JP3763985B2 - Shearing interferometer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a shearing interference measuring apparatus that three-dimensionally measures a transmitted wavefront of an optical element such as a plastic lens by analyzing shearing interference fringes.
[0002]
[Prior art]
In recent years, molded articles made of plastic materials have become widespread as optical lenses used in optical devices such as laser printers and cameras, and other optical elements. Such plastic molded lenses are superior in aspherical lens manufacturability and inexpensive compared to glass polished lenses, but the refractive index distribution in production is unstable and non-uniformity occurs inside the lens. There are many. The non-uniformity of the refractive index inside the lens greatly affects the optical characteristics, causing image quality and resolution degradation. For this reason, it is necessary to measure the refractive index distribution inside the optical lens with high accuracy and evaluate the homogeneity of the optical lens.
[0003]
There are various methods for measuring the refractive index of such an optical lens, and one of them is a method using shearing interference fringes. For example, according to Japanese Patent Application Laid-Open No. 9-257591, shearing is performed by dividing a laser beam that has passed through a test object and superimposing it slightly shifted in order to measure the refractive index distribution of a plastic material having a refractive index distribution. The transmitted wavefront of the test object is measured by forming an interference fringe and measuring the shearing interference fringe.
[0004]
Here, the entire configuration of the shearing interferometer disclosed in Japanese Patent Application Laid-Open No. 9-257591 is omitted (see FIG. 2 in the same publication), but the shearing generator used in this shearing interferometer is not shown. A configuration example is shown in FIG. The shearing generator 1 is composed of a pair of parallel plates 2 and 3 disposed on the optical path after the coherent light beam emitted from the light source device passes through the test object. These parallel flat plates 2 and 3 are made to face each other in parallel and at a predetermined interval d, and the inner surfaces facing each other are formed as polished surfaces with high surface accuracy, and the first reflecting surface 2a and the second reflecting surface are formed. A surface 3a is provided on the outer surface side, and non-reflective surfaces 2b and 3b are provided.
[0005]
With such a configuration, a part of the test wave a that has passed through the test object is reflected by the first reflecting surface 2 a of the parallel plate 2, and the remaining part of the test wave a that has passed through the parallel plate 2 is transmitted. The part is reflected by the second reflecting surface 3 a of the parallel plate 3, returns to the first reflecting surface 2 a side, and passes through the parallel plate 2 while being refracted. A part of the detected wave a reflected by the first reflecting surface 2a of the parallel plate 2 and a remaining part of the detected wave a reflected by the second reflecting surface 3a of the parallel plate 3 are the shearing generator 1 Are injected parallel to each other. The test wave a that has passed in this manner is divided into two optical paths whose optical paths are divided by the shearing generator 1 and are superimposed with a lateral shift amount proportional to the distance d between the first and second reflecting surfaces 2a and 3a. It becomes a test wave and shearing interference occurs.
[0006]
[Problems to be solved by the invention]
The refractive index distribution of the test object is calculated by measuring the shearing interference fringes. At this time, the value of the distance d between the first and second reflecting surfaces 2a and 3a in the parallel plates 2 and 3 is required. For this reason, if the distance d between the reflecting surfaces 2a and 3a is set accurately or the distance d cannot be measured accurately, a highly accurate refractive index distribution cannot be obtained. Furthermore, in order to generate shearing interference fringes efficiently, the distance d between the first and second reflecting surfaces 2a and 3a in the parallel plates 2 and 3 must be set to a very small distance of several tens of μm to 100 μm. In general, it is very difficult to accurately measure such a minute surface interval. However, in the above-mentioned publication, there is no mention of accurately measuring such a minute surface interval.
[0007]
Therefore, the present invention can measure a minute interval between the first and second reflecting surfaces of a pair of parallel plates for forming a shearing interference fringe close to each other with high accuracy, and transmits the transmitted wavefront of the test object. It is an object of the present invention to provide a shearing interference measuring apparatus capable of obtaining a high accuracy.
