JP2014149190A - Measuring device, measuring method, light source device, and article manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring device capable of measuring a position of a test surface with higher accuracy than a conventional one.SOLUTION: A measuring device includes: a plurality of lasers each of which emits a beam different in wavelength; a first modulation element for modulating the intensity or the phase of a plurality of first beams among the beams from the plurality of lasers; and a second modulation element for modulating the intensity or the phase of a plurality of second beams which are the other beams among the beams from the plurality of lasers. The first and second modulation elements differ in modulation cycle.

Description

  The present invention relates to a measuring device, a measuring method, a light source device, and an article manufacturing method for measuring the position of a test surface.

  2. Description of the Related Art Conventionally, there is a light wave interference measuring apparatus that measures an optical path length from a phase difference between a test signal obtained by measuring interference light between a reference light and test light from a test surface and a reference signal. Patent Document 1 discloses a light wave interference measuring apparatus that measures an optical path length difference between a test optical path and a reference optical path using an interferometer of an optical frequency comb light source having a wavelength distribution of about 100 and having an evenly spaced spectral distribution. Has been. This technique can be applied to measurement of a rough surface having a rough surface shape by using a synthetic wavelength of a plurality of wavelengths, thereby increasing the measurement range. However, a phase error (speckle error) generated by speckle becomes a rate-determining factor for measurement accuracy. Non-Patent Document 1 discloses that the speckle error is related to the intensity of the test signal.

JP 2010-14549 A

“Higher-order static properties of speckle fields and ther application to rough-surface interface” U. Vry and A.M. F. Fercher, J. et al. Opt. Soc. Am. A, 3, 7, 988-1000 (1986)

  Non-Patent Document 1 merely describes the relationship between the speckle error and the intensity of the test signal at a specific wavelength, and does not describe the relationship between the wavelength and the speckle error. Thus, as a result of intensive studies by the inventor, it was found that the speckle error changes depending on the wavelength.

  In Patent Document 1, an optical frequency comb generator is used. The wavelength band of the optical comb generated by the optical frequency comb generator is narrow, for example, limited to about 2.5 THz. If the wavelength band is narrow, it greatly depends on the speckle error in the wavelength band, and if the speckle error in the wavelength band is large, the measurement error becomes large.

  Therefore, an object of the present invention is to provide a measuring device, a measuring method, and a light source device that can measure the position of the surface to be measured with higher accuracy.

  A measuring apparatus as one aspect of the present invention that solves the above-described problem is a measuring apparatus that measures the position of a surface to be measured, and divides light from a light source into first light and second light, and the first light and A light source that emits the second light with a different frequency, the first light emitted from the light source, and the second light before being reflected by the test surface are interfered and emitted from the light source. An interferometer that causes the first light that has been reflected and the second light after being reflected by the test surface to interfere with each other, a measurement unit that measures interference light by the interferometer, and measurement data obtained by the measurement unit A processing unit for determining the position of the test surface, the light source unit includes a plurality of lasers, each of the plurality of lasers emits light having different wavelengths, and the light from the lasers Intensities of a plurality of first lights from a plurality of lasers divided into a first light and a second light Or a first modulation element that modulates the phase and a second modulation element that modulates the intensity or phase of the plurality of second lights from the plurality of lasers, the first modulation element and the second modulation The modulation period with the element is different from each other.

  A light source device according to one aspect of the present invention that solves the above problems divides light from a light source into first light and second light, and emits the first light and the second light with different frequencies. An apparatus comprising a plurality of lasers, each of the plurality of lasers emitting light having different wavelengths, and dividing the light from the laser into the first light and the second light, and a plurality of the lasers A first modulation element that modulates the intensity or phase of the plurality of first lights from the plurality, and a second modulation element that modulates the intensity or phase of the plurality of second lights from the plurality of lasers, The modulation periods of the first modulation element and the second modulation element are different from each other.

  ADVANTAGE OF THE INVENTION According to this invention, the measuring device, measuring method, and light source device which can measure the position of a to-be-tested surface with higher precision can be provided.

