Optics: measuring and testing – By dispersed light spectroscopy – With monochromator structure
Reexamination Certificate
2000-04-13
2002-06-25
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
With monochromator structure
C356S328000, C356S300000
Reexamination Certificate
active
06411382
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a monochromator and a spectrometric method for projecting a measured beam (a beam which is measured) on one and the same diffraction grating a plurality of times.
Conventionally, a spectroscope called “monochromator,” has been used as an instrument to measure wavelength characteristics of a measured beam. Particularly, a double monochromator is widely used to allow keeping a high resolution or a wide dynamic range by incidence of a beam into one or more diffraction gratings a plurality of times.
For example, a variety of monochromators have been Japanese Patent Laid-Open No. 8-145795.
FIGS. 4 and 5
are perspective side views showing the configuration of representative monochromators disclosed in the publication.
The monochromator shown in
FIG. 4
converts a beam emitted from an optical fiber
100
to a parallel beam by a collimator
102
followed by diffracting this parallel beam by a plane diffraction grating
104
. The diffracted beam is reflected by a plane mirror
106
having a reflecting surface perpendicular to the beam path, diffracted by the plane diffraction grating
104
followed by condensing by the collimator
102
, and finally passes through a slit
108
. A monochromator shown in
FIG. 4
allows increasing the resolution of the wavelength &lgr; of the diffracted beam passing through the exit slit
108
, because the measured beam is diffracted twice in the identical plane diffraction grating
104
.
In comparison with the structure shown in
FIG. 4
, the monochromator shown in
FIG. 5
has a structure comprising an intermediate slit
110
and two mirrors
112
and
114
. In the monochromator shown in the
FIG. 5
, the diffracted beam returned by reflection by the collimator
102
is reflected 90° by one mirror
112
, passed through the intermediate slit
110
located in the condensing position of the diffracted beam, and reflected 90° by the other mirror
114
to return one more time through an optical system comprising the collimator
102
, the plane diffraction grating
104
, the plane mirror
106
. Thus, the monochromator shown in
FIG. 5
allows the dynamic range of the beam to widen by passing through the intermediate slit
110
and the exit slit
108
.
As other conventional examples of the monochromator, those disclosed in U.S. Pat. Nos. 3,069,966 and 4,025,196 have been known.
Meanwhile, the conventional monochromator shown in
FIG. 4
requires to locate both the optical fiber
100
used for incidence of the measured beam and the exit slit
108
in around the position of the focal point of the collimator
102
to make the structure around the focus position complex to disturb such work as assembling. Furthermore, the conventional monochromator shown in
FIG. 5
requires to locate around the two mirrors
112
and
114
and the intermediate slit
110
in addition to the optical fiber
100
and the exit slit
108
around the position of the focal point of the collimator
102
to make the structure around the focus position more complex to disturb further such work as assembling.
SUMMARY OF THE INVENTION
The present invention created in consideration of such problems; the object is to provide a monochromator and a spectrometric method to allow such work as assembling by simplify the structure of the part where a measured beam is incoming and outgoing.
A monochromator of the present invention comprises a plane diffraction grating; a first collimator and a second collimator that are located in parallel to rulings of the plane diffraction grating; a first reflecting member that has at least two reflecting surfaces and returns a diffracted beam emitted from the plane diffraction grating so that an incident beam and an outgoing beam of the diffracted beam separate from each other along the rulings; and an exit slit located near a position of a focal point of the second collimator. By having the first reflecting member to separate and return an incident beam and an outgoing beam and the first and the second collimators for respective two separated rays, the exit slit may be located in the position of the focal point of the second collimator and other optical members may be located in the position of the focal point of the first collimator with a distance from each other. Therefore, the structures around respective positions of focus are simplified to improve such work as assembling.
More specifically, it is preferable that the incident member receiving the measured beam is located around the position of the focal point of the first collimator. Separating the incident member from exit slit with a distance simplifies respective fitting portions, increases a freedom of designing, and makes such work as mounting easy. Besides, improvement of resolution may become possible on the basis of that the identical plane diffraction grating carries out diffraction a plurality of times.
Alternatively, it is preferable that the exit slit and the incident member that receives the measured beam are located around the position of the focal point of the first collimator and that the intermediate slit and the second reflecting member, which is located in both outsides of the intermediate slit to reflect the emitted beam from the second collimator toward the second collimator, are located around the position of the focal point of the second collimator. Structures around the exit slit may be separated from the intermediate slit and the second reflecting member with a distance. Therefore, in comparison with that all these are located around the exit slit as conventional examples, respective parts maybe arranged more freely to allow freedom of designing and easy mounting work. Further, the dynamic range of the beam that passes through the exit slit may be widened by allowing to pass the measured beam through the intermediate slit in reflection of the measured beam by the second reflecting member.
Particularly, it is preferable that the direction of the intermediate slit in parallel to the rulings and that the two reflecting surfaces of the second reflecting member are located along the direction in which the beam emitted from the second collimator is swayed, when the plane diffraction grating is rotated about an axis which is parallel to the rulings of the grating. By such arrangement, an additive dispersion state may be realized to increase furthermore angular dispersion within the width of wavelength of the incident beam on the plane diffraction grating and also an increase in resolution becomes possible.
Alternatively, it is preferable that the intermediate slit is located in a direction that is perpendicular to the rulings and that the second reflecting member is located in a direction along the rulings. By such arrangement, a differential dispersion may be realized to reduce the angular dispersion within the width of wavelength of the incident beam on the plane diffraction grating. Under the condition of differential dispersion, the width of the exit slit need not change, even if the wavelength of the measured beam is changed, to make simplifying the structure possible.
The above described first reflecting member is preferable to emit the outgoing beam in a direction that is almost 180° opposite the direction of the incident beam. The exit slit may be easily disposed separately with a distance from other parts easily by locating the two collimators corresponding to these positions with the distance, because almost parallel reflected beam separated from the incident beam with the distance is returned.
Further, a spectrometric method of the present invention comprises the steps of: diffracting a measured beam converted into a parallel beam by a first collimator, by a plane diffraction grating; returning the diffracted beam so that the diffracted beam after the return is separated from and is almost parallel to that before the return along rulings of the plane diffraction grating; diffracting the diffracted beam again by the plane diffraction grating; condensing the diffracted beam by a second collimator; and allowing the diff
Advantest Corporation
Dellett and Walters
Punnoose Roy M.
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