JPH11201895A - Inspection method for internal heterogeneity of optical member and tool glass - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To easily inspect the internal heterogeneity of an optical glass member without the need for polishing. SOLUTION: A tool glass 32a has a first surface 34a which can be fitted on a surface of an optical member 24, and a first surface 3a.
Second surface 34b which is a flat optically polished surface facing 4a
And The tool glass 32b includes a first surface 36a that can be fitted to the surface of the optical member 24, and a second surface 36 that is a planar optical polishing surface facing the first surface 36a.
b. These tool glasses are respectively mounted on the surface of the optical member in such a manner as to face each other via the optical member. The mounting of these tool glasses is performed such that the respective second surfaces are parallel to each other. And
At the time of inspection, for example, the second surface 3 of the tool glass 32a
4b serves as a light incident surface, and the second surface 36b of the tool glass 32b serves as a light emitting surface. Therefore, with this configuration, the incident surface 34b and the output surface 36 of the test sample 12 are formed.
b can be substantially parallel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting the inside of optical members for inhomogeneity.

[0002]

2. Description of the Related Art When manufacturing an optical member, internal inhomogeneities such as striae, bubbles, fine bubbles, and microcrystals are generated in a glass member due to fluctuations in various conditions during melting in a manufacturing process. Sometimes. Therefore, the manufactured glass member needs to be inspected for internal heterogeneity for quality assurance. For example, in the case of quartz glass, when inspecting for internal heterogeneity, a cylindrical optical glass member (hereinafter, also simply referred to as a member) is cut out by cutting an ingot into rings at appropriate intervals. Then, for each of the cut-out members, inspection for internal heterogeneity was performed by using a method such as visual observation or a pinhole method. The visual inspection is, for example, a method in which a member is exposed to light to find internal inhomogeneity with the naked eye. Further, in the method using the pinhole method, for example, “Method for measuring striae of optical glass (JOGIS 11-1975)” of the Japan Optical Glass Industrial Association is used. In addition, as a method for inspecting bubbles, for example, “Method for measuring bubbles in optical glass (JOGI)” of the Japan Optical Glass Industrial Association
S12-1994) ". Examples of the method for inspecting microcrystals and microbubbles include, for example, “Method for measuring foreign matter in optical glass (JOG)” of the Japan Optical Glass Industrial Association.
IS13-1994) ".

[0003] In these inspection methods,
In each case, two opposing surfaces of the member to be inspected were optically polished in parallel in order to obtain an image of an internal heterogeneity (observed image), and the inspection was performed using these optically polished surfaces as a light incident surface and a light emitting surface, respectively. . Furthermore, in order to save the labor of optical polishing, two opposing surfaces of the member are ground in parallel, a matching oil having the same refractive index as the member is applied thereto, and a flat optically polished glass is applied thereto. The oil-on-plate method for obtaining a surface has also been commonly used.

[0004]

In recent years, with the advance of laser precision processing and optical lithography technology, higher precision optical design and control have been required. For this reason, there is an increasing demand for the internal homogeneity of the optical glass member to be used, and not only in the optically polished surface direction (optical axis direction) used as an optical element, but also in the lateral direction without optical polishing (in the direction perpendicular to the optical axis direction). It is also necessary to understand and control the internal homogeneity of).

[0005] Therefore, conventionally, there has been performed an operation of forming an optical surface capable of inspecting the inside in the lateral direction in addition to the optically polished surface. FIG. 6 is a plan view showing an example of a polishing process performed on the optical glass member in a lateral direction for inspection based on the above-described inspection methods. Optical glass member 10 shown in FIG.
Reference numeral 0 denotes a substantially cylindrical shape before processing, and FIG. 6 shows the upper surface (or lower surface) thereof. The optical polishing is performed on the cylindrical surface of the optical glass member 100.
As shown in FIG. 6, two parallel and
The surfaces are formed as an entrance surface 100a and an exit surface 100b, respectively. The broken line a in the figure indicates the completed size of the optical element. As described above, in order to inspect the internal homogeneity, a polishing allowance (a portion outside the broken line a) is required. Accordingly, when such a cylindrical optical glass member is inspected by irradiating light from the lateral direction (the direction indicated by the arrow b in FIG. 6), it is necessary to grind the cylindrical surface. There is a problem that the size of the optical element formed from the later member is slightly smaller than the original member.
Further, in order to inspect the internal heterogeneity with a wide field of view, it is necessary to use a plurality of optical surfaces or to grind a relatively wide area.

[0006] Therefore, it has been desired to simply inspect the internal inhomogeneity of an optical glass member without the need for polishing.

[0007]

According to the method for inspecting the homogeneity of the inside of an optical member according to the present invention, the homogeneity of the inside of the optical member is determined by an observation image obtained by irradiating a test sample including the optical member with light. Upon inspection, by mounting a tool glass having a surface that can be fitted to the surface of the optical member, the light incident surface and the light exit surface of the test sample are made substantially parallel. I do.