It is a figure of the lightwave interference measuring device in a 1st embodiment. It is a figure which shows the spectral distribution of the light inject | emitted from a multiwavelength light source. It is a figure which shows the spectrum distribution of the reference light inject | emitted from each laser, and measurement light. It is a figure which shows the spectrum distribution of the beat signal obtained by measuring the interference light of reference light and measurement light. It is a figure which shows the flowchart of the arithmetic processing which the process part 17 performs. It is a figure of the lightwave interference measuring device in a 2nd embodiment. It is a figure which shows the spectrum distribution of the beat signal in 2nd Embodiment. It is a figure which shows the relationship between the speckle error with respect to a wavelength, and the intensity | strength of a to-be-tested signal.

  FIG. 8A shows the relationship between the speckle error due to a plurality of wavelengths that are close to each other at intervals of several hundred pm and the intensity of the signal under test with respect to the wavelength. The plot of ■ in FIG. 8A shows speckle errors (left axis) due to a plurality of wavelengths close to the center of a certain wavelength of light incident on the test surface. The plot shows the intensity of the test signal obtained by measuring the interference light between the reference light and the measurement light from the test surface. FIG. 8A shows that the intensity of the test signal changes depending on the wavelength. This is considered to be due to wavelength dependence due to the characteristics of the surface to be measured. The speckle error also changes depending on the wavelength, and it can be seen that the speckle error is small when the intensity of the signal under test is large. In other words, it is effective to use a wavelength having a high intensity of the test signal for reducing speckle errors.

  FIG. 8B shows the relationship between the number of wavelengths of measurement light including a plurality of wavelengths and the measurement accuracy. The plot of ■ in FIG. 8B shows the case where the maximum wavelength difference (difference between the minimum wavelength and the maximum wavelength) of the measurement light is 4.2 THz, and the plot of ● in FIG. 8B is the maximum wavelength. A case where the difference is 9.5 THz is shown. FIG. 8B shows that the measurement accuracy is improved by widening the maximum wavelength difference. This is because by increasing the maximum wavelength difference, it is possible to include a wavelength with a high intensity of the test signal, and the speckle error is reduced.

  Further, from FIG. 8B, it can be seen that even when the maximum wavelength difference is made constant and the number of wavelengths is increased, the measurement accuracy is saturated and converges to a certain value. Therefore, it can be seen that increasing the maximum wavelength difference without changing the number of wavelengths tends to improve the measurement accuracy rather than increasing the number of wavelengths without changing the maximum wavelength difference.

(First embodiment)
FIG. 1 is a configuration diagram of the optical interference measuring apparatus according to the first embodiment. As shown in FIG. 1, the optical interference measuring apparatus of the present embodiment includes a plurality of semiconductor lasers 1a, 1b, and 1c, and modulation elements 3a and 3b that modulate the intensity or phase of input light fluxes with different modulation periods. Is used as a measurement light source. For example, an electro-optic modulation element is used as the modulation element. Two light beams emitted from the multi-wavelength light source 100 are defined as reference light (first light) and measurement light (second light). The measuring device is a test signal obtained by interfering the reference light and the measurement light before being reflected by the test surface, and the reference light and the measurement light after being reflected by the test surface. From the signal, the position of the test surface of the object to be measured is obtained.

  Hereinafter, the light wave interference measuring apparatus of this embodiment will be described in detail. The semiconductor lasers 1a, 1b, and 1c are single longitudinal mode lasers having different oscillation wavelengths, and each laser emits light of a single wavelength. Since these semiconductor lasers can be independently wavelength-controlled, a large wavelength difference can be easily made between the oscillation wavelengths of the semiconductor lasers. Thereby, the difference between the maximum wavelength and the minimum wavelength is large, and a light source capable of oscillation in a wider wavelength band can be configured. The number of semiconductor lasers is not limited to three, and may be two, or may be increased as necessary. By using a DFB laser as such a semiconductor laser, stable single mode oscillation can be realized at a relatively low cost. However, the present invention is not limited to this, and an external resonator type semiconductor laser (ECLD) or a surface emitting laser (VCSEL) may be used. Further, it is not necessary that the laser elements are independent from each other, and a type in which multiple wavelengths are integrated, such as a DFB laser for optical communication, may be used. These lasers are cheaper than expensive optical frequency comb generators.

