Patent Application
20120243000
The present invention relates to a shape measurement method and a shape measurement apparatus which are based on optical interferometry with a high resolution.
A shape measurement apparatus based on optical interferometry is shown in
The signal light 604 enters the measurement object 605 via a light scanning optical system 600, and reflected off the measurement object 605. A specific example of the light scanning optical system 600 is an objective lens. The light scanning optical system 600 scans the signal light 604 entering the measurement object 605 in a prescribed direction. The reflected light from the movable reference mirror 607 and the reflected light from the measurement object 605 interfere with each other, to form interfering light. By detecting the interfering light with a detecting means 609 via a lens 608, information on the measurement object 605 is measured.
By the scanning in the axial direction of the incident light on the measurement object 605 from the movable reference mirror 607, the intensity data of the interfering light is successively acquired via a spectroscope 621 and an A/D converter 622. Then, based on the intensity data of the interfering light, a data arithmetical processing unit 623 made up of a PC (personal computer) structures a three dimensional image.
By scanning the signal light 604 entering the measurement object 605 in one direction in the plane of the measurement object 605, one-dimensional data can successively be acquired.
In this manner, using the images that can successively be obtained, a two dimensional image can be acquired by the data arithmetical processing unit 623. Further, by scanning the signal light 604 in two directions, a three dimensional image can be acquired by the data arithmetical processing unit 623.
In
However, when the shape measurement based on the optical interferometry is performed by means of the conventional shape measurement apparatus shown in
An object of the present invention is to solve the problem stated above, and to provide a shape measurement method and a shape measurement apparatus that can increase the resolution without introducing any displacement of the wavefront in performing shape measurement based on the optical interferometry.
In order to achieve the object stated above, the present invention is composed of as follows.
A shape measurement method of the present invention is characterized by comprising:
splitting light from a light source into reference light and signal light;
correcting a wavefront of the signal light by a first wavefront correction optical system that is placed on an optical axis of the signal light entering a measurement object, and thereafter, allowing the signal light to enter the measurement Object;
correcting a wavefront of the reference light by a second wavefront correction optical system that is placed on an optical axis of the reference light entering a reference mirror, and thereafter, allowing the reference light to enter the reference mirror; and
detecting interfering light of light being the reference light entering the reference mirror and being reflected off, and light being the signal light entering the measurement object and being reflected off, to measure a shape of the measurement object.
A shape measurement apparatus of the present invention is characterized by comprising:
a light source;
a beam splitter that splits light from the light source into reference light and signal light;
a processor device that detects interfering light of light being the reference light entering a reference mirror and being reflected off, and light being the signal light entering a measurement object and being reflected off, to measure a shape of the measurement object;
a first wavefront correction optical system that is placed on an optical axis of the signal light entering the measurement object, to correct a wavefront on the optical axis; and
a second wavefront correction optical system that is placed on an optical axis of the reference light entering the reference mirror, to correct a wavefront on the optical axis.
In accordance with the present invention, in the shape measurement based on the optical interferometry, with the measurement object-use wavefront correction optical system and the reference mirror-use wavefront correction optical system, the effect of the aberration of the wavefront can be reduced, and the resolution can be increased without introducing any displacement of the wavefront.
These and other aspects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which:
In the following, with reference to the drawings, a description will be given of embodiments of the present invention.
The shape measurement apparatus has: a light source 101; a lens 102; a beam splitter 103; a reference light aberration correction lens 111; a lens (optical system) 90; a movable reference mirror 107; an incident light aberration correction lens 110; an objective lens 91; a condenser lens 108; a detecting means 109; a spectroscope 121; an A/D converter 122; and a data arithmetical processing unit 123. The beam splitter 103 is one example of a splitting means or a splitter member. The data arithmetical processing unit 123 is composed of, e.g., a PC (personal computer) that functions as one example of a processor device. As the light source 101, a laser light source which emits light having a width of, e.g., wavelength λ=1200, 1300, 1400 nm is used.
The light emitted from the light source 101 radiates the beam splitter 103 via the lens 102. The light radiating the beam splitter 103 is spilt by the beam splitter 103 into reference light 106 and signal light 104. The reference light 106 passes through the reference light aberration correction lens 111, and thereafter, the reference light 106 is condensed by the lens 90, to arrive at the movable reference mirror 107. The reference light 106 arrived at the movable reference mirror 107 is reflected off the movable reference mirror 107 toward the beam splitter 103. Hence, the light has reflected off the movable reference mirror 107 returns to the beam splitter 103 via the lens 90 and the reference light aberration correction lens 111.
