JP2011226785A - Surface shape measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device capable of quickly measuring the surface shape of a measurement object with depth larger than the coherence length.SOLUTION: This device is provided with a reference light generation part 20 with reference mirrors 251, 252, 253, 254, 25N each of which are different in optical path length to a photo coupler 13. The reference mirrors 251, 252, 253, 254,...25N are arranged in this order with an optical path length difference of the coherence length ΔZ between them. By oscillating a scanning mirror 23 around a scanning axis 24, light reflected by the scanning mirror 23 can be radiated on the reference mirrors 251, 252, 253, 254, ...25N in turns.

Description

  The present invention relates to a surface shape measuring device that causes reflected light from a surface of a measured object to interfere with reference light and identifies the surface shape of the measured object from a change in the intensity of interference light obtained.

There is an interferometer as a method for measuring the three-dimensional shape of a measurement object with high accuracy below the wavelength of light. However, the measurement range in the depth direction is as narrow as several times the wavelength, and it is difficult to operate because it is greatly affected by disturbance vibrations such as floor vibrations.
As a method for compensating for this disadvantage, white interference method (OCT) has been developed and widely used. The main OCT currently used includes a time domain OCT (Time Domain OCT) and a Fourier domain OCT (Fourier Domain OCT, or Spectral Domain OCT). The measurement accuracy of OCT using light interference is one digit or more higher than the wavelength of light and other general shape measurement methods.

The principle will be briefly described by taking time domain OCT as an example. In FIG. 9A, the broadband light emitted from the light source 101 is divided by the beam splitter 103, and one is directed to the measured object 105 and the other is directed to the reference mirror 107. The reflected lights are combined by the beam splitter 103 and interfere with each other. The interference intensity is measured by the detector 109.
The light output from the light source 101 has a wide band. Therefore, the reference optical path length E1 until the light reflected from the beam splitter 103 by the reference mirror 107 (hereinafter referred to as reference light) enters the detector 109 and the light reflected by the measured object 105 from the beam splitter 103 (hereinafter referred to as reference light). The object light path length E2 until it enters the detector 109 is the strongest interference. On the other hand, when the difference between the reference optical path length E1 and the object optical path length E2 increases, the contrast of the interference fringes rapidly decreases.

The reference optical path length E1 can be adjusted by moving the reference mirror 107 in the optical axis direction indicated by the white arrow. FIG. 12B shows an example of interference fringes (interference signal) obtained by the detector 109 while moving the reference mirror 107. When the reference optical path length E1 and the object optical path length E2 are equal (E1 = E2). The interference signal shows a peak. Therefore, by reading the position of the reference mirror 107 when the interference signal shows a peak, the distance from the beam splitter 103 to the irradiation point of the object light on the measured object 105 is obtained. The scanning for obtaining the distance in the depth direction is called A-scan.
Scanning the surface of the object to be measured 105 with the irradiation point of the object light, and sequentially reading the position of the reference mirror 107 where the contrast of interference fringes (interference signal) at each irradiation position shows a peak, The surface shape of the body 105 can be specified. This scanning is called B-scan.
However, each time the object light irradiation point is moved, the reference mirror 107 is moved to obtain the interference fringe contrast peak, that is, to perform both A-scan and B-scan. is required. Furthermore, a mechanism for accurately moving the reference mirror 107 and a mechanism for measuring the position thereof with high accuracy are expensive and large.

On the other hand, the Fourier domain OCT enables measurement of a three-dimensional shape only by scanning corresponding to B-scan. However, even in the Fourier domain OCT, the depth of the range within the range in which the reference beam and the object beam interfere on the detector 109 formed of a line CCD or the like (hereinafter, this range is referred to as a coherent distance in the present invention). If the object to be measured has a three-dimensional shape, it is only possible to measure the three-dimensional shape without moving the reference mirror. Generally, this coherent distance is several mm, and in order to measure a surface shape having a depth exceeding this distance, the reference mirror must be moved, so that the same problem as in the time domain OCT remains.
Here, in the measurement of distance or length using optical interference, the number of changes in the intensity of interference fringes when the reference mirror is accurately moved from the starting point along the optical axis is measured. If the optical path between the measuring bodies is interrupted even instantaneously, the measurement must be performed again from the starting point, which causes a great problem in operability. Based on such a background, there has been a strong demand for a measuring device with high accuracy and good operability in the Fourier domain OCT. The mechanism for accurately moving the reference mirror from the starting point along the optical axis is also expensive and significantly impedes operability.

In Patent Document 1, by collecting and irradiating light to the object to be measured in one line, in addition to the information in the depth direction by one shot of the CCD camera, in the lateral (or longitudinal) direction of the object to be measured. There has been proposed a Fourier domain interference shape measuring apparatus capable of obtaining position information at a time.
Further, in Patent Document 2, the reference mirror has a plurality of reference surfaces, and the plurality of reference surfaces are minute based on the wavelength of light output from the light source between the reference light generated on each of the adjacent reference surfaces. There has been proposed a surface shape measuring device arranged so that an optical path length difference corresponding to a measurement interval is generated.

JP 2006-116028 A JP 2007-333470 A

According to Patent Document 1, it is possible to measure one object to be measured with a single shot of a CCD camera without mechanical scanning, and one of the scans necessary for obtaining a two-dimensional image in conventional OCT is not necessary. Therefore, it contributes to high-speed measurement of Fourier domain OCT. Also in Patent Document 2, an apparatus capable of measuring the surface shape of the surface of the object to be measured with high accuracy and speed is provided. However, Patent Document 1 and Patent Document 2 are premised on measurement within the range of the coherence distance or less, and do not show a solution for measuring a measured object having a depth exceeding the coherence distance at high speed.
The present invention has been made based on such a technical problem, and an object of the present invention is to provide an apparatus capable of quickly measuring the surface shape of a measurement object having a depth exceeding a coherent distance.