  Lights from the semiconductor lasers 1a, 1b, and 1c are emitted from the polarization-maintaining fiber, and are multiplexed by the polarization-maintaining type 3 × 2 fiber coupler 2 and then demultiplexed into two. Each of the demultiplexed light beams enters the electro-optic modulation element. One of the two separated light beams (measurement light) is shifted in frequency by the frequency shifter 4 and then enters the electro-optic modulation element. The other of the two demultiplexed light beams (reference light) enters the electro-optic modulation element without passing through the frequency shifter 4. The frequency shifter may be used not only for the frequency shifter 4 that shifts the frequency of the measurement light but also for the optical path of the reference light. That is, in order to make the frequencies of the measurement light and the reference light different, at least one frequency of the measurement light and the reference light may be shifted.

  The electro-optic modulation element modulates the intensity or phase of incident light and generates light having a sideband whose frequency is shifted from the frequency of the incident light. Since each of the demultiplexed light includes light of different wavelengths from the semiconductor lasers 1a, 1b, and 1c, when the demultiplexed light is modulated by the electro-optic modulation element, for each light from the semiconductor laser, Sideband frequency intervals can be matched with high accuracy. For high-accuracy rough surface measurement, it is necessary to average the measurement values over a wide wavelength range generated by an independent semiconductor laser, and therefore, from each laser generated by one electro-optic modulation element. The frequency intervals of the sidebands of the light need to match.

As the electro-optic modulation elements 3a and 3b, for example, an intensity modulator common in optical communication is used. This has a Mach-Zehnder interferometer structure using lithium niobate, and generates a plurality of side bands at equal intervals by intensity modulation. And the modulation frequency _{f m, (1 + cos [} 2πf m t]) when generating the square of the intensity modulation of the number of sidebands can be suppressed to two, it is possible to increase the light amount per single spectrum. Therefore, even when it is necessary to measure relatively weak scattered light as in the case where the surface to be measured is a rough surface, the influence of noise can be reduced, and more accurate measurement can be performed.

In the present embodiment, a case where two sidebands are generated by an intensity modulator will be described. The oscillation frequencies of the semiconductor lasers 1a, 1b, and 1c are assumed to be f ₁ , f ₂ , and f ₃ , respectively. By passing light from a plurality of semiconductor lasers through a common electro-optic modulation element, the light from each laser has a plurality of narrow-band spectra having equal spectral intervals as shown in FIG. 2, and the frequency f ₁ It generates light of a broad wavelength band up ~f _3.

Semiconductor lasers 1a, 1b, the oscillation frequency of 1c and _f i (i = 1,2,3), shows the spectral distribution of two of the light emitted from the multi-wavelength light source 100 (the reference light and the measurement light) in FIG. 3 . The measurement light is given a frequency shift of df with respect to the reference light by the frequency shifter 4. The first electro-optic modulation element 3a for reference light and the second electro-optic modulation element 3b for measurement light have different intensity or phase modulation periods. Therefore, the modulation frequency of the first electro-optical modulator element 3a frequency _{f m,} the modulation frequency of the second electro-optic modulation device 3b is _f m + df _m, is modulated by a different frequency predetermined amount df _m.

When the measurement light and the reference light interfere with each other, interference between the respective spectra occurs. When the interference signal component between the sidebands is removed by a low-pass filter with f _m >> df and df _m , the frequency df _{m is} separated on both sides with the frequency shift amount df as the center as shown in FIG. A beat signal having a spectral distribution is obtained. The horizontal axis is the frequency of the signal. df corresponds to a frequency difference between the measurement light incident on the second electro-optic modulation element 3b and the reference light incident on the first electro-optic modulation element 3a.

  The reference light incident on the interferometer 101 is converted into a parallel light beam by the collimator lens 5a, transmitted through the λ / 2 plate 6a, and then split into two by the polarization beam splitter 7. The reference light reflected by the polarization beam splitter 7 is transmitted through the λ / 2 plate 8 so that the polarization direction is rotated by 90 degrees, passes through the polarization beam splitter 9 and the polarizer 10, and then enters the spectroscopic element 11a. Further, the measurement light incident on the interferometer 101 is converted into a parallel light beam by the collimator lens 5b, transmitted through the λ / 2 plate 6b, and then demultiplexed by the polarization beam splitter 9. The measurement light beam reflected by the polarization beam splitter 9 passes through the polarizer 10 and enters the spectroscopic element 11a.

