JPH0634315A - Interference measuring apparatus - Google Patents

Abstract

PURPOSE:To carry out interference measurement and direct observation simultaneously by dividing measurement light fluxes into two equivalent light fluxes by wavefront dividing and rejoining them by a second beam splitter. CONSTITUTION:Measurement light fluxes from a light source 10 go to a first beam splitter 14 anal while a part of them pass, the rest are reflected and go to a second beam splitter 22. The light fluxes which passed the splitter 12 are reflected by a semi-transparent mirror prism 16 and a mirror prism 18 and go to the splitter 22 through an image reversing prism 20. The coming in light fluxes are joined to the light fluxes, which come directly from the splitter 14 and are reflected by the splitter 22, by passing the splitter 22 and interference patterns are generated on a screen 24 and an image is formed on a pattern reading out apparatus 28. Meanwhile, the light fluxes which pass the splitter 14 and the prism 16 form an image on a CCD camera 15 through an objective lens 11 and an image forming lens 13 in an observation part and thus the image can be observed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer.

[0002]

2. Description of the Related Art Two measuring beams having equivalent wave fronts are used.
There is known an interferometer that splits a wavefront into light beams, causes these two light beams to interfere with each other to generate interference fringes, and measures and analyzes the interference fringes to obtain information contained in the wavefront of the measurement light beam. Conventionally, this type of interferometer has a problem that it is not possible to simultaneously perform interferometry and direct observation of the measurement light beam.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel interferometric measuring device capable of simultaneously performing interferometric measurement and direct observation.

[0004]

An interference measuring apparatus according to claim 1 comprises a measuring light beam generating section, first and second beam splitters, two or more mirror members, a light receiving section, and an observing section. Have. The “measurement light flux generation unit” includes a measurement light flux light source that emits coherent monochromatic light and generates a measurement light flux. The “first beam splitter” splits a measurement light beam including measurement information as a wavefront shape into two light beams having equivalent wavefronts. "Second beam splitter"
Rejoins the two light beams separated by the first beam splitter. The “two or more mirror members” form two optical paths from the first beam splitter to the second beam splitter. Optical elements such as a semi-transparent mirror and a semi-transparent mirror prism can be used as the first and second beam splitters.

The "light receiving section" reads the interference fringes. The "observation section" is a section for forming an image of one of the light beams whose wavefront is divided by the first beam splitter for observation.

In the interferometer according to the first aspect of the present invention, in the above configuration, "one of the two or more mirror members is a beam splitter, and a part of one of the light beams having the wavefront division is separated to the observation part side, One of the mirror members of (1) displaces one of the light fluxes divided into the wavefronts with respect to the other. That is, in the interference measurement apparatus according to the first aspect, the interference measurement is performed by the measurement method conventionally known as “sharing interference measurement method”.

An interferometer according to a second aspect of the present invention comprises a measuring light beam generator, first and second beam splitters, and a second beam splitter.
It has the above-mentioned mirror member, a light sensing portion, and an observation portion. Among these, the measurement light flux generating unit, the first and second beam splitters, the light receiving unit, and the observing unit are the same as those in the interferometer according to claim 1.

In the interferometer according to the second aspect of the present invention, in the above configuration, "the mirror member realizes reflection even number of times for a light beam following one optical path and odd number reflection for a light beam following the other optical path. , One of the mirror members splits a part of one of the light beams whose wavefront is split by the beam splitter to the observation side, and the other one of the mirror members stores the image while preserving the direction of the optical axis rays. It is an image reversing prism that reverses the direction of "in one direction." Here, "the number of reflections from the wavefront division to the generation of interference fringes" includes the reflection at the time of wavefront division and light flux merging. In addition, the case where the number of reflections is an even number includes the case where the number of reflections is "0". Further, that the image inverting prism "preserves the direction of the optical axis ray" means that the optical axis ray incident on the image inverting prism and the optical axis ray exiting from the prism are on the same straight line. .

The "image inverting prism" in the interferometer according to the second aspect may be fixed in the apparatus space or may be "rotatable about the optical axis" (third aspect). Further, in the interferometer according to claim 2 or 3, one of the mirror members other than the image inverting prism can be displaceable so that "one of the light fluxes can be laterally displaced from the other" ( According to claim 4), in this case, the image inverting prism can be "retractable from the optical path" (claim 5).

[0010]

As described above, according to the present invention, the measurement light beam is divided into two light beams and interferes with each other to generate interference fringes. At the same time, however, a part of the wavefront-divided light beams is observed by the observation section side. In the invention according to claim 1, the two light beams divided into the wavefronts are laterally offset from each other and interfere with each other. In the invention according to claim 2, there is an "odd number difference" in the number of reflections of the two light beams that interfere with each other to generate interference fringes. Therefore, when these light beams interfere with each other, one of the wavefronts of the respective light beams is the other. It is related to the mirror image of.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an interferometer 1 according to claims 3 and 4.
Only an essential part of the embodiment is schematically shown. This embodiment is an example in which the interference measuring apparatus according to claims 3 and 4 is configured for "lens performance measurement", and the illustrated one measures the imaging performance of an objective lens used in an optical pickup. This is the case.

The lens 0, which is the subject, is held in a measurement position by an appropriate holder (not shown) and is irradiated by the light source 10. The light source 10 is a semiconductor laser in this embodiment, and emits coherent monochromatic light. The radiated light beam passes through the lens 0, is condensed at the focusing point P, becomes divergent light, enters the objective lens 12, and is converted into a substantially parallel light beam to be a measurement light beam. That is, in this embodiment, a holder (not shown) for holding the lens 0 and the light source 1 are provided.
0 and the objective lens 12 constitute a “measurement light flux generating section”. The light intensity distribution at the condensing point P gives the light intensity distribution of the light spot irradiated on the recording surface of the optical information recording medium such as an optical disc.

The wavefront of the measurement light beam made into a substantially parallel light beam by the objective lens 12 is ideally a plane, but in reality, it is a "distorted surface" due to the influence of the aberration in the lens 0 and the like. , The “distortion degree” includes optical information about the lens 0.

The measurement light beam first enters a semi-transparent mirror prism 14 which is a first beam splitter. The semi-transparent mirror prism 14 is formed by sandwiching an aluminum reflective film having a reflectance of 30% between the inclined surfaces of a pair of right angle prisms. When the measurement light beam enters the semi-transparent mirror prism 14, a part of the light beam is transmitted as it is and the rest is reflected to the left in the figure. In this way, the measurement light beam is divided into two light beams having equivalent wavefronts.

The light beam reflected by the semi-transparent mirror prism 14 is a semi-transparent mirror prism 2 which is a second beam splitter.
Incident on 2. The semitransparent prism 22 has a reflectance of 50.
% Aluminum reflective film sandwiched between the slopes of a pair of right angle prisms.

On the other hand, the light flux transmitted through the semitransparent mirror prism 14 is sequentially reflected by the semitransparent mirror prism 16 and the mirror prism 18, which are mirror members, and the image inverting prism 18 is used.
It is incident on the semi-transparent mirror prism 22 via. The semi-transparent mirror prism 16 is the same as the semi-transparent mirror prism 22, and the mirror prism 18 is formed by sandwiching a total reflection film made of aluminum between the slopes of a pair of right-angle prisms.

The image inverting prism 20 is a symmetrical trapezoidal prism having a reflective film 21 formed on the bottom surface thereof, and is rotatable about the optical axis. A light ray (optical axis light ray) incident on the image inverting prism 20 in conformity with its optical axis is refracted by the incident surface, reflected by the reflecting surface of the bottom surface, refracted again by the exit surface and emitted in conformity with the optical axis. To do. Therefore, in the light flux transmitted through the image inverting prism 20, the image inverting prism 20
Since the optical axis of the light beam incident on the optical axis and the optical axis of the light beam emitted from the image inverting prism 20 are on the same straight line, "the optical axis ray direction and the light beam polarization direction are preserved", but the image direction ,
That is, the direction of the cross section of the light beam is reversed in one direction (in the example of the figure, the horizontal direction of the figure). The total reflection on the bottom surface may be used without providing the reflection film 21.

The light flux which has passed through the image inverting prism 20 and has entered the semi-transparent mirror prism 22 passes through the semi-transparent mirror prism 22, whereby "the light beam directly enters from the semi-transparent mirror prism 14 and is reflected by the semi-transparent mirror prism 22." Light fluxes ”and interfere with each other to generate interference fringes on the screen 24. The interference fringes are transferred to the CCD by the imaging lens 26.
An image is formed on the light receiving surface of the pattern reading device 28 such as a camera. Therefore, in this embodiment, the screen 24, the imaging lens 26, and the pattern reading device 28 constitute a light receiving portion. By setting the reflectance of each of the semitransparent mirror prisms 14, 16 and 22 as described above, the two light beams that interfere with each other have substantially equal light intensities.