Since the Fourier domain OCT basically does not require a mechanism for moving the reference mirror, it is an excellent method in terms of operability. However, the range in which the measurement in the depth direction can be performed with the reference mirror fixed is as narrow as the coherence distance ΔZ or less (several mm). Therefore, the application range is limited. Therefore, when the depth of the object to be measured is deep, if an area in the depth direction is divided for each coherent distance ΔZ and an optimum optical path length of reference light is given to each area, an object having a deep depth can be measured. It becomes like this. As a method of changing the optical path length of the reference light, a method of moving the reference mirror is generally performed. However, this method takes time to move and takes time to measure a deep object, and is not practical. Moreover, the mechanism for accurately moving the reference mirror is large and expensive.
The surface shape measuring device of the present invention made there is provided with a light source, a light splitting unit, a reference light generating unit, an interference light generating unit, and a detecting unit.
The light source outputs inspection light.
The light splitting unit splits the inspection light output from the light source into first split light that is applied to the measurement position on the surface of the object to be measured and second split light that is applied to the reference light generation unit. is there.
The interference light generation unit interferes by interfering the object light obtained by reflecting the first divided light on the surface of the measurement object and the reference light obtained by reflecting the second divided light on the reference light generation unit. It generates light.
The detection unit detects the intensity of the interference light generated by the interference light generation unit.
The reference light generation unit, which is a characteristic part of the present invention, has a light reflection surface at the end of each optical path, and is arranged with a difference in optical path length with respect to the light splitting unit. A plurality of reference light generation units each including an N generation unit (an integer greater than or equal to N = 2) are provided. And the sum total of the difference of the optical path length from a 1st production | generation part to the Nth production | generation part is set to 2 times or more of coherence distance (DELTA) Z.

In the apparatus of the present invention, the sum of the optical path length differences from the first generation unit to the Nth generation unit is set to at least twice the coherence distance ΔZ, so the first generation unit to the Nth generation unit By sequentially irradiating the second divided light and obtaining the reflected reference light, the surface shape of the measurement object having a depth exceeding the coherent distance can be quickly obtained without moving the Nth generation unit from the first generation unit. Can be measured. Note that N is selected from an integer of 2 or more, but N should be appropriately set according to the degree of the depth of the measured object in view of the coherence distance being several mm.
In addition, the apparatus of the present invention can be applied to Fourier domain OCT, but can also be applied to time domain OCT and spectrum scanning OCT.

Since the present invention functions if the sum of the optical path length differences from the first generation unit to the Nth generation unit is set to be twice or more the coherence distance ΔZ, the difference between the optical path lengths is arbitrary. However, it is preferable to make the difference between the optical path lengths coincide with the coherence distance ΔZ. By doing so, the surface shape of the measurement object having a depth exceeding the coherence distance ΔZ can be measured without omission while minimizing the number of first to Nth generation units. For example, the number of first to Nth generation units can be halved compared to a case where the difference between the optical path lengths is ½ΔZ.
In this case, it is preferable to arrange the first generation unit to the N-th generation unit in order from the first generation unit toward the N-th generation unit so that the optical path length difference increases by ΔZ.

  The reference light generation unit that is a characteristic part of the present invention includes at least first to third modes. In the first embodiment, the first generation unit to the Nth generation unit are configured by N reference mirrors arranged on different optical paths. In the second embodiment, a first generation unit to an Nth generation unit are configured by N optical fibers arranged on different optical paths. Further, in the third mode, the first generation unit to the Nth generation unit are configured by N partial transmission mirrors arranged on the same optical path at intervals in the optical axis direction.

In the first mode, the reference light generation unit includes a first reference mirror to an Nth reference mirror arranged corresponding to each light reflection surface of the first generation unit to the Nth generation unit, and second A first scanning mirror is provided that reflects the split light and irradiates the first reference mirror to the Nth reference mirror.
In the first embodiment, the surface of the measured object having a depth exceeding the coherence distance ΔZ is obtained by scanning the first scanning mirror so that the reference light is sequentially reflected from the first reference mirror to the Nth reference mirror. The shape can be measured without omission.

  In the first embodiment, the first scanning mirror is disposed so as to be rotatable about a scanning axis in a direction parallel to the light reflecting surface, and the first reference mirror to the Nth reference mirror are arcs centered on the scanning axis. The optical path length difference of ΔZ is provided in the order from the first reference mirror to the Nth reference mirror. Then, the first scanning mirror is driven so as to emit the second divided light in the order of the first reference mirror to the Nth reference mirror. Since the first scanning mirror is driven by a rotational movement that is much easier than a linear movement, it contributes to speeding up the surface shape of the object to be measured having a depth.

In the second mode, the reference light generation unit includes the first optical fiber to the Nth optical fiber that guides the second divided light toward the light reflecting surfaces of the first light generation unit to the Nth generation unit. And a second scanning mirror that reflects the second divided light and irradiates the first divided optical fiber or the Nth optical fiber.
In the second embodiment, the second measuring mirror scans the second scanning mirror so that the reference light is output in order from the first optical fiber to the Nth optical fiber, so that the measurement object having a depth exceeding the coherent distance ΔZ is obtained. The surface shape can be measured without omission.

In the second embodiment, the second scanning mirror is disposed so as to be rotatable around a scanning axis in a direction parallel to the light reflecting surface. Then, the second scanning mirror is driven so as to irradiate the second divided light in the order of the first optical fiber to the Nth optical fiber. Since the second scanning mirror is driven by a rotational movement that is much easier than a linear movement, it contributes to speeding up the surface shape of the measurement object having a depth. Further, the second embodiment using the optical fiber having a thin wire diameter can realize a reduction in the size of the apparatus as compared with the first embodiment using a plurality of mirrors.
The first scanning mirror and the second scanning mirror described above are rotary polyhedral mirrors (so-called polygon mirrors), and switching of irradiation of the second divided light to the first reference mirror or the Nth reference mirror or the first light is performed. It is preferable for switching the irradiation of the second split light to the fiber or the Nth optical fiber.

In the third embodiment, the reference light generation units are sequentially arranged coaxially with an interval corresponding to the optical path length difference corresponding to the first generation unit to the Nth generation unit (N = 2 or greater integer). A first reference partial transmission mirror to an Nth reference partial transmission mirror.
In the third mode, the measured object is output from the light splitting unit without providing the first scanning mirror and the second scanning mirror necessary for the first mode and the second mode, although there are restrictions to be described later. The second divided light can be directly applied to the first reference partial transmission mirror or the Nth reference partial transmission mirror. In other words, since the third embodiment does not need to drive the optical system, there is an advantage that the surface shape of the object to be measured having a depth can be measured more quickly.

  According to the present invention, since the sum of the optical path length differences from the first generation unit to the Nth generation unit is set to at least twice the coherence distance ΔZ, the first generation unit to the Nth generation unit The surface shape of the measurement object having a depth exceeding the coherence distance ΔZ is obtained without moving the Nth generation unit from the first generation unit by sequentially irradiating the second divided light and obtaining the reflected reference light. It can be measured quickly.

