Optical: systems and elements – Mirror – Plural mirrors or reflecting surfaces
Reexamination Certificate
2000-02-11
2001-09-18
Chang, Audrey (Department: 2872)
Optical: systems and elements
Mirror
Plural mirrors or reflecting surfaces
C359S199200, C359S214100
Reexamination Certificate
active
06290363
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an apparatus for reflecting light and increasing or decreasing the length of an optical path. Specifically, the invention relates to an apparatus in which when an optical beam enters a beam splitter, the incident light is splitted into two kind of lights (reflecting light and transmitting light) and caused to emerge; one of the emerged lights (transmitted light) is reflected by a plurality of light reflecting mirrors, and reentered in the splitter in the direction opposite to the emerging direction of the emerged light; the optical path (length of reciprocating optical path) from the point where the light emerges from the splitter to the point where the emerged light from the splitter is reflected by a plurality of the light reflecting mirrors, and finally to the point where the light is reentered in the splitter is increased or decreased on a cycle.
Accordingly, the apparatuses of the present invention can be used as moving mirrors in conventional Michelson interferometers used in FT-IR (Fourier-transform Infrared Spectroscopy).
Further, the present invention is concerned with an apparatus for moving (a) a light reflecting member, and (b) a device for changing the length of an optical path using the apparatus for moving a light reflecting member.
Hereinafter the term “increasing or decreasing” is sometimes referred to as “changing” for brevity, and the words “for reflecting a light and changing the length of an optical path” is sometimes condensed into “for changing the length of an optical path”)
BACKGROUND ART
In FT-IR, a Michelson interferometer has generally been used. The Michelson interferometer is composed of a beam splitter and two light reflecting systems.
FIG. 27
schematically shows the structure of a general purpose Michelson interferometer.
In
FIG. 27
, a Michelson interferometer is provided with beam splitter
01
having a transmittance of 50%, fixed mirror M
0
placed so as to face to the beam splitter
01
at a prescribed angle &thgr; (45°), and moving mirror M
1
. The interferometer is fabricated such that when the light which was emerged from measuring light source
02
is converted by collimator
03
into a beam of parallel lights and then enters the beam splitter
01
described above, half of the optical beam is reflected by beam splitter
01
and reaches fixed mirror M
0
, remaining half of the optical beam passes through beam splitter
01
to reach moving mirror M
1
, and each of the beams reached mirror M
0
and mirror M
1
is reflected by them, reenters beam splitter
01
, and then collected at detector
05
through condenser lens
04
, respectively.
In this case, the two kind of lights interfere to mutually amplify or attenuate (interference action of light) due to twofold difference (difference in optical path) between the distance L
0
from beam splitter
01
to fixed mirror M
0
and the distance LI from the beam splitter
01
to moving mirror M
1
. Thus, when moving mirror M
1
is reciprocated in parallel to beam splitter
01
, twofold value of the moved distance is plotted as abscissa, and the out put from detector
05
is recorded as ordinate, then the interferogram of measuring light (interference waveform) based on the interference action of the lights described above can be obtained. The interferogram is determined and then subjected to Fourier transformation to obtain a spectrum.
In conventional apparatuses for changing the length of an optical path on a cycle in which the length of an optical path of an optical beam from the point where an optical beam emerges from a beam splitter to the point where the optical beam is reflected by a moving mirror, and finally to the point where the reflected optical beam reenters the beam splitter is changed on a cycle by moving the moving mirror, a linear driving mechanism such as a linear ball bearing or a rotational driving mechanism such as a rotary bearing has been used as mechanism for varying the difference in the optical path described above.
FIGS. 28A
to
28
D schematically show apparatuses for moving a moving mirror (apparatus for moving a light reflecting member) used in conventional interferometers.
FIG. 28A
is an illustration of an example of conventional apparatuses using a linear driving mechanism.
FIG. 28B
is an illustration of a sort of prior art technology using a mechanism by which a moving mirror is reciprocated in a prescribed angular range.
FIG. 28C
is an illustration of another sort of prior art technology using a mechanism by which a moving mirror is reciprocated in a prescribed angular range in a manner different from that of FIG.
28
B.
FIG. 28D
is an illustration of still another sort of prior art technology using a rotational driving mechanism.
In
FIG. 28A
, supporting member S which supports moving mirror M
1
is slidably supported by a guide member. Rack R formed on supporting member S is engaged with gear G. Gear G is reciprocated with a motor (not shown in the drawing) in the range of a prescribed angle, and thus the moving mirror M
1
linearly reciprocates in a direction along the incident light.
In
FIG. 28B
, supporting member S which supports moving mirror M
1
is rotatably connected to the free end of swingable parallel links, A
1
and A
2
. Gear G is attached to rotation axis A
1
a
of one side of the parallel links, A
1
. Gear G is reciprocated with a motor (not shown in the drawing) in a prescribed angular range, and thus the moving mirror M
1
linearly reciprocates in a direction along the incident light.
In
FIG. 28C
, moving mirror M
1
, and moving mirror M
0
′ which is a substitute for a fixed mirror are supported at the ends of lever L having rotation axis La. Gear G is attached to the rotation axis La. Gear G is reciprocated with a motor (not shown in the drawing) in the range of a prescribed angle. Thus, the moving mirrors M
1
and M
0
′ simultaneously swing, and a difference in the length of optical path (difference in an optical path) from the point where a transmitting light and a reflecting light splitted by beam splitter B are caused to emerge to the points where the lights are reflected by the moving mirrors M
1
and M
0
′, and finally to the point where the reflected lights reenter beam splitter B, respectively, is produced.
However, the apparatuses shown in
FIGS. 28A
to
28
C have such problems as follows:
In the conventional technology using any one of the apparatuses shown in
FIGS. 28A
to
28
C, it is necessary to reciprocate gear G in the range of a prescribed angle. Accordingly, it is required to once stop the rotational movement of the gear G every time the motion of the gear comes to both ends in the prescribed angle described above and then start the motion in the opposite direction. Thus, it is difficult to make the moving mirror perform a reciprocation at a high speed by a method wherein rotation of the gear is stopped every time it comes up to both ends of the prescribed angle (a method wherein a moving mirror is once stopped at both ends of its moving range, and then the moving of the mirror is started).
FIG. 28D
shows a method which has been conducted by Dr.
Griffith of America who is studying on interferometers intended for high speed moving of moving mirrors (that is, interferometers of which the cycle of increasing or decreasing the length of a reciprocative optical path described above is shortened). In
FIG. 28D
, moving mirror M
1
rotates at a high speed together with supporting member S which supports the mirror M
1
. At that time, the normal of the mirror surface is inclined toward the rotation axis. During a scanty period of time when the moving mirror described above is in the range of a prescribed rotation angle, light L
1
which is incident on moving mirror M
1
is reflected by moving mirror M
1
, reflected by mirror M
2
, M
1
, M
3
, M
1
, M
2
, and M
1
in turn, and then reentered in a beam splitter (not shown in the drawing). The reincident light which reenters the beam splitter can be obtained only during a scanty period of time when the mov
Chang Audrey
Mattingly Stanger & Malur, P.C.
Robinson Mark A.
S.T. Japan Inc.
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