JPS61294327A - Interference method and interferrometer for measuring surface shape of parabolic mirror - Google Patents

Abstract

PURPOSE:To easily, surely and inexpensively measure the surface shape of a parabolic mirror by reflecting illumination light by the parabolic mirror to be measured and observing the interference fringe of the parallel reflected light reflected therefrom and standard light. CONSTITUTION:The beam from a laser light source 3 is split by a beam splitter BS1 to measure the surface shape of the parabolic mirror TM to be measured. One of the split beams is conducted to a divergent spherical wave generating optical system 4. The luminous flux is made into the divergent spherical wave by a microscopic objective lens Mo1 and a pinhole P1 and is reflected by the TM. The reflected flux arrives as the parallel reflected light at an observation lens OL. The other luminous flux is conducted to a parallel light forming optical system 5 and is made by a collimator lens CL to parallel light. The parallel light is reflected by a flat mirror FM and arrives at the lens OL. The parallel light and the parallel reflected light reflected from the TM overlap on each other but the light reflected from the TM deviates from the parallel light which is standard by receiving the influence of the ruggedness at the specular surface of the TM and therefore the interference fringe is generated. The surface shape of the TM is measured from the pitch of the interference fringe and the deviation quantity.

Description

Detailed Description of the Invention (a) Purpose of the Invention [Field of Industrial Application] This invention relates to an interferometer for measuring the surface shape of a parabolic mirror.

[Prior art] A parabolic mirror can condense incident parallel light to a point outside the incident light without aberration, and conversely can reflect diverging spherical wave light from one point as parallel light in another direction. It is one of the important optical elements, and is essential, for example, as a focusing mirror for laser fusion.

In order to inspect the surface shape of this parabolic mirror, the surface shape is inspected by the size of the point when parallel light is focused on the parabolic mirror that is the object to be inspected. This is the current situation. In this case, the better the surface shape precision of the mirror surface to be inspected, the smaller the light spot at the focal point. However, this surface shape inspection method only measures the light convergence and cannot measure the surface shape.

In addition, as shown in FIG. 5, as a conventionally known interferometer for measuring the shape of a parabolic mirror, a beam from a laser light source 51 is made into parallel light by a collimator lens 52, and then, as shown in FIG.
The beam splitter 53 splits the beam into two parts, one of the divided beams is reflected by the standard plane 154, and the other beam is reflected by the object paraboloid ITM to cause interference between the two reflected beams and create interference fringes. Screen 56 through observation lens 55
There is something to observe above. However, in this interferometer, the converging lens 57 needs to be composed of an aspherical lens, so the accuracy of the aspherical lens affects the accuracy of shape measurement of the object parabolic mirror TM, and implementation is not necessarily easy. do not have.

Furthermore, another inspection method is to create a computer-generated hologram, but the manufacturing process is complicated and it is difficult to put it into practical use.
The current situation is that we are still far from reaching that goal.

Another inspection method is to create a spherical wave closest to the paraboloid, make it interfere with the reflected light from the parabolic mirror of the object, measure the position of the interference fringes, and then measure the position of the interference fringes. There is also a method of measuring the shape, but analysis of interference fringes is quite troublesome.

[Problems to be Solved by the Invention] The present invention has been made in view of the above circumstances, and provides a measurement method that allows the surface shape of a parabolic mirror to be measured easily, reliably, and at low cost. The purpose is to provide technology.

(B) Structure of the Invention [Means for Solving the Problem] Corresponding to this object, an interference method for measuring the surface shape of a parabolic mirror according to the present invention includes a laser light source and a light beam from the laser light source. A beam splitter that splits the beam into two beams is used to generate illumination light for illuminating the object parabolic mirror from one of the two beams, and to generate a standard illumination light from the other of the two beams. The method is characterized in that light is generated, the illumination light is reflected by an object parabolic mirror, and interference fringes between the reflected parallel light and the standard light are observed.

Further, the interferometer for measuring the surface shape of a parabolic mirror according to the present invention includes a laser light source and a light beam from the laser light source that is
a beam splitter that splits the beam into a beam; a divergent spherical wave generation optical system that generates a divergent spherical wave from one of the two beams; and a parallel light generator that generates parallel light from the other of the two beams. and an optical system, configured to reflect the generated divergent spherical wave on a subject parabolic mirror and observe interference fringes between the reflected parallel light and the parallel light. .

Hereinafter, details of the present invention will be explained with reference to the drawings showing one embodiment.

First, a case will be described in which the present invention is applied to shape measurement of an off-axis parabolic mirror among parabolic mirrors.

In FIG. 1, 1 is an interferometer. The interferometer 1 includes, for example, a laser light source 3 that generates an argon ion laser, an optical path changing mirror BRI, a beam splitter BS1, a diverging spherical wave generating optical system 4, a parallel light generating optical system 5, and a flat surface 11F.
M, a beam splitter (or semi-transparent 1) 882, and an observation lens OL1 screen S.

The diverging spherical wave generating optical system 4 includes a reflecting mirror BR2, a microscope objective lens MO1, and a pinhole P1.

On the other hand, the parallel light generating optical system 5 includes a reflecting mirror BR3, a microscope objective lens MO2, a pinhole P2, and a collimator lens C.
It is equipped with L.

[, Effect] In the interferometer 1 shown in FIG. 1, the object parabolic mirror T
To measure the surface shape of M, a beam from the laser light source 3 is split by a beam splitter BS1, and one of the beams is guided to a divergent spherical wave generating optical system 4 to generate a divergent spherical wave. In the divergent spherical wave generation optical system 4, the beam splitter BS1
One of the two beams divided into two beams is changed in its optical path by a reflecting mirror BR2, and then converted into a diverging spherical wave by a microscope objective lens MO1 and a pinhole P1. The divergent spherical wave thus generated enters the object parabolic mirror TM from off-axis, is reflected by the object parabolic mirror TM, becomes a reflected parallel beam, is reflected by the beam splitter BS2, and reaches the observation lens OL. On the other hand, the other beam split by the beam splitter 881 is guided to the parallel light generation optical system 5 to generate parallel light. In the parallel light generating optical system 5, reflection tt! After being reflected by BR3, it is made into a divergent spherical wave by the microscope objective lens Mo2 and pinhole P2, and then parallel light is generated by the collimator lens CL. This parallel light is reflected by the beam splitter BS2, reaches the plane 11FM, is reflected by the plane mirror FM, is turned back, and passes through the beam splitter BS2, reaching the observation lens OL.

This parallel light and the reflected parallel light reflected from the previous object parabolic mirror TM overlap, but the reflected light from the object parabolic mirror TM is affected by the unevenness of the mirror surface of the object parabolic mirror TM. Since it deviates from parallel light, which is the standard for reception, interference fringes as shown in FIG. 3 are generated between the two directions of light.

The difference between the interference fringe pitch D, the deviation Ind, and the shape error Δh of the surface to be measured in this interference fringe is Δh =
Since there is a relationship of (d/D)・(λ/2), the shape error Δh is calculated from the interference fringe pitch D and the deviation md, as shown in FIG.
2TM surface topography can be measured.

[Embodiment] FIG. 2 shows another embodiment in which the present invention is applied to shape measurement of an in-axis parabolic mirror.

That is, as shown in FIG. 2, when the subject parabolic mirror TM is an in-axis parabolic mirror, the diverging spherical wave generating optical system 4
A semi-transparent mirror 8 is disposed within the axis of the object parabolic mirror TM on the exit side of the specimen parabolic mirror TM.
83, the diverging light from the diverging spherical wave generating optical system 4 is changed in optical path by the semi-transparent mBs3, and is incident on the subject parabolic mirror TM in the axial direction, and the reflected light is transmitted through the semi-transparent mirror BS3. to reach the beam splitter BS2.

(c) Effects of the invention As described above, according to the interference method and interferometer of this invention,
It does not require a standard parabolic mirror surface or a high-precision aspherical lens, uses a microscope objective lens with extremely small aberrations, and can be manufactured easily and inexpensively. However, the measurement operation does not become complicated, and it is possible to measure the surface shape with a high degree of M. In addition, various F
Measurement of the shape of a numbered parabolic mirror can be handled by simply replacing the microscope objective lens or moving its position, providing high flexibility with respect to the object to be measured.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an interferometer for measuring the surface shape of a parabolic mirror according to the present invention, FIG. 2 is a block diagram showing an interferometer for measuring the surface shape of a parabolic mirror according to another embodiment of the present invention, and FIG. The figure is a diagram showing an example of interference fringes, and FIG. 4 is a configuration diagram showing a conventional interferometer for measuring the surface shape of a parabolic mirror. 1... Interferometer 3... Laser light source 4... Divergent spherical wave generation optical system 5... Parallel light generation optical system BS
1, BS2...beam splitter BRI...
Optical path changing mirror Mo1. Mo2...Microscope objective lens PI, P2...Pinhole CL・
...Collimator lens Bf12, [3R3...
Anti-OA mirror MT...Object parabolic mirror surface

Claims (4)

[Claims] (1) using a laser light source and a beam splitter that splits the light beam from the laser light source into at least two light beams,
Illumination light that illuminates the object parabolic mirror is generated from one of the two light beams, standard light is generated from the other of the two light beams, and the illumination light is used to illuminate the object parabolic mirror. An interference method for measuring the surface shape of a parabolic mirror, characterized by reflecting the reflected parallel light with an object mirror and observing interference fringes between the reflected parallel light and the standard light. (2) a laser light source, a beam splitter that splits the light beam from the laser light source into at least two light beams, and a divergent spherical wave generation optical system that generates a diverging spherical wave from one of the two light beams; a parallel light generation optical system that generates parallel light from the other of the light beams, the generated divergent spherical wave is reflected by the object parabolic mirror, and the reflected reflected parallel light and the parallel light are An interferometer for measuring the surface shape of a parabolic mirror, characterized in that it is configured to observe interference fringes with a parabolic mirror. (3) An interferometer for measuring the surface shape of a parabolic mirror according to claim 2, wherein the object parabolic mirror is an off-axis parabolic mirror. (4) An interferometer for measuring the surface shape of a parabolic mirror according to claim 2, wherein the object parabolic mirror is an in-axis parabolic mirror.