Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Reexamination Certificate
2000-10-12
2003-07-22
Evans, F. L. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
C356S334000
Reexamination Certificate
active
06597451
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a spectrometry measuring apparatus of a spectrograph type using a concave holographic diffraction grating manufactured by a holographic method.
BACKGROUND OF THE INVENTION
A conventional spectrometry measuring apparatus of a spectrographic type using a concave holographic diffraction grating has been disclosed in Japanese Patent of Publication No. 62-27681 and Japanese Patent of Publication No. 63-46371.
For the conventional apparatus, an exposure layout for a concave holographic diffraction grating is shown in
FIG. 8
, and a spectral layout is shown in FIG.
9
. As shown in
FIG. 8
, concave diffraction grating
23
is exposed by two exposure light sources
21
,
22
near Rowland circle
20
. Concave diffraction grating
23
exposed in the exposure condition in
FIG. 8
disperses and converges a light to be measured diverged from incident slit
24
installed as shown in FIG.
9
. An array sensor is placed at spectrograph focal position
25
, and the spectral intensity of the dispersed light is measured.
In the concave holographic diffraction grating, since the diffraction grating also serves as a condenser, as compared with the ordinary plane diffraction grating, a collimating mirror or a condensing mirror is not necessary, and hence, the measuring apparatus is compact. It is a further advantage of this diffraction grating that the aberration state of the spectral graph in the condenser is excellent because an aberration can be corrected at the exposure position in the spectral layout.
In the prior art as shown in
FIG. 10A
, however, the diffracted light principal ray emitted from the center of the concave diffraction grating enters a photo detector surface
26
of a plane obliquely at a spectrograph forming position. Consequently, when the position of detector surface
26
is changed due to thermal deformation by temperature changes as shown in
FIG. 10A
, the spectral position varies on the detector surface
26
accordingly. The conventional apparatus must be calibrated intermittently with a reference light.
To prevent such a fluctuation of spectrum position, as shown in
FIG. 10B
, a telecentric configuration is required for entering diffracted light
27
vertically to detector surface
26
. The problem can, be solved by a structure comprising a plane diffraction grating, a collimating, and a condensing optical system. However, since the diffraction grating surface is at the incident pupil position, to realize a telecentric configuration, the distance between the diffraction grating and the spectral condensing plane must be twice as long as the focal length of the condensing optical system. In the conventional apparatus, therefore, the optical path from the incident slit to the spectrograph detector surface increases, and the apparatus becomes larger.
Further, in the spectrometry measuring apparatus of a spectrographic type using array elements, a high reproducibility is required, in addition to the requirement for high resolution, so that the precision of measurement may not vary in spite of measuring environments, especially temperature changes.
SUMMARY OF THE INVENTION
A small-size and light-weight spectrometry measuring apparatus with high reliability is presented, in which the spectrum position on the detector surface does not change regardless of temperature changes during detection of such spectral intensity.
A optical system of the spectrometry measuring apparatus of the invention comprises: a condensing device operable to condense a light to be measured; a reflection type concave holographic am diffraction grating produced by exposure from two exposure light sources or a replica of the diffraction grating; and a diffracted-ray condensing device comprising a group of one or more lenses, one or more reflective mirrors having a curvature, or combined optical system of a lens and a mirror for condensing the diffracted-ray diffracted from the center of the diffraction grating telecentrically to a spectral condensing plane.
In the apparatus having such structure, since the spectral ray enters vertically to a photo detector surface disposed on a spectrum focal plane, if the photo detector is moved in the direction of an optical axis due to a temperature change, a spectrum is not moved on the photo detector surface. Consequently, it is not necessary to calibrate the optical element due to an ambient temperature change. Further, since the condensing operation of the concave holographic diffraction grating is directly utilized, it is not necessary to increase the distance between the concave diffraction grating and the spectral condensing plane, so that a small-size and light-weight spectrometry measuring apparatus may be provided.
REFERENCES:
patent: 4673292 (1987-06-01), Pouey
patent: 4747678 (1988-05-01), Shafer et al.
patent: 4773756 (1988-09-01), Blechinger
patent: 4832426 (1989-05-01), Kaser
patent: 5159492 (1992-10-01), Hayashi
patent: 5285255 (1994-02-01), Baranne et al.
patent: 5815261 (1998-09-01), Brooks et al.
patent: 5822073 (1998-10-01), Yee et al.
patent: 6101034 (2000-08-01), Cox et al.
patent: 62-27681 (1987-06-01), None
patent: 63-46371 (1988-09-01), None
patent: 6-26986 (1994-02-01), None
Evans F. L.
Geisel Kara
Wenderoth , Lind & Ponack, L.L.P.
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