[0008]
[Means for Solving the Problems]
According to the first aspect of the present invention, the first reflecting surface and the first reflecting surface by the inner surfaces of a pair of closely opposed parallel plates capable of moving the coherent test wave emitted from the light source device and passing through the test object in the optical axis direction. A shearing generator that forms a shearing interference fringe by separating and reflecting the two light beams separated from each other and superimposing the separated and reflected light beams slightly, and measuring the shearing interference fringes formed by the shearing generator. In the shearing interferometer for measuring the transmitted wavefront of the test object, the distance between the first and second reflecting surfaces in the parallel plate is measured in a non-contact manner, and in the vicinity of the first reflecting surface and Bei position in the same plane, the second reflecting surface interval measurement means for chromatic said parallel flat plate fixed knife edge as near and by each position on the position in the same plane facing each other of That.
[0009]
Therefore, by measuring the distance between the first and second reflecting surfaces in the parallel plate in a non-contact manner by the distance measuring means, the parallel plate is not distorted, deformed, or scratched. The interval between them can always be measured with high accuracy, and the transmitted wavefront of the test object can be obtained with high accuracy . Further, since the distance between the first and second reflecting surfaces always appears equivalent to the distance between the knife edges, the distance measurement means and the first and first parallel plates are measured by measuring the distance between the knife edges. It is possible to measure the distance between the first and second reflecting surfaces with high accuracy even if the parallelism with the second reflecting surface is slightly shifted, and to obtain the transmitted wavefront of the test object with high accuracy. Can do .
[0010]
According to a second aspect of the present invention, in the shearing interference measuring apparatus according to the first aspect, the interval measuring unit is an optical measuring unit using an image sensor in which read pixels are arranged in the interval direction.
[0011]
Therefore, in realizing the invention of claim 1, by using an optical measuring means using an image sensor such as a CCD as the non-contact distance measuring means, the distance between the first and second reflecting surfaces can be reduced to μm. It is possible to measure with high accuracy up to the level, and to obtain the transmitted wavefront of the test object with high accuracy.
[0012]
According to a third aspect of the present invention, in the shearing interference measuring apparatus according to the first aspect, the interval measuring unit causes the laser light source and a light beam emitted from the laser light source to pass through the interval portion of the shearing generation unit. Deflection scanning means for deflecting and scanning, condensing means for condensing the light beam deflected and scanned by the deflection scanning means, and detecting the light beam collected by the condensing means and converting it into an electrical signal Conversion means.
[0013]
Therefore, in order to realize the invention according to claim 1, by using a non-contact distance measuring means of a laser beam scanning system using a deflection scanning means or the like, the distance between the first and second reflecting surfaces is obtained. Can be measured with high accuracy down to the μm level, and the transmitted wavefront of the test object can be obtained with high accuracy.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
A first embodiment of the present invention will be described with reference to FIGS. In the present embodiment, for example, the shearing generator 1 as shown in FIG. 16 is almost used as it is (see FIG. 2), and the same parts as those shown in FIG. Accordingly, the shearing interferometer itself may be an interferometer as disclosed in Japanese Patent Laid-Open No. 9-257591, for example.
[0031]
FIG. 1 is a perspective view showing the external configuration of the shearing generator 1, and here, the configuration of an embodiment described later is also shown.
[0032]
In FIG. 2 showing a side view of the shearing generator 1, the laser beam (test wave a) that has passed through the test object (not shown) and entered from the left side of the paper passes through the non-reflecting surface 2b of the parallel plate 2. Incident. Thereafter, a part of the light is reflected by the first reflecting surface 2 a of the parallel plate 2 and at the same time, a part of the light passes and is reflected by the second reflecting surface 3 a of the parallel plate 3. These reflected lights again pass through the parallel plates 2 and 3 and are emitted from the shearing generator 1. At this time, since the first and second reflecting surfaces 2a and 3a are separated by a distance d, the two parallel lights are in a slight distance proportional to the distance d in the direction perpendicular to the optical axis (the lateral direction of the paper). Are only shifted in parallel. For this reason, the two light beams overlap and interfere with each other, generating a shearing interference fringe. By measuring the shearing interference fringes, the transmitted wavefront of the test object can be known. At this time, since the transmitted wavefront is calculated using the value of the interval d, it is necessary to accurately know the value of the interval d in order to accurately know the transmitted wavefront.
[0033]
Therefore, in the present embodiment, the laser deflection scanning measuring means 4 is provided as an interval measuring means for measuring the interval d with respect to the shearing generator 1 in a non-contact manner.
