JP3318965B2 - Hologram interferometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hologram interferometer for measuring the state of the surface of an object to be measured.

[0002]

2. Description of the Related Art An interferometer is used to precisely measure the surface shape of a lens or other object to be measured in a non-contact manner. As a typical example of this interferometer, there is a Fizeau-type interferometer as shown in FIG.

In FIG. 1, reference numeral 1 denotes an interferometer main body. The interferometer main body 1 has a main body casing 1a and a tubular body 1b vertically suspended from a lower surface of the main body casing 1a.
The main body casing 1a has He-N parallel to the cylindrical body 1b.
The laser light source 2 made of e-laser or the like is attached. A reflection mirror 3, a condenser lens 4, and a pinhole 5 are provided in the main body housing 1a. The laser beam from the laser light source 2 is bent 90 ° by the reflection mirror 3, passes through the diverging lens 4, and passes through the diverging lens 4. After diverging after passing through the pinhole 5 disposed at the light condensing position of No. 4 and widening the spot diameter, the light is reflected by the beam splitter 6 and turned again by 90 °, so that the cylindrical body 1
The laser beam travels from the laser light source 2 in the direction opposite to the emission direction along the axial direction of b, is converted into a parallel light beam by the collimator lens 7, and is incident on the reference lens 8 provided in front of the collimator lens.

The reference lens 8 has a surface opposite to the entrance surface 8a serving as a reference surface 8b having, for example, a spherical shape, and the entrance surface 8a is coated with an antireflection coating. A part of the laser beam incident on the reference lens 8 is reflected by the reference surface 8b, and most of the laser beam passes through the reference lens 8 and is transmitted to the surface 9a of the lens 9 to be measured which is set in front of the lens. The light is incident and a part of the light is reflected by the surface 9a to be detected. Then, the reflected light from the test surface 9a and the reflected light from the reference surface 8b of the reference lens 8 interfere with each other to generate interference fringes.
The reflected light having the interference fringes is transmitted to the collimator lens 7.
Then, the light passes through the beam splitter 6 and is incident on the imaging unit 12 via the screen 10 and the interference fringe imaging lens 11, and the imaging unit 12 captures the interference fringe.
The video can be displayed on a monitor device.

In recent years, a hologram interferometer for measuring the surface state of a test object by using a computer-generated hologram has been put to practical use. The computer-generated hologram was obtained by applying a photoresist film on a glass substrate and scanning the photoresist film with an electron beam, thereby exposing an interference fringe pattern equivalent to the interference fringe between the object wave and the reference wave. Then, the optical element is developed to develop interference fringes. When the same reproduction wave as the reference wave enters the interference fringes in the hologram optical element, the object wave can be reproduced. According to the interferometry using this hologram, inspection and measurement of a special shape are possible, so that it is expected to be widely used in the future.

In addition, various interferometers other than those described above are known, and these various interferometers form a laser light source, an optical system for transmitting light, and interference fringes according to the type and use of each interferometer. It is manufactured as an apparatus incorporating various members necessary for constructing an interferometer, such as a means for causing the interference and a means for observing interference fringes.

[0007]

By the way, the present applicant has developed a hologram interferometer having a structure shown in FIG. 9 as a kind of the hologram interferometer. In the figure, reference numeral 20 denotes a laser light source, and a laser beam is emitted from the laser light source 20 to a beam splitter 23 via a diverging lens 21 and a pinhole 22 and reflected by the beam splitter 23 to bend the optical path by 90 °. Is done. The laser beam that diverges after passing through the pinhole 22 disposed at the converging position of the diverging lens 21 is reflected by the beam splitter 23, is converted into a parallel beam by the collimator lens 24, and is incident on the hologram optical element 25. . When a laser beam is incident on the hologram optical element 25, the laser beam is divided into regular reflected light and diffracted light. In the optical path of the regular reflection light, a reference reflection plate 26 having a reference reflection surface 26a perpendicular to the regular reflection light is provided.