  On the other hand, the reference light transmitted through the polarizing beam splitter 7 passes through the polarizing beam splitter 12 and the polarizer 13 and then enters the spectroscope 11b. The measurement light beam that has passed through the polarizing beam splitter 9 passes through the polarizing beam splitter 12 and then becomes circularly polarized light by the λ / 4 plate 14, and is collected as a condensed light beam by the condenser lens 15 on the surface to be measured. . After being reflected by the surface to be measured and converted to circularly polarized light in the reverse direction, it is transmitted through the λ / 4 plate 14 again to become linearly polarized light whose polarization plane is rotated by 90 degrees from the incident time, and is again applied to the polarizing beam splitter 12. Incident. Thereafter, the light is reflected by the polarization beam splitter 12, passes through the polarizer 13, and then enters the spectroscopic element 11 b. It is assumed that interference light is obtained by extracting a common polarization component of the reference light and the measurement light by the polarizers 10 and 13. An optical path reflected by the polarizing beam splitters 7 and 9 and incident on the spectroscopic element 11a is referred to as a reference optical path, an optical path transmitted through the polarizing beam splitters 7 and 9 and incident on the spectroscopic element 11b is referred to as a test optical path.

  As the spectroscopic elements 11a and 11b, for example, arrayed waveguide diffraction type wavelength demultiplexers are used. In the following description, the arrayed waveguide diffraction type wavelength demultiplexer is referred to as AWG. The AWG is an element that demultiplexes by diffraction after emission of waveguides on an array having different optical path length differences, and is small and available at low cost. The spectroscopic elements 11a and 11b are not limited to AWG, and for example, a bulk type diffraction grating may be used. Further, a band-pass interference filter may be used as the spectroscopic element of the present embodiment. Use of such an interference filter has an advantage that the configuration of the spectroscopic element is simplified when the number of wavelengths to be measured by the multi-wavelength light source is small.

  The light branched into the light from the semiconductor laser of the multi-wavelength light source 100 by the spectroscopic elements 11a and 11b includes a plurality of detectors corresponding to the number of semiconductor lasers (measuring unit). Light is received at 16a and 16b. The detector is, for example, a photoelectric conversion element such as a photodetector or a sensor. Hereinafter, the interference light signal measured by the measurement device 16a is referred to as a reference signal, and the interference light signal measured by the measurement device 16b is referred to as a test signal. The processing unit 17 such as a processor calculates the position of the test surface (distance to the test surface) using the phase difference between the reference signal output from the measuring devices 16a and 16b and the test signal. If the positions of a plurality of test surfaces are acquired, the shape of the test surface can be obtained.

  Next, arithmetic processing performed by the processing unit 17 of the present embodiment will be described. FIG. 5 is a flowchart thereof.

First, the processing unit 17 acquires measurement data from the measurement unit. In S101, the phase (interference phase) of the interference signal obtained for each spectrum (for each frequency) is measured with respect to the reference signal and test signal obtained for each semiconductor laser. That is, the processing unit 17 measures the phase from each interference signal for a plurality of frequencies for each semiconductor laser. The interference phase can be measured by configuring a phase meter. As an example, the light from the semiconductor laser 1a (oscillation frequency is f ₁ ) branched by the spectroscopic elements 11a and 11b will be described. The reference light of the light from the semiconductor laser 1a measured by the measuring device 16a and the electric field amplitudes E ^ref _R and E ^test _R of the measuring light are each expressed by the equation (1).

  The phase difference between the intensity modulation signal of the reference light and the measurement light in the reference optical path is represented by φ, and the phase difference of the light wave is represented by θ.

The reference signal I _Ref due to the interference between the electric field amplitudes E ^ref _R and E ^test _R of the reference light and the measurement light can be expressed as shown in Equation (2).

However, a component higher than the frequency (df + df _m ) is not shown as being removed by the low-pass filter.

Similarly, the test signal I _Test can be expressed as Equation (3).

  φ ′ and θ ′ are expressed by Equation (4) as the phase difference between the intensity modulation signal of the reference light and the measurement light and the light wave in the test light path. The optical path length difference between the reference light and the measurement light in the test light path is referred to as nD. n represents a refractive index, and the dispersion of the refractive index can be ignored. The refractive index n is obtained by measuring environmental conditions such as atmospheric pressure, temperature, and humidity in the vicinity of the light wave interference measuring apparatus, and calculating from the refractive index dispersion formula according to the measurement wavelength.

When the phase of the reference signal and the signal to be detected when the signal of the frequency df is detected by the phase meter is Φ _ref ^df and Φ _test ^df , respectively, it is expressed by the following equation (5).

Similarly, the phases of the reference signal and the test signal of the frequency (df + df _m ) are Φ _ref ^{(df + dfm)} and Φ _test ^{(df + dfm),} and are expressed by the following formula (6).

Further, the phases of the reference signal and the test signal of the frequency (df−df _m ) are Φ _ref ^(df−dfm) and Φ _test ^(df−dfm), and are expressed by the following equation (7).

Next, the processing unit 17 calculates a phase difference between the reference signal and the test signal in S102. The phase difference is calculated for each of the frequency df, the frequency (df + df _m ), and the frequency (df−df _m ). The phase difference ΔΦ ^(df) between the reference signal and the test signal at the frequency df is obtained as shown in the following formula (8) by calculating the difference between the two formulas of the above formula (5).

Similarly, the phase differences ΔΦ ^{(df + dfm)} and ΔΦ ^(df−dfm) in the reference signal and the test signal of the frequencies (df + df _m ) and (df−df _m ) are expressed by the following expressions (9) and (10). It is.

  Next, the processing unit 17 calculates a phase difference between adjacent spectra in S103. The phase difference between adjacent spectra is expressed by the following equations (11) and (12).

Next, in S104, the processing unit 17 calculates the optical path length difference nD between the reference light and the measurement light in the test optical path from the above formulas (11) and (12), and uses the following formula (13). Then, an average value nD ₁ ^ave thereof is calculated. The optical path length difference nD corresponds to the position of the test surface.

Optical path length difference is calculated in S104 nD has a calculated value for the synthetic wavelength can be by adjacent spectrum _{c / (f m + df m} ). Therefore, by increasing the modulation frequency f _m by electro-optical modulation device, it is possible to shorten the synthetic wavelength. Thereby, the measurement accuracy of the phase can be improved, and the optical path length difference can be obtained with high accuracy.

In the above description of the steps S101 to S104, the light from the semiconductor laser 1a has been described as an example. However, the semiconductor lasers 1b and 1c are similarly executed to obtain nD ₂ ^ave and nD ₃ ^ave .

Next, in step S105, an average value nD _i ^ave (i = 1 to 3) of optical path length differences obtained for each semiconductor laser is averaged to obtain a final output value nD _total . Equation 14 shows an example of a simple average.

When the wavelength difference between the semiconductor lasers is large, the average value nD _i ^ave of the optical path length difference for each semiconductor laser has different speckle effects. Therefore, the speckle error can be reduced by averaging the average value nD _i ^ave of the optical path length difference for each semiconductor laser.

Further, as described above, the speckle error has a correlation with the intensity of the test signal, and it is effective to improve the measurement accuracy to select a wavelength having a high intensity of the test signal. Therefore, when averaging nD _i ^ave (i = 1 to 3), more accurate measurement can be realized by performing weighted averaging using the intensity of the test signal for each semiconductor laser as a weight (coefficient).

  As described above, according to the present embodiment, the influence of speckle errors is reduced by having a plurality of lasers that emit light of a single wavelength and increasing the wavelength difference by changing the oscillation wavelength of each laser. be able to. Therefore, it is possible to provide a measuring device that can measure the position of the surface to be measured with higher accuracy.

  An optical frequency comb light source typified by a mode-locked laser has a narrow mode frequency interval of several tens of MHz and a large number of wavelengths. Therefore, measurement accuracy due to noise is particularly high when measuring rough surfaces where reflected light from the surface to be measured is weak. Will get worse.

  Note that a phase modulator may be used instead of the intensity modulator as the electro-optic modulation elements 3a and 3b. The phase modulator can easily generate a harmonic component with respect to the modulation frequency. Specifically, it is known that the amplitude given by the Bessel function when modulated at the modulation depth π is fundamental wave 0.28, second harmonic 0.49, third harmonic 0.33. . If a decrease in the amount of light per spectrum is not a problem by using an optical amplifier or the like, the use of the phase modulator can provide an averaging effect by increasing the sideband, and thus can be highly accurate.