[0034]
The principle of measurement by the laser deflection scanning measuring means 4 will be described with reference to FIG. In FIG. 3, a light beam emitted from a laser light source 5 rotates at high speed in synchronization with a clock pulse, and is scanned by a polygon mirror 6 which constitutes a deflection scanning means together with a polygon motor or the like, and at the same time is converted into a parallel beam by a collimator lens 7. The measured object 8 is deflected and scanned. In FIG. 3, the measurement object 8 is two objects 8A and 8B having a distance d, and the light not blocked by these objects 8A and 8B is converted into a conversion means by a condenser lens 9 as a condenser means. The light beam guided to the light receiving element 10 and received by the light receiving element 10 is detected and converted into an electric signal of voltage. The distance d between the objects 8A and 8B can be measured by measuring the generated voltage and the clock pulse for the polygon motor. In this measurement method, the distance of the gap d can be measured on the order of 1 μm or less by accurate rotation of the polygon motor and accurate measurement of the clock pulse. This is sufficiently accurate to measure the distance d between the first and second reflecting surfaces 2a and 3a of the parallel plates 2 and 3.
[0035]
Therefore, it can be seen that the distance d between the first and second reflecting surfaces 2a and 3a can be accurately measured by applying the measurement object 8 to the parallel plates 2 and 3 as shown in FIG. Further, according to the laser deflection scanning measuring means 4 of this embodiment, since it is a non-contact distance measuring means that does not contact the parallel plates 2 and 3 at all, scratches, deformations, etc. occur on the surfaces of the parallel plates 2 and 3. Therefore, it is possible to prevent the occurrence of a measurement error factor and to measure with high accuracy since there is no actual deformation.
[0036]
A second embodiment of the present invention will be described with reference to FIGS. 1 and 5 to 9. The same parts as those shown in the first embodiment are denoted by the same reference numerals, and description thereof is omitted (the same applies to the following embodiments). In the present embodiment, even when the positional relationship between the laser deflection scanning measuring means 4 as the interval measuring means and the parallel plates 2 and 3 is shifted in the θ direction (rotating direction) as shown in FIG. It is configured. First, a problem when such a shift occurs will be described with reference to FIG. When the positional relationship between the laser deflection scanning measuring means 4 and the parallel flat plates 2 and 3 is shifted in the θ direction (rotation direction) as shown in FIG. 5, the parallel beam by the collimating lens 7 is clear from FIG. Since the first and second reflecting surfaces 2a and 3a are not parallel (that is, in the optical axis direction of the laser deflection scanning measuring means 4), the distance d between the first and second reflecting surfaces 2a and 3a is measured. An error will occur in the value. Here, it is very important to accurately set the distance d between these parallel plates 2 and 3, but at the same time, how to keep them parallel is also important. For this reason, such a shearing interferometer is provided with a parallelism adjusting mechanism that adjusts the parallelism between the parallel plates 2 and 3, although not particularly illustrated. Therefore, when adjusting the parallelism between the parallel plates 2 and 3 by the parallelism adjusting mechanism, the situation shown in FIG. 5 can naturally occur. Another problem is that the value of the interval d cannot be accurately grasped. This is presumably because the parallel plates 2 and 3 (first and second reflecting surfaces 2 a and 3 a) have a width with respect to the optical axis direction of the laser deflection scanning measuring means 4.
[0037]
Therefore, in the present embodiment, a pair of knife edges, that is, members having no width with respect to the optical axis direction are placed at positions equivalent to the first and second reflecting surfaces 2a and 3a in the parallel plates 2 and 3. They are placed opposite to each other, and the distance between these members is measured by the laser deflection scanning measuring means 4 based on the principle described above. Then, by setting this as the distance d between the first and second reflecting surfaces 2a and 3a, this distance d can be obtained accurately, and at the same time, an error occurs even in a tilted situation as shown in FIG. There is no.
[0038]
FIG. 6 is a principle diagram for explaining this mechanism. That is, the pair of knife edges 11 and 12 are installed so that the front edge side thereof is flush with the first and second reflecting surfaces 2a and 3a, and the distance between the edges of the knife edges 11 and 12 is measured by laser deflection scanning measuring means. 4 is measured.
[0039]
FIG. 1 also shows a state in which these knife edges 11 and 12 are fixedly attached to holders 13 and 14 that actually hold the periphery of the parallel plates 2 and 3. That is, the knife edges 11 and 12 are positioned at positions near the first reflecting surface 2a and in the same plane and positions near the second reflecting surface 3a and in the same plane via the holders 13 and 14, respectively. And are fixed to the parallel flat plates 2 and 3 so as to face each other.