The movable reference mirror 107 is mechanically shifted by a movable reference mirror driver apparatus 107D in one-dimensional direction. By shifting the movable reference mirror 107, a measurement position in a measurement object 105 in the optical axis direction of the signal light 104 entering the measurement object 105 is defined. Examples of the measurement object 105 may include inside of the human body, the oral cavity, and the like, which are observed by an endoscope or an optical element such as a lens, an endoscope or the like. The reference light 106 is reflected off the beam splitter 103 and the movable reference mirror 107, and thereafter, detected by the detecting means 109 via the beam splitter 103. The movable reference mirror driver apparatus 107D may substantially be structured with, for example, a motor that is driven in forward and reverse rotation directions; a screw shaft fixed to the rotary shaft of the motor; a nut portion that is screwed with the screw shaft and that is coupled to the movable reference mirror 107; and a guide member that guides the movable reference mirror 107 in the optical axis direction so as to linearly advance and retract.
The signal light 104 passes through the incident light aberration correction lens 110, and thereafter, the signal light 104 is condensed by the objective lens 91, to enter the measurement object 105, and then the signal light 104 reflected off the measurement object 105. The signal light 104 reflected off the measurement object 105 passes through the incident light aberration correction lens 110 and the objective lens 91, and is reflected off the beam splitter 103, to be detected by the detecting means 109. The objective lens 91 scans the signal light 104 entering the measurement: object 105 in a prescribed direction.
The reflected light from the movable reference mirror 107 and the reflected light from the measurement object 105 interfere with each other at the beam splitter 103. And the resultant interfering light is condensed at the detecting means 109 through the condenser lens 108. The condensed interfering light is detected by the detecting means 109, and information on the measurement object 105 is measured. As the detecting means 109, a photodetector including indium gallium arsenide that has sensitivity at the wavelengths λ=1200, 1300, 1400 nm is used.
Based on the scanning in the axial direction of the incident light to the measurement object 105 from the movable reference mirror 107, the interfering light is dispersed and acquired by the spectroscope 121. Then, the acquired information on the interfering light is converted analog information to digital information by the A/D converter 122, and intensity data of the interfering light is successively acquired. Based on the successively acquired intensity data of the interfering light, a three dimensional image is structured with the data arithmetical processing unit 123.
By scanning the signal light 104 entering the measurement object 105 in one direction in the plane of the measurement object 105, one-dimensional data can successively be acquired. In order to scan in one direction, for example, a support member (not shown) that supports the measurement object 105 is shifted by a support member driver apparatus 105D in the optical axis direction of the measurement object 105. The support member driver apparatus 105D is similarly structured with the movable reference mirror driver apparatus 107D.
In this manner, using the images that can successively be acquired and performing arithmetical processing with the data arithmetical processing unit 123, a two dimensional image can be acquired. Further, using images that can be acquired by scanning the signal light 104 in two directions and performing arithmetical processing with the data arithmetical processing unit 123, a three dimensional image can be acquired.
In
With reference to
The Abbe number of the collimator lens 201 is Vdc=50.3. The Abbe numbers of the three lenses 202, 203, and 204 of the compound lens are Vd1=35.3, Vd2=45.7, and Vd3=35.3, respectively.
The refractive index of the collimator lens 201 is nc=1.605. The refractive indices of the three lenses 202, 203, and 204 of the compound lens are n1=1.750, n2=1.744, and n3=1.750, respectively.
The focal length of the collimator lens 201 is fc=15.52. The focal lengths of the three lenses 202, 203, and 204 of the compound lens are f1=−8.08, f2=4.35, and f3=−8.08, respectively.
The achromatic condition X1 with the structure of the working example 1 can be expressed by the following formula (Formula 1). The achromatic condition X1 as used herein is a condition for reducing the aberration of the focal lengths of a plurality of wavelengths through a plurality of convex lenses and concave lenses.
X
1=1/fc*Vdc+1/*f1*Vd1+1/f2*Vd2+1/f3*Vd3 (Formula 1)
As the value of the achromatic condition X1 approaches zero, the wavefront aberration becomes smaller. That is, the more the following formula
(X1=0) (Formula 1A)
is approximated, the wavefront aberration becomes smaller. The value of the achromatic condition X1 obtained in the working example 1 is −0.0006. For the purpose of reducing the aberration of the focal lengths of a plurality of wavelengths, the value of the achromatic condition X1 is desirably a value close to zero. Specifically, the value of the achromatic condition X1 is desirably −0.05 or more and +0.05 or less.
The beam diameter condition X2 with the structure of the working example 1 can be expressed by the following formula (Formula 2). The beam diameter condition X2 as used herein is a condition for reducing the wavefront aberration through a plurality of convex lenses and the concave lenses.