On the other hand, a test object 27 is arranged on the optical path of the diffracted light. Here, assuming that the test object 27 is a cylindrical lens, the hologram pattern of the hologram optical element 25 is a stripe pattern arranged in parallel straight lines.
Then, the direction of the stripes of the hologram optical element 25 is directed to the generatrix direction of the cylindrical surface 27a of the test object 27, and the hologram optical element 25 is arranged at a position where the diffracted light is focused on the central axis.

A laser beam from a laser light source 20 passes through a diverging lens 21 and a pinhole 22 constituting a light transmitting optical system, is reflected by a beam splitter 23, and is converted into a parallel beam by a collimator lens 24. Is incident on the hologram optical element 25. Then, the diffracted light emitted from the hologram optical element 25 is once condensed at a position on the central axis of the cylindrical surface 27a of the test object 27, then diverges, and irradiates the cylindrical surface 27a.
The light is reflected by the cylindrical surface 27a and returns to the hologram optical element 25. The return light from the test object 27 is reflected by the hologram optical element 25 and returns to the collimator lens 24 as original parallel light. On the other hand, the specularly reflected light from the hologram optical element 25 is applied to the reference reflection surface 26 of the reference reflection plate 26.
The reflected light is reflected by the hologram optical element 25, and the reflected light returns to the collimator lens 24.

Therefore, the object wave light in the pattern by the hologram optical element 25 overlaps with the reference wave light from the reference reflection plate 26 and interferes with each other to form interference fringes. This light passes through the beam splitter 23, and forms an interference fringe on the image forming surface of the imaging unit 29 via the image forming lens 28 provided at the rear focal position of the collimator lens 24.

Since the hologram optical element 25 converts the plane wave into an aspherical wave corresponding to the cylindrical surface 27a by the action of the hologram optical element 25, the interference fringes are generated as a result of interference between the parallel lights. An extremely clear interference fringe pattern is imaged by the imaging means 29. Therefore, the test object 2
7, the shape of the cylindrical surface 27a can be measured with extremely high accuracy.

The hologram interferometer having the above configuration is
In general, it is constructed as one device which assembles the whole including a laser light source, a light transmitting optical system, interference fringe forming means and interference fringe observing means.

By the way, compared with the case where all the various members constituting the optical device including the interferometer are assembled to form one device, the constituent members are divided into a plurality of units, and these units are combined. It is often advantageous to configure the device as a device having predetermined functions and uses in terms of the mass production effect of the common members and the convenience of maintenance such as repair, inspection, and replacement of parts.

Here, the hologram interferometer shown in FIG. 9 and the hologram interferometer shown in FIG.
Comparing with the Fizeau interferometer, the laser light source and the optical system for transmitting the light from the laser light from the laser light source to a collimator lens through a beam splitter and a collimator lens among the configurations of the two devices are as follows. Substantially the same structure can be used, and the image forming lens and the image pickup means forming the interference fringe observation system can also have the same structure. If common members can be shared, a part of the device configuration can be made versatile.

The present invention has been made on the basis of the above findings, and has as its object to enable the sharing of some components constituting the hologram interferometer apparatus. It is.

[0016]

In order to achieve the above-mentioned object, a laser light source device for converting a laser beam from a laser light source into a parallel light beam and an interferometer main body are provided. A first reflecting mirror for reflecting the laser beam transmitted from the device, a second reflecting mirror for reflecting the reflected light from the first reflecting mirror again, and the second reflecting mirror facing at a predetermined angle A hologram optical element disposed at a position, a sample table provided at a light receiving position of the diffracted light by the hologram optical element, and a sample table on which a test object is set, and a light receiving position of the regular reflection light from the hologram optical element. And a reference reflector provided.

[0017]

Generally, when an interferometer is used to inspect the surface condition of a test object having a certain size, the interferometer irradiates the laser beam irradiating the test object irrespective of its type. It often becomes a light flux. If the light beam is formed into a parallel light beam, the optical path of the parallel light beam can be freely shortened or extended. Further, if a reflection mirror is used, it is possible to direct the laser beam in an arbitrary direction.

