JPH02156106A - Spherometer - Google Patents

Abstract

PURPOSE:To enable implementing of a highly accurate measurement of a radius of curvature in safety by measuring an interference fringe between a wave front passing as intact through a filter and a wave front diffracted with a pinhole. CONSTITUTION:A light wave 25 containing information as reflected on a surface to be measured and returning to an original optical path after leaving a light source 20 passes as intact through a filter 22 to form a wave front 26 while being diffracted with a pinhole 24. The diffraction light 27 is regarded as a spherical wave 28 for the smaller pinhole 24 and interferes with the wave front 26. When the surface to be measured is at a focus position P of an objective lens 7, the resulting interference fringe presents a straight fringe or a state without fringe (monochromatic) on the surface to be measured comprising a sphere as two wave fronts, namely, the wave front 26 passing through the filter and the spherical wave 28 coincide completely. With a deviation from the coincidence, a change is caused in the interference fringe and the surface moves to a position Q where it presents a straight state without fringe. Thus, a movement R of the surface to be measured coincides with a radius of curvature of the surface to be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spherical meter that optically measures the radius of curvature of a spherical surface using interference fringes.

[Conventional technology]

BACKGROUND ART In recent years, with the advancement of high precision and optical technology in optical application equipment, high precision and high quality optical components (lenses, prisms, etc.) have been required. To do this, it is first necessary to improve the accuracy of the measurement technology for optical components itself, and measurement of the radius of curvature of spherical surfaces such as lenses is no exception. consists of a meter,
Measurements have been devised that measure accurately and indirectly.

Fig. 3 shows a spherical meter using such a Fizeau type interferometer.To briefly explain this, 1 is a He- as a light source that emits a visible, infrared, or ultraviolet light beam 2 with good coherence. Ne laser, 3 is a diverging lens that diverges the luminous flux 2, 4 is a collimator lens that converts the diverging light into parallel rays parallel to the optical axis and guides it to the half mirror 5, and 6 is arranged between the half mirror 5 and the objective lens T. The flat prototype 8 is a concave lens as an object to be measured having a surface to be measured 9 which is applied from a spherical surface, and this concave lens 8 is installed on a slide table using a bearing so that it can be moved and adjusted in the optical axis direction. , is moved from the focal point P of the objective lens 7 to a point Q that is shifted in the optical axis direction by the radius of curvature of the concave lens 8 itself.

Now, when the concave lens 8 is in the focused fffP of the objective lens 7, the light beam 2 emitted from the He-Ne laser 1 is converted into a diverging light by the diverging lens 3, and the collimator lens 4
As a result, parallel light parallel to the optical axis is generated and transmitted through the half mirror 5 and the flat prototype 6. At this time, a part of the light beam is reflected by the reference surface 11 of the flat prototype 6, and is reflected in the direction of the screen 10 by hitting the half mirror 5, which moves along the original optical path. On the other hand, the transmitted light that has passed through the flat prototype 6 passes through the objective lens 7 and hits the surface to be measured 9 at point P. When the reflected light passes through the flat prototype 6 through the original optical path, the flat prototype 6 The interference pattern from the interference fringes at this time is projected onto the screen 10.

FIG. 4(a) shows the interference fringes at this time, which are straight fringes or a monochromatic state with no fringes at all.

Next, when the concave lens 8 is gradually moved from the focal position P to the 9th position, the interference fringes are curved as shown in the 41st false image, and when the concave lens 8 is continued to be moved further, it becomes a concentric circle as shown in the same figure (c). This results in interference fringes. Then, when it reaches near the position Q, it begins to curve as shown in Figure (b), and at position 9, it becomes a straight force stripe or a monochromatic state with no stripes at all, as shown in Figure (a). Therefore, the radius of curvature of the surface to be measured 9 is measured by measuring the moving distance R of the surface to be measured 9 using a magnescale or the like.

When the concave lens 8 is moved from the focal position P by the radius of curvature of the surface to be measured 9, the light beam focused at the focal position P hits the surface to be measured 9 and is reflected, and the spherical center of the surface to be measured 9 is reflected. The light is again focused on the focused ff1p, and the light beam is further passed through the objective lens 7.
, screen 1 via flat prototype 6 and half mirror 5
Projected onto 0.

Therefore, when the concave lens 8 is in two positions, focused @P and 9, there will be no interference fringes, and if you measure the distance between these two positions, you will essentially have measured the radius of curvature. That's why.

[Problem to be solved by the invention]

A spherical meter like this with a Fizeau interferometer built into the head can indirectly measure the radius of curvature with high measurement accuracy, but requires a highly stable light source, so a stabilized laser light source is used. There was a problem that I had no choice but to do. That is, the light wave reflected by the reference surface 11 that causes interference and the light wave having the surface-to-be-measured information reflected by the surface to be measured 9 are separated from each other when the flat prototype 6 and the concave lens 8 are physically separated from each other. Therefore, an optical path difference that is twice the distance between the two occurs, and this optical path difference becomes even larger as the radius of curvature of the surface to be measured 9 increases, and the larger the optical path difference, the clearer the interference fringes appear. Therefore, high stability is required for the light lees. As a result, the price of the spherical meter becomes very expensive.

Another problem is that it is necessary to select the reflectance of the reference surface 11 in accordance with the reflectance of the surface to be measured 9.

The reason for this is that if the reflectance of the reference surface 11 is kept constant without being changed, the clarity of the interference fringes will deteriorate if the reflectance of the surface to be measured 9 is high or low.

In addition, since a laser light source is used, there is a problem that it is dangerous for people who become blind to look directly at the light beam with the naked eye.