(Second Embodiment)
Based on FIG. 6, the optical interference measuring apparatus of 2nd Embodiment is demonstrated. FIG. 6 is a diagram showing a lightwave interference measuring apparatus according to the second embodiment.

As shown in FIG. 6, the optical interference measurement apparatus of the present embodiment is different from the first embodiment in the configuration of the multi-wavelength light source 200. In the present embodiment, the multi-wavelength light source 200 has frequency shifters 4a, 4b, and 4c corresponding to the plurality of semiconductor lasers 1a, 1b, and 1c, and the respective lights from the semiconductor lasers have different frequency shifts. The quantity df _i (i = 1-3) is given. Therefore, the interference light signal of the reference light and the test light measured by the measuring devices 16a and 16b is a beat signal in which different frequencies df _i and df _i ± df _m are multiplexed for each of the plurality of semiconductor lasers. FIG. 7 shows the spectral distribution of the beat signal from each laser. The horizontal axis is the frequency of the signal.

  In this way, since the frequency of the beat signal is different for each laser, there is no need for a spectroscopic element that separates interference light for each output wavelength of a plurality of semiconductor lasers, and there is one reference signal and one test signal for the detector of the measuring apparatus. Just do it.

  Hereinafter, the light wave interference measuring apparatus of this embodiment will be described in detail. Outputs from the plurality of semiconductor lasers are demultiplexed by polarization plane holding type 1 × 2 fiber couplers 21a, 21b, and 21c, respectively, and one of them is multiplexed by polarization plane holding type 3 × 2 fiber coupler 22a. The light enters the optical modulation element 3a. The other is combined by a polarization plane holding type 3 × 2 fiber coupler 22b via frequency shifters 4a, 4b, and 4c having different frequency shift amounts, and enters the second electro-optic modulation element 3b. The reference light emitted from the first electro-optic modulation element 3a and the measurement light emitted from the second electro-optic modulation element 3b enter the interferometer 201, and enter the measuring devices 16a and 16b without passing through the spectroscopic element. The basic flow until the reference light emitted from the first electro-optic modulation element 3a and the measurement light emitted from the second electro-optic modulation element 3b enter the interferometer 201 and enter the measuring devices 16a and 16b is first. Since it is the same as 1 embodiment, the overlapping description is omitted. The interferometer 201 is different from the interferometer 101 in that there is no spectroscopic element.

The reference signal I _Ref and the test signal I _Test from each laser have three different frequencies df ₁ , df ₂ , and df _{3 in} which df in the equations (2) and (3) are different. A signal corresponding to each laser can be extracted by synchronously detecting only the frequency component for a certain semiconductor laser using the measurement data of the beat signal measured by the measuring device. The phase measured by the processing unit 27 is basically the same except that df in the equations (5), (6), and (7) is different for each laser. Since the calculation process by the processing unit 27 for obtaining the optical path length difference is the same as that of the first embodiment, the description is omitted.

  In the present embodiment, only the frequency component for the specific semiconductor laser has been described by synchronous detection. However, the phase of the specific frequency component may be extracted after Fourier-transforming the multiplexed interference signal.

  Thus, according to the present embodiment, a spectroscope and a plurality of detectors corresponding to the number of spectra are not required, and thus a compact and low-cost measuring device can be provided.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

<Embodiment of Method for Manufacturing Article>
The method for manufacturing an article in the present embodiment is used, for example, when processing an article such as a metal part such as a gear or an optical element. The article processing method of the present embodiment includes a step of measuring the shape of the test surface of the article using the measuring device, and a step of processing the test surface based on the measurement result in the process. . For example, the shape of the test surface is measured using a measuring device, and based on the measurement result, the test surface is processed so that the shape of the test surface becomes a desired shape such as a design value. Since the shape of the test surface can be measured with high accuracy by the measuring device, the article manufacturing method of the present embodiment is advantageous in at least the processing accuracy of the article as compared with the conventional method.