[0040]
More detailed arrangement examples are shown in FIGS. 7 is a side view seen in the direction of arrow A in FIG. 1, FIG. 8 is a plan view seen in the direction of arrow B in FIG. 1, and these knife edges 11 and 12 are in the optical axis direction of the laser deflection scanning measuring means 4. Has no width (see FIG. 8), but has a slight width in a direction perpendicular to the width (see FIG. 7).
[0041]
According to such a configuration, as shown in FIG. 9, the optical axis direction of the laser deflection scanning measuring means 4 and the first and second reflecting surfaces 2a and 3a of the parallel plates 2 and 3 are in the θ direction (rotation direction). Even when there is a deviation, the distance d between the first and second reflecting surfaces 2a, 3a always appears equivalent to the distance between the knife edges 11, 12, so that the distance between the edges of the knife edges 11, 12 is measured by laser deflection scanning. By measuring by means 4, the distance d between the first and second reflecting surfaces 2a, 3a can be accurately measured.
[0042]
A third embodiment of the present invention will be described with reference to FIG. In the present embodiment, an optical measuring means 16 using a one-dimensional CCD 15 as an image sensor is used as an interval measuring means for measuring the interval d with respect to the shearing generator 1 in a non-contact manner. As this optical measuring means 16, if the one-dimensional CCD 15 is used instead of the light receiving element 10, the laser deflection scanning measuring means 4 can be used as it is. The one-dimensional CCD 15 has reading pixels arranged in the direction d between the first and second reflecting surfaces 2a and 3a.
[0043]
According to the present embodiment, the reading pixels of the one-dimensional CCD 15 are generally several μm in size, but the images of the knife edges 11 and 12 (that is, the first and second reflecting surfaces 2a) are collected by the condenser lens 9. , 3a) is magnified and formed on the one-dimensional CCD 15, and the distance d can be measured with an accuracy of 1 μm or less.
[0044]
A fourth embodiment of the present invention will be described based on FIG. 1, FIG. 11, and FIG. First, as shown in FIG. 1, the holders 13 and 14 are separately provided with drive stages 17 and 18 for moving the parallel plates 2 and 3 in the thickness direction (that is, in the direction of contact and separation), respectively. . The drive stage 17 provided for the holder 13 functions as a first drive mechanism, and is used to move the parallel plate 2 when measuring shearing interference fringes. The drive is performed on the order of several tens of nm. Is called. Therefore, a high-precision drive actuator such as a piezoelectric element is used as the drive actuator of the drive stage 17. Such a high-precision drive actuator has a high drive resolution, but the drive distance that can be sent with a full stroke is at most several hundred μm.
[0045]
On the other hand, the drive stage 18 provided for the holder 14 functions as a second drive mechanism, and is used to move the parallel plate 3 in order to adjust the parallelism between the parallel plates 2 and 3. Is performed on the order of several tens of μm. That is, the drive stage 18 is mainly used for the purpose of separating the parallel plates 2 and 3 to a large distance of about several millimeters. At this time, although not shown in particular, the parallelism of the parallel plates 2 and 3 is adjusted by the angle adjusting actuators housed in the holders 13 and 14 in order to measure the shearing interference fringes. After this adjustment, the parallel flat plate 3 is moved using the drive stage 18 to bring the first and second reflecting surfaces 2a and 3a closer to the optimum distance d for measuring shearing interference fringes. Thus, by dividing the drive stages 17 and 18 into two units for measuring the shearing interference fringes and for adjusting the parallelism of the parallel plates 2 and 3, the drive stage 17 for measuring the shearing interference fringes provides the shearing interference fringes. It is possible to use an interference fringe having the optimum resolution and accuracy, and the measurement accuracy is improved. The two drive stages 17 and 18 are attached to the holders 13 and 14, respectively, so that the two drive stages are never attached to the same holder. This is because, when the two drive stages 17 and 18 are attached to the same holder, when the high-precision drive stage 17 is driven, vibration due to feed screw rattle existing in the drive stage 18 or insufficient rigidity of the guide is generated. This is because it is likely to occur and the driving accuracy of the driving stage 17 may be impaired.