As described above, in the present invention, the laser light source device and the interferometer main body are composed of two units, and the laser light output from the laser light source device is guided to the interferometer main body. The laser light source device includes a laser light source and a light transmitting optical system that converts a laser beam from the laser light source into a parallel light beam and outputs the parallel light beam. On the other hand, the main body of the interferometer is for forming interference fringes, and includes a hologram optical element, a reference reflector, and a sample table on which a test object is installed. A reflection mirror is provided to guide the laser beam, which has been converted into a parallel beam by the laser light source device, to the interferometer main body so that the hologram optical element can be irradiated with the laser beam from a predetermined angle. At least two reflecting mirrors are used.

The angle of incidence of the laser beam on the hologram optical element must be strictly controlled. Therefore, the second reflection mirror provided to enter the hologram optical element is fixedly provided in a state of being strictly controlled so as to face a predetermined angle with respect to the hologram optical element. When the laser light from the laser light source device is directly sent to the second reflection mirror, members constituting the device interfere with the optical path between the laser light source device and the interferometer main body, and a so-called optical path In addition to the risk of injury,
There is a possibility that the assembly layout is restricted and the overall device configuration becomes large. Therefore, a first reflection mirror is provided so that the laser beam from the laser light source device is once reflected by the first reflection mirror. Thereby, when assembling the laser light source device and the interferometer main body, it is possible to provide a degree of freedom in the arrangement of each member.

Further, when the laser light source device and the interferometer main body are assembled, it is necessary to adjust the optical path. However, if the first reflecting mirror can be adjusted in angle, the optical path between the two can be easily adjusted. It can be carried out.

The laser light flux converted into a parallel light flux by the laser light source device is first reflected by the first reflection mirror and again reflected by the second reflection mirror, and is incident on the hologram optical element. The reflected light from the hologram optical element is divided into specularly reflected light and diffracted light with respect to the incident light. The diffracted light is incident on the test object, the specularly reflected light is reflected on the reference reflector, and the two reflected lights interfere with each other when they are reflected again on the hologram optical element, so that interference fringes are generated. Is formed. The reflected light having the interference fringes is sequentially reflected by the second reflection mirror and the first reflection mirror and returned to the inside of the laser light source device. Therefore, a beam splitter is provided in the laser light source device, and the beam splitter branches a light transmission path from the laser light source and a reflected light path from the interferometer body, and the objective lens and the imaging means are provided in the reflected light path. If an interference fringe observation system consisting of is provided, interference fringes can be observed.

Here, the sample stage on which the test object is set is disposed horizontally, and the test surface of the test object is disposed thereon with the test surface facing upward. Is preferred.
By providing the first and second reflection mirrors, the laser beam can be directed in a free direction. If the members are arranged so that the diffracted light from the hologram optical element is directed in the vertical direction, the test object can be detected. The object can be stably set in the direction in which its own weight acts.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, FIG. 1 shows the overall configuration of the hologram interferometer device of the present invention. In the figure, reference numeral 30 denotes a laser light source device, and the laser light source device 30 has a built-in interference fringe observation mechanism 40. Reference numeral 50 denotes an interferometer body. The laser light source device 30 and the interferometer main body 50 constitute separate units, respectively, and are detachably connected to each other. Here, the separate units mean a structure including members that are separately assembled and adjusted in position between each other, and do not necessarily need to be entirely provided in one housing.

The laser light source device 30 includes a main body casing 30.
and a cylindrical body 30b, a laser light source 31 composed of a laser oscillator is mounted on the main body casing 30a, and a reflection mirror 32, which constitutes a light transmitting optical system, is provided from the main body casing 30a to the cylindrical body 30b. Condenser lens 3
3, a pinhole 34, a beam splitter 35, and a collimator lens 36, which are the same as the light source unit and the light transmission optical system in the Fizeau interferometer shown in FIG. However, this collimator lens 3
The reference lens and the test object are not disposed at a position in front of 6 and a pair of reflection mirrors 37 for routing the optical path,
38 are provided. An interference fringe observation mechanism 40 is built in the main body casing 30a. The interference fringe observation mechanism 40 includes a screen 41 facing the optical path of the transmitted light from the beam splitter 35, and an interference fringe imaging lens 4
2 and imaging means 43 for imaging the interference fringes.
This interference fringe observation mechanism 40 also has the same configuration as the Fizeau interferometer of FIG.

