JPH0915149A - Optical material homogeneity inspection device - Google Patents

Abstract

(57) [Abstract] [Purpose] An object is to provide a device capable of detecting the presence or absence of inhomogeneity due to a gradual change in refractive index inside an optical material by a simple means. Provided is a device capable of detecting the presence or absence of inhomogeneity due to a large change in refractive index and the presence or absence of striae in which the refractive index changes abruptly by a simple switching operation. In an apparatus for inspecting the homogeneity of an optical material 4 by injecting parallel light into the optical material 4 to be inspected and forming an image of transmitted light transmitted through the optical material 4 by an imaging lens 5. At the condensing position of the parallel light by the image lens 5, a phase plate 8 that shifts the phase of the light passing through the condensing position by π / 2 with respect to the phase of the light not passing through the condensing position.
Is arranged, and the phase plate 8 and the knife edge 7 that is arranged to move back and forth toward the converging position are
It is characterized by being provided so that it can be switched.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an apparatus for inspecting the homogeneity of optical materials.

[0002]

2. Description of the Related Art In order for an optical material to fully exhibit its characteristics, it must be a homogeneous optical material free of striae, bubbles, foreign matters and the like. Conventionally, there is a Schlieren method as a method for inspecting the homogeneity of an optical material. The Schlieren method will be described with reference to FIG.
Through the collimator lens 3 to form a parallel light beam, and the parallel light beam is incident on the optical material to be inspected, that is, the object 4 to be inspected, and the transmitted light that has passed through the object 4 is projected onto the screen 6 by the imaging lens 5. Form an image. The transmitted light that has passed through the inspection object 4 converges on the focus position of the imaging lens 5, that is, the focus position, and then becomes divergent light and reaches the screen 6. Therefore, when the knife edge 7 is brought close to the condensing position of the imaging lens 5, the screen 6 changes from a uniformly bright state to a uniformly dark state. However, if striae or the like are present on the subject 4, the parallel light incident on the subject 4 is bent at the striae and does not pass through the focusing position of the imaging lens 5. Therefore, when the parallel light is bent in the direction approaching the knife edge 7 due to the striae, the bent light is blocked by the knife edge 7, so that the position on the screen 6 corresponding to the striae is larger than that in other portions. It gets dark.
On the other hand, when the parallel light is bent in the direction away from the knife edge 7 by the striae, even if the screen 6 is uniformly darkened by the other light being gradually blocked by the knife edge 7, the bent light is Since it is not shielded by the knife edge 7, the position corresponding to the striae on the screen 6 is brighter than other parts. In this way, the distribution of the refractive index of the object 4 to be inspected, particularly striae, is projected on the screen 6 as a contrast of light and dark. As another method, the inhomogeneity of the gradual change in the refractive index was inspected using an interferometer.

[0003]

The Schlieren method is simple and effective for striae where the change in the refractive index is abrupt. I have to rely on it. However, the interferometer is complicated and expensive. Therefore, an object of the present invention is to provide an apparatus capable of detecting the presence or absence of inhomogeneity due to a gradual change in refractive index inside an optical material by a simple means. The present invention also provides an apparatus capable of detecting both the presence or absence of inhomogeneity due to a gradual change in the refractive index inside an optical material and the presence or absence of striae where the refractive index changes rapidly by a simple switching operation. The purpose is to do.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, that is, parallel light is incident on an optical material to be inspected, and transmitted light transmitted through the optical material is imaged. In an apparatus for inspecting the homogeneity of an optical material by forming an image with a lens, the image forming lens passes the light collecting position to the light collecting position of the parallel light and the phase of the light that does not pass the light collecting position. A homogeneity inspection apparatus for an optical material, characterized in that a phase plate for shifting the phase of light by π / 2 is arranged. At this time, the phase plate and the knife edge that is arranged to move back and forth toward the converging position can be provided so as to be switchable.

[0005]

The 0th-order light passing through the condensing position of the imaging lens shifts the phase by π / 2 to reach the imaging plane because the phase plate is arranged at the condensing position. The primary light that has passed through the non-uniform refractive index portion reaches the image forming surface without passing through the condensing position of the image forming lens. Therefore, according to the principle of the phase contrast microscope, what appears as a change in phase difference on the image plane when there is no phase plate is converted into a change in contrast by interposing a phase plate in the portion where the 0th order light passes. Therefore, it is possible to inspect for the presence of inhomogeneities in the refractive index. Furthermore, by arranging this phase plate in a switchable manner with the knife edge, striae, bubbles and foreign substances can also be inspected and thus different types of homogeneity can be inspected with one device.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. The light emitted from the light source 1 passes through the pinhole 2, becomes a parallel light flux by the collimator lens 3, and the test light 4 is transmitted through the parallel light flux with the test object 4 interposed. As the light source 1, a halogen lamp, a laser or the like can be used, but when a halogen lamp or the like is used,
It is preferable to put a filter or the like into monochromatic light. The diameter φ of the pinhole 2 is set in consideration of the focal length of the collimator lens 3 and the thickness of the object to be inspected 4 so that a sufficiently parallel light beam can be obtained, and the thickness of the object to be inspected 4 with respect to the image plane In order to obtain a sufficient depth of focus, it is preferable to set the thickness to about several tens of μm to several hundreds of μm.

The light flux that has passed through the object 4 to be inspected is formed by the imaging lens 5
The light is focused at the focal position by and is focused on the screen 6. A phase plate 8 is arranged at the focusing position of the imaging lens 5. As shown in FIG. 2, the phase plate 8 is formed by attaching a phase changing portion 8a to the center of the constant phase portion 8b. The diameter φ ′ of the phase changing portion 8 a is formed to be slightly larger than the diameter of the conjugate image of the pinhole 2, and the phase changing portion 8 a
The thickness of a is formed such that the phase is advanced or delayed by π / 2. A glass plate can be used as the constant phase portion 8b, and a transparent film or the like can be used as the phase change portion 8a. Further, a knife edge 7 is provided so as to be switched with the phase plate 8, and the knife edge 7 is arranged so as to be movable back and forth in the direction orthogonal to the optical axis at the focusing position of the imaging lens 5.

This embodiment is configured as described above.
When inspecting the inspection object 4 for striae, bubbles, and foreign matter,
The knife edge 7 is arranged in the vicinity of the converging position of the imaging lens 5, the position of the knife edge 7 is adjusted, and the presence or absence of striae is judged from the light and dark projected on the screen 6. On the other hand, when inspecting the presence or absence of inhomogeneity of the test object 4, the phase plate 8 is inserted in the optical path in place of the knife edge 7, and the 0th-order light transmitted through the test object 4 passes through the phase changing portion 8a. Place it so that it is transparent. As a result, when primary light is present,
The change in phase becomes a change in lightness and darkness and is projected on the screen 6, thus measuring the uneven distribution of the refractive index inside the test object 4. The image on the screen 6 can be detected by using a CCD or the like, or instead of the screen 6, a CCD or the like can be directly arranged at that position.

As described above, according to this embodiment, the presence or absence of inhomogeneity of the object 4 can be inspected by a simple device without using an interferometer. Further, in this embodiment, since the phase plate 8 and the knife edge 7 are arranged in a switchable manner, a simple switching operation of the same device allows inspection of striae and a more inhomogeneous change in refractive index. It can be done together with the sex examination.

FIG. 2B shows another embodiment of the phase plate 8. In the phase plate 8 of this embodiment, the upper half part and the lower half part are the light shielding parts 8c, and the constant phase parts are provided on both sides of the intermediate part. 8b is provided, and a circular phase change portion 8a is provided at the center of the intermediate portion.
The phase plate 8 is arranged so as to be rotatable about the optical axis. The refractive index distribution in the test object 4 may have a certain directionality, and in that case, the phase plate 8 of this embodiment is used and excess light is cut by the light shielding portion 8c.
Moreover, by rotating the phase plate 8 according to the direction of the inhomogeneity, the inhomogeneity can be inspected more clearly.

FIG. 2C shows still another embodiment. The phase plate 8 of this embodiment is provided with a constant phase portion 8b on the left and right and an elongated phase changing portion 8a at the center. The phase plate 8 is also arranged so as to be rotatable about the optical axis. In the configuration of FIG. 2B, the light shielding portion 8c is provided in the vertical direction in the figure, and the phase changing portion 8 is provided in the horizontal direction.
a and the constant phase portion 8b are provided, the test object 4
When the refractive index of is changing in the vertical direction, it cannot be inspected, and only the change in the refractive index in the horizontal direction can be observed. Similarly, in the configuration of FIG. 2C as well, the phase plate 8 is uniformly formed in the vertical direction, and the phase changing portion 8a and the constant phase portion 8b are provided in the horizontal direction. Only changes in the refractive index in the left-right direction can be observed. However, since the phase plate 8 is rotatably arranged in any of the configurations, it is necessary to clearly grasp the inhomogeneity when the refractive index distribution in the DUT 4 has a certain directionality. You can The above-mentioned respective examples function particularly effectively when the test object 4 is an infrared optical material.

[0012]

As described above, according to the present invention, the presence or absence of inhomogeneity of the optical material can be inspected by a simple device without using an interferometer. Further, by disposing the phase plate and the knife edge so as to be switchable, the inspection of striae and the inspection of inhomogeneity can be performed by the same apparatus.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of the present invention.

FIG. 2A is a front view showing a phase plate of the embodiment;
(B) A front view showing a phase plate of another embodiment, and (C) a front view showing a phase plate of still another embodiment.

FIG. 3 is a schematic configuration diagram showing a conventional example.

[Explanation of symbols]

1 ... Light source 2 ... Pinhole 3
... Collimator lens 4 ... Test object 5 ... Imaging lens 6
… Screen 7… Knife edge 8… Phase plate 8
a ... phase changing portion 8b ... constant phase portion 8c ... light shielding portion

Claims (2)

[Claims] 1. An apparatus for inspecting the homogeneity of an optical material by injecting parallel light to an optical material to be inspected and forming an image of transmitted light transmitted through the optical material by an imaging lens. A phase plate that shifts the phase of the light passing through the condensing position with respect to the phase of the light not passing through the condensing position by π / 2 is arranged at the condensing position of the parallel light by the lens. Homogeneity inspection device for optical materials. 2. The homogeneity inspection apparatus for an optical material according to claim 1, wherein the phase plate and a knife edge which is arranged to move forward and backward toward the converging position are provided so as to be switchable.