It is a block diagram which shows the structure of the surface shape measuring apparatus concerning 1st Embodiment. It is a block diagram which shows the structure of the surface shape measuring apparatus concerning 2nd Embodiment. It is a block diagram which shows the structure of the surface shape measuring apparatus concerning 3rd Embodiment. It is a figure which shows the partial change of the surface shape measuring apparatus concerning 4th Embodiment. It is a block diagram which shows the structure of the surface shape measuring apparatus concerning a 2nd modification. It is a block diagram which shows the structure of the surface shape measuring apparatus concerning a 3rd modification. It is a block diagram which shows the structure of the surface shape measuring apparatus concerning a 4th modification. It is a block diagram which shows the structure of the surface shape measuring apparatus concerning a 4th modification. It is a figure explaining the principle of time domain OCT (Time Domain OCT).

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
[First Embodiment]
<Overview of overall configuration>
Based on FIG. 1, the structure of the surface shape measuring apparatus 10 concerning 1st Embodiment is demonstrated.
The surface shape measuring apparatus 10 splits the inspection light L0 output from the light source 11 into a first split light L1 for generating the object light LS and a second split light L2 for generating the reference light LR. The surface shape measuring apparatus 10 also generates the detection light LC by superimposing the reference light LR that has passed through the reference mirror unit 25 and the object light LS that has passed through the measurement target MB, and the detection result of the detection light LC is displayed. It is configured to analyze and measure the surface shape of the measurement object MB. The surface shape measuring apparatus 10 measures the shape of the surface of the measurement object MB based on the Fourier domain OCT.

<Light source 11>
The surface shape measuring apparatus 10 includes a light source 11. The light source 11 outputs inspection light L0 having low coherence. As the light source 11, a broadband light source such as a super luminescent diode (SLD) or a light emitting diode (LED) is used.

<Optical fiber and each component connected to it>
The surface shape measuring apparatus 10 includes an optical fiber 12a made of, for example, a single mode fiber that receives the inspection light L0 output from the light source 11 at one end thereof. The other end side of the optical fiber 12 a is connected to a photocoupler 13. The photocoupler 13 has both functions of a means for splitting light (splitter) and a means for superposing light (coupler). Here, it is conventionally referred to as a “photocoupler”. . The inspection light L0 output from the light source 11 is guided to the photocoupler 13 through the optical fiber 12a, where it is split into the first split light L1 and the second split light L2.

  An optical fiber 12b, an optical fiber 12c, and an optical fiber 12d are connected to the photocoupler 13 at one end thereof. A reference light generation unit 20 is provided on the other end side of the optical fiber 12b. An object light generation unit 30 is provided on the other end side of the optical fiber 12c. Further, a measurement unit 40 is provided on the other end side of the optical fiber 12d.

<Reference light generator 20>
The second split light L2 split by the photocoupler 13 is emitted from the other end surface toward the reference light generation unit 20 through the optical fiber 12b. The reference light generation unit 20 includes a collimator lens 21, a scanning mirror 23, and a reference mirror unit 25. The second split light L2 emitted from the optical fiber 12a is converted into a parallel light beam by the collimator lens 21, and then scanned. The light is reflected by the reference mirror unit 25 via the mirror 23 and becomes the reference light LR.

  The scanning mirror 23 is swung as indicated by an arrow 26 in the figure within a predetermined swing angle range with the scanning axis 24 as the central axis. The second split light L <b> 2 received from the collimator lens 21 is reflected by the scanning mirror 23 and guided toward the reference mirror unit 25 in a direction corresponding to the swing position. Note that the mechanism for swinging the scanning mirror 23 is lighter and less expensive than the conventional reference mirror 107 reciprocating linearly.

The reference mirror unit 25 includes a plurality of reference mirrors 251, 252, 253, 254,... 25N. The reference mirrors 251, 252, 253, 254,... 25 N are arranged on arcs having different diameters around the scanning axis 24. The reference mirrors 251, 252, 253... 25 N use mirrors having the same specifications, but are arranged at different positions. Specifically, when the optical path lengths D1, D2, D3, D4, DN from the photocoupler 13 to the reference mirrors 251, 252, 253, 254,..., 25N via the scanning mirror 23 are satisfied, the following is satisfied. Here, ΔZ is the range of the optical path length difference in which interference occurs between the object light LS and the reference light LR, and the reference mirrors 251, 252, 253, 254,..., 25N provide the optical path length difference of ΔZ in this order. Are arranged. By swinging the scanning mirror 23 about the scanning axis 24, the reference mirrors 251, 252, 253, 254,.
D2 = D1 + ΔZ
D3 = D1 + 2 × ΔZ = D2 + ΔZ
D4 = D1 + 3 × ΔZ = D3 + ΔZ
DN = D1 + N × ΔZ

The reference light LR generated by being reflected by the respective reference mirrors 251, 252, 253, 254,... 25N passes through the scanning mirror 23 again and is condensed on the other end surface of the optical fiber 12b by the collimator lens 21. The collected reference light LR is guided to the photocoupler 13 through the optical fiber 12b.
In addition, as a delay means for adjusting the optical path length (optical distance) of the reference light LR and the object light LS, and as a means for adjusting the dispersion characteristics of the reference light LR and the object light LS, a glass block, a density filter, etc. These optical systems may be arranged.

<Object light generation unit 30>
The first split light L1 split by the photocoupler 13 is emitted toward the object light generation unit 30 from the other end face through the optical fiber 12c. The object light generation unit 30 includes a collimator lens 31, a scanning mirror 33, and an objective lens 35. The first split light L1 emitted from the optical fiber 12c is converted into a parallel light beam by the collimator lens 31, and then the scanning mirror. 33. The scanning mirror 33 irradiated to the measurement object MB via the objective lens 35 can be swung in a two-dimensional direction. The first divided light L1 is imaged L and reflected on the surface of the measurement object MB to become object light LS. The object light LS reflected by the measurement object MB passes through the objective lens 35 and the scanning mirror 33 in this order, and is collected by the collimator lens 31 on the other end surface of the optical fiber 12c. The condensed object light LS is guided to the photocoupler 13 through the optical fiber 12c.

<Detection light LC generation>
The photocoupler 13 generates the detection light LC by superimposing the reference light LR that has passed through the optical fiber 12a and the object light LS that has passed through the optical fiber 12c. The generated detection light LC is guided to the measurement unit 40 through the optical fiber 12d.

<Measurement unit 40>
The measuring unit 40 includes a collimator lens 41, a diffraction grating 43, an imaging lens 45, and a line CCD (Line Charge Coupled Device) 47. The diffraction grating 43 of this embodiment is a transmissive diffraction grating, but of course, a reflective diffraction grating can also be used. Of course, other photodetecting elements (detecting units) may be applied in place of the line CCD 47.

  The detection light LC incident on the measurement unit 40 is converted into a parallel light beam by the collimator lens 41 and then split (spectral decomposition) by the diffraction grating 43. The split detection light LC is imaged on the imaging surface of the line CCD 47 by the imaging lens 45. The line CCD 47 receives this detection light LC, converts it into an electrical detection signal, and outputs this detection signal to the control unit 50. The line CCD 47 includes pixels corresponding to each wavelength of light decomposed by the diffraction grating 43.