The interferometer main body 50 has a support plate 50a, on which the first reflection mirror 5 is mounted.
1, the second reflection mirror 52, and the hologram optical element 5
3, a reference reflection plate 54, and a sample table 56 on which a test object 55 is set. In the configuration of the interferometer main body 50, the means for forming interference fringes has the same configuration as that of the hologram interferometer shown in FIG. However, the point that the first and second reflection mirrors 51 and 52 are provided in order to route the optical path necessary to reduce the size and size of the entire configuration of the interferometer apparatus is the same as the hologram shown in FIG. Different from interferometer. Since the principle of generating interference fringes in this hologram interferometer is the same as that of the hologram interferometer of FIG. 9, detailed description thereof will be omitted.

Here, the surface on which the test object 55 is set is horizontal so that the test object 55 can be set in a stable state without providing a special positioning and holding mechanism. The test surface of the test object 55 is directed upward, and the diffracted light from the hologram optical element 53 is irradiated vertically from above.
The test object 55 must be set to have a strictly predetermined positional relationship with the hologram optical element 53. In order to make the position adjustment of the test object 55 possible, Is mounted on a well-known XYθ table 57, and the XYθ table 57 can adjust the horizontal and rotational positions of the test object 55 set on the sample table 56. If the XYθ table 57 is provided with a tilt function in order to make it possible to further adjust the tilt angle, the position of the test object 55 can be adjusted more accurately.

The XYθ table 57 is mounted on an elevating member 59 that moves up and down along a guide rail 58. By this elevating member 59, the surface of the object 55 to be inspected condenses the diffracted light of the hologram optical element 53. When the cat's eye position, which is the position, and the measurement position, that is, the test surface of the test object 55 is the cylindrical surface 55a, the position is separated from the cat's eye position by the radius of curvature of the curved surface portion of the cylindrical surface 55a. You can move between the position.

To measure the surface shape of the test object 55,
At the measurement position, first, the test object 55 is arranged at the cat's eye position indicated by the imaginary line in FIG. 1 by the lifting / lowering means 59, and is moved to the measurement position indicated by the solid line with this position as the origin. The radius of curvature of the inspection object 55 can also be measured. Since the cat's eye position and the measurement position are the positions where the interference fringes are the least, the raising and lowering means 59 is slightly raised and lowered near each position of the cat's eye position and the measurement position while visually observing the image taken by the imaging means 43. It is sufficient to detect the position where the number of interference fringes is minimized in this image.

The laser light source device 30 incorporating the interference fringe observation mechanism 40 and the interferometer main body 50 are composed of independent units, respectively, and these are columns 60 and 61, respectively.
The pedestals 62, 63 are provided, and the pedestals 62, 63 are independently provided, and the bases 64, 63 are accurately aligned with each other.
By fixing it on the top with bolts or other means,
It is assembled to function as a hologram interferometer device.

The laser light emitted from the laser light source 31 travels upward by the laser light source device 30, and the light path is changed in the horizontal direction by the reflection mirror 32.
Further, by being reflected by the beam splitter 35,
The light path is directed downward. The laser beam, which has been converted into a parallel beam by the collimator lens 36, is reflected by the two reflecting mirrors 37 and 38, is turned upward so as to enter the interferometer main body 50.

The sample table 56 is provided in the horizontal direction because the test object 55 is set thereon. Therefore, the hologram optical element 53 is directed downward so as to have a positional relationship facing the test object 55, and the diffracted light from the hologram optical element 53 is directed in the vertical direction. Therefore, the light incident on the hologram optical element 53 must be made to enter obliquely from below. However, if the laser beam from the laser light source device 30 is directly incident on the hologram optical element 53, the optical path is
6, the XYθ table 57 and the like may cause the vibration. Further, the interferometer main body 50 must be positioned considerably higher than the laser light source device 30, and the overall configuration of the device increases. From the above, the laser beam guided into the interferometer main body 50 is reflected by the first reflection mirror 51, and is reflected again by the second reflection mirror 38. Then, the second reflection mirror 38 is moved to a position below the intersection of the optical path of the incident light to the hologram optical element 53 and the diffracted light from the hologram optical element 53 and above the cat's eye position. The hologram optical element 53 is arranged and fixed so as to have an angle at which a laser beam can enter so that the diffracted light from the hologram optical element 53 is vertical. As a result, the optical path is not deviated, and the entire apparatus configuration can be made compact.

