Optics: measuring and testing – Plural test
Reexamination Certificate
2000-02-11
2003-07-22
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Plural test
C356S218000
Reexamination Certificate
active
06597439
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical measurement method and an optical measurement apparatus for performing measurement of light which has been emitted from a specimen in response to illumination of the specimen, or has been reflected by or has penetrated through a specimen when the specimen is illuminated, under a condition that background light behaves as background noise. The background light is caused, for example, by room illumination.
2. Description of the Related Art
An optical measurement apparatus performing measurement of light as described above is conventionally known. In such an apparatus, it is not possible to perform precise measurement when light to be measured is incident on an optical detector together with room illumination light and other light from outside as background noise. Therefore, in a conventional technique, the background light is eliminated by an attenuation filter or a spatial filter before the background light is incident on the optical detector, where the attenuation filter attenuates light intensity in a specific wavelength range, and the spatial filter utilizes a pinhole.
Nevertheless, when using the above attenuation filter or spatial filter, it is not possible to separate the light to be measured from the background light when the wavelength range of the background light overlaps the wavelength range of the light to be measured. That is, a portion of the background light is mixed into the light to be measured and the quality of measurement deteriorates.
Alternatively, a technique of shortening an exposure time is proposed. In the technique, the exposure time is made so short, for example, not longer than 100 nsec, that the background light does not affect measurement data. In order to shorten the exposure time to not longer than 100 nsec, a short-pulse light source and a high-speed, high-sensitivity detector (e.g., an image intensifier) are necessary. However, these components are expensive, and therefore increase the manufacturing cost of the measurement apparatus. From the viewpoint of cost reduction, it is not possible to use such expensive components. On the other hand, the exposure time cannot be shortened to less then one micrometer when an inexpensive laser diode and charge-coupled device (CCD) are used. That is, the influence of the background light cannot be eliminated by use of the inexpensive laser diode and charge-coupled device (CCD). Further, even if the laser diode is driven to emit a short-pulse beam and the image intensifier is used for detection, it is not possible to obtain a high peak with a usual operation of driving the laser diode. That is, sufficient exposure energy cannot be supplied to a specimen with the above construction.
SUMMARY OF THE INVENTION
The first object of the present invention is to provide an optical measurement method and an optical measurement apparatus which can perform measurement of light with high accuracy even when the wavelength range of the background light overlaps the wavelength range of the light to be measured, which has been emitted from a specimen, or has been reflected by or has penetrated through a specimen when the specimen is illuminated.
The second object of the present invention is to provide an optical measurement method and an optical measurement apparatus enabling precise measurement of light which has been emitted from a specimen, or has been reflected by or has penetrated through a specimen when the specimen is illuminated, under a plurality of types of background light respectively having a plurality of different periods of cyclic intensity variations.
In order to accomplish the above-mentioned first object, according to the first aspect of the present invention, there is provided an optical measurement method for performing measurement of first light, which has been emitted from or reflected by a specimen, or has penetrated through the specimen, under background light having an intensity which varies cyclically with a period. The method contains steps of: (a) performing a first operation of measuring the first light for a first duration beginning at a first time, while illuminating the specimen with second light, to obtain a first measurement result; (b) performing a second operation of measuring the first light for a second duration having the same length as the first duration and beginning at a second time which is different from the first time by an integer multiple of the above period, while illumination of the specimen is stopped, to obtain a second measurement result; and (c) subtracting the second measurement result from the first measurement result, to obtain a third measurement result which is not affected by the background light.
In order to accomplish the above-mentioned first object, according to the second aspect of the present invention, there is provided an optical measurement apparatus for performing measurement of first light, which has been emitted from or reflected by a specimen, or has penetrated through the specimen, under background light having intensity which varies cyclically with a period. The apparatus contains a first measurement unit which performs a first operation of measuring the first light while illuminating the specimen by second light, to obtain a first measurement result; a second measurement unit which performs a second operation of measuring the first light while illumination of the specimen is stopped, to obtain a second measurement result; a control unit which controls timing of the operations of the first and second measurement units so that the first operation is performed for a first duration beginning at a first time, and the second operation is performed for a second duration having the same length as the first duration and beginning at a second time which is different from the first time by an integer multiple of the above period; and a calculation unit which obtains a third measurement result, which is not affected by the background light, by subtracting the second measurement result from the first measurement result.
According to the first and second aspects of the present invention, the difference between the beginning times of the first and second operations of measuring the first light is an integer multiple of the period of the cyclic variation of the intensity of the background light, and the first and second operations are performed for the same length of time. Since the specimen is not illuminated with the second light during the second operation, it is considered that an amount of influence by the background light included in the first measurement result of the first operation will be the same as the amount of the second measurement result of the second operation. Therefore, it is expected that the amount of influence by the background light included in the first measurement result of the first operation will be removed by subtracting the amount of the second measurement result of the second operation from the amount of the first result of the first operation. Thus, a final (third) measurement result can be obtained with high accuracy even when the wavelength range of the background light overlaps the wavelength range of the light to be measured, which has been emitted from a specimen in response to illumination of the specimen, or has been reflected by or has penetrated through a specimen when the specimen is illuminated.
In order to accomplish the above-mentioned first object, according to the third aspect of the present invention, there is provided an optical measurement method for performing measurement of first light, which has been emitted from or reflected by a specimen, or has penetrated through the specimen, under background light having an intensity which varies cyclically with a period. The method contains steps of: (a) performing a first operation of measuring the first light for a first duration having a length equal to an integer multiple of the above period, while illuminating the specimen by second light, to obtain a first measurement resu
Font Frank G.
Punnoose Roy M.
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