X
2=1/f1+1/f2+1/f3 (Formula 2)
As the value of the beam diameter condition X2 approaches zero, the wavefront aberration becomes smaller. That is, the more the following formula
(X2=0) (Formula 2A)
is approximated, the wavefront aberration becomes smaller. The value of the beam diameter condition X2 obtained in the working example 1 is −0.018. For the purpose of reducing the wavefront aberration, the value of the beam diameter condition X2 is desirably a value close to zero. Specifically, the value of the beam diameter condition X2 is desirably −0.05 or more and +0.05 or less.
The color difference reduction condition X3 with the structure of the working example 1 can be expressed by the following formula (Formula 3). The color difference reduction condition X3 as used herein is a condition for reducing the color aberration of high-order of a plurality of wavelengths through a plurality of convex lenses and concave lenses.
X
3
=|f
c
/f
2| (Formula 3)
The color difference reduction condition X3 is desirably 0 or more and 5 or less, such that the curvature of the lens correcting the wavefront (the incident light aberration correction lens 110 or the reference light aberration correction lens 111) does not become too large. The color difference reduction condition X3 obtained in the working example 1 is 3.56. The reason why the color difference reduction condition X3 is desirably 5 or less is that, when the color difference reduction condition X3 exceeds 5, the wavefront aberration becomes great, and the resolution cannot be increased.
(X3≦5) (Formula 3A)
In the first embodiment, use of the incident light aberration correction lens 110 and the reference light aberration correction lens 111 realizes the shape measurement being free of the effect of the wavefront aberration. Here, the incident light aberration correction lens 110 and the reference light aberration correction lens 111 are each structured with one collimator lens 201, the compound lens including the three lenses 202, 203, and 204, and the imaging lens 205.
In other words, with the provision of the incident light aberration correction lens 110 and the reference light aberration correction lens 111 each including the compound lens including the three lenses 202, 203, and 204 whose achromatic condition, beam diameter condition, and color difference reduction condition are optimized, can reduce the effect of the wavefront aberration and correct the wavefront. Thus, the aberration correction optical systems (i.e., the incident light aberration correction lens 110 and the reference light aberration correction lens 111) each structured with the compound lens including the three lenses 202, 203, and 204 can increase the resolution without introducing any displacement of the wavefront.
More specifically any optical system whose incident light aberration correction lens 110 and reference light aberration correction lens 111 satisfy any one of (Formula 1A), (Formula 2A), and (Formula 3A) for the purpose of optimizing the achromatic condition, the beam diameter condition, and the color difference reduction condition can reduce the effect of the wavefront aberration. Further, satisfaction of a plurality of formulas out of (Formula 1A), (Formula 2A), and (Formula 3A) realizes the shape measurement with which the effect of the wavefront aberration is more surely reduced.
It is to be noted that, in a case where the shape measurement apparatus is automatically operated, a control apparatus 100 shown in
With reference to
The Abbe number of the collimator lens 301 is Vdc=50.3. The Abbe numbers of the three lenses 302, 303, and 304 of the compound lens are Vd1=35.3, Vd2=45.7, and Vd3=35.3, respectively.
The refractive index of the collimator lens 301 is nc=1.605. The refractive indices of the three lenses 302, 303, and 304 of the compound lens are n1=1.750, n2=1.744, and n3=1.750, respectively.
The focal length of the collimator lens 301 is fc=15.52. The focal length of the three lenses 302, 303, and 304 of the compound lens are f1=8.08, f2=3.97, and f3=8.08, respectively.
The achromatic condition X1 with the structure of the working example 2 can be expressed by the foregoing (Formula 1). As the value of the achromatic condition X1 approaches zero, the wavefront aberration becomes smaller. That is, the value of the achromatic condition X1 obtained in the working example 2 is −0.0031.
The beam diameter condition X2 with the structure of the working example 2 can be expressed by the foregoing (Formula 2). As the value of the beam diameter condition X2 approaches zero, the wavefront aberration becomes smaller. The value of the beam diameter condition X2 obtained in the working example 2 is −0.0045.
The color difference reduction condition X3 with the structure of the working example 2 can be expressed by the foregoing (Formula 3). The color difference reduction condition X3 is desirably 5 or less, such that the curvature of the lens correcting the wavefront (the incident light aberration correction lens 110 or the reference light aberration correction lens 111) does not become too large. The color difference reduction condition X3 obtained in the working example 2 is 3.91.
In the second embodiment, the incident light aberration correction lens 110 and the reference light aberration correction lens 111 each structured with the above-mentioned the collimator lens 301, the three lenses 302, 303, and 304 of the compound lens, and an imaging lens 305 are used. Use of the structure of the second embodiment realizes the shape measurement with which the effect of the wavefront aberration is reduced. In other words, in the second embodiment, in each of the incident light aberration correction lens 110 and the reference light aberration correction lens 111, the compound lens including the three lenses 302, 303, and 304 whose achromatic condition, beam diameter condition, and color difference reduction condition are optimized are used. With the aberration correction optical systems (i.e., the incident light aberration correction lens 110 and the reference light aberration correction lens 111) each structured with the three lenses 302, 303, and 304 of the compound lens, the effect of the wavefront aberration can be reduced, and the wavefront can be corrected. Thus, the resolution can be increased without introducing any displacement of the wavefront.
More specifically, any optical system whose incident light aberration correction lens 110 and reference light aberration correction lens 111 satisfy any one of (Formula 1A), (Formula 2A), and (Formula 3A) for the purpose of optimizing the achromatic condition, the beam diameter condition, and the color difference reduction condition can reduce the effect of the wavefront aberration. Further, satisfaction of a plurality of formulas out of (Formula 1A), (Formula 2A), and (Formula 3A) can more surely reduce the effect of the wavefront aberration.
With reference to
The Abbe number of the collimator lens 401 is Vdc=50.3. The Abbe numbers of the two lenses 402 and 403 of the compound lens are Vd1=18.9 and Vd2=32.3, respectively.
The refractive index of the collimator lens 401 is nc=1.605. The refractive indices of the two lenses 402 and 403 of the compound lens are n1=1.923 and n2=1.850, respectively. The focal length of the collimator lens 401 is fc=15.52. The focal lengths of the two lenses 402 and 403 of the compound lens are f1=8.77 and f2=9.56, respectively.
The achromatic condition X1 with the structure of the working example 3 can be expressed by the foregoing (Formula 1). As the value of the achromatic condition X1 approaches zero, the wavefront aberration becomes smaller. That is, the value of the achromatic condition X1 in the working example 3 is −0.0015.
The beam diameter condition X2 with the structure of the working example 3 can be expressed by the foregoing (Formula 2). As the value of the beam diameter condition X2 approaches zero, the wavefront aberration becomes The value of the beam diameter condition X2 obtained in the working example 3 is −0.004.
The color difference reduction condition X3 with the structure of the working example 3 can be expressed by the foregoing (Formula 3). The color difference reduction condition X3 is desirably 5 or less, such that the curvature of the lens correcting the wavefront (the incident light aberration correction lens 110 or the reference light aberration correction lens 111) does not become too large. The color difference reduction condition X3 obtained in the working example 3 is 1.77.
In the third embodiment, the incident light aberration correction lens 110 and the reference light aberration correction lens 111 each structured with the above-described the collimator lens 401, the two lenses 402 and 403 of the compound lens, and an imaging lens 405 are used. Use of the structure of the third embodiment realizes the shape measurement with which the effect of the wavefront aberration is reduced. In other words, in the third embodiment, in each of the incident light aberration correction lens 110 and the reference light aberration correction lens 111, the compound lens including the two lenses 402 and 403 whose achromatic condition, beam diameter condition, and color difference reduction condition are optimized are used. With the aberration correction optical systems (i.e., the incident light aberration correction lens 110 and the reference light aberration correction lens 111) each structured with the two lenses 402 and 403 of the compound lens, the effect of the wavefront aberration can be reduced, and the wavefront can be corrected. Thus, the resolution can be increased without introducing any displacement of the wavefront.
More specifically, any optical system whose incident light aberration correction lens 110 and reference light aberration correction lens 111 satisfy any one of (Formula 1A), (Formula 2A), and (Formula 3A) for the purpose of optimizing the achromatic condition, the beam diameter condition, and the color difference reduction condition can reduce the effect of the wavefront aberration. Further, satisfaction of a plurality of formulas out of (Formula 1A), (Formula 2A), and (Formula 3A) can more surely reduce the effect of the wavefront aberration.
Further, in the third embodiment, the compound lens including the two lenses 402 and 403 are structured with lenses smaller in number than the shape measurement apparatus according to the first embodiment and the shape measurement apparatus according to the second embodiment. Hence, with the shape measurement apparatus according to the third embodiment, the material costs when being practiced becomes more inexpensive, and the structure thereof can further be simplified.
By properly combining the arbitrary embodiments of the aforementioned various embodiments, the effects possessed by the embodiments can be produced.
Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.
The shape measurement method and the shape measurement apparatus according to the present invention are a shape measurement method and a shape measurement apparatus that can increase the resolution without introducing displacement of the wavefront, and that are based on optical interferometry with a high resolution. Therefore, they are applicable to industrial process quality control, various modes of measurement, or test apparatuses. Further, the present invention can also be used for vital observation, i.e., as an endoscope or the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-128052 | Jun 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/003044 | 5/31/2011 | WO | 00 | 5/31/2012 |