Since the laser light source device 30 and the interferometer main body 50 are separately attached and fixed to the base 64, the optical axis of the laser light source device 30 and the optical axis of the interferometer main body 50 are separated. It is extremely difficult to mount in an exactly matched state. For this purpose, the first reflection mirror 51 is provided with an angle fine adjustment mechanism. Therefore, the first reflection mirror 51 will be described below with reference to FIGS.
The angle fine adjustment mechanism will be described.

The first reflecting mirror 51 is mounted on a frame 70, and the frame 70
It is supported in a floating state on a support plate 72 fixed to a support shaft 71 attached to the support shaft 0a. Frame 70
The support plate 72 is rectangular, and an X-axis adjustment screw 73 and a Y-axis adjustment screw 74 are screwed into two opposing corners of the support plate 72.
The receiving members 75 attached to the support plate 72
76 are engaged with receiving recesses 75a, 76a. Further, one of the remaining two opposite corners of the frame 70 and the support plate 72 is connected by a spherical joint 77, and the other is provided with a tension spring 78. Therefore, if the X-axis adjustment screw 73 is screwed in and out, the first
The angle of the reflection mirror 51 can be adjusted in the X-axis direction as shown by the arrow X in FIG. When the Y-axis adjusting screw 74 is screwed in and out, as shown by an arrow Y in FIG.
Angle adjustment in the Y-axis direction becomes possible. Further, when the adjusting screws 73 and 74 are screwed, the angle of the first reflecting mirror 51 can be adjusted in an arbitrary direction. Thereby, the adjustment can be performed so that the optical axis of the laser light source device 30 and the optical axis of the interferometer main body 50 are aligned. In this optical axis alignment, the angle of the reflection mirror 38 of the laser light source device 30 may be adjusted in the same manner as described above, and the angle of the reflection mirror 38 may be adjusted.

As described above, by constructing the laser light source device 30 and the interferometer main body 50 as independent mechanisms, it is possible to perform maintenance such as repair, inspection and replacement of parts constituting the device. Can be performed independently by separating the laser light source device 30 side and the interferometer main body 50 side. For example, adjustment between the members after maintenance of the laser light source device 30 side is performed Only the side is performed, and adjustment of the first reflection mirror 51 is necessary, but position adjustment of other components of the interferometer main body 50 is not required. Further, when performing maintenance on the interferometer main body 50 side, it is not necessary to modify the laser light source device 30 side at all. Therefore, maintainability is significantly improved.

Here, the laser light source device 30 is provided with the reflection mirrors 37 and 38 on the output side of the laser light beam which has been converted into a parallel light beam by the collimator lens 36, and is combined with the interferometer main body 50 to form a hologram interferometer. A device can be formed, but this reflecting mirror 37,
By mounting a reference lens and a test object instead of 38,
It can be configured as a Fizeau-type interferometer. Therefore, as shown in FIGS. 2 and 3, the reference lens mounting section 80 which can be mounted on the laser beam output section of the laser light source device 30 so as to be finely adjustable in the tilt direction or the XY and tilt directions.
If a test object mounting portion 81 capable of similarly mounting the test object in the tilt direction or the XY and tilt directions so as to be finely adjustable is provided, the Fizeau interferometer is part of the configuration of the hologram interferometer device as it is. Can be shared with.

In addition, the reflection mirrors 37 and 38 are connected to the support plate 8.
And a structure in which the positions of the reference lens mounting section 80 and the test object mounting section 81 can be opened by making the support plate 82 detachable or by rotating and retracting in the horizontal direction. Then, it can be used both as a Fizeau interferometer and as a hologram interferometer, and it becomes possible to measure the surface state of the test object over a wide range.