Here, suppose that the image inverting prism 20 is not provided. Of the light fluxes reaching the screen 24, the light fluxes reflected by the semitransparent mirror prism 14 are reflected by the semitransparent mirror prisms 14 and 22. Since it is reflected and reaches the screen 24, it is reflected twice from the wavefront division to the occurrence of interference fringes. On the other hand, the light flux transmitted through the semi-transparent mirror prism 14 is reflected only by the mirror prisms 16 and 18 when the image inversion prism is excluded, so the number of reflections is two. Therefore, if the image inverting prism 20 is not provided, the light beams overlap with each other in the same state, and there is no share (sideways shift) between the light beams, so that interference fringes do not occur on the screen 24 even if they interfere with each other.

However, when the image inverting prism 20 is arranged as shown in the figure, the number of reflections of the light beam passing through the semi-transparent mirror prism 22 is three times, and its wavefront is the wavefront of the other light beam. It will be flipped to the left and right. Therefore, when the wavefront of the measurement light beam is asymmetric with respect to the optical axis of the optical system, the interference fringes are generated as emphasizing the asymmetry of the wavefront. Therefore, the optical characteristics of the lens 0 can be effectively measured by reading and analyzing such interference fringes.

In the above embodiment, the image inverting prism 20
When the position of is fixed at the position shown in the figure, the wavefront of the light beam that passes through the image inverting prism and interferes with the other light beam is the wavefront of the other light beam inverted in the left-right direction of the figure,
The direction of wavefront inversion is limited to the left-right direction in the figure. Although the wavefront inversion direction may be fixed with respect to the optical system space as described above, if the position of the image inversion prism 20 is rotatable around the optical axis as in the above-described embodiment, the direction of wavefront inversion is obtained. Can be set freely, so that the wavefront can be inverted in a desired direction and the interference fringes in this direction can be emphasized.
For example, when the lens 10 has an inclination of the optical axis, the direction in which the inclination of the optical axis is generated can be detected by rotating the image inverting prism and searching for the position where the interference fringes appear most significantly.

On the other hand, the light flux that has been wavefront-divided by passing through the semi-transparent mirror prism 14 and then passing through the semi-transparent mirror prism 16 is converged by the objective lens 11 of the observing section and condensed at point Q. This Q point has a conjugate relationship with the above-mentioned condensing point P. The condensed state of the point Q is appropriately enlarged by the imaging lens 13 and is focused on the CCD camera 15 as a light spot. That is, in the illustrated embodiment, the objective lens 11
The imaging lens 13 and the CCD camera 15 constitute an observation section.

After all, the condensing point P and the light receiving surface of the CCD camera have a conjugate relationship with each other. The light spot imaged on the CCD camera 15 is the image of the converging point P, but it is affected by the aberration of the optical system between the point P and the light receiving surface,
The light intensity distribution at the focal point P is not accurately reproduced. However, the influence of the above-mentioned aberration is uniquely determined as the characteristic of the measuring device, and therefore can be corrected, and by appropriately calculating and correcting the light intensity distribution of the light spot received by the CCD camera 15, the correction can be performed. It is possible to know the light intensity distribution at the light point P (light intensity distribution of the light spot formed on the recording surface of the optical information recording medium).

As described above, in the apparatus of this embodiment, it is possible to simultaneously perform optical observation measurement by the observation section and measurement by interference fringe analysis for the measurement light flux, and it is also possible to collate the results of both measurements in real time. Is.

A modified example will be described below. First, regarding the arrangement of the light receiving portion, the light receiving portion may be arranged at a position on the left side of the semitransparent mirror prism 22 instead of the arrangement shown in the drawing. In this case, the light flux that has undergone wavefront division joins the light flux that has entered from the semitransparent mirror prism 14 side and transmitted through the semitransparent mirror prism 22 and the light flux that has entered from the image inversion prism 20 side and reflected by the semitransparent mirror prism 22. Then, interference fringes are generated. The number of reflections is once for the former luminous flux and four times for the latter luminous flux. Similarly, the measurement light flux generator may be arranged to the right of the first beam splitter 14 in FIG.

As another modification, in the optical arrangement shown in FIG. 1 or in the above-mentioned "optical arrangement in which the light portion is located to the left of the semi-transparent mirror prism 22", the image inverting prism 20 is used.
May be placed between the semi-transparent mirror prisms 14 and 22 in place of the position shown in FIG.

As another modification, a semi-transparent mirror prism 16
Is displaceable in the vertical direction of FIG. 1 or the mirror prism 18 is displaceable in the horizontal direction of the figure, the displaceable mirror prisms are displaced so that a "share Can be given. In this case, if the image reversing prism 20 is retracted from the optical path and the image reversing prism 20 is retracted from the optical path, the optical system of FIG. Can be used as

The amount of "shear" given by the semi-transparent mirror prism 16 or the mirror prism 18 may be variable as described above, but the shift amount of these prisms is fixed so that a constant amount of shear is always obtained. You can
In the case where the sharing is performed by the semi-transparent mirror 16 or the mirror prism 18 as described above, if the image inverting prism 20 is removed from the embodiment of FIG. 1, one embodiment of the invention according to claim 1 can be obtained.

As another modification, the screen 24 is omitted in the above-described embodiment and each modification, each light beam is imaged on the pattern reading device 28 by the imaging lens 26, and these imaged light beams are directly patterned. You may make it interfere on the light-receiving surface of the reader 28, and measure and analyze the interference fringe.

In each of the above-mentioned embodiments and modifications, the two light beams having the wavefront division interfere with each other while preserving the polarization directions, so that the interference efficiency is good.

[0031]

As described above, according to the present invention, a novel interference measuring device can be provided. In the interference measuring apparatus of the present invention, it is possible to simultaneously perform the direct observation measurement and the interference measurement on the measurement light beam as described above.

In the interferometer according to the second aspect of the present invention, since the wavefront of one of the wavefront-divided light beams is mirror-inverted and interfered with the other light beam, the wavefront shape of the measurement light beam is left, right, up, or down. In the case of asymmetry in a specific direction, the asymmetry can be emphasized to generate interference fringes, and good measurement can be realized. Further, since the number of reflections of the two light beams divided into the wavefronts is made to differ by an odd number of times, the optical path of one light beam becomes longer than the optical path of the other light beam, and the wavefront shape of the light beam passing through this optical path is better "referenced wavefront". This also contributes to the improvement of measurement accuracy.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing only a main part of one embodiment of the present invention.

[Explanation of symbols]

10 light source 0 lens (subject) 14 first beam splitter 24 second beam splitter 16 semi-transparent mirror prism (mirror member) 18 mirror prism (mirror member) 20 image inverting prism 28 pattern reader 11 objective lens 13 imaging lens 15 CCD camera (constitutes an observation unit together with the objective lens 11 and the imaging lens 13)

Claims (5)

[Claims] 1. A measurement light beam generator including a light source for measurement light beam that emits coherent monochromatic light; and a measurement light beam including measurement information in the form of a wavefront, which is wavefront-divided into two light beams having equivalent wavefronts. A first beam splitter, a second beam splitter that rejoins the two light beams separated by the first beam splitter, and two optical paths from the first beam splitter to the second beam splitter 2 The mirror member includes the above-described mirror member, a light receiving unit for reading interference fringes, and an observation unit for forming an image of one of the light beams split by the first beam splitter for observation. One is a beam splitter, which splits a part of one of the wavefront-divided light beams toward the observation section side, and one of the two or more mirror members is subjected to the wavefront division. An interferometer which is characterized in that one of the light beams is laterally displaced with respect to the other. 2. A measuring light flux generating section including a light source for measuring light flux that emits coherent monochromatic light; and a measuring light flux including measurement information in the form of a wavefront, which is wavefront-divided into two light fluxes having equivalent wavefronts. A first beam splitter, a second beam splitter that rejoins the two light beams separated by the first beam splitter, and two optical paths from the first beam splitter to the second beam splitter 2 The mirror member includes the above-described mirror member, a light-receiving unit for reading interference fringes, and an observation unit for forming an image of one of the light beams split by the first beam splitter for observation. One of the two or more mirror members is arranged so as to realize an even number of reflections for a light beam following the optical path and an odd number of reflections for a light beam following the other optical path. In the liter, a part of one of the light fluxes divided into the wavefronts is separated to the observation section side, and another one of the mirror members changes the direction of the image in one direction while preserving the direction of the optical axis ray. An interferometer that is an image reversing prism that reverses to the right. 3. The interference measuring apparatus according to claim 2, wherein the image inverting prism is rotatable about the optical axis. 4. The interferometer according to claim 2 or 3, wherein one of the mirror members other than the image inverting prism is displaceable so that one of the light beams can be laterally displaced with respect to the other. Interferometer. 5. The interference measuring apparatus according to claim 4, wherein the image inverting prism is retractable from the optical path.