<Control unit 50>
The control unit 50 analyzes the detection signal input from the line CCD 47 and performs processing for specifying the surface shape of the measurement object MB. The analysis method at this time is the same as the conventional Fourier domain OCT method.
Further, the control unit 50 executes control of each part of the surface shape measuring apparatus 10. This control includes the output of the inspection light L0 from the light source 11, the driving of the scanning mirror 23 applied to the reference light generating unit 20, the driving of the scanning mirror 33 applied to the object light generating unit 30 and the stage on which the measurement object MB is placed. It is out. More detailed control contents will be described later.
The control unit 50 has a hardware configuration similar to that of a known computer. Specifically, it includes at least a microprocessor such as a CPU, storage means such as a RAM, a ROM, and a hard disk drive, input means such as a keyboard and a mouse, display means such as a display, and a communication interface. . Then, the control program is stored in the hard disk drive, developed on the RAM, and interpreted by the CPU, thereby realizing the control performed by the control unit 50.

<Measurement procedure>
Next, the measurement procedure concerning the surface shape measuring apparatus 10 will be described.
The inspection light L0 output from the light source 11 is split into two light beams, a first split light L1 and a second split light L2, by the photocoupler 13. The first split light L1 becomes the object light LS, and the second split light L2 becomes the reference light LR. The object light LS is reflected by the measured object MB, and the reference light LR is reflected by the reference mirrors 251, 252, 253, 254,... 25N, and returns to the original optical path. Then, it enters the photocoupler 13 again, and these two lights are superimposed. Part of the superimposed light becomes detection light LC and travels toward the line CCD 47. Only when the optical path lengths of the object light LS and the reference light LR are equal, the two lights, that is, the object light LS and the reference light LR interfere with each other. The range of the optical path length difference in which interference occurs between the object light LS and the reference light LR, that is, the coherence distance ΔZ varies depending on the type of the light source 11, but is generally several millimeters at most for a light source used for OCT. .

In the Fourier domain OCT, after being emitted from the photocoupler 13, the detection light LC is guided to the collimator lens 41 to be parallel-constrained and then incident on the diffraction grating 43. The low coherence light output from the light source 11 can be considered as an aggregate of coherence light having different frequencies. Accordingly, since the detection light LC has a diffraction angle different for each frequency component, when the light enters the diffraction grating 43, the wavelength is resolved before being irradiated to the line CCD 47.
The pixels included in the line CCD 47 particularly strongly interfere only with light having a wavelength in which the phases of the object light LS and the reference light LR, which are generated due to the optical path length difference. Since each pixel of the line CCD 47 corresponds to each wavelength decomposed by the diffraction grating 43, the light intensity due to interference increases on the pixel corresponding to the wavelength having the same phase. The longer the optical path length difference is, the higher the frequency of appearance of wavelengths with the same phase is. Therefore, the interval between pixels on the line CCD 47 where the light intensity is increased is narrowed. That is, the frequency of the output signal from the line CCD 47 is increased. When the frequency analysis of the output signal is performed, the optical path length difference can be calculated. Therefore, when the reference mirror is fixed and the object light LS is scanned on the measured object MB by the scanning mirror 33, the surface shape of the measured object MB can be measured. The frequency analysis of the output signal is obtained by Fourier transform. In the Fourier domain OCT, the position of the measurement point of the measured object MB is instantaneously obtained in this way.

The surface shape measuring apparatus 10 includes reference mirrors 251, 252, 253, 254,... 25 N, and the reference mirrors 251, 252, 253, 254,. The second divided light L2 is irradiated in order. When the second split light L2 irradiated to each of the reference mirrors 251, 252, 253, 254,... 25N is L21, L22, L23, L24,... L2N, the reference mirrors 251, 252, Reference light LR1, reference light LR2, reference light LR3, reference light LR4, and reference light LRN are reflected from each of 253, 254,... 25N. The reference light LR1, the reference light LR2, the reference light LR3, the reference light LR4, and the detection light LC1, the detection light LC2, the detection light LC3, and the detection light LC4 generated by superimposing each of the reference light LRN and the object light LS in order. Then, the measurement of the surface shape described above for the detection light LCN is performed. The second split light L2, the reference light LR, and the detection light LC are associated with each other as follows. If a series of steps until detection light is generated by the same reference mirror is referred to as a “step”, the surface shape measuring apparatus 10 performs the first step to the Nth step at the same measurement position on the measured object MB. A surface shape measurement consisting of steps is performed.
First step: second split light L21 → reference light LR1 → detection light LC1
Second step: second split light L22 → reference light LR2 → detection light LC2
Third step: second split light L23 → reference light LR3 → detection light LC3
Fourth step: second split light L24 → reference light LR4 → detection light LC4
Nth step: second split light L2N → reference light LRN → detection light LCN

Here, the N reference mirrors 251, 252, 253, 254,... 25 N are arranged so that the optical path length is increased by ΔZ in order from the reference mirror 251. If the optical path length of the reference light from the photocoupler 13 to the reference mirror 251 is D1, the optical path length to the reference mirror 25N is D1 + N × ΔZ. That is, the shape can be measured if the optical path length of the object light LS from the photocoupler 13 to the measured object BM is within the range of D1 to D1 + N × ΔZ.
For example, if the optical path length of the object light LS is D1 + ΔZ, the position on the surface of the measurement object MB can be specified in the second step described above. In this case, the steps after the third step can be omitted, and all the steps up to the Nth step may be executed. If the optical path length of the object light LS is D1 + 3 × ΔZ, the position on the surface of the measurement object MB can be specified in the fourth step described above. In this case, the steps after the fifth step can be omitted, and all the steps up to the Nth step may be executed. Note that when the measured object BM is deep, the number N of reference mirrors may be increased accordingly.

  As the scanning mirror 23 constituting the reference light generation unit 20 used in the surface shape measuring apparatus 10, it is only necessary to have a diameter (about several mm) slightly larger than the diameter of the reference light. Can be used. In addition, since the scanning mirror 23 is oscillated, the time required for scanning by the scanning mirror 23 is one digit than the time required for operating the reference mirror 107 that reciprocates linearly described in the time domain OCT described above. 2 digits shorter. The measurement time in the Fourier domain OCT depends on the data acquisition time from the line CCD 47 and the calculation time. However, since the scanning time of the scanning mirror 23 can be shortened, the measurement time per point (1st step to Nth step). Can be set to ms or less. Therefore, according to the surface shape measuring apparatus 10, highly accurate shape measurement can be performed in a very short time.

In the surface shape measuring apparatus 10 described above, the reference mirrors 251, 252, 253, 254,... 25 N are arranged so that the optical path length is increased by ΔZ in order from the reference mirror 251. Absent. Even if the reference mirrors 251, 252, 253, 254,. The surface shape can be measured when the optical path length of the object light LS from the photocoupler 13 to the measured object BM is in the range of D1 to D1 + N × ΔZ.
In the surface shape measuring apparatus 10 described above, the difference in optical path length between the reference mirrors 251, 252, 253, 254,... 25N (interval of the reference mirror) is ΔZ, but this is not essential in the present invention. It is clear that the effect of the present invention can be enjoyed if the distance between the reference mirrors is not more than ΔZ. However, it is preferable to determine the distance between the reference mirrors in consideration of the fact that the number of reference mirrors must be increased if the distance between the reference mirrors is made smaller than ΔZ.
Further, although the reference mirror spacing is preferably the same, the present invention allows individual spacing to be different. Of course, it is assumed that this interval is equal to or less than ΔZ.
Furthermore, instead of using the diffraction grating 43, the present invention can also be applied to spectral scanning OCT that obtains an equivalent signal by changing the wavelength of the light source with time.

[Second Embodiment]
Next, the surface shape measuring apparatus 110 according to the second embodiment will be described with reference to FIG.
The surface shape measuring apparatus 110 has the same configuration as the surface shape measuring apparatus 10 according to the first embodiment except for the reference light generation unit 120, and the procedure for measuring the surface shape of the measurement object MB is the same. . Therefore, while the reference light generation unit 120 will be described below, the same components as those in the first embodiment are denoted by the same reference numerals as those in FIG. 1 and description thereof is omitted.

  The reference light generation unit 120 of the surface shape measuring apparatus 110 includes a collimator lens 21, a scanning mirror 23, and a reference optical fiber unit 27, and the second split light L <b> 2 emitted from the optical fiber 12 a is parallel by the collimator lens 21. After being converted into a light beam, the light is reflected by the reference optical fiber portion 27 via the scanning mirror 23, and the reference light LR is generated.

  The reference optical fiber unit 27 includes a plurality of optical fibers 271, 272, 273,. The optical fibers 271, 272, 273,... 27 N are arranged so that the second split light L 2 reflected from the scanning mirror 23 is incident on one end side, and the incident second split light L 2 is input to the other end side. Reflecting reference mirrors 281, 282, 283,... 28N are provided. In FIG. 2, the dimensions of the reference mirrors 281, 282, 283,... 28 N are shown large for easy understanding, but the diameters of the optical fibers 271, 272, 273,. If so, the second split light L2 can be reflected on the other end side. The second split light L2 incident from one end side is reflected by reference mirrors 281, 282, 283,..., 28N, respectively, and becomes reference light LR. One end side of the optical fibers 271, 272, 273,... 27 N is arranged on a common arc centered on the scanning axis 24. The reference mirrors 281, 282, 283,... 28 N use mirrors having the same specifications.

The optical path lengths D1, D2, D3,... DN from the photocoupler 13 to the reference mirrors 281, 282, 283,... 28N via the scanning mirror 23 are provided with an optical path length difference of ΔZ in this order. The relationship between D1, D2, D3,... DN and ΔZ is shown below, but is the same as in the first embodiment. The difference in optical path length is provided by changing the lengths of the optical fibers 271, 272, 273,. The relationship between ΔZ and ΔD is ΔZ = nΔD. Here, n is the refractive index of the optical fiber.
D2 = D1 + ΔZ
D3 = D1 + 2 × ΔZ = D2 + ΔZ
DN = D1 + N × ΔZ

  As described above, the shape can be measured if the optical path length of the object light LS from the photocoupler 13 to the measured object BM is within the range of D1 to D1 + N × ΔZ. That is, the range in which the optical path length of the object light LS is D1 to D1 + Z is the measurement range in the depth direction of the surface shape measuring apparatus 110.

  The difference in measuring the surface shape of the object MB to be measured is that the scanning mirror 23 is swung around the scanning axis 24 so that the reflected light from the scanning mirror 23 is irradiated in the order of optical fibers 271, 272, 273,. To do. The reference light LR generated by being reflected by the optical fibers 271, 272, 273,... 27N passes through the scanning mirror 23 again and is condensed on the other end surface of the optical fiber 12b by the collimator lens 21. The collected reference light LR is guided to the photocoupler 13 through the optical fiber 12b.

According to the surface shape measuring apparatus 110, the following effects can be obtained in addition to the effects obtained by the surface shape measuring apparatus 10 according to the first embodiment.
By increasing the number of optical fibers 271, 272, 273,... 27N, measurement in the depth direction can be performed in an arbitrary range. The optical fibers 271, 272, 273,... 27 N can have a wire diameter of several μm, and are lightweight and can be bent. In addition, the reference mirrors 281, 282, 283,... 28N need only have the same diameter as the optical fibers 271, 272, 273,. Further, since it is sufficient that the scanning mirror 23 has a size exceeding the diameter of the reference light LR, a minute mirror can be used. Therefore, according to 2nd Embodiment, the small and lightweight surface shape measuring apparatus 110 is obtained.

Further, if the one end side where the second split light L2 of the optical fibers 271, 272, 273,... 27N enters is bundled, the range (oscillation angle) for scanning the scanning mirror 23 can be made minute. Therefore, since the second split light L2 can be sequentially irradiated onto the optical fibers 271, 272, 273,... 27N in a very short time of the ms order, the surface shape measuring device 110 has a shorter measurement time than the surface shape measuring device 10. it can. The optical fibers 271, 272, 273,... 27 N can be arranged in a straight line to form a bundle, or arranged in a lattice shape to form a bundle. However, in the case of arranging in a grid pattern, it is necessary to drive the scanning mirror 23 two-dimensionally.
Further, the reference mirrors 281, 282, 283,... 28N are attached to the other ends of the optical fibers 271, 272, 273,... 27N, respectively, but a reflection film may be coated on the other end surface of the optical fibers. If the refractive index of the optical fiber is sufficiently high, the other end surface becomes a reflecting surface and a part of the light is reflected. Therefore, it is not necessary to provide a reference mirror and a reflecting film.

[Third Embodiment]
Next, a surface shape measuring apparatus 210 according to the third embodiment will be described based on FIG.
The surface shape measuring apparatus 210 has the same configuration as the surface shape measuring apparatus 10 according to the first embodiment except for the reference light generation unit 220, and the procedure for measuring the surface shape of the measurement object MB is the same. . Therefore, while the reference light generation unit 220 will be described below, the same components as those in the first embodiment are denoted by the same reference numerals as those in FIG. 1 and description thereof is omitted.

  The reference light generation unit 220 of the surface shape measuring apparatus 210 includes the collimator lens 21 and the partial transmission mirror unit 29, and the second split light L2 emitted from the optical fiber 12a is converted into a parallel light beam by the collimator lens 21. Thereafter, the light is reflected by the partial transmission mirror unit 29, and the reference light LR is generated.

The partial transmission mirror unit 29 includes a plurality of partial transmission mirror units 291, 292, 293, 294,... 29N. Each of the partially transmissive mirror portions 291, 292, 293, 294,... 29N is arranged coaxially with an interval of ΔZ.
The optical path lengths D1, D2, D3, D4,... DN from the photocoupler 13 to the respective partial transmission mirror portions 291 292 293 294... 29N via the collimator lens 21 are provided with an optical path length difference of ΔZ in this order. ing. That is, the relationship between D1, D2, D3, D4,... DN and ΔZ is the same as that in the first embodiment as shown below. Therefore, the range in which the optical path length of the object light LS of the surface shape measuring apparatus 210 is D1 to D1 + Z is the measurement range in the depth direction of the surface shape measuring apparatus 210.
D2 = D1 + ΔZ
D3 = D1 + 2 × ΔZ = D2 + ΔZ
D4 = D1 + 3 × ΔZ = D3 + ΔZ
DN = D1 + N × ΔZ

In the reference light generation unit 220, a part of the second split light L2 is reflected by the partial transmission mirrors 291, 292, 293, 294,... 29N, and the reference light LR is generated. For example, when the reflectance of the partial transmission mirrors 291, 292, 293, 294,... 29N is α and the transmittance is β (α + β = 1), the partial transmission mirrors 291, 292, 293, 294,. The reflected light (reference light LR) and the transmitted light are shown as follows. However, the reference light LR by the partial transmission mirrors 292, 293, 294,... 29N excluding the partial transmission mirror 291 is again transmitted through the partial transmission mirror located in the preceding stage.
Partially transmitting mirror 291: Reference light LR1; α transmitted light; β
Partially transmitting mirror 292: Reference light LR2; α + (β × α × β) Transmitted light; β ²
Partial transmission mirror 293: Reference light LR3; α + (β × α × β) ² transmitted light; β ³
Partial transmission mirror 294: Reference light LR4; α + (β × α × β) ³ transmitted light; β ⁴

  If any of the reference lights LR1, LR2, LR3, LR4,... LRN generated as described above has an optical path length difference from the object light LS equal to or less than the coherence distance ΔZ, the surface shape of the measurement object MB Can be measured. However, since the reference light LR generated by which partial transmission mirrors 291, 292, 293, 294,... Accordingly, the surface shape measuring apparatus 210 performs the following processing.

  The measured value MB usually has a design value. Therefore, by referring to this design value, the optical path length of the object light LS from the point on the measurement object MB irradiated with the first divided light L1 by the scanning mirror 33 is roughly estimated. From the estimated value of the optical path length of the object light LS, it is possible to estimate which reference fringe from which reference partial transmission mirror has formed a high-contrast interference fringe.

  Since the surface shape measuring apparatus 210 does not have an operating part, the measurement time can be shortened compared with the surface shape measuring apparatuses 10 and 110, and the cost of the apparatus can also be reduced.

By the way, when the surface of the measurement object MB is rough, speckle pattern noise is generated by light interference. The speckle pattern is a granular pattern, and when multiple grain patterns are introduced into the fiber coupler fiber, the interference intensity is averaged and the contrast is significantly reduced. Therefore, in order to be able to detect the contrast of the interference intensity, it is desirable that the size of the speckle pattern grains is larger than the fiber diameter of the fiber coupler. This includes a method of making the diameter of the fiber equal to or smaller than the particle size of the speckle pattern, and a method of decreasing the numerical aperture of the collimator lens 31 to make the speckle pattern particle size larger than the fiber diameter. In this way, the shape can be measured even when the surface of the measured object is rough.
Also in the surface shape measuring apparatus 210 using the basic type of the Fourier domain OCT, the particle size of the speckle pattern appearing on the surface of the line CCD 47 is adjusted to be larger than the size of each pixel of the sensor.

[Fourth Embodiment]
Next, a surface shape measuring apparatus 310 according to the fourth embodiment will be described with reference to FIG.
The first to third embodiments are examples in which the present invention is applied to the Fourier domain OCT, but the present invention can also be applied to the time domain OCT as described below.
In the surface shape measuring apparatus 310 according to the fourth embodiment, when the reference optical path length changing mechanism 60 is added to the configuration shown in FIG. 1, the reference light generation unit 320 is provided instead of the reference mirror 107. There are features. Further, the surface shape measuring apparatus 310 includes a biaxial orthogonal moving table 108 that moves the measured object 105.

The reference optical path length changing mechanism 60 includes a prism 61, a mirror 62 that reflects the second split light L2 emitted from the beam splitter 103 toward the prism 61, and an actuator that moves the prism 61 in the range of ΔX in the X-axis direction. (Not shown). If the position where the prism 61 is closest to the mirror 62 is called a start point, and the position where the prism 61 is farthest from the mirror 62 is called an end point, the prism 61 moves from the start point to the end point by ΔX. The mirror 62 is fixed.
The second split light L2 from the beam splitter 103 is irradiated to the first surface 60a of the prism 61 by changing the direction by 90 degrees by the mirror 62. The second split light L2 passes through the first surface 60a orthogonal to the second split light L2, and after the direction is changed by 90 degrees in order on the second surface 60b and the third surface 60c, the second split light L2 then passes through the first surface 60a. The light is emitted toward the scanning mirror 223.
The reference optical path length changing mechanism 60 configured as described above can change the optical path length of the second divided light L2 (reference light LR) by 2ΔX by moving the prism 61 by ΔX.

The reference light generation unit 320 includes a scanning mirror 223 and a reference mirror unit 225, and constituent members (except for the collimator lens 21) are common to the reference light generation unit 20 according to the first embodiment. However, the plurality of reference mirrors 2251, 2252, 2253, 2254,... 225N constituting the reference mirror unit 225 satisfy the following when the distances from the scanning mirror 223 are X1, X2, X3, X4,. Are arranged to be. That is, the difference in distance from the scanning mirror 223 of the adjacent reference mirrors 2251, 2252, 2253, 2254,.
X2 = X1 + 2ΔX
X3 = X1 + 4ΔX
X4 = X1 + 6ΔX
XN = X1 + 2 (N-1) ΔX

The surface shape measuring apparatus 310 configured as described above sequentially moves the reference mirrors 2251, 2252, 2253, 2254,... 225 N by driving the scanning mirror 223 while repeatedly moving the prism 61 of the reference optical path length changing mechanism 60. The second split light L2 is irradiated. More specifically, it is as follows.
With the scanning mirror 223 facing the reference mirror 2251, the prism 61 is moved by ΔX from the start point to the end point. During this time, the reference light LR21 reflected and generated by the reference mirror 2251 changes in optical path length by 2ΔX. This process is the first step. Here, making the scanning mirror 223 face the reference mirror 2251 means that the second split light L 2 reflected from the scanning mirror 223 is at an oscillation angle at which the reference mirror 2251 is irradiated. The same applies to the following.
The prism 61 is returned to the starting point, and the scanning mirror 223 is opposed to the reference mirror 2252. If so, the prism 61 is moved by ΔX from the start point to the end point. During this time, the reference light LR21 reflected and generated by the reference mirror 2252 changes in optical path length by 2ΔX. This process is the second step.
Thereafter, when the prism 61 is returned to the start point and the scanning mirror 223 is opposed to the reference mirror 2253, the procedure of moving the prism 61 from the start point to the end point by ΔX is repeated to the reference mirror 225N. The step in which the scanning mirror 223 is opposed to the reference mirror 2253 is the third step, the step in which the scanning mirror 223 is opposed to the reference mirror 2254 is the fourth step, and the scanning mirror 223 is opposed to the reference mirror 225N. This process is called the Nth step.

The optical path length from the beam splitter 103 to the scanning mirror 223 via the prism 61 (positioned at the start point) is set to D21.
In the first step, the optical path length from the beam splitter 103 to the reference mirror 2251 changes from D21 + X1 to D21 + X1 + 2ΔX.
Next, in the second step, the optical path length from the beam splitter 103 to the reference mirror 2251 changes from D21 + X2 (= X1 + ΔX) to D21 + X1 + 2ΔX. The range of the optical path length in each step including the third step to the Nth step will be described below.
First step: D21 + X1 to D21 + X1 + 2ΔX
Second step: D21 + X1 + 2ΔX to D21 + X1 + 4ΔX
Third step: D21 + X1 + 4ΔX to D21 + X1 + 6ΔX
Fourth step: D21 + X1 + 6ΔX to D21 + X1 + 8ΔX
Nth step: D21 + X1 + 2 (N−1) ΔX to D21 + X1 + 2NΔX

  As described above, the reference mirror 223 facing the scanning mirror 223 is sequentially switched from the reference mirror 2251 to the reference mirror 225N, thereby changing the optical path length of the reference light LR over a wide range of D21 + X1 to D21 + X1 + 2NΔX. Can do. That is, if the optical path length of the object light LS from the beam splitter 103 to the measured object BM is within the range of D21 + X1 to D21 + X1 + 2NΔX, the surface shape measuring device 310 can measure the surface shape. When the Nth step is completed, the first split light L1 is moved to the next measurement point by driving the movement table 108.

In the surface shape measuring apparatus 310, the time required for scanning by the scanning mirror 223 is one digit less than the time required for operating the reference mirror 107 that reciprocates linearly described in the time domain OCT as in the first embodiment. 2 digits shorter. Therefore, according to the surface shape measuring apparatus 310, highly accurate shape measurement can be performed in a very short time compared to the conventional time domain OCT.
In addition, by using the prism 61 of the reference optical path length changing mechanism 60, the change in the optical path length of the reference light LR is doubled with respect to the movement distance of the prism 61, and the movement of the prism 61 with respect to the same change in optical path length. The distance can be shortened. Therefore, the surface shape measuring apparatus 310 can further shorten the measurement time. Furthermore, since the movement distance of the prism 61 can be shortened, high-precision movement can be realized with an ultraprecision actuator such as a piezo element.
Instead of the reference light generation unit 320, the reference light generation unit 120 of the second embodiment and the reference light generation unit 220 of the third embodiment can be used.

[First Modification]
In the first to third embodiments, the scanning mirror 33 is used as a method of scanning the object light LS on the measurement object MB. This method has an advantage that the irradiation point of the first split light L1 (object light LS) can be moved in a short time. However, the method is very accurate for accurately irradiating the object light LS to a desired position, that is, cost. High rotating mechanism is required. In contrast, the biaxial orthogonal moving table 108 used in the fourth embodiment can be positioned with high accuracy while being low in cost. Therefore, when the measurement time may be sacrificed to some extent, it is preferable to move the irradiation position of the first divided light L1 by moving the measurement object MB by the biaxial orthogonal moving table 108.

[Second Modification]
In the first embodiment, N reference mirrors must be accurately placed at predetermined positions, but the positions may need to be calibrated. In this case, a calibration mechanism can be used. As the calibration mechanism, a calibration mirror moving mechanism 70 can be used instead of the measurement object MB as shown in FIG. The calibration mirror moving mechanism 70 includes a base 71 and a calibration mirror 72 that can move on the base 71 with high accuracy while specifying the position in the optical axis direction of the first split light L1 (object light LS).
The calibration mirror 72 is accurately moved. In the process of this movement, the position of the calibration mirror 72, that is, the optical path length of the object light LS is known. Therefore, by comparing the position of the calibration mirror 72 with the measurement result, it is possible to specify the position error of the reference mirrors 251, 252, 253, 254,. By using this error as a correction value and adding this correction value to the actual measurement value of the object to be measured MB, accurate shape measurement can be performed regardless of the position error of the reference mirrors 251, 252, 253, 254,. It can be carried out.

[Third Modification]
In the second embodiment, the scanning mirror 23 oscillated by the reference light generation unit 120 is used. However, as shown in FIG. 6, a polygon mirror 80 can be used. When the polygon mirror 80 is used, the irradiation of the second split light L2 with respect to the optical fibers 271, 272, 273,.

[Fourth Modification]
In the first to third embodiments, the scanning mirror 33 is operated to irradiate the measurement target MB with the first divided light L1, but as shown in FIG. 7, a rotary table 83 provided with a rotary encoder. If the measurement object MB is placed on the measurement object MB and the measurement object MB is irradiated with the first divided light L1 while rotating the rotary table 83, the first divided light L1 only needs to be scanned in the vertical direction. In addition, in the above-described two-axis orthogonal type moving table, if the rotation table 83 receives the movement in the horizontal axis direction, the cost of the apparatus is reduced and the moving accuracy is improved. When the measured object MB is an axisymmetric rotating body or a shape approximating it, it is effective to use the rotating table 83.