[0046]
After adjusting the parallelism of the parallel plates 2 and 3, the drive stage 17 is used to approach the optimum position for measuring shearing interference fringes. This distance is as small as several tens of μm to 100 μm. For this reason, there is a possibility that the parallel plates 2 and 3 collide when some abnormality occurs in the controller that controls the drive stage 17. By colliding, the parallel plates 2 and 3 are damaged, and the measurement accuracy is lowered.
[0047]
In this regard, in the present embodiment, as shown in FIGS. 11 and 12, a thin ring-shaped member 19 that is a restricting member is provided as a spacer between the parallel plates 2 and 3. The ring-shaped member 19 is for restricting the distance between the first and second reflecting surfaces 2a, 3a to a certain value or more, specifically, to the thickness of the ring-shaped member 19 or more. The ring-shaped member 19 is provided by being fixed to the inner surface side of either one of the parallel plates 2 and 3 by adhesion or the like. However, the ring-shaped member 19 has a ring shape and a light beam passes through the central portion, so that it does not affect the formation of shearing interference fringes. . By interposing such a ring-shaped member 19, the parallel flat plates 2, 3 do not collide directly (d> d ′) even if the drive stage 17 is abnormally driven (d> d ′). Measurement accuracy is not reduced by scratching.
[0048]
A fifth embodiment of the present invention will be described with reference to FIGS. In the present embodiment, a minimum interval adjusting mechanism 20 for defining a minimum interval between the first and second reflecting surfaces 2a and 3a is added to the shearing generator 1. The minimum distance adjusting mechanism 20 is mainly composed of, for example, a plurality of adjusting screws 21 which are provided in one holder 14 so as to be able to advance and retreat in the thickness direction and whose distance d ′ between the opposing surfaces of the other holder 13 is variable. Has been.
[0049]
In such a configuration, by adjusting the protruding length of the adjusting screw 21 and adjusting the distance d ′ between the tip of the adjusting screw 21 and the opposing surface of the holder 13 that opposes, it is set so that d> d ′. Even when the parallel plates 2 and 3 are closest to each other, the adjustment screw 21 is in contact with the opposing surface of the holder 13 so that the minimum distance d-d '> 0 can be maintained at least, and the parallel plates 2 and 3 are in contact with each other. Can be prevented. Here, the minimum value of the distance d between the first and second reflecting surfaces 2a and 3a is as small as several tens of μm. However, if the protruding length of the adjusting screw 21 is finely adjusted, the collision of the parallel plates 2 and 3 will be reduced. The distance d can be reduced to an ideal value while avoiding danger.
[0050]
A sixth embodiment of the present invention will be described with reference to FIGS. In the present embodiment, a minimum interval detection mechanism 22 is added to detect when the interval between the first and second reflecting surfaces 2a and 3a approaches the minimum interval with respect to the shearing generator 1. . The minimum interval detection mechanism 22 is of a photo interrupter type, and is, for example, a sensor unit 23 fixed to the holder 13 holding the parallel plate 2 and disposed at a predetermined position, and a holder 14 holding the parallel plate 3. It is comprised by the light-shielding plate 24 by the thin plate fixed to the side and advancing / retreating with respect to the sensor part 23 with the movement of the holder 14. FIG. As is well known, the sensor unit 23 is formed in an upward U-shape, and the light emitting diode 25 and the light receiving element 26 are arranged to face each other. The sensor unit 23 detects the intermittent light beam between the light emitting diode 25 and the light receiving element 26 by the light shielding plate 24. Is. FIG. 15A shows a state in which a voltage corresponding to the amount of light received can be generated in the light receiving element 26 because the light shielding plate 24 does not enter the sensor unit 23 and the light emitting diode 25 and the light receiving element 26 are not shielded from light. FIG. 15B shows a state in which the light shielding plate 24 enters the sensor unit 23 and shields between the light emitting diode 25 and the light receiving element 26 so that no light reaches the light receiving element 26 and no output voltage is generated. .
[0051]
Therefore, by arranging the sensor unit 23 so that the position where such a voltage change can occur in the light receiving element 26 is the boundary line 27 shown in FIG. 14 corresponding to the minimum interval, the parallel plate 2 or 3 is moved in the approaching direction by the drive stage 17 or 18, it can be detected that it has moved to a position that becomes the minimum interval, and the drive stage 17 or 18 is stopped at that position, thereby Collisions can be avoided.
[0052]
【The invention's effect】
According to the first aspect of the present invention, since the distance between the first and second reflecting surfaces in the parallel plate is measured by the non-contact method by the distance measuring means, the parallel plate may be distorted or deformed. Without being scratched, the distance between the two can always be measured with high accuracy, and the transmitted wavefront of the test object can be determined with high accuracy . Further, since the distance between the first and second reflecting surfaces always appears equivalent to the distance between the knife edges, the distance between the knife edges is measured by the distance measuring means, so that the distance between the distance measuring means and the parallel plate is measured. Even if the parallelism with the first and second reflecting surfaces is slightly deviated, the distance between the first and second reflecting surfaces can be measured with high accuracy, and the transmitted wavefront of the test object can be measured with high accuracy. Can be requested .
[0053]
According to the second aspect of the present invention, in order to realize the first aspect of the invention, by using an optical measuring means using an image sensor such as a CCD as the non-contact distance measuring means, Therefore, it is possible to measure the distance between the reflecting surfaces to a micrometer level with high accuracy and to obtain the transmitted wavefront of the test object with high accuracy.
[0054]
According to the third aspect of the present invention, in order to realize the first aspect of the invention, the non-contact distance measuring means is a first laser beam scanning type using a deflection scanning means or the like. , 2 can be measured with high accuracy up to the μm level, and the transmitted wavefront of the test object can be obtained with high accuracy.
[Brief description of the drawings]
FIG. 1 is a perspective view showing embodiments of the present invention together.
FIG. 2 is a side view showing a shearing generator according to the first embodiment of the present invention.
FIG. 3 is a side view showing the interval measurement principle.
FIG. 4 is a side view showing a configuration example of laser deflection scanning measurement means.
FIG. 5 is a side view for explaining a second embodiment of the present invention.
FIG. 6 is a side view showing a configuration example of a second embodiment of the present invention.
FIG. 7 is a side view showing the knife edge arrangement.
FIG. 8 is a plan view thereof.
FIG. 9 is a side view showing an example of a measurement state.
FIG. 10 is a side view showing a third embodiment of the present invention.
FIG. 11 is an exploded perspective view showing a fourth embodiment of the present invention.
FIG. 12 is a side view thereof.
FIG. 13 is a side view showing a fifth embodiment of the present invention.
FIG. 14 is a side view showing a sixth embodiment of the present invention.
FIG. 15 is a perspective view showing the configuration and operation of the sensor unit.
FIG. 16 is a side view showing a configuration example of a shearing generator described in the publication.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Shearing generation | occurrence | production part 2 Parallel plate 2a 1st reflective surface 3 Parallel plate 3a 2nd reflective surface 4 Space | interval measurement means 5 Laser light source 6 Deflection scanning means 9 Condensing means 10 Conversion means 11, 12 Knife edge 15 Image sensor 16 Optical Type measuring means 17 first driving mechanism 18 second driving mechanism 19 regulating member, ring-shaped member 20 minimum interval adjusting mechanism 22 minimum interval detecting mechanism

Claims (3)

A coherent test wave emitted from the light source device and passing through the test object is separated and reflected by the first reflection surface and the second reflection surface by the inner surfaces of a pair of closely opposed parallel plates capable of moving in the optical axis direction. And a shearing generator that forms a shearing interference fringe by superimposing the separated and reflected light beams slightly shifted and measuring the shearing interference fringe formed by the shearing generator. In a shearing interferometer that measures the transmitted wavefront,
The distance between the first and second reflecting surfaces in the parallel plate is measured in a non-contact manner, and is located in the vicinity of the first reflecting surface and in the same plane, and in the vicinity of the second reflecting surface and in the same plane. A shearing interference measuring apparatus comprising: a distance measuring means having knife edges fixed to the parallel plates so as to be opposed to each other at the positions.   2. The shearing interference measuring apparatus according to claim 1, wherein the interval measuring unit is an optical measuring unit using an image sensor in which read pixels are arranged in the interval direction.   The interval measuring means includes a laser light source, deflection scanning means for deflecting and scanning a light beam emitted from the laser light source so as to pass through the interval portion of the shearing generation unit, and scanning and deflecting by the deflection scanning means. 2. The shearing interference measurement according to claim 1, further comprising: condensing means for condensing the light beam that has passed through the portion; and conversion means for detecting the light beam condensed by the condensing means and converting it into an electrical signal. apparatus.

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