JPH02259505A - Fringe scanning type interference measuring instrument - Google Patents

Abstract

PURPOSE:To detect the phase difference between reference light and light from an object to be measured with sufficient accuracy and magnitude by processing light from a light source and generating light flux including two light wave components whose phase difference is temporally changed. CONSTITUTION:The light flux including two light wave components whose phase difference is temporally changed is generated by a phase difference changing means consisting of an electrooptical element 15 or the like. Two light wave components, that means, the ordinary light component and the abnormal light component interfere each other on the boundary surface of a polarization beam splitter 3 and they are detected by a photodetector 10 as the intensity of interference fringes by being passed through a polarizing plate 11 and an image-forming lens 9. Then, based on the phase difference of the intensity of the interference fringes which is temporally changed, the shape or the shape of the transmitted wave surface of the object to be measured is measured. Thus, even when the electrooptical element and a reference mirror which vibrates are used, the phase difference between the reference light and the light from the object to be measured is detected with sufficient accuracy and magnitude.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention performs fringe scanning by temporally changing the phase difference between a reference beam and light from an object to be measured. This article relates to a stripe scanning measuring device that measures .

[Prior Art J] Conventionally, a fringe scanning type interference measuring device as shown in FIG. 3 has been known.

In the figure, 1 is a laser light source, 2 is a beam expander optical system, and 3 is a polarizing beam splitter 14a, 4b.
5 is a quarter-wave plate, 5 is an electro-optical element, 6 is a power source for applying a changing voltage to the electro-optical element 5 to change the magnitude of optical anisotropy of the electro-optical element 5, and 7 is a device to be measured. object, 8
9 is a reference mirror, 9 is an imaging lens 10 is a photodetector, and 11 is a polarizing plate.

Here, the beam from the laser light source 1 is expanded in diameter by the beam expander optical system 2 and then enters the polarizing beam splitter 3. According to the difference in polarization direction, the transmitted component enters the wave plate 4a, and the reflected component is electrical. The light is incident on the optical element 5 and the wavelength plate 4b. The transmitted component is converted into circularly polarized light by the wavelength plate 4a, reflected by the object to be measured 7, and then returned to the wavelength plate 4a.
By passing through a, the beam returns to the polarizing beam splitter 3 with the plane of polarization rotated by 90 degrees compared to when it was incident thereon.

Therefore, this time, the light beam from the object to be measured 7 is reflected downward in FIG. 3 by the polarizing beam splitter 3.

On the other hand, for example, a reflected component having a polarization plane perpendicular to the plane of the paper is transmitted through the electro-optical element 5 whose optical axis is appropriately oriented under the effect of the refractive index with respect to the extraordinary ray, and passes through the wavelength plate 4b in the figure. It is reflected by the reference mirror 8. Then, the light passes through the wavelength plate 4b again and enters the electro-optical element 5 again with the deflection plane rotated by 90 degrees compared to the initial incidence. Therefore, this time, the reflected component is transmitted through the electro-optical element 5 under the effect of the refractive index with respect to the ordinary ray, and then enters the deflection beam splitter 3, where it is transmitted as it is, and heads downward in FIG.

In this way, the reference light from the reference mirror 8 and the light flux from the object to be measured 7 are superimposed, and the polarizing plate 1 is properly oriented.
1 and an imaging lens 9 to reach a photodetector 10.

At this time, the two light beams interfered on the boundary surface of the polarizing beam splitter 3 pass through the polarizing plate 11 and are detected by the photodetector lO as interference fringe intensity.

At this time, the optical anisotropy of the electro-optical element changes in magnitude depending on the applied voltage, and the ordinary refractive index and extraordinary refractive index change (if one increases, the other decreases).
, the phase of the reflected component that passes through the electro-optical element 5 twice is changed. Therefore, the phase difference between this reference light and the light from the object to be measured 7 changes, and the interference fringes on the photodetector 10 are moved. Then, in synchronization with the operation of the power supply 6 that changes the optical anisotropy of the electro-optical element 5, the above-mentioned moving interference fringe data is captured and analyzed by the combination machine to determine the shape of the object to be measured 7. is measured. This is a measurement method called fringe scanning, which minimizes errors caused by atmospheric fluctuations and noise, resulting in more accurate measurements (e.g., S., Yokozeki, Pat.
orski and K, 0hnishi: 0pt
ics Commun.

14 (1975) 401 and DigitalWavef
rontMeasuringInterferom
eter for Testing 0ptic
al 5 surfaces and lenses
:Applfed 0ptics/Vo1.13
．． N.

11/Novemher 19749) Furthermore, a configuration is also known in which the electro-optical element 5 is eliminated and the reference mirror 8 is vibrated by a voltage element or the like to change the phase difference between the reference light and the light from the object to be measured 7.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional example, when measuring the shape of an object to be measured whose area is large enough, the diameter of the light beam becomes correspondingly large, and therefore it is difficult to use the reference light. The electro-optical elements and vibrating mirrors also need to have a sufficient area. This means that the electro-optical element must have uniform characteristics over an area that is large enough, and that it must vibrate precisely in the optical axis direction without tilting over an area that is large enough for a vibrating mirror. . Therefore, sophisticated and troublesome techniques are required for the production and positioning of electro-optical elements, piezoelectric elements, reference mirrors, etc., resulting in high costs.

In particular, in the conventional example in which an electro-optical element is provided in the reference optical path,
Since the configuration is such that a phase change is given to the light beam on the round trip of the reference optical path, if it is affected by the extraordinary refractive index of the electro-optical element on the outgoing path, the polarization plane is rotated by 90 degrees on the return path, so that it is affected by the ordinary refractive index. Since the ordinary and extraordinary refractive indices change in opposite directions (and vice versa), the amount of phase change in the round trip cancels out. Therefore, in order to obtain a large phase change, it is necessary to apply a large electric field to the electro-optical element.

Therefore, an object of the present invention is to solve the above-mentioned drawbacks by ensuring that the phase difference between the reference light and the light from the object to be measured has sufficient precision and magnitude even when an electro-optical element or a vibrating reference mirror is used. It is an object of the present invention to provide a fringe scanning type interference measuring device configured so that it can be easily obtained.

[Means for Solving the Problems] In the fringe scanning interference measurement device of the present invention that achieves the above object, light from a light source such as a laser light source is processed to generate two light wave components whose phase difference changes over time. A phase difference changing means is provided, and a beam splitter such as a polarizing beam splitter splits two light wave components of the light beam from the phase difference changing means into light directed toward the object to be measured and light directed toward the 9111i plane. Specifically, the phase difference changing means is composed of a reflection mirror vibrated by an electro-optical element or a piezoelectric element, and the phase difference is changed by controlling the voltage applied to these electro-optical elements or piezoelectric elements. changes are controlled.

How to distribute the two light wave components from the phase difference changing means into light directed toward the object to be measured and the reference surface may be determined as appropriate depending on the design.

[Function] In the present invention, the reflected or transmitted light flux from the object to be measured and the light flux from the reference surface are caused to interfere with each other, and these two
The phase difference of the light flux is controlled and temporally changed, and the shape of the object to be measured or the shape of the transmitted wavefront is measured from the phase difference of the interference fringe intensity that changes accordingly. Before being split by a beam splitter into an incident light beam and a reference light beam to a reference surface, a light beam containing two light wave components whose phase difference changes over time is created and made to enter the beam splitter. Since the phase difference changing means is provided, the phase difference changing means can process a relatively narrow beam of light, minimizing the negative impact on accuracy associated with the phase difference changing operation and providing flexibility regarding the degree of phase difference changing. EMBODIMENT OF THE INVENTION FIG. 1 shows a first embodiment of the present invention. In the configuration shown in the figure, an electro-optical element 15 is arranged in the optical path between the laser light source 1 and the beam expander optical system 2, compared to the conventional example shown in FIG.

The light beam emitted from the laser light source 1 first passes through the electro-optical element 1
5. The electro-optical element 15 is made of, for example, PLZT.
It consists of a plate, and when an electrode is provided on the end face and an electric field is applied in the direction of the luminous flux, two
It is designed to generate optical anisotropy in two directions. Therefore, when a changing voltage is applied to the electro-optical element 15 from the power source 6, the polarized light components having polarization planes in the two mutually orthogonal directions change over time as ordinary rays and extraordinary rays, respectively. Since the light experiences an ordinary refractive index and an extraordinary refractive index, the light emitted from the electro-optical element 15 has two different phases that change over time due to the difference in its polarization direction.

At this time, the diameter of the incident luminous flux is still relatively small, so
The area of the uniform characteristic portion of the electro-optical element 15 is small, and the ordinary ray component and the extraordinary ray component included in the emitted light beam have an ordinary refractive index and an extraordinary refractive index that change in opposite directions, respectively. 15, the phase difference or amount of change between the two components can be increased.

The light beam including the ordinary ray component and the extraordinary ray component emitted from the electro-optical element 15 is transmitted to the beam expander optical system 2.
Then, its diameter is expanded to an appropriate size according to the size of the object to be measured 7, and the beam is incident on the polarizing beam splitter 3.
The polarizing beam splitter 3 is arranged, for example, so that the polarization direction of its transmitted component matches that of the ordinary ray component, and therefore the polarization direction of its reflected component matches that of the extraordinary ray component.

Therefore, the ordinary ray component is directly transmitted to the polarizing beam splitter.
After passing through the electromagnetic wave plate 4a, it is reflected by the object to be measured 7, passes through the electromagnetic wave plate 4a again, and returns to the polarizing beam splitter 3. The reason why the returning ordinary ray component is reflected by the polarizing beam splitter 3 and directed downward in FIG. 1 is due to the same reason as stated in the explanation of FIG. 3.

On the other hand, the extraordinary ray component is reflected by the polarizing beam splitter 3, passes through the radio wave plate 4b, is reflected by the reference mirror 8, which is a reference surface, and returns to the polarizing beam splitter 3 through the wavelength plate 4b again. The reason why this returned extraordinary ray component passes through the polarizing beam splitter 3 as it is and goes downward in FIG. 1 is due to the same reason as stated in the explanation of FIG. 3.

In this way, the ordinary and extraordinary ray components interfere on the boundary surface of the polarizing beam splitter 3, pass through the polarizing plate 11 and the imaging lens 9, and are detected as interference fringe intensity by the photodetector IO.

Here, since the magnitude of the electric field applied to the electro-optical element 15 is changed, the phase difference between the two luminous flux components is changed, and measurement by fringe scanning is performed, which is different from the conventional example shown in FIG. It's the same.

In this manner, in the first embodiment, a light beam containing two light wave components whose phase difference changes over an hour is created by the phase difference changing means consisting of the electro-optical element 15, etc., and the polarizing beam splitter
Since the configuration is such that this light beam is incident on the interferometer side having a 3.5-meter beam, the phase difference changing means only needs to process a relatively narrow light beam, which is advantageous in terms of accuracy, flexibility, and cost of phase difference control.

Next, a second embodiment shown in FIG. 2 will be explained.

In the same figure, the interferometric measurement consisting of the polarizing beam splitter 3 and the like is the same as the first embodiment in FIG. Only this differs from the first embodiment.

In the second embodiment, 21 is a piezoelectric element that is expanded and contracted in the optical axis direction by a power source 6, 22 is a reflection mirror fixed to the piezoelectric element 21, 23 is a fixed reflection mirror 24a,
24b is a residual liquid long plate, and 25 is a polarizing beam splitter 116 provided separately from the polarizing beam splitter 3, which is a pinhole provided in the beam expander optical system 2 for adjusting the shape of the light beam.

The light beam emitted from the laser light source 1 enters the polarizing beam splitter 25, and due to the difference in polarization direction, the transmitted component is directed toward the vibrating mirror 22, and the reflected component is directed toward the fixed mirror 23.
It is divided in the direction of The light beam that has passed through the polarizing beam splitter 25 passes through the wave plate 24a, is reflected by the mirror 22, passes through the wave plate 24a again, and returns to the polarizing beam splitter 25, but it passes through the wave plate 24a twice. Since the light passes through the light, its polarization directions are orthogonal on the outbound and return trips. Therefore, it is reflected by the polarizing beam splitter 25 and enters the beam expander optical system 2.

On the other hand, the reflected component at the polarizing beam splitter 25 passes through the wavelength plate 24b, is reflected by the fixed mirror 23, and returns to the polarizing beam splitter 25 through the wavelength plate 24b again. For essentially the same reason, the light passes through the polarizing beam splitter 25 and enters the beam expander optical system 2. In this way, both the transmitted and reflected light beams follow the same optical path again and enter the beam expander optical system 2.

At this time, since the phase difference between the two light beams whose polarization directions are orthogonal to each other depends on the position of the vibrating mirror 22, this phase difference is temporally changed by the voltage of the power source 6.

Next, both beams are expanded in diameter and passed through a polarizing beam splitter.
3 and is split here according to the difference in polarization direction, but since the behavior on the interferometer side is essentially the same as in the first embodiment, the explanation will be omitted.

In the second embodiment, as in the first embodiment, the phase difference changing means such as the vibrating mirror 22 is separated from the interferometer, and the relatively thin beam immediately after being emitted from the light source is processed to change the phase difference over time. Since a light beam containing a changing two-wavelength acid component is generated, it is possible to minimize the possibility that the tilt of the vibrating mirror 22 etc. degrades the accuracy of the phase difference change. Although a phase difference that changes over time is realized by changing the phase difference over time, in the second embodiment, only the phase of one light wave component is changed over time.

[Effects of the Invention] As described above, according to the configuration of the present invention, the phase difference is calculated using an electro-optical element, a vibrating mirror, etc. before dividing the light beam incident on the object to be measured and the reference light beam. Since a light beam containing a temporally varying two-wavelength acid component is created, and this light beam is divided to create a light beam incident on the object to be measured and a reference light beam, the phase difference changing means can be used with sufficient accuracy and at a relatively low cost. realizable.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention, FIG. 2 is a block diagram of a second embodiment of the present invention, and FIG. 3 is a block diagram of a conventional example. l...Laser light source, 2...Beam expander optical system, 3.25...Polarizing beam splitter-14a, 4b, 24a, 24b...4 wavelength handling, 6. ...Power source, 7...Object to be measured, 8...
...Reference mirror 1O...Photodetector 11...
...Polarizing plate, 15...Electro-optical element, 21...
...Piezoelectric element, 22.23...Reflection mirror, 26
·····Pinhole

Claims (1)

[Claims] 1. By causing light from the object to be measured and light from the reference surface to interfere with each other and by temporally changing the phase difference between these two lights, the interference fringe intensity changes accordingly. In a fringe scanning interferometry device that measures the shape of an object to be measured from the phase difference of A fringe scanning interference measuring device, characterized in that the two light wave components of the light beam from the phase difference changing means are split by a beam splitter into light directed toward the object to be measured and light directed toward the reference surface. . 2. A measuring device according to claim 1, wherein a beam expander optical system is provided in the optical path between the phase difference changing means and the beam splitter. It has an electro-optic element whose optical anisotropy changes depending on the electric field strength, and either one of the ordinary ray component and the extraordinary ray component of the luminous flux emitted from the electro-optic element is covered by the beam splitter. 2. A phase difference between the two incident light beams on the object to be measured and the reference surface is controlled by controlling the intensity of the electric field. measuring device. 4. The phase difference changing means includes another beam splitter that splits the light beam from the light source, a fixed reflection mirror that receives one of the two light beams split by the another beam splitter, and the other of the two split light beams. 2. The measuring device according to claim 1, further comprising a moving reflecting mirror that receives the light, and a phase difference between these two beams is controlled by controlling the movement of the moving reflecting mirror.