[Fifth Modification]
If the object light LS returning on the optical path until the first split light L1 is irradiated onto the surface to be measured becomes weak, measurement with high accuracy cannot be performed. Therefore, the first split light L1 is required to be incident perpendicularly to the surface (measurement surface) irradiated on the measurement object MB. Therefore, when the measured object MB has a glossy surface such as a rearview mirror and the surface irradiated with the first divided light L1 has a curved surface, the first divided light L1 is perpendicular to the measured surface. It is desirable to control so that it is incident on.

Therefore, as shown in FIG. 8, it is preferable to provide a posture control mechanism 90 that controls the posture of the measurement object MB so that the first split light L1 is incident on the measurement surface perpendicularly.
The posture control mechanism 90 includes a position sensor 91 that measures the position of the object light LS, an objective lens 93 that condenses the object light LS on the position sensor 91, and a measurement result of the position sensor 91 based on the measurement result of the position sensor 91. An attitude control device 95 that controls the attitude is provided. The scanning mirror 33 in the attitude control mechanism 90 employs a partial transmission mirror that transmits a part of the object light LS.
The posture control mechanism 90 includes mechanical elements that can move the measurement object MB in the X-axis direction (horizontal direction) and the Z-axis direction (vertical direction) and can also perform rotation correction and skew correction. The attitude control mechanism 90 includes an encoder. The output from the position sensor 91 is fed back to the attitude control device 95, and the attitude of the measurement object MB is controlled so that the first split light L1 is perpendicularly incident on the measurement surface. At this time, the posture and position of the measurement object MB are grasped by the encoder, and the values are corrected to the three-dimensional measurement values. In this way, even if the surface to be measured is curved and glossy, the shape of the surface to be measured can be measured with high accuracy.
Note that if the posture of the measurement object MB is controlled in advance so that the first divided light L1 is incident vertically based on the design value of the measurement object MB, the position sensor 91 is reliably irradiated with the object light LS. Can be made.

[Sixth Modification]
In the embodiment described above, the line CCD 47 is used for the measurement unit 40. However, as proposed in Patent Document 1, a combination of a two-dimensional CCD and a cylindrical lens can be applied to the present invention. Then, as described in Patent Document 1, in addition to the information in the depth direction, one-shot information on the position in the horizontal (or vertical) direction of the measured object can be obtained at one time. In this case, the moving mechanism of the measurement object MB does not need to be a biaxial orthogonal moving table, and a uniaxial moving table is sufficient, so that the cost of the apparatus can be reduced and the measurement time can be shortened. To do.

  In addition to the above description, the configurations described in the above embodiments can be selected or changed to other configurations as appropriate without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 10,110 ... Surface shape measuring apparatus 11 ... Light source, 12a, 12b, 12c, 12d ... Optical fiber, 13 ... Photocoupler 20, 120, 220 ... Reference light generation part 21 ... Collimator lens, 23 ... Scanning mirror, 24 ... Scanning Axis 25 ... Reference mirror part, 251, 252, 253, 254, 25N ... Reference mirror 27 ... Reference optical fiber part, 271, 272, 273, 27N ... Optical fiber 29 ... Partially transmitting mirror part, 291, 292, 293, 294 , 29N: Partial transmission mirror 30 ... Object light generation unit 31 ... Collimator lens, 33 ... Scanning mirror, 35 ... Objective lens 40 ... Measurement unit 41 ... Collimator lens, 43 ... Diffraction grating, 45 ... Imaging lens, 47 ... Line CCD
DESCRIPTION OF SYMBOLS 50 ... Control part, 60 ... Reference optical path length change mechanism, 70 ... Calibration mirror moving mechanism 80 ... Polygon mirror, 83 ... Rotary table 90 ... Attitude control mechanism, 91 ... Position sensor, 93 ... Objective lens, 95 ... Attitude control device MB ... object to be measured L0 ... inspection light, LS ... object light, LR ... reference light, LC ... detection light L1 ... first split light, L2 ... second split light

Claims (7)

A light source that outputs inspection light;
A light splitting unit that splits the inspection light output from the light source into a first split light that is irradiated to a measurement position on the surface of the measurement object and a second split light that is irradiated to a reference light generation unit; ,
Interfering the object light obtained by reflecting the first divided light on the surface of the object to be measured and the reference light obtained by reflecting the second divided light on the reference light generation unit to produce interference light An interference light generating unit to generate,
A detection unit that detects the intensity of the interference light generated by the interference light generation unit,
The reference light generator is
From the 1st generation part thru / or the Nth generation part (an integer greater than or equal to 2) which has a light reflective surface at the end of each optical path, and is arranged with a difference in optical path length with respect to the light splitting part A plurality of reference light generators,
The sum of the optical path length differences from the first generation unit to the Nth generation unit is set to at least twice the coherence distance ΔZ;
The surface shape measuring apparatus characterized by the above-mentioned. The difference in optical path length is the coherence distance ΔZ,
From the first generation unit to the Nth generation unit, the first generation unit to the Nth generation unit are sequentially arranged so that the optical path length difference is increased by ΔZ.
The surface shape measuring apparatus according to claim 1. The reference light generator is
A first reference mirror to an Nth reference mirror disposed corresponding to the light reflecting surface of each of the first generation unit to the Nth generation unit;
A first scanning mirror that reflects the second split light and irradiates the first reference mirror to the Nth reference mirror;
The surface shape measuring device according to claim 1 or 2. The first scanning mirror is disposed so as to be rotatable around a scanning axis in a direction parallel to the light reflecting surface,
The first reference mirror to the N-th reference mirror are arranged on an arc centered on the scanning axis with an optical path length difference ΔD in order from the first reference mirror to the N-th reference mirror,
The scanning mirror is driven to irradiate the second divided light in the order of the first reference mirror to the Nth reference mirror.
The surface shape measuring apparatus according to claim 3. The reference light generator is
A first optical fiber to an Nth optical fiber that guides the second split light toward the light reflecting surface of each of the first generation unit to the Nth generation unit;
A second scanning mirror that reflects the second split light and irradiates the first optical fiber to the Nth optical fiber;
The surface shape measuring device according to claim 1 or 2. The second scanning mirror is disposed so as to be rotatable about a scanning axis in a direction parallel to the light reflecting surface,
Driven to irradiate the second split light in the order of the first optical fiber to the Nth optical fiber,
The surface shape measuring apparatus according to claim 5. The reference light generator is
Corresponding to the first generation unit through the Nth generation unit (an integer equal to or greater than N = 2), a first reference partial transmission mirror is sequentially arranged coaxially with an interval corresponding to the optical path length difference ΔD. Or an Nth reference partial transmission mirror,
The surface shape measuring apparatus according to claim 1 or 2.

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