Claims (15)

A measuring device for measuring the position of a surface to be tested,
The light from the light source is divided into the first light and the second light, the light source part that emits the first light and the second light with different frequencies, the first light emitted from the light source part, and the test object An interferometer that interferes with the second light before being reflected by a surface, and that causes the first light emitted from the light source unit to interfere with the second light after being reflected by the test surface;
A measurement unit for measuring interference light by the interferometer;
A processing unit for determining the position of the test surface using measurement data obtained by the measurement unit,
The light source unit is
Have multiple lasers,
The plurality of lasers emit light having different wavelengths from each other, and split the light from the laser into the first light and the second light,
A first modulation element that modulates the intensity or phase of the plurality of first lights from the plurality of lasers;
A second modulation element that modulates the intensity or phase of the plurality of second lights from the plurality of lasers,
The measuring apparatus, wherein the first modulation element and the second modulation element have different modulation periods.   The measurement apparatus according to claim 1, wherein the processing unit calculates a position of the test surface for each of the light from the plurality of lasers, and averages the calculated positions.   The processing unit calculates the intensity of the test signal obtained by measuring the interference light between the first light emitted from the light source unit and the second light after being reflected by the test surface as a weight. The measuring apparatus according to claim 2, wherein a weighted average of each position is calculated.   4. The measuring apparatus according to claim 1, further comprising a frequency shifter that collectively shifts the frequencies of the plurality of light beams from the plurality of lasers. 5. A first frequency shifter for shifting the frequency of light from the first laser;
A second frequency shifter for shifting the frequency of light from the second laser,
4. The measuring apparatus according to claim 1, wherein the first frequency shifter and the second frequency shifter have different frequency shift amounts. 5.   6. The measuring apparatus according to claim 1, wherein an oscillation wavelength of the laser can be changed.   The measuring apparatus according to claim 1, wherein the oscillation wavelengths of the plurality of lasers can be controlled independently. Each of the first modulation element and the second modulation element generates light having two sidebands shifted in frequency with respect to the frequency of incident light,
The measuring apparatus according to claim 1, wherein the frequency shift amount differs by a predetermined amount between the first modulation element and the second modulation element.   The signal obtained by measuring the interference light between the first light and the second light has a frequency difference between the first light incident on the first modulation element and the second light incident on the second modulation element. The measurement apparatus according to claim 8, wherein the measurement apparatus is a signal having a spectrum including a corresponding frequency and a frequency different from the frequency corresponding to the frequency difference by the predetermined amount.   The processing unit emits a reference signal obtained by measuring interference light between the first light emitted from the light source unit and the second light before being reflected by the test surface, and emitted from the light source unit. A phase difference between the first light and a test signal obtained by measuring interference light between the second light after being reflected by the test surface is obtained, and the test is performed based on the obtained phase difference. The measuring device according to claim 1, wherein the position of the surface is obtained.   The measuring apparatus according to claim 1, wherein the laser emits light having a single wavelength.   The measuring apparatus according to claim 1, wherein the modulation element is an electro-optic modulation element. A step of measuring the shape of the test surface of the article using the measuring device according to claim 1;
And a step of processing the surface to be measured based on the measured shape. A light source device that divides light from a light source into first light and second light, and emits the first light and the second light at different frequencies,
Have multiple lasers,
The plurality of lasers emit light having different wavelengths from each other, and the light from the laser is divided into the first light and the second light,
A first modulation element that modulates the intensity or phase of the plurality of first lights from the plurality of lasers;
A second modulation element that modulates the intensity or phase of the plurality of second lights from the plurality of lasers,
The light source device, wherein the first modulation element and the second modulation element have different modulation periods. A measurement method for measuring the position of a test surface,
An emission step of dividing light from the laser into first light and second light, and emitting the first light and the second light at different frequencies;
Interfering the first light and the second light before being reflected by the test surface, causing the first light and the second light after being reflected by the test surface to be interfered, and measuring interference light Determining the position of the test surface using data,
In the injection step,
Dividing each light from a plurality of lasers emitting light having different wavelengths from each other into the first light and the second light,
Modulating the intensity or phase of a plurality of the first lights from a plurality of the lasers;
Modulating the intensity or phase of a plurality of the second lights from a plurality of the lasers;
The measurement method, wherein the intensity or phase modulation period of the first light and the intensity or phase modulation period of the second light are different from each other.

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