As described above, according to this inspection method, a tool glass transparent to the inspection light is mounted on the surface of the optical member to be inspected. Preferably, the tool glass has the same refractive index as the optical member to be inspected. This tool glass has a surface whose shape matches the surface of the optical member. Therefore, the surfaces can be aligned with the surface of the optical member. The surface of the tool glass facing the surface to be bonded to the optical member is a flat surface (optically polished surface). By using such a tool glass, the light entrance surface and the light exit surface of the test sample can be made substantially parallel. Therefore, it is not necessary to grind the optical member as in the related art.

In the method for inspecting internal heterogeneity of an optical member according to the present invention, preferably, when an inspection image is obtained by irradiating the inspection sample with light from the first direction, the light incident surface and the emission surface of the inspection sample light. At least one of the surfaces is marked at a position where the image of the mark substantially overlaps the observed image, and the test sample is placed in a second direction different from the first direction with respect to the incident surface of the test sample. If the observed image and the image of the mark substantially overlap when irradiating light, it is good to judge that the observed image is not derived from the internal heterogeneity of the optical member but is derived from the marked surface. .

As described above, when the observation image and the image of the mark substantially overlap each other when the optical glass is irradiated with light from the second direction different from the first direction, the observation image is formed on the optical glass. Judgment is not due to internal heterogeneity, but to the marked surface. When the observed image is derived from internal heterogeneity, the observed image and the image of the mark do not overlap. Therefore, it is possible to easily determine whether or not the observed image is derived from the internal heterogeneity of the optical glass or from the marked surface, depending on how the observed image and the image of the mark overlap. Therefore, it is possible to realize a more reliable inspection method for the internal heterogeneity of the optical glass.

In the method for inspecting the internal heterogeneity of an optical member according to the present invention, it is preferable that a mark is provided on an incident surface on an entrance surface and a mark on an exit surface is provided on an exit surface, and light is irradiated from a second direction. When, the distance between the image of the incident side mark and the image of the exit side mark, based on the ratio of the distance between the observed image and at least one of the image of the entrance side mark and the image of the exit side mark, the internal heterogeneity Find the position.

As described above, if the incident side mark and the output side mark are attached, the position of the internal inhomogeneity can be obtained.

In the method for inspecting internal heterogeneity of an optical member according to the present invention, when the optical member is quartz glass, a quartz glass ingot or a member cut out of the ingot is preferably used as an inspection sample.

As described above, if the position of the internal inhomogeneity of the quartz glass ingot can be determined, when cutting the ingot, for example, by cutting at a position where the internal inhomogeneity exists, a plurality of optical elements with less internal inhomogeneity can be obtained. The members can be cut out efficiently. Further, in cutting the ingot, for example, when a plurality of internal inhomogeneities are present in close proximity, the ingot can be cut so that the thickness of the member including these internal inhomogeneities is reduced. . Further, if the position of the internal heterogeneity of the member can be obtained, it is possible to cut out a slightly smaller member that does not include the internal heterogeneity by further cutting this member, avoiding the internal heterogeneity. .

Therefore, if the position of the internal inhomogeneity can be obtained, the efficiency of non-defective products can be improved. Here, the non-defective product efficiency (or non-defective product ratio) is expressed, for example, as a ratio (w / W) of the total mass w of the members in which the internal inhomogeneity was not detected to the mass W of the ingot.

In the method for inspecting the inside of an optical member for inhomogeneity according to the present invention, it is preferable that the light applied to the optical member is irradiated light via a pinhole.

The use of the so-called pinhole method using irradiation light through a pinhole allows a simple structure to be used to inspect for internal heterogeneity.

In the method for inspecting the inside of an optical member for inhomogeneity according to the present invention, it is preferable that the light applied to the optical member be the irradiation light in the schlieren optical system.

If the schlieren optical system is used, the observation image and the image of the mark can be obtained as a bright image on a dark background, so that the internal heterogeneity can be inspected with higher accuracy.

In the method for inspecting the internal heterogeneity of an optical member according to the present invention, preferably, the irradiation light in the schlieren optical system is set to parallel light, and the inspection sample is rotated using an axis which is not parallel to the parallel light as a rotation axis. By changing the incident angle of the parallel light on the incident surface to an angle different from the angle in the first direction, the inspection sample may be irradiated with the parallel light from the second direction.

As described above, if the irradiation light for irradiating the test sample in the schlieren optical system is parallel light, the sample can be rotated and the incident angle of the test sample to the incident surface can be easily changed in the second direction. Irradiation light can be obtained.

Further, according to the tool glass of the present invention, it is used when inspecting the internal heterogeneity of the optical member by an observation image obtained by irradiating the inspection sample including the optical member with light, and the surface of the optical member is used. And a second surface which is a flat optically polished surface facing the first surface.

As described above, the tool glass has the first surface having a shape corresponding to the surface of the optical member. Therefore, the surfaces can be aligned with the surface of the optical member. The second surface of the tool glass opposite to the surface to be bonded to the optical member is a planar optical polished surface. By using such a tool glass, the light entrance surface and the light exit surface of the test sample can be made substantially parallel. Therefore, it is not necessary to grind the optical member as in the related art.

In the tool glass of the present invention, the first surface is preferably an optically polished surface.

The tool glass of the present invention is preferably made of a material having a refractive index substantially equal to the refractive index of the optical member.

According to this structure, the tool glass becomes transparent to the inspection light, and it is possible to suppress reflection, refraction, scattering and the like at the joint surface.

[0027]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a method of inspecting an optical member for inhomogeneity in an optical member according to an embodiment of the present invention; It should be noted that the drawings referred to schematically show the size, shape, and arrangement relationship of each component so that the present invention can be understood, and the present invention is not limited to the illustrated examples.

In general, the performance of an optical element can be known only when it has a final shape such as a lens. However, if the internal heterogeneity is grasped at the stage of a semi-finished product (optical member) during processing and the performance of the optical element as the final product can be predicted, the productivity and the yield rate can be increased. In the conventional inspection method, since an inspection sample for evaluating internal heterogeneity was used, it was difficult to evaluate the optical element in a form close to the usage state. In particular, among the internal inhomogeneities, since the striae are inhomogeneous portions of the refractive index, the appearance changes depending on the thickness and inclination of the sample. Therefore, it was easier to inspect with the naked eye when a somewhat thick sample was used, and it was difficult to evaluate the optical element in a form close to the usage state. According to the inspection method and the tool glass described in this embodiment, the above-described inconvenience is eliminated.

An inspection method according to this embodiment will be described. In this embodiment, an inspection sample including an optical member is irradiated with light to obtain an observation image, and the homogeneity inside the optical member is inspected based on the observation image. At this time, by attaching a tool glass having a surface that can be fitted to the surface of the optical member, the light entrance surface and the light exit surface of the test sample are made substantially parallel. First, the configuration of the tool glass and how to attach the tool glass to the optical member will be described with reference to FIG. FIG. 1 is a diagram showing a configuration of the tool glass.

FIG. 1A is a plan view showing a state where a tool glass is mounted on an optical member to be inspected. FIG.
As shown in (A), in this example, a cylindrical optical member 24 is used as an inspection target. FIG. 1A shows the upper surface side (or the lower surface side) of the optical member 24. The optical member 24 is, for example, a quartz glass member. The cylindrical surfaces of the optical member 24 (hereinafter simply abbreviated as cylindrical surfaces) have tool glasses 32a and 32a.
The test sample 12 is attached by attaching the sample b.

The above-mentioned tool glasses 32a and 32b
Have the same shape. FIG. 1B is a perspective view showing the shape of the tool glass 32a. FIG. 1 (B)
As shown in FIG. 3, the tool glass 32a is
And a second surface 3 which is a planar optically polished surface facing the first surface 34a.
4b. That is, the tool glass 32a is
This is a cylindrical lens-shaped glass member having a cylindrical first surface 34a and a flat second surface 34b.

The tool glasses 32a and 32b are mounted on the surface of the optical member 24 so as to face each other via the optical member 24. The mounting of these tool glasses 32a and 32b is carried out on each second surface 34b.
And 36b are parallel to each other. And
At the time of inspection, for example, the second surface 3 of the tool glass 32a
4b serves as a light incident surface, and the second surface 36b of the tool glass 32b serves as a light emitting surface. Therefore, as a result of such a configuration, the entrance surface 34b and the exit surface 3
6b can be substantially parallel.

The tool glasses 32a and 32b are each made of a material having a refractive index substantially equal to the refractive index of the optical member 24. In this way, the tool glasses 32a and 32b are transparent to the inspection light, and the reflection, refraction, scattering, and the like of the inspection light at the joint surface with the optical member 24 can be suppressed.

The first surface 34 of the tool glass 32a
a and the first surface 36a of the tool glass 32b are preferably optically polished. If optical polishing is performed in this manner, there is no need to use a so-called oil-on-plate method. When the first surfaces 34a and 36a of these tool glasses 32a and 32b are merely ground surfaces,
It is necessary to perform an oil-on-plate method. In this case, a matching oil is applied between the first surface 34a of the tool glass 32a and the surface of the optical member 24 and between the first surface 36a of the tool glass 32b and the surface of the optical member 24, respectively. And then attach it. It is preferable to use a matching oil having the same refractive index as that of the optical member 24 as the matching oil.

Next, a procedure for inspecting the inside of the optical member 24 for inhomogeneity using the above-described inspection sample 12 will be described.

In the inspection method described in this embodiment,
Inspection accuracy is flat optically polished surface of tool glass (surface 34b,
36b), the bonding surface (surfaces 34a, 36a), the processing accuracy of the inspection surface of the test object (optical member 24), and the selection of the matching oil. The surface roughness of the ground surface is determined by the refractive index of the test object as in the case of the matching oil. When the test object has a high refractive index, the amount of scattering at the interface with air increases, so that it is necessary to reduce the surface roughness. In addition, since the test object has a relatively large thickness, the transmittance of the test object at the test wavelength also has a large effect on the test accuracy.

The object to be inspected can be inspected not only with ordinary optical glass and quartz glass but also with an optical crystal material such as fluorite. In particular, since the optical crystal material is difficult to process and expensive, the inspection method of this embodiment is effective.

As described above, by using the test object on which the tool glass is disposed as an inspection sample, it is possible to inspect the internal homogeneity without working the optical member small. Further, the present test sample 12 can support various test methods.
As a specific inspection method, general visual observation, a projection method, a Schlieren method, an interference method, or the like can be used. However, it is the projection method that requires the least skill of the inspector, facilitates the inspection operation, and simplifies the apparatus.

(First Embodiment) An example of the inspection method will be described below with reference to FIG. In this embodiment, an example of a method for inspecting the above-described inspection sample 12 for inhomogeneity inside an optical member when a pinhole method is used will be described. FIG. 2 is a conceptual diagram for explaining a method for inspecting an optical member for inhomogeneity inside according to the first embodiment.

In the first embodiment, the light source 10, the test sample 12, and the screen 14 are arranged in order in a dark room, and the light source 10 irradiates the test sample 12 with light. Observe the observation image projected on.

Here, a 450 W ultra-high pressure mercury lamp is used as the light source 10. Further, a pinhole 18 is provided in the lamp house 16 in which the ultrahigh-pressure mercury lamp is stored in order to remove flare of the light source 10. This pinhole 18
Is emitted to the inspection sample 12 through the convex lens 20 and the stop 22 in order to remove stray light and adjust the inspection light flux. The light transmitted through the test sample 12 reaches the screen 14. Here, as the screen 14, it is preferable to use a screen that is defined by the printing paper A and the JISP 3101 (printing paper) so that the observation image is easily visible without irregular reflection of light on the screen. Further, as the screen 14, for example, a screen in which a white paint is uniformly applied to an acrylic plate may be used.

If the inspection sample 12 has internal inhomogeneity, the projected image is projected on the screen 14 as an observation image. When the size of the pinhole 18 is reduced,
The resolution of the observation image projected on the screen 14 is improved, but the light amount is reduced. On the other hand, when the size of the pinhole 18 is increased, the resolution of the observed image is reduced, but the light amount is increased. Therefore, in this embodiment, the size of the pinhole 18 and the distance between the light source 10 and the screen 14 are adjusted so that the illuminance on the screen is, for example, 100 lux or more.

The size of the observation image projected on the screen 14 is larger than the size of the internal heterogeneity of the inspection sample 12. This magnification is expressed as a / b, where a is the distance from the light source 10 to the screen 14 and b is the distance from the light source 10 to the test sample 12. For example, a = 1
The magnification in the case of 35 mm and b = 60 mm is a / b =
It becomes 2.25.

Next, the test sample 12 will be described. The optical member 24 is a cylindrical member cut out from a quartz glass ingot manufactured by a flame hydrolysis method. The optical member 24 has a diameter of 200 mm and a refractive index nd of 1.4585. The ground surface on the side surface (cylindrical surface) of the optical member 24 is a sanding surface of # 170. On this side surface, tool glasses 32a and 32b having a cylindrical ground surface having the same refractive index as the quartz glass member having a refractive index of nd = 1.45885 and the same shape as the subject are attached. The ground surfaces of the tool glasses 32a and 32b are # 170 sanding surfaces. As described above, the tool glasses 32a and 32b are applied to the side surfaces of the test object so as to face each other in the diametrical direction of the optical member 24. Further, a matching oil having the same refractive index as the test object is applied between the test object, that is, the optical member 24 and the tool glasses 32a and 32b, and an inspection light capable of inspecting the inside for inhomogeneity is applied. Obtain an optical surface to transmit.

Therefore, the tool glass 32 on the side where light is incident
The surface 34b of “a” becomes the incident surface 34b of the test sample 12.
The surface 36b of the tool glass 32b on the side from which light is emitted
Becomes the emission surface 36b of the test sample 12.

Then, when inspecting the inside of the optical member 24 for inhomogeneity, first, the optical member 24 is irradiated with light from a first direction. In this embodiment, in order to obtain light from the first direction, the test sample 12 is set so that the optical axis 38 is perpendicular to the incident surface 34b near the center of the incident surface 34b.
Place. Then, the inspection sample 12 is irradiated with light from the first direction, and an observation image projected on the screen 14 is observed.

On the other hand, when the observation image is not observed, it can be understood that there is no internal heterogeneity in the portion of the optical member 24 through which light is transmitted.

In the case where the observation image is observed, a position on at least one of the light incident surface 34b and the light exit surface 36b of the inspection sample 12 where the mark image substantially overlaps the observation image. To the mark with magic or tape.
That is, a mark is made on at least one of the light incident surface 34b and the light exit surface 36b of the test sample 12 and on the optical path passing through the observation image. Here, a mark is made on the incident surface 34b.

Incidentally, even when there is no internal heterogeneity, an observation image may be observed. For example, the incident surface 3
The observation image is also observed when there is a flaw or fogging on 4b or the exit surface 36b. For this reason, whether the observed image is derived from internal heterogeneity, or whether the incident surface 34b or the exit surface 36
It is necessary to judge whether the damage is caused by the damage of b or the like.

Therefore, in this embodiment, the incident surface 34
Light is applied to the optical member 24 from a second direction different from the first direction with respect to b. In order to irradiate light from the second direction, in this embodiment, the test sample 12 is moved along the optical axis 38.
, Ie, in a plane parallel to the screen 14. Since the light emitted from the pinhole 18 is a light having a spread and not a parallel ray, the incident angle of the light incident on the incident surface 34b of the test sample 12 is changed by moving the test sample 12 in parallel. It can be changed with respect to the direction.

When the observation image projected on the screen 14 and the image of the mark substantially overlap with each other by irradiating the inspection sample 12 with light from the second direction, the observation image is not reflected inside the optical member 24. It is judged that it does not originate from homogeneity but originates from the marked surface.

On the other hand, if the observed image and the mark image do not overlap, it is determined that the observed image is not derived from the marked surface. Therefore, it is determined that the observed image is substantially derived from internal heterogeneity.

As described above, it is easy to judge whether the observed image is derived from the internal heterogeneity of the optical member 24 or the marked surface based on how the observed image and the image of the mark overlap. can do. Therefore, it is possible to realize a more reliable inspection method for the internal heterogeneity of the optical member 24.

In the first embodiment, the tool glass 32 is attached to the optical member 24 to be measured via the matching oil.
Although a and 32b are attached, if a polished surface is obtained on the side surface of the optical member 24 or the surfaces 34a and 36a of the tool glasses 32a and 32b, it is not necessary to apply the matching oil.

Although only the incident surface 34b is marked here, in the present invention, only the emitting surface 36b may be marked. Further, both the incident surface 34b and the output surface 36b may be marked.

In this case, the test sample 12 is translated in order to make light incident from the second direction. However, for example, the test sample 1 is set with an axis that is not parallel to the optical axis 38 as a rotation axis.
2, the incident angle of the parallel light on the incident surface 34b may be changed to an angle different from the angle in the first direction.

In the first embodiment, the test sample 12 is moved so that light is incident from the second direction. For example, the test sample 12 is moved on the optical axis 38 during irradiation from the first direction. By moving the light source 10 to a position other than the first direction, the test sample 12 may be irradiated with light from a direction different from the first direction.

(Second Embodiment) In the second embodiment, the position of the internal heterogeneity is determined. In the second embodiment, FIG.
The incident surface 34b and the exit surface 36 of the test sample 12 shown in FIG.
Both b are marked with light incident from the first direction. The entrance surface 34b is marked on the entrance side, and the exit surface 36
An emission side mark is attached to b. The image of the entrance mark, the image of the exit mark and the observation image are projected on the screen 14 in an overlapping manner.

Then, also in the second embodiment, the test sample 12 is irradiated with light from the second direction. And
If the observed image remains substantially overlapping either the image of the entrance mark or the image of the exit mark, the observed image is not due to internal heterogeneity, but rather substantially overlaps the observed image. It can be seen that they are derived from scratches and fogging on the surface with the mark.

On the other hand, when light is irradiated from the second direction, the observation image does not overlap any of the image of the incident side mark and the image of the emission side mark, In the case where the image, the observation image, and the image of the emission side mark are sequentially projected on a straight line, it is determined that the observation image is derived from internal heterogeneity.

Then, based on the ratio of the distance between the observation image and the image of the incident side mark to the distance between the image of the incident side mark and the image of the exit side mark, the position of the internal heterogeneity is determined. For example, when the distance between the image of the incident side mark and the image of the emission side mark is W and the distance between the observation image and the image of the incident side mark is L (<W), the incident surface 34 is used.
From b, it can be seen that there is internal inhomogeneity at a depth of L / W times the thickness of the test sample 12, which is the distance between the entrance surface 34b and the exit surface 36b.

Further, for example, when the internal inhomogeneity is found at a shallow position near the surface, the internal inhomogeneity is removed by grinding only the portion of the optical member 24 near the internal inhomogeneity. It is possible. For this reason, it becomes possible to use the optical member 24, which has been slightly reduced by grinding, as an optical element. As a result, non-defective product efficiency can be improved.

(Third Embodiment) In the first and second embodiments, the optical member 24 cut out from the quartz glass ingot is used as the test sample 12, but the third embodiment is not limited to the above. In the embodiment, an ingot before cutting out the optical member 24 is used for the test sample 12.

In this embodiment, the test sample of the ingot had a substantially cylindrical shape with one end having a hemispherical shape, a diameter of 370 to 383 mm, and a weight of 197.8 kg. The tool glasses 32a and 3a are placed on the cylindrical side surface of the ingot through a immersion liquid of a matching oil having a refractive index close to that of quartz glass.
Inspection sample 12 was added with 2b.

When the tool glasses 32a and 32b having a size smaller than the entire length of the ingot are used, the tool glass 3 is moved along the side of the ingot depending on the inspection position.
It is preferable to sequentially move 2a and 32b for observation.
Since an ultra-high pressure mercury lamp is used as the light source 10,
Even if light from the light source 10 is transmitted through the ingot, brightness of 100 lux or more on the screen 14 can be secured.

Next, FIG. 3 shows the test sample 12 shown in FIG.
9 shows internal heterogeneity found by observing a test sample using an ingot instead of the ingot. The ingot 40 has internal heterogeneity such as micro bubbles 42, bubbles 44, stria 46, and large bubbles 48.

Conventionally, members have been cut out by cutting the ingot at equal intervals. However, if the position of the internal inhomogeneity is known before cutting, the ingot is cut so that the thickness of the member including internal inhomogeneity is reduced. Can be cut. In FIG. 3, the cutting positions of the ingot 40 are indicated by broken lines I to VI. The number at the lower end of each broken line represents the length (mm) of the ingot 40 from the head (tip). By cutting the ingot 40 at each broken line, the first to seventh members are cut out. The first member 50 is obtained by cutting off the tip portion of the ingot 40 having an irregular thickness. And the second member 5
The second and third members 54 are cut out at a constant thickness of 150 mm. Further, the fourth member 56 includes the microbubbles 42.
And two bubbles 44 are included. The fifth member 58 includes the stria 46. The sixth member 60 contains the large bubbles 48. The fourth and sixth members 56 and 60 are each cut out at a thickness of 80 mm, which is thinner than 150 mm. In addition, the fifth member 58 includes 70
Cut out to a thickness of mm. Then, the remaining part is cut out as a seventh member 62 with a thickness of 290 mm. As described above, by cutting out a member including the internal heterogeneity with a reduced thickness, it is possible to improve non-defective product efficiency.

Further, in order to improve the efficiency of non-defective products, a part or all of the internal inhomogeneity may be included in the cutting margin by cutting the ingot at a portion where the internal inhomogeneity exists. Also cut the ingot near the internal heterogeneity,
The cut surface may be ground to remove internal heterogeneity.

(Fourth Embodiment) In the fourth embodiment, an example of a method for inspecting the internal inhomogeneity of an optical member when a schlieren optical system is used will be described with reference to FIG. FIG. 4 is a conceptual diagram serving to explain a method for inspecting the inside of an optical member for inhomogeneity according to the fourth embodiment.

In the fourth embodiment, the light source 70, the first convex lens 72, the test sample 74, the second convex lens 76, and the screen 78 are arranged in this order in a dark room. The test sample 74 is irradiated with light through the light source. The light applied to the test sample 74 is
Focus on 0. Then, the light converged on the converging point 80 is shielded. The inspection sample 74 includes the converging point 80 and the convex lens 7.
2 are arranged.

In the fourth embodiment, the same test sample 12 as that described with reference to FIG. 1 is used as the test sample 74. Then, the surfaces of the tool glass mounted on the entrance side and the exit side are respectively attached to the entrance surface 82 and the exit surface 84.
And In the Schlieren optical system, the higher the degree of parallelism between the entrance surface 82 and the exit surface 84, the better the measurement accuracy.

When the inspection sample 74 has internal inhomogeneity, the light irradiated to the internal inhomogeneity does not pass through the converging point 80 and is not blocked. The light that is not blocked reaches the screen 78 via the second convex lens 76. Therefore, the observation image on the screen 78 having an internal inhomogeneity is observed as a bright image on a dark background. Further, the observation image is observed as, for example, a streak-like or spot-like image due to the internal heterogeneous shape. In the Schlieren optical system, the observation image is observed as a bright image on a dark background, so that observation is easy.

In observation, first, the incident surface of the test sample 74 is arranged in parallel with the screen 78, and light is irradiated from a first direction. If no observation image is observed on the screen 78, it is determined that there is no internal heterogeneity. On the other hand, when an observation image is obtained by irradiating the optical glass with light from the first direction, the mark image is formed on at least one of the light incident surface and the light exit surface of the test sample. The mark is placed at a position substantially overlapping with. Here, the substantially overlapping position is not limited to a position where the observation image and the mark image exactly match, but may be, for example, a position where the mark image comes near the observation image.

By the way, even if there is no internal inhomogeneity, an observation image may be observed if the entrance surface 82 or the exit surface 84 is damaged. For this reason, it is necessary to determine whether the observed image is derived from internal inhomogeneity or whether it is derived from a scratch or the like on the incident surface 82.

Then, the inspection sample 74 is irradiated with light from a second direction different from the first direction with respect to the incident surface. Here, the test sample 74 is translated in a plane parallel to the screen 78 in order to obtain the second direction. Inspection sample 74
Is incident on the incident surface 82 of the test sample 74 by moving the test sample 74 in parallel because the light is a condensing system via the first convex lens 72 and is not a parallel light beam. Can be varied with respect to the first direction.

When the inspection sample 74 is irradiated with light from the second direction and the observation image on the screen 78 and the image of the mark substantially overlap, the observation image is derived from the internal inhomogeneity of the optical glass. It is determined that it is derived from the marked surface, not the surface.

On the other hand, if the observation image and the mark image do not overlap, it is determined that the observation image is not derived from the marked surface. Therefore, it is determined that the observed image is substantially derived from internal heterogeneity.

As described above, it is easy to judge whether the observed image is derived from the internal heterogeneity of the optical member or the marked surface based on how the observed image and the image of the mark overlap. be able to. Therefore, it is possible to realize a more reliable inspection method for the internal heterogeneity of the optical member.

In the case of the schlieren optical system, if both the entrance surface and the exit surface of the test sample are marked, the second
In the same manner as in the embodiment, the position of the internal heterogeneity can be obtained.

(Fifth Embodiment) In the fifth embodiment, an example of a method for inspecting the internal inhomogeneity of an optical member when a schlieren optical system is used will be described with reference to FIG. FIG. 5 is a conceptual diagram serving to explain a method for inspecting the inside of an optical member for inhomogeneity according to the fifth embodiment.

In the fifth embodiment, the fourth embodiment
Similarly to the embodiment, the light source 70, the first convex lens 72, the test sample 74, the second convex lens 76, and the screen 78 are sequentially arranged in the dark room, and the test sample is supplied from the light source 70 through the first convex lens 72. 74 is irradiated with light.

However, in the fifth embodiment, unlike the above-described fourth embodiment, the light source 70 is arranged at the focal point of the first convex lens 72. As a result, the light emitted from the light source 70 passes through the first convex lens 72 and becomes parallel light.
The parallel light is incident on the second convex lens 76 and is focused on the focal point 86 of the second convex lens 76 on the screen 78 side.
The light collected at the focal point 86 is blocked. Then, the test sample 74 is disposed between the first convex lens 72 and the second convex lens 76 to irradiate a parallel light beam.

Then, in order to obtain the first direction, here, the incident surface of the test sample 74 is arranged in parallel with the screen 78, and the test sample 74 is irradiated with parallel light. In the case where an observation image is obtained by irradiating the inspection sample 74 with light from the first direction, a position on the light incident surface of the inspection sample 74 where the image of the mark substantially overlaps the observation image is obtained. Mark.

Next, in order to irradiate the test sample 74 with parallel light from the second direction, the test sample is rotated about an axis that is not parallel to the parallel light as a rotation axis, and the incident angle of the parallel light with respect to the incident surface is set to the second angle. The angle is changed to an angle different from the angle in the first direction. As described above, if the irradiation light for irradiating the test sample in the schlieren optical system is parallel light, the irradiation from the second direction can be easily performed simply by rotating the sample and changing the incident angle of the test sample with respect to the incident surface. You can get light.

If the observation image on the screen 78 and the image of the mark are substantially overlapped by irradiating the inspection sample 74 from the second direction, the observation image is derived from the internal heterogeneity of the optical member. Instead, it is determined that the origin is from the marked surface.

On the other hand, if the observed image and the image of the mark do not overlap, it is determined that the observed image is not derived from the marked surface. Therefore, it is determined that the observed image is substantially derived from internal heterogeneity.

In each of the embodiments described above, the present invention has been described only with respect to an example in which a specific material is used and a specific condition is used. However, the present invention can be variously modified and modified. For example, in the above-described embodiment,
Although the case where the pinhole method or the schlieren optical system is used has been described, the present invention is not limited to these cases, and can be applied to, for example, an interferometry.

Further, in each of the embodiments described above, the classification of the test sample is not performed, but the present invention may be applied to the classification by comparison with a standard sample. For example, on a homogeneous light-transmitting substrate where internal heterogeneity such as striae is not detected,
It is also possible to standardize by vapor-depositing a light-transmitting substance so as to have a known optical path difference and further using an artificially formed striae as a standard sample for comparison.

In each of the embodiments described above, the observation image on the screen is observed. However, in the present invention, it is not always necessary to use the screen. For example, a camera is provided instead of the screen to observe the observation image. You may.

As a result of the inspection using the inspection sample and the apparatus described above, a method for inspecting the striae of the optical glass (JOGI
S11-1975) could be examined for the striae corresponding to the standard sample B (thin with a thinly dispersed striae and visible limit).

As described above, since the inside can be inspected by using the outer peripheral portion of the test object as it is, accurate inspection can be performed in the state of the completed optical element. This is a great advantage, especially for expensive crystalline materials. Further, since it is not necessary to form a flat portion on the outer peripheral portion, the labor for processing can be omitted.

[0092]

According to the method for inspecting the internal heterogeneity of an optical member according to the present invention, when inspecting the internal homogeneity of the optical member based on an observation image obtained by irradiating a test sample including the optical member with light, an optical system is required. By mounting a tool glass that can be fitted to the surface of the member, the light incident surface and the light emitting surface of the test sample are made substantially parallel.

As described above, according to this inspection method, a tool glass transparent to the inspection light is mounted on the surface of the optical member to be inspected. This tool glass has a surface whose shape matches the surface of the optical member. Therefore, the surfaces can be aligned with the surface of the optical member. The surface of the tool glass facing the surface to be bonded to the optical member is a flat surface (optically polished surface). By using such a tool glass, the light entrance surface and the light exit surface of the test sample can be made substantially parallel. Therefore, it is not necessary to grind the optical member as in the related art.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a tool glass.

FIG. 2 is a diagram for explaining a method for inspecting the inside of the optical member according to the first embodiment for homogeneity;

FIG. 3 is a diagram showing the inhomogeneity inside an ingot observed in a third embodiment.

FIG. 4 is a diagram provided for explaining a method for inspecting the inside of an optical member for homogeneity according to a fourth embodiment;

FIG. 5 is a diagram for explaining a method for inspecting the inside of an optical member according to a fifth embodiment of the present invention;

FIG. 6 is a diagram showing an example of polishing processing of an optical glass member.

[Explanation of symbols]

 10: Light source 12: Inspection sample 14: Screen 16: Lamp house 18: Pinhole 20: Convex lens 22: Aperture 24: Optical member 32a, 32b: Tool glass 34a, 36b: First surface 34b: Incident surface 36b: Exit surface 38: optical axis 40: ingot 42: microbubble 44: bubble 46: striae 48: large bubble 50: first member 52: second member 54: third member 56: fourth member 58: fifth 60: Sixth member 62: Seventh member 70: Light source 72: First convex lens 74: Test sample 76: Second convex lens 78: Screen 80: Focus point 82: Incident surface 84: Exit surface 86 :focus

Claims (10)

[Claims] When inspecting the internal heterogeneity of an optical member using an observation image obtained by irradiating a test sample including the optical member with light, a surface that can be fitted to the surface is provided on the surface of the optical member. A method for inspecting the inside of an optical member for inhomogeneity, wherein a light incident surface and a light exit surface of a test sample are made substantially parallel planes by mounting a tool glass having the same. 2. The method according to claim 1, wherein when an observation image is obtained by irradiating the test sample with light from a first direction, the light of the test sample is measured. The mark is attached to a position on at least one of the entrance surface and the exit surface where the image of the mark substantially overlaps the observation image, and is different from the first direction with respect to the entrance surface of the test sample. When the observation image and the image of the mark substantially overlap when the test sample is irradiated with light from the second direction, it is determined that the observation image is derived from the surface with the mark. A method for inspecting the inside of an optical member for inhomogeneity. 3. The method for inspecting the inside of an optical member for inhomogeneity according to claim 2, wherein an incident side mark is attached to the incident surface and an exit side mark is attached to the exit surface as the mark, and the second direction is provided. When light is irradiated from the distance between the image of the incident side mark and the image of the emission side mark, the distance between the observation image and at least one of the image of the incident side mark and the image of the emission side mark. A method for inspecting internal inhomogeneity of an optical member, wherein a position of internal inhomogeneity is obtained based on a ratio. 4. The method according to claim 1, wherein the optical member is a quartz glass ingot or a member cut out of the ingot. Inspection method. 5. The method according to claim 2, wherein the light irradiating the optical member is radiated through a pinhole. Homogeneous inspection method. 6. The method according to claim 2, wherein the light irradiating the optical member is irradiating light in a schlieren optical system. Homogeneous inspection method. 7. The method for inspecting internal inhomogeneity of an optical member according to claim 6, wherein the irradiation light in the Schlieren optical system is a parallel light,
By rotating the test sample around an axis that is not parallel to the parallel light and changing the incident angle of the parallel light to the incident surface to an angle different from the angle in the first direction, the second A method of inspecting the inside of an optical member for heterogeneity, comprising irradiating the inspection sample with the parallel light from a direction. 8. A tool glass used for inspecting internal heterogeneity of an optical member by an observation image obtained by irradiating a test sample including the optical member with light, wherein the tool glass is fitted to a surface of the optical member. A possible first surface and the first
And a second surface which is a flat optically polished surface facing the surface of the tool glass. 9. The tool glass according to claim 8, wherein the first surface is an optically polished surface. 10. The tool glass according to claim 8, wherein the tool glass is made of a material having a refractive index substantially equal to a refractive index of the optical member.