Therefore, the present invention solves the above-mentioned problems,
By using a semi-transparent filter with a pinhole instead of a flat prototype, we have made it possible to safely perform inexpensive, high-precision measurements using light sources with poor coherence such as white light. The purpose of this invention is to provide a spherical meter.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a light source, a half mirror disposed on the optical path of the light source, and a surface to be measured consisting of a spherical surface disposed so as to be able to move and adjust the light transmitted through the half mirror in the direction of the optical path. and a semi-transparent filter having a pinhole arranged on a converging surface of the light that hits the surface to be measured and returns along the original optical path and is reflected by the half mirror. The interference fringes between the wavefront that has passed through the filter and the wavefront that has been diffracted by the pinhole are measured.

[For production]

In the present invention, the light diffracted by the pinhole of the semi-transparent filter forms a spherical wavefront as the pinhole becomes smaller, and this wavefront and the wavefront transmitted by the surface to be measured that passes directly through the filter. interfere with each other,
Shape accuracy of the surface to be measured.

Forms interference fringes with position and tilt information. At this time,
The diffracted light hits the surface to be measured and is reflected, and when the returning light passes through the filter, it is generated by a pinhole, so the optical path difference between the two wavefronts described above is almost zero.

〔Example〕

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 is a configuration diagram showing an embodiment of a spherical meter according to the present invention. The same components as in Figure 3 are shown in the figure.

Components are designated by the same reference numerals and their explanations will be omitted. In the figure, this embodiment uses a white light source 20 instead of a laser light source as a light source, and a slit 21 is arranged between the diverging lens 3 and the half mirror 5.
This differs from the conventional spherical meter shown in FIG. It's different.

The semi-transparent filter 22 has a thickness of 5 to 20μ as shown in FIG.
It has a pinhole 24 with a diameter of approximately m, and is placed on the condensing surface where light υ reflected from the surface to be measured 9, that is, a light wave 25 containing information about the surface to be measured 9, is focused by the objective lens 7. . A light wave 25 containing information that is emitted from the light source 20, hits the surface to be measured 9, is reflected, and returns along the original optical path passes through the filter 22 as it is, forms a wavefront 26, and at the same time is diffracted by the pinhole 24. The smaller the pinhole 24 is, the more this diffracted light 2T appears as a spherical wave 28, and the filter 2
2 and interferes with the wavefront 26 that passed through the wavefront 26 as it is.

Therefore, the semi-transparent filter 22 performs the same function as the flat prototype 6 shown in FIG.

The interference fringes resulting from the transparent wavefront 26 and the spherical wave 28 of the diffracted light have information on the position and inclination of the surface to be measured 9, and are projected onto the screen 10 by the projection lens 23. is projected onto the surface to form an interference pattern.

At this time, when the surface to be measured 9 is at the focal position P of the objective lens 7, the interference fringes are 2
The two wavefronts, that is, the passing wavefront 26 and the spherical wave 28, completely match, and on the spherical surface to be measured, either straight stripes as shown in FIG. 4(a) or no stripes at all (monochromatic) are formed. 4 (b) and (c).
) and move to the Q position where there are no stripes again. Therefore, when the movement amount R of the surface to be measured 9 is measured, this value coincides with the radius of curvature of the surface to be measured 9, and therefore, this radius of curvature has been measured.

Thus, in a spherical meter with such a configuration, the optical path difference between the wavefront 26 that passes through the semi-transparent filter 22 and the spherical wave 28 diffracted by the pinhole 24 is zero, so the measured surface has a large radius of curvature. Even if the interference pattern is measured, good interference fringes can be obtained, there is no need for a highly stable laser light source, and it is possible to use an inexpensive white light source with poor coherence. Can be measured with high precision.

Furthermore, since a constant proportion of the light beam reflected from the surface to be measured 9 always serves as the reference light, clear interference fringes can always be obtained regardless of the reflectance of the surface to be measured 9.

〔Effect of the invention〕

As described above, the spherical meter according to the present invention has a semi-transparent filter having a pinhole placed at the converging surface position of the light that comes out from the light source, hits the surface to be measured, is reflected, and returns. The interference pattern formed by the mutual interference between the passing wavefront and the wavefront diffracted by the pinhole is obtained, and this is used to measure the amount of movement of the surface to be measured, in other words, the radius of curvature, so high measurement accuracy is achieved. Despite the K obtained, there is no optical path difference between the two wavefronts, and an inexpensive light source such as a white light source can be used instead of an expensive laser light source, making it possible to reduce the cost and improve the clarity of interference fringes. Although it is safe to directly view the light beam from a good light source with the naked eye, its effects are very large.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing wavefront interference by a semi-transparent filter, and Fig. 3 is a schematic configuration diagram of a spherical meter using a conventional Fizeau type interferometer. , FIGS. 4(a), 4(b), and 4(c) are diagrams showing interference fringes. 1... Φ He-Ne laser, 3... Diverging lens, 4... 9 collimator lens, 5... Half mirror 6... Flat prototype, 7... Objective lens, 811
...Concave lens, 911...Measurement surface, 11...
Screen, 20 rounds...white light L21-...slit, 22...number semi-transparent filter, 23...projection lens, 24-...pinhole, 26, 28...φ...
wave surface.

Claims (1)

[Claims] a light source, a half mirror placed on the optical path of the light source,
An objective lens that guides the light transmitted through the half mirror to a surface to be measured consisting of a spherical surface arranged so as to be movable and adjustable in the direction of the optical path; A semi-transparent filter having a pinhole placed on a converging surface of the reflected light, and measuring interference fringes between a wavefront passing through the filter and a wavefront diffracted by the pinhole. A spherical meter characterized by: