JPH0626830A - Method and apparatus for measuring interference - Google Patents

Abstract

PURPOSE:To make it possible to measure and analyze interference fringes by generating the interference fringes by reflecting one of luminous fluxes, which interfere to each other, by odd number of times from the division of the wave front to the generation of the interference fringes, and reflecting the other by even number of times. CONSTITUTION:Luminous flux to be measured is cast into a semi-transparent prism 14, which is the first beam splitter. When the luminous flux to be measured is cast into the prism 14, a part of it directly passes, and the other is reflected to the left. Thus, the wave front of the luminous flux is divided into two luminous fluxes having the equal wave front. The luminous flux, which is reflected from the prism 14, enters into a semitransparent prism 22, which is the second beam splitter. Meanwhile, the luminous flux, which is transmitted through the prisim 14, is reflected from prisms 16 and 18 and reflected when the flux passes through an image inverting prism 20. The flux is reflected by three times as a whole and cast into the prism 22. The luminous flux is reflected with the prism 14 and combined with the luminous flux, which is reflected by two times with the prism 22. The luminous fluxes interfere to each other, and the interference fringes are generated on a screen 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interference measuring method and apparatus.

[0002]

2. Description of the Related Art Two measuring beams having equivalent wave fronts are used.
An interference measurement method is known in which a wavefront is divided into light beams, these two light beams interfere with each other to generate interference fringes, and the interference fringes are measured and analyzed to obtain information contained in the wavefront of the measurement light beam. Conventionally, in this type of interferometric measurement method, two light beams divided into wavefronts are laterally displaced from each other in order to generate interference fringes, and it may be difficult for the interference fringes to occur depending on the shape of the wavefront.

[0003]

SUMMARY OF THE INVENTION The present invention provides an interferometry method for interfering two wavefront-divided light fluxes with each other.
It is an object of the present invention to provide a novel interference measurement method that has never existed before and an apparatus for performing this method.

[0004]

The interferometric measuring method of the present invention is described as follows: "A measuring beam is split into two beams having equivalent wavefronts by a first beam splitter, and these two beams are split by a second beam splitter. An interferometric method of merging and interfering with each other ", characterized in that" one of the light beams interfering with each other is reflected an odd number of times between the wavefront division and the generation of interference fringes, and the other is reflected an even number of times " (Claim 1).

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. Moreover, the case where the number of reflections is an even number includes the case where the number of reflections is "0".

In the interferometric method according to claim 1, "an image reversing prism for reversing an image direction to one direction while preserving the direction of the optical axis ray is preserved in one optical path of the two divided light beams. Used, and by rotating it around the optical axis, the interference fringes in a desired direction can be emphasized ”.

The interferometer according to claim 3 is the interferometer according to claim 1.
An apparatus for carrying out the interference measurement method described in 1., which has a measurement light beam generator, first and second beam splitters, two or more mirror members, and a light receiver.
The “measurement light flux generator” includes a light source that emits coherent monochromatic light and generates a measurement light flux. The "first beam splitter" splits the measurement light flux, which is converted into a parallel light flux by the objective lens, into two light fluxes having equivalent wavefronts. The "second beam splitter" rejoins the two light beams separated by the first 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 "two or more mirror members" form two optical paths from the first beam splitter to the second beam splitter. The "light receiving section" reads the interference fringes.
The above-mentioned mirror member is arranged so as to “reflect even number of times for a light beam that follows one optical path and odd number of times for a light beam that follows the other optical path”, and one of the mirror members is “optical axis It is an image inverting prism that reverses the direction of an image in one direction while preserving the direction of light rays. As the mirror member other than the image inverting prism, an optical element such as a plane mirror or a mirror prism can be used.

The image inverting prism can be provided "rotatably around the optical axis" (claim 4). Further, one of the mirror members other than the image inverting prism can be displaceably provided so that "one of the light fluxes can be laterally displaced from the other" (claim 5). Further, in the interferometer according to claim 5, "the image inverting prism can be retracted from the optical path" (claim 6).

[0010]

As described above, according to the present invention, there is an "odd number difference" in the number of reflections of two light beams that interfere with each other to generate interference fringes. Therefore, when these light beams interfere with each other, the wavefront of each light beam is changed. Is a mirror image of the other.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically shows only an essential part of one embodiment of the interference measuring apparatus of the present invention. This embodiment is an example in which the interference measuring apparatus according to claim 4 is configured for "lens performance measurement".

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 and then passes through the focal point to become divergent light, which is then incident on the objective lens 12 and converted into a substantially parallel light beam to be a measurement light beam. That is, in this embodiment,
A holder (not shown) that holds the lens 0, the light source 10 and the objective lens 12 constitute a “measurement light flux generating section”. In the case of this example, the wavefront of the measurement light flux is ideally a plane, but in reality, it is a “distorted surface” due to the influence of the aberration or the like in the lens 0, and the “distortion degree” is an optical value related to the lens 0. Contains information.

The measurement light beam first enters a semi-transparent mirror prism 14 which is a first beam splitter. The semi-transparent prism 14 is formed by sandwiching an aluminum reflective film having a reflectance of 50% between the inclined surfaces of a pair of rectangular prisms. When the measuring light beam enters the semi-transparent mirror prism 14, a part of it is transmitted as it is,
The rest is reflected to the left of the figure. In this way, the measurement light beam is divided into two light beams having equivalent wavefronts.

The luminous flux reflected by the semi-transparent mirror prism 14 is the second semi-transparent mirror prism 2 which is a second beam splitter.
Incident on 2. The semi-transparent mirror prism 22 has the same structure as the semi-transparent mirror prism 14. On the other hand, the light flux transmitted through the semi-transparent mirror prism 14 is sequentially reflected by the mirror prisms 16 and 18 which are mirror members, and the image inverting prism 18
It is incident on the semi-transparent mirror prism 22 via. Both the mirror prisms 16 and 18 are made of an aluminum total reflection film.
It is sandwiched between the slopes of a pair of right-angled prisms.

The image inverting prism 20 is a symmetrical trapezoidal prism having a reflection film 21 formed on the bottom surface thereof, and is rotatable about the optical axis. A light ray incident on the image inverting prism 20 in alignment with the optical axis is refracted by the incident surface, reflected by the reflecting surface on the bottom surface, refracted again by the exit surface, and emitted in conformity with the optical axis. Therefore, in the light flux transmitted through the image inverting prism 20, "the direction of the optical axis ray is preserved".
However, the direction of the image, that is, the direction of the cross section of the light flux is reversed in one direction (in the example of the figure, the left-right direction of the figure). The total reflection on the bottom surface may be used without providing the reflection film 21.

The light flux that has passed through the image inverting prism 20 and has entered the semitransparent mirror prism 22 passes through the semitransparent mirror prism 22 and thus "directly enters from the semitransparent mirror prism 14 and is reflected by the semitransparent 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.

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 prisms 14 are reflected by the semitransparent mirror prisms 14 and 22. Screen 24
Therefore, it is reflected twice from the wavefront division to the generation of interference fringes. On the other hand, the semi-transparent mirror prism 14
The light flux that has passed through is only reflected by the mirror prisms 16 and 18 when the image reversal 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 the wavefront thereof 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
If the position of is fixed at the position shown in the figure, the wavefronts of the rays that pass through the image inversion prism and interfere with the other ray will be the wavefronts of the other ray inverted in the left-right direction of the figure. The inversion direction of the wavefront is limited to the horizontal direction in the figure. Of course, the wavefront inversion direction may be fixed with respect to the optical system space as described above, but if the position of the image inversion prism 20 is rotatable around the optical axis as in the above-described embodiment, the wavefront inversion is performed. Since the direction can be freely set, the wavefront can be inverted to 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 fringe appears most significantly.

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 divided into the wavefront is merged with the light flux that is incident from the semitransparent mirror prism 14 side and transmitted through the semitransparent mirror prism 22 and the light flux that is incident from the image inverting prism 20 side and reflected by the semitransparent mirror prism 22. Then, interference fringes are generated. The former light beam has one reflection, and the latter light beam has four reflections. 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 still another modification, if the mirror prism 16 is displaceable in the vertical direction in FIG. 1 or the mirror prism 18 is displaceable in the horizontal direction in the figure,
By displacing these displaceable mirror prisms, it is possible to give a “shear” between the two light fluxes that are wavefront-divided. In this case, if the image inverting prism 20 is retracted from the optical path and the image inverting prism 20 is retracted from the optical path, the optical system of FIG. Can be used as a "device".

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 imaging 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 embodiments and modifications, the wavefront is divided into two parts.
Since the light beams interfere with each other while preserving the polarization direction,
Good interference efficiency.

[0025]

As described above, according to the present invention, a novel interference measuring method and apparatus can be provided. As described above, the present invention "mirrors the wavefront of one light beam with the wavefront of the other light beam to cause interference", so that the wavefront shape of the measurement light beam is asymmetrical in a specific direction such as left / right or up / down. In this case, the asymmetry can be emphasized to generate interference fringes, and good measurement can be realized. In addition, the wavefront is divided into 2
Since the number of times the light beam is reflected is different by an odd number, the light path of one light beam becomes longer than the light path of the other light beam, and the wavefront shape of the light beam passing through this light path is better "referenced wavefront". This 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) 12 objective lens 14 first beam splitter 24 second beam splitter 16, 18 mirror prism (mirror member) 20 image inverting prism 28 pattern reader

Claims (6)

[Claims] 1. An interference measuring method in which a measurement light beam is wavefront-split by a first beam splitter into two light beams having equivalent wavefronts, and these two light beams are merged by a second beam splitter to interfere with each other. An interference measuring method characterized in that one of the interfering light beams is reflected an odd number of times between the wavefront division and the generation of interference fringes, and the other is reflected an even number of times. 2. The interferometric measuring method according to claim 1, further comprising an image reversing prism for reversing an image direction in one direction while preserving a direction of an optical axis ray in one optical path of the two divided light beams. An interference measurement method characterized by using this and rotating it around an optical axis to enhance interference fringes in a desired direction. 3. 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 are formed. The mirror member has two or more mirror members and a light receiving unit for reading interference fringes, and the mirror member reflects the light beam that follows one optical path an even number of times and the light beam that follows the other optical path an odd number of times. And one of the mirror members is an image reversing prism that reverses the direction of the image in one direction while preserving the direction of the optical axis ray. Interference measurement device. 4. The interference measuring apparatus according to claim 3, wherein the image inverting prism is rotatable around the optical axis. 5. The interferometer according to claim 3 or 4, 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. 6. The interference measuring apparatus according to claim 5, wherein the image inverting prism is retractable from the optical path.