In recent years, a long cylindrical lens has been used as a facsimile or the like. However, when inspecting the surface finishing accuracy of the cylindrical lens, the hologram interferometer apparatus described above requires:
In some cases, the entire cylindrical surface cannot be brought into view. In this case, the movable range of the XYθ table 57 on which the sample table 56 is mounted in the generatrix direction of the test object, that is, in the X direction, is set large.
In the direction, there are provided two moving means, a coarse moving means for largely moving at once, and a fine moving means for finely adjusting the position,
By sending the object to be measured by the coarse movement means, it is also possible to image the interference fringes in a plurality of sections and combine them by means such as image processing. However, in this case, the support column 61 for supporting the interferometer main body 50 must not be provided on the extension line in the generatrix direction of the test object, but must be provided on a portion orthogonal to the generatrix direction.

[0038]

As described above, according to the present invention, various members constituting the interferometer device are divided into the laser light source device and the interferometer main body, and the laser light source device emits laser light from the laser light source. A unit necessary for forming a parallel light beam is unitized, and as a main body of the interferometer, a first reflecting mirror for reflecting the laser light beam sent from the laser light source device and the reflected light from the first reflecting mirror are again reflected. Second to reflect
A reflection mirror, a hologram optical element provided at a position facing the second reflection mirror at a predetermined angle, and a light receiving position for diffracted light by the hologram optical element, and an object to be measured is provided. Of the interferometer device and other components constituting the interferometer device, since it is composed of a sample stage and a reference reflector disposed at the position for receiving specularly reflected light from the hologram optical element. The components up to the parallel beam formation of the laser beam from the device and the laser light source can be made into a common part, and the effect of mass production can be expected,
Various effects such as easy maintenance such as repair, inspection, and replacement of parts are achieved.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view of a hologram interferometer showing one embodiment of the present invention.

FIG. 2 is a front view of the hologram interferometer device.

FIG. 3 is a side view of the laser light source device in FIG.

FIG. 4 is a side view of the main body of the interferometer of FIG. 2;

FIG. 5 is an explanatory diagram of a configuration of a first reflection mirror.

FIG. 6 is a sectional view taken along line XX of FIG. 5;

FIG. 7 is a sectional view taken along line YY of FIG. 5;

FIG. 8 is a diagram illustrating the principle of a Fizeau interferometer.

FIG. 9 is a diagram illustrating the principle of a hologram interferometer.

[Explanation of symbols]

 Reference Signs List 30 laser light source device 31 laser light source 35 beam splitter 36 collimator lens 40 interference fringe observing means 50 interferometer main body 51 first reflection mirror 52 second reflection mirror 53 hologram optical element 54 reference reflection plate 55 test object 56 sample table 70 Frame 72 Support plate 73 X-axis adjustment screw 74 Y-axis adjustment screw 77 Spherical joint 78 Tension spring

Claims (3)

(57) [Claims] A laser light source device for converting a laser beam from a laser light source into a parallel light beam, and an interferometer main body, wherein the interferometer main body has a first reflection for reflecting a laser light beam sent from the laser light source device. A mirror, a second reflecting mirror for reflecting the reflected light from the first reflecting mirror again, a hologram optical element arranged at a position where the second reflecting mirror faces at a predetermined angle, and the hologram optical element It is arranged at a light receiving position of diffracted light by the element, a sample stage on which a test object is installed, and a reference reflector disposed at a light receiving position of regular reflection light from the hologram optical element. Hologram interferometer device. 2. The hologram interferometer apparatus according to claim 1, wherein said first reflection mirror is mounted on an angle adjusting means for adjusting an inclination angle of said first reflection mirror with respect to an optical axis with respect to said laser light source device. 3. The laser light source device comprises: a laser light source;
A beam splitter disposed in the middle of the optical path from the laser light source, a collimator lens for converting the transmitted laser beam into a parallel beam, and an interference fringe observation means attached to the laser source device. The hologram interferometer device according to claim 1, wherein: