JPH055610A - Measuring device - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain a measuring device capable of detecting the shape of a three-dimensional object with high precision using interference. Constitution: Illumination means for irradiating the measured part of the measured object with coherent light, and light as a reference for the light from each point of the measured part illuminated by the illuminating means. Interference means for causing interference, interference information detection means for sequentially detecting interference information of light from each of the points, and inclination variation information detection for detecting inclination variation information of the measured portion being detected by the interference information detection means. Means, and wavefront aberration information detecting means for detecting information on wavefront aberration given to the light of the measured portion based on the detection results of the interference information detecting means and the tilt variation information detecting means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring device, and for example, detects a three-dimensional shape of an object to be measured by detecting an optical phase change of an incident light wave associated with the shape of a three-dimensional object which is the object to be measured. The present invention relates to such a measuring device.

[0002]

2. Description of the Related Art Conventionally, an optical heterodyne interferometer has been known as a measuring instrument capable of relatively accurately detecting the shapes of optical members such as lenses and mirrors by utilizing light wave interference. For example, Applied Optics Vol. .19.No.1 (1980) P.
154-P.160.

FIG. 6 is a schematic view of a main part of an optical system of a conventional optical heterodyne interferometer. In the figure, the light wave emitted from the laser 1 is reflected by the mirror M1 and is split into two by the beam splitter 2 into reflected light and transmitted light. Of these, transmitted light (first
After passing through the black cell 5a, the mirror M2, and the λ / 2 plate 4, the reflected light (second light wave) is emitted from the black cell 5a.
b, after passing through the mirror M3, they are multiplexed by the beam splitter 3.

At this time, the first light wave that has passed through the black cell 5a undergoes a frequency shift of frequency f1, passes through the λ / 2 plate 4, and the plane of polarization is rotated by 90 degrees. Black cell 5b
The second light wave that has passed through has undergone a frequency shift of frequency f2. Then, these light waves are combined by the beam splitter 3, the beam diameter is expanded by the beam expander 6, and the light beams enter the polarization beam splitter 7. Of these, the first light wave having the frequency f1 is the polarization beam splitter 7
Through the λ / 4 plate 8b to be circularly polarized light, and then enters the DUT 11 through the collimator lens 10. Then, the wavefront to be detected reflected by the DUT 11 returns to the original optical path. At this time, the polarization direction (polarization plane) when re-incident on the λ / 4 plate 8b and passing therethrough is displaced by 90 degrees compared with the time of incidence. Therefore, this time it is reflected by the polarization beam splitter 7.

On the other hand, the second light wave of frequency f2 is reflected by the polarization beam splitter 7 and circularly polarized by the λ / 4 plate 8a, and the reference wavefront reflected by the reference plane mirror 9 becomes circularly polarized light in the reverse direction. Return the optical path. Then, the light passes through the λ / 4 plate 8a and becomes a linearly polarized light whose polarization direction (polarization plane) is displaced by 90 degrees from that at the time of incidence. This time, it passes through the polarization beam splitter 7 and is combined (combined) with the previous wavefront to be detected. It

Here, the two light waves of the test wave surface and the reference wave surface, which are recombined, pass through the polarizing plate 12 to become wave surfaces capable of interfering with each other, so that they interfere with each other. The interference light wave at this time is detected by the photodetector 15 and the image detection camera (image dissector camera) 16 as a heterodyne signal having a frequency shift difference f1-f2.

The image detection camera 16 is a computer 18
Is a camera capable of selecting an arbitrary one point of a two-dimensional image by the command and detecting the intensity signal of the light incident on that point in real time.

Heterodyne signal f1- in this embodiment
The phase distribution of f2 directly represents an error in the shape of the DUT 11 from the spherical wave generated by the collimator lens 10 if the reference plane mirror 9 is an ideal plane.

Then, the heterodyne signal obtained by the photodetector 15 is used as a reference signal R, each signal from the image detection camera 16 is used as a measurement signal S, and the phase difference φ between the reference signal R and the measurement signal S is calculated by the phase meter 17. To detect. Further image detection camera 16
2D is scanned two-dimensionally by a command from the computer 18, and a two-dimensional distribution of the phase difference φ between the measurement signal S and the reference signal R at each measurement point is obtained. As a result, the object to be measured 11
The wavefront aberration based on the shape of is detected. At this time, assuming that the phase resolution of the electric signal is 0.1 ° and the oscillation wavelength from the laser is λ = 632.8 nm.

[0010]

[Equation 1] The wavefront aberration can be measured with a resolution of.

[0011]

In the optical heterodyne interferometer shown in FIG. 6, the image detection camera 16 scans the measurement surface two-dimensionally, and in many cases it is necessary to detect the optical signals at all points. It takes about 0.1 seconds to several seconds. Therefore, for example, if the DUT 11, the reference plane mirror 9, or the like vibrates and tilts during measurement, the tilt component centered at the point where the reference signal is detected is detected as a measurement error in the vibration amplitude, and the measurement is performed. There was a problem that the accuracy was lowered.

The present invention eliminates the influence of measurement error factors such as mechanical vibrations that occur during two-dimensional scanning of scanning type photodetection means such as an image detection camera, and can detect the shape of an object to be measured with high accuracy. The first purpose is to provide a measuring device capable of performing the measurement.

Other objects of the present invention will become clear in the description of the detailed embodiments of the present invention described later.

[0014]

A measuring device according to the present invention comprises an illuminating means for irradiating a measured part of an object to be measured with coherent light, and a measured part illuminated by the illuminating means. Interference means for interfering the light from each point with the reference light, the interference information detecting means for sequentially detecting the interference information of the light from each point, and the object being detected by the interference information detecting means. Tilt fluctuation information detecting means for detecting tilt fluctuation information of the measuring section, and wavefront aberration for detecting information of wavefront aberration given to the light of the measured section based on the detection results of the interference information detecting means and the tilt fluctuation information detecting means. And an information detecting means.

When the measuring device of the present invention is used as an optical heterodyne interferometer, (a) a light emitting part for emitting light of a first frequency for irradiating the measured part of the object to be measured; An interference optical system for forming interference light by interfering the light from each point of the measured portion, which is irradiated with the light of the first frequency, with the light of the second frequency as the reference light, and the interference. A scanning photodetector that sequentially detects light corresponding to each point, a first phase meter that detects the phase of the interference light corresponding to each point detected by the scanning photodetector, and the scanning Type photodetector during detection by a plurality of photodetectors for continuously detecting the interference light corresponding to a plurality of specific points of the measured portion,
A second phase meter for detecting the phase of the interference light corresponding to the specific plurality of points respectively detected by the plurality of photodetectors, and the part to be measured based on the detection results of the first and second phase meters. And a calculator for detecting the wavefront aberration information given by.

(B) Two light waves, a first light wave and a second light wave having different frequencies, are generated, one light wave of which is used as a test light wave through an object to be measured, and the other light wave is used as a reference light wave. When combining and detecting the heterodyne signal based on both light waves by the first detecting means and the second detecting means, the first detecting means is at least at three points which are not on a straight line in the measuring region of the object to be measured. The heterodyne signal is detected, the second detecting means detects the heterodyne signal at each point in the measurement region of the object to be measured, and the second detection and the mutual relation of the three heterodyne signals obtained by the first detecting means. It is characterized in that the optical phase change of the incident light wave by the object to be measured is detected by utilizing the heterodyne signal of each point in the measurement region obtained by the means.

In particular, in the present invention, during the measurement period in which the second detecting means two-dimensionally scans the inside of the measuring area of the object to be measured to measure the heterodyne signal at each point, the first detecting means keeps the measuring area within the measuring area. Detects the heterodyne signal obtained at three locations,
A signal based on the mutual relationship between the heterodyne signal obtained at the three positions and the heterodyne signal obtained at a predetermined position of the second detecting means is recorded in a buffer memory, and the signal recorded in the buffer memory is used to The signal at each point in the measurement area obtained by the second detecting means is corrected, and the first detecting means has three photodetectors, that is, first, second and third photodetectors. When measuring the phase difference at each point from the heterodyne signal obtained at the first photodetector and the heterodyne signal at each point in the measurement region obtained by the second detecting means, the first light Measurement of both the phase difference between the heterodyne signals obtained from the detector and the second photodetector and the phase difference between the heterodyne signals obtained from the second photodetector and the third photodetector The displacement amount during the period is detected and the detection result is used. It is characterized in the can or the like.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of the essential parts of an optical system according to a first embodiment of the present invention. Compared with the conventional optical heterodyne interferometer of FIG. 6, this embodiment detects the heterodyne signal reflected by the beam splitter 12 not on a straight line, that is, with three photodetectors arranged at each point on the plane, The difference is that the shape of the DUT 11 is detected by using the output signals from the three photodetectors.

Next, the features of the configuration of the present invention will be described, although it partially overlaps with the description of FIG. In the figure, reference numeral 1 denotes a light source, which is a laser that emits a coherent light beam. A beam splitter 2 splits the light flux from the laser 1 into two light fluxes of reflected light and transmitted light. Black cells 5a and 5b each give a frequency shift to the incident light due to the acousto-optic effect. In this embodiment, the black cell 5a
, A light wave having a frequency shift of frequency f1 is emitted, and a light wave having a frequency shift of frequency f2 is emitted from the black cell 5b. Reference numeral 4 denotes a λ / 2 plate, which rotates the polarization plane of incident light by 90 °. Reference numeral 3 denotes a beam splitter, which multiplexes a light wave having a frequency f1 via the black cell 5a and a light wave having a frequency f2 via the black cell 5b. A beam expander 6 expands the diameter of the incident light beam and emits it. Reference numeral 7 denotes a polarization beam splitter, which reflects or transmits the incident light beam according to the polarization state of the incident light beam to change the traveling direction of the light beam. Reference numerals 8a and 8b denote λ / 4 plates, which convert linearly polarized light into circularly polarized light.

A reference plane mirror 9 forms a reference wavefront. Reference numeral 10 denotes a collimator lens that collects an incident light beam and makes it incident on a DUT 11 described later. The object to be measured 11 is composed of a mirror, a lens and the like, and detects the three-dimensional shape and the uniformity of the material thereof. Here, the DUT 11 is a concave mirror, and the concave mirror surface shape is measured by this device.

Reference numeral 12 denotes a polarizing plate, which extracts a specific polarized component from the light waves having two linearly polarized light components which are orthogonal to each other and interferes with it. A beam splitter 13 splits the incident light flux into two light fluxes of reflected light and transmitted light. Reference numeral 14 denotes a pinhole plate, which has a plurality of pinholes that allow only a light beam incident on a specific position to pass through. In this embodiment, as shown in FIG. 2A, three pinholes 14a, 14b, 14c are provided in the x direction and the y direction. (In FIG. 1, for convenience, they are displayed side by side in one row.) 15 is a first detection means, and three photodetectors 15 are provided.
It has a, 15b, and 15c. Three photo detectors 15
a, 15b, and 15c are not on a straight line (in FIG. 1, they are shown in one column for convenience.) For example, as shown in FIG. 2B, they are separated by a predetermined distance L _X , L _Y in the x direction and the y direction. It is arranged.

Reference numeral 16 denotes an image detection camera (scanning photodetector / image dissector camera) as the second detection means, which reads the optical signal at the position addressed by the computer 18 in real time. Reference numeral 17 denotes a phase detecting means, which is three phase meters 17a, 17b, 17c.
have. The phase meters 17a, 17b, 17c measure the phase difference between the two signals input from the photodetector or the image detection camera 16. Reference numeral 20 denotes a buffer memory, which temporarily stores signals relating to the phase difference sent from the phase meters 17a, 17b, 17c.

The computer 18 uses the measurement data from the buffer memory 20 to perform an arithmetic process as described later.

In this embodiment, the light wave emitted from the laser 1 is reflected by the mirror M1 and is split by the beam splitter 2 into reflected light and transmitted light. Among them, the transmitted light (first light wave) passes through the black cell 5a, the mirror M2 and the λ / 2 plate 4, and the reflected light (second light wave) passes through the black cell 5b and the mirror M3 and then at the beam splitter 3. Combined.

At this time, the first light wave that has passed through the black cell 5a undergoes a frequency shift of the frequency f1, passes through the λ / 2 plate 4, and the plane of polarization is rotated by 90 °. Black cell 5b
The second light wave that has passed through has undergone a frequency shift of frequency f2.

Then, these light waves are combined by the beam splitter 3, and then the beam diameter is expanded by the beam expander 6 to be incident on the polarization beam splitter 7.
Of these, the first light wave of frequency f1 passes through the polarization beam splitter 7, is circularly polarized by the λ / 4 plate 8b, and is incident on the DUT 11 through the collimator lens 10. Then, the wavefront to be detected reflected by the DUT 11 returns to the original optical path.
At this time, the light wave when re-incident on the λ / 4 plate 8b is reflected by the DUT 11 as compared with that at the time of incidence, and thus is circularly polarized in the reverse direction. Therefore, when passing through the λ / 4 plate 8b, The polarization direction (polarization plane) is displaced by 90 degrees compared with the time of incidence.
Therefore, this time it is reflected by the polarization beam splitter 7.

On the other hand, the second light wave of frequency f2 is reflected by the polarization beam splitter 7 and circularly polarized by the λ / 4 plate 8a, and the reference wavefront reflected by the reference plane mirror 9 becomes circularly polarized light in the reverse direction. Return the optical path. Then, the light passes through the λ / 4 plate 8a and becomes a linearly polarized light whose polarization direction (polarization plane) is displaced by 90 degrees from that at the time of incidence. This time, it passes through the polarization beam splitter 7 and is combined (combined) with the previous wavefront to be detected. It

The two light waves of the test wavefront and the reference wavefront recombined here are made into wavefronts capable of interfering with each other by passing through the polarizing plate 12 and interfere with each other. The interference light wave at this time is detected by the photodetectors 15a, 15b, 15c and the image detection camera 16 as a heterodyne signal having a frequency shift difference f1-f2.

The phase distribution of the heterodyne signals f1-f2 detected by the image detection camera 16 in this embodiment is assumed to have no error component of other optical elements, such as the reference plane mirror 9 being an ideal plane. Assuming that the measurement object has no shape error, if the phase difference from the reference signal is 0 at all measurement positions, the error in the shape of the DUT 11 from the spherical wave generated by the collimator lens 10 is directly expressed. ing.

Therefore, one of the heterodyne signals obtained by the photodetectors 15a, 15b, 15c, for example, the heterodyne signal obtained by the photodetector 15a is used as a reference signal R, and the object to be detected from the image detection camera 16 is detected. a signal corresponding to a specific point of the upper so as to detect a phase difference phi _a of the reference signal R in the phase meter 17a and the measurement signal S as a measurement signal S.

The image detection camera 16 two-dimensionally scans each measurement point according to a command from the computer 18, and measures each measurement point (x,
y) the phase difference between the measured signal S and the reference signal R φ _a (x,
The two-dimensional distribution of y) is calculated. Thereby, the wavefront aberration based on the shape of the DUT 11 is detected.

At this time, the object to be measured 11 is detected by the image detection camera 16.
When the measurement surface is scanned two-dimensionally, for example, when the object to be measured 11 or the reference plane mirror 9 vibrates and the tilting effect occurs, a measurement error occurs.

Therefore, in this embodiment, the phase difference between the reference signal R from the photodetector 15a and the signals from the two photodetectors 15a and 15b spatially separated as shown in FIG. The data of a certain phase difference φ _{a, b} , similarly φ _{a, c} which is the phase difference of the signals from 15 a and 15 c is converted into the phase difference φ _a (x,
Simultaneously with the measurement of y) or at a period sufficiently shorter than the period of mechanical vibration, the measurement is performed from the beginning to the end of the two-dimensional scanning by the image detection camera 16 and stored in the buffer memory 20.

3A and 3B show the phase difference φ at this time.
_{a, b} , Φ _{a, c} Is an explanatory diagram when time is plotted on the horizontal axis.
It In the figure, 31 and 32 respectively indicate that there is no mechanical vibration.
Values (phase difference), 31a and 32b indicate mechanical vibration.
It is a value (phase difference) when it is turned on and is displaced with time.

Thus, the phase difference φ associated with the temporal displacement _{a, b} 
And φ_{a, c} By detecting the
Displacement due to tilting of DUT or reference plane mirror
Are seeking. And two-dimensional running by the image detection camera 16
After the inspection, the information on the wavefront aberration of the DUT 11 and its
By using the information of the amount of vibration at
18 corrects the vibration amount and corrects the measured object 11.
Seeking accurate wavefront aberration.

Next, an example of the correction method at this time will be described. Now, as shown in FIG. 2B, the image detection camera 16
When the photodetectors 15a and 15c are arranged in parallel with the x-axis of the imaging surface 16a at a distance L _X, and the photodetectors 15a and 15b are arranged in parallel with the y-axis at a distance L _Y. To do.

The signal obtained from the photodetector 15a is used as a reference signal.
Image detection camera 1 corresponding to measurement point (x, y) as signal R
6 at the address (X, Y) on the imaging surface 16a
The phase difference between the measurement signal S and this signal R is φ_a (X,
Y), at the time of measurement at this address (X, Y)
Reference signal R obtained by photodetector 15a and photodetector 15
The phase difference from the measurement signal measured at b and 15c is φ
_{a, b} (X, Y), φ _{a, c} (X, Y).

If the pixel spacing on the image pickup surface 16a of the image detection camera 16 is dw in both the X and Y directions, the phase correction amount C at the coordinates X, Y on the image pickup surface 16a is

[0039]

[Equation 2] Becomes

Therefore, the true wavefront aberration φ (X, Y) based on the shape of the DUT 11 is φ (X, Y) = φ _a (X, Y) -C (X, Y) (2) Becomes In the present embodiment, the computer 18 calculates the three-dimensional shape of the DUT 11 by performing the calculation of the expressions (1) and (2) for each point.

At this time, the phase difference φ _a corresponding to each point when there is no error in the measured object (shape here) of the measured object
(X, Y) is stored in advance as a system error, and the actually measured φ _a (X, Y) is subtracted from this system error and then substituted into the equation (2) as data.

FIG. 4 is a schematic view of the essential parts of an optical system according to a second embodiment of the present invention. The same members as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the present embodiment, the object to be measured 11T is a plate of a light-transmitting object, and this apparatus shows the uniformity of the material of the object to be measured.
It is measured as a refractive index distribution. 10R is a second reference plane mirror.

In the same manner as in Example 1, the first light wave of frequency f1 which has passed through the beam splitter 7 is circularly polarized by the λ / 4 plate 8b, is incident on the object to be measured 11T and is transmitted therethrough. The light reflected by the second reference plane 10R is the object to be measured 11T.
To the original optical path, returns to the original optical path, is reflected by the polarization beam splitter 7 and is combined with the reference wavefront in the same manner as in the above-described first embodiment, and is made coherent by the polarizing plate 12 to be detected by the photodetector 15a.
15c and the image detection camera 16.

The phase distribution of the heterodyne signals f1-f2 detected by the image detection camera 16 in this embodiment is assumed to be an ideal plane with the reference plane mirror 9 and the second reference plane mirror 10R, and both sides of the object 11T to be measured are also ideal planes. Then, the distribution of the refractive index of the object to be measured 11T is represented in the form of the distribution of the optical path length of each part, that is, the distribution of the optical path difference.

The method of signal processing is the same as that in the first embodiment, and the description thereof will be omitted. The wavefront aberration φ (X, Y) corresponding to each part obtained by the equation (2) is the object to be measured 11 which is obtained in advance.
It may be converted into a refractive index error by a well-known method based on the plate thickness data. That is, in this example, if the plate thickness is L, the frequency of the measurement light is f, and the luminous flux is C, the refractive index n (X, Y) of each part is
Can be converted by the following formula.

[0047]

[Equation 3] FIG. 5 is a schematic view of the essential portions of Embodiment 3 of the present invention. Example 2
On the other hand, a lens is used as the object to be measured 11L. Again 1
Reference numeral 0W is a reference curved mirror having a reflecting surface having the same shape as the wavefront when the lens 11L forms an ideal outgoing wavefront. Since the other points are the same as those in the second embodiment, the description thereof will be omitted.

The phase distribution of the heterodyne signals f1-f2 detected by the image detection camera in this embodiment is the reflection surface shape of the reference curved surface mirror 10W of the spherical wave produced by the lens 11L if the reference plane mirror 9 is an ideal plane. The error from is shown as being doubled. That is, in this embodiment, the aberration from the ideal of the wavefront emitted by the lens is measured.

In the second and third embodiments described above, signal processing is performed as in the first embodiment, so that the reference plane mirror 9, the second reference plane mirror 10R, the reference curved surface mirror 10W, and the like are affected by tilt, vibration, and other influences. It can be removed and the measurement can be performed.

Incidentally, in each embodiment, at least three photodetectors 15a, 15b, 15c may be arranged at any positions as long as they are not arranged on a straight line as described above. That is, as long as it is an arrangement capable of detecting the tilting effect in the x direction and the y direction of the object to be measured, the reference plane mirror, or the like due to vibration or the like, any arrangement may be used even if they are not orthogonal.

Further, it is preferable that three or more photodetectors are used and signals obtained from a plurality of positions are used to use, for example, an average value because detection can be performed with higher accuracy.

In addition to this, in this embodiment, the light detecting means 1
A structure in which a plurality of elements are two-dimensionally arranged in one element is also applicable.

When the measurement error component is generated in only one direction in this embodiment, the same effect as described above can be obtained by arranging two photodetectors at a predetermined interval in that direction. it can.

[0054]

According to the present invention, as described above, by correcting the measurement error caused by the mechanical vibration of the DUT or the reference plane mirror, which occurs during the overall scanning measurement of the measurement surface of the DUT, the object to be measured is corrected. It is possible to achieve a measuring device that can measure the shape or the like of an object to be measured with high accuracy even in a vibrating state.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is an explanatory view of a part of FIG.

FIG. 3 is an explanatory diagram of an output signal from the phase meter of FIG.

FIG. 4 is a schematic view of the essential portions of Embodiment 2 of the present invention.

FIG. 5 is a schematic view of the essential portions of Embodiment 3 of the present invention.

FIG. 6 is a schematic view of a main part of a conventional optical heterodyne interferometer.

[Explanation of symbols]

 1 Laser 2,3 Beam Splitter 4 λ / 2 Plate 5a, 5b Black Cell 7 Polarization Beam Splitter 8a, 8b λ / 4 Plate 9 Reference Plane Mirror 11 DUT 12 Polarizing Plate 14 Pinhole Plate 15, 15a, 15b, 15c Photodetector 16 Image detection camera 17, 17a, 17b, 17c Phase meter 18 Computer 20 Buffer memory

Claims (1)

Claims: 1. From each point of an illuminating means for irradiating a measured part of an object to be measured with coherent light, and a measured part illuminated by the illuminating means. Means for interfering the light of the reference light with the reference light, an interference information detecting means for sequentially detecting the interference information of the light from each of the points, and an inclination variation of the measured portion being detected by the interference information detecting means. Tilt variation information detecting means for detecting information, and wavefront aberration information detecting means for detecting information of wavefront aberration given to the light of the measured portion based on the detection results of the interference information detecting means and the tilt variation information detecting means. A measuring device having. 2. A light emitting part for emitting light of a first frequency for irradiating the measured part of the measured object, and a measured part irradiated with the light of the first frequency. An interference optical system for forming the interference light by causing the light from the point to interfere with the light of the second frequency as the reference light, and the scanning photodetector for sequentially detecting the interference light corresponding to each point. A first phase meter for detecting the phase of the interference light corresponding to each point detected by the scanning photodetector; and a plurality of specific points of the measured portion during detection by the scanning photodetector. A plurality of photodetectors for continuously detecting the interference light corresponding to the second phase, and a second phase for detecting the phase of the interference light corresponding to the specific plurality of points respectively detected by the plurality of photodetectors. Meter and the part to be measured based on the detection results of the first and second phase meters And a computing unit that detects the wavefront aberration information given by the measuring device. 3. A first light wave and a second light wave having different frequencies.
Two light waves are generated, one of these light waves is used as the test light wave via the object to be measured, and the other light wave is used as the reference light wave, and both are combined, and the heterodyne signal based on both light waves is combined with the first detection means and the first detection means. When detecting with the two detecting means, the first detecting means detects the heterodyne signal at at least three positions which are not on a straight line in the measuring region of the measured object, and the second detecting means measures the measured object. Detecting a heterodyne signal at each point in the area, and using the mutual relationship of the three heterodyne signals obtained by the first detecting means and the heterodyne signal at each point in the measurement area obtained by the second detecting means. The measuring device is configured to detect the optical phase change of the incident light wave by the object to be measured. 4. During the measurement period in which the second detection means two-dimensionally scans the inside of the measurement area of the object to be measured to measure the heterodyne signal at each point, the first detection means includes three locations within the measurement area. The obtained heterodyne signal is detected, the signal based on the mutual relationship between the heterodyne signal obtained at the three positions and the heterodyne signal obtained at the predetermined position of the second detecting means is recorded in the buffer memory, and the buffer memory stores the signal. 4. The signal recorded at each point in the measurement area obtained by the second detecting means is corrected by using the recorded signal.
The measuring device described. 5. The first detection means has three photodetectors, first, second and third photodetectors, and a heterodyne signal obtained by the first photodetector and the second detection. When measuring the phase difference at each point from the heterodyne signal at each point in the measurement area obtained by means, the position between the heterodyne signals obtained from the first photodetector and the second photodetector The displacement amount during the measurement period of both the phase difference and the phase difference between the heterodyne signals obtained from the second photodetector and the third photodetector is detected, and the detection result is used. The measuring device according to claim 3.