattern image of the surface
2
a
that is recorded by the television camera
108
. The surface contours of the surface
2
a
can then be measured based on the recorded interference pattern image.
However, the lengths of the optical paths from each location on the surface
2
a
to the interference pattern image formed by imaging lens
106
differ. Thus, there is a problem in that distortions are formed in the interference pattern image recorded by the television camera
108
. Hence, the surface contours of surface
2
a
cannot be accurately measured to as high a precision as would otherwise be possible.
As a partial solution to this problem, a grazing incidence interferometric device as shown in
FIG. 16
is known that avoids distortions from being formed in the interference pattern image by positioning an interference pattern observation screen
110
so that its surface lies at the conjugate image of surface
2
a
. As is apparent from the spacing of the components in
FIG. 16
, the lens
106
and
112
form an optical system that relays the image of object
2
a
at unit magnification to interference pattern observation screen
110
. As a result of the orientation of the interference pattern observation screen
110
now being conjugate to the object (i.e., the surface
2
a
to be measured), an interference pattern image that more accurately represents the surface
2
a
is formed on interference pattern observation screen
110
.
The conjugate image arrangement with unit magnification is achieved as shown in
FIG. 16
, wherein imaging lens
106
is arranged with its focal point at a mid-point of the surface
2
a
, collimator lens
112
is arranged with its focal point at the image of this mid-point as formed by the imaging lens
106
, and the interference pattern observation screen
110
is provided with its mid-point at the focal point of lens
112
. Further, the focal distance of the lens
112
is made equal to the focal distance of lens
106
, and the interference pattern observation screen is oriented so that its surface is aligned with the conjugate points of the surface
21
as imaged by lens
106
and lens
112
.
An alternative prior art arrangement is shown in prior art
FIG. 17
, wherein a reflecting mirror
114
is arranged at the second focal point of the imaging lens
106
for conveying a bundle of rays of the interference pattern in the reverse direction. A beam splitter
116
is provided between the imaging lens
106
and the diffractive beam combiner
104
to reflect the rays from the reflecting mirror
114
to an interference pattern observation screen
110
that is, once again, provided to have its surface coincide with the conjugate image of unit magnification of the surface
2
a
. Once again, interference pattern images formed on interference pattern observation screen
110
are viewed by the television camera
108
. In this manner the total length of the interferometric device may be prevented from becoming too long.
In the above-described grazing incidence interferometric devices shown in
FIGS. 16 and 17
, the surface
2
a
and the observation screen
110
are provided at the conjugate positions where the magnification is 1. In
FIG. 16
, lens
106
and lens
112
form a lens system, and object
2
a
and observation screen
110
are positioned with their mid-points a focal length away from this lens system so that unit magnification is achieved. Similarly, in
FIG. 17
, lens
106
and mirror
114
form an optical system, with object
2
a
and observation screen
110
again positioned in respective paths with their mid-points positioned a focal length away from the lens system so that unit magnification is achieved. In this way, the television camera
108
records the interference pattern formed by the image of object (surface
2
a
) and the collimated light from the reference beam, assuming the difference in path length of the object and reference beams does not exceed the coherence length of the light. Thus, instead of using collimator lens
112
as in
FIG. 16
to form a unit magnification image of the surface
2
a
onto observation screen
110
, in
FIG. 17
the mirror
114
is positioned at the focus of lens
106
to redirect the light backwards through lens
106
to beam splitter
116
. The unit magnification image of the surface
2
a
is thus formed on surface
110
, and recorded by television camera
108
.
The imaging requirements of such an imaging lens
106
are unique and two-fold. First, the lens
106
must generate only very small aberrations when imaging an object at infinity (i.e., the collimated light of the reference beam). Second, the lens
106
must generate only very small aberrations when imaging surface
2
a
at unit magnification onto surface
110
. Only if both imaging requirements of the lens
106
occur with very small aberrations will the interference pattern observed by television camera
110
accurately enable the surface contours of the surface
2
a
to be measured accurately. When the collimator lens
112
is used as in
FIG. 16
, the first requirement mentioned above is nearly satisfied; however, the second requirement mentioned above is not satisfied. As a result, each single point on the surface
2
a
will not be imaged to a corresponding single point on the screen
110
, thus causing problems in that the location of lines in the interference pattern will be imprecise, and the periphery portions of the surface
2
a
will appear as being out of focus.
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is to provide an imaging lens for an interferometric device that can simultaneously image an object at unit magnification (i.e., light in the object beam) and can relay collimated light (i.e., light in the reference beam) while generating very low aberrations in both so as to provide a high quality interference pattern image, thereby enabling precise measurements of the object surface contours to be obtained with high accuracy.
REFERENCES:
patent: 4787723 (1988-11-01), Uetake
patent: 5055663 (1991-10-01), Morimoto et al.
patent: 5202795 (1993-04-01), Kashima
patent: 5650878 (1997-07-01), Estelle
patent: 5682258 (1997-10-01), Yamakawa
patent: 6014266 (2000-01-01), Obama
patent: 04-221704 (1992-08-01), None
patent: 2000-249531 (1999-09-01), None
patent: 2000-275006 (2000-10-01), None
Kanda Hideo
Koizumi Noboru
Arnold Bruce Y.
Epps Georgia
Fuji Photo Optical Co., Ltd.
International Arnold
Spector David N.
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