JPH0875434A - Surface form measuring device - Google Patents

Abstract

PURPOSE: To provide a compact surface from measuring device which can measure, in real time, a variation in surface form of an object to be measured sensitively and accurately at a high speed, and also excellent in noise resistance. CONSTITUTION: A laser beam of which oscillating frequency and luminous intensity are modulated at a specified frequency is introduced into a detector main body through an optical fiber 16, and divided into two directions by a beam splitter 36. One is reflected by a reflection mirror 33, and the other is reflected by a reference mirror 37. Both reflected beams are superimposed on each other again by a beam splitter 36. Between both reflected beams, there is a time delay corresponding to the distance of movement of a probe which moves following the surface form of an object to be measured W and, therefore, both frequencies are different from each other. By this, a heterodyne interference is produced. Then the interference signal is photoelectrically transduced by a photo diode 38 and processed at a control part so as to measure the surface form of an object to be measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention utilizes the movement of the tip of a probe to measure the surface shape and surface roughness of an object to be measured.
The present invention relates to a surface shape measuring device.

[0002]

2. Description of the Related Art A conventional stylus-type roughness detector pickup includes a fulcrum, a lever swinging about the fulcrum, a probe attached to one end of the lever, and a probe. Is composed of a detector core (differential transformer) arranged at the opposite end. In order to measure the surface roughness of an object to be measured with a surface roughness meter having such a structure, a probe of the pickup is brought into contact with the object to be measured and a probe that moves following the surface shape of the object to be measured is used. The motion of the tentacle was changed to the motion of the core sandwiching the fulcrum via the lever, and this was electrically detected by the detector (differential transformer).

[0003]

The stylus roughness detector has the following problems because it is electrically detected by using a differential transformer. (1) Since it is a balance type and the core of the differential transformer is arranged on the opposite side of the probe, the moment of inertia is large and a high-speed response is not possible.

(2) The response speed is limited due to the carrier frequency of the differential transformer. (3) To increase the magnification, it is necessary to electrically amplify
The higher the amplification factor, the worse the S / N. (4) Since the movement of the probe is detected via the lever, a minute movement of the probe is absorbed by the lever, or the accuracy of the fulcrum causes an error.

(5) Electrical detection by the differential transformer is weak against noise. (6) The current that excites the differential transformer generates heat, which causes long-term drift. (7) Since the differential transformer is an analog type sensor, it has to be calibrated before it is used.

The present invention has been made in view of such circumstances, and it is excellent in high sensitivity, high accuracy, high speed, and noise resistance by optically detecting the motion of the probe by the Abbe's principle. Another object of the present invention is to provide a surface profile measuring device.

[0007]

In order to achieve the above object, the present invention provides a laser light source section for generating a frequency-modulated laser beam and a probe movably supported in the uneven direction of a measured section to be measured. A laser beam introduced from the laser light source unit, and a laser beam introduced from the laser light source unit. Through the object light optical system that is almost aligned with the motion line of the child, the reflected mirror is irradiated to obtain the reflected light, and the other laser beam is irradiated to the reference reflective mirror to obtain the reflected light. A heterodyne interference optical system that interferes with light, a photoelectric conversion unit that receives the interference light generated by the heterodyne interference optical system, and converts the received optical interference signal into an electrical signal, and a search based on the detection signal of the photoelectric conversion unit. Displacement of tentacle Calculates a is characterized by comprising a control unit for controlling the frequency modulation of the laser light source.

[0008]

According to the present invention, the probe that is brought into contact with the surface shape of the object to be measured is moved in the direction of the unevenness of the object to be measured and the movement of the probe is performed. The reflector arranged on the line reflects the motion of the probe without error. Further, by arranging the motion line of the probe and the optical axis of the object light of the interference optical system so as to substantially coincide with each other, the object light of the interference system (light reflected by a reflecting mirror provided in the probe) The change in optical path distance of is detected with high accuracy.

Since the detection method also uses an optical interference system, it is not easily affected by electrical noise, and the received detection light uses the Doppler frequency shift of the heterodyne interference. Since the obtained interference signal is processed by an electric signal, sensitivity calibration is not required, and the shape change of the measured object can be measured in real time with high sensitivity and high speed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the surface profile measuring apparatus according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows an embodiment of a surface profile measuring apparatus according to the present invention. This surface profile measuring apparatus includes a laser light source unit 10 for generating a laser beam, a roughness detector main body 11, and a laser light source. The laser light source unit 10 and the roughness detector main body 11 are detachably attached to both ends of the optical connector 16A, which has a control unit 14 for calculating a surface shape displacement of the object to be measured W based on a signal from the control and detector. , 16B. The optical fiber 16 is composed of a single mode fiber.

The detector body 11 and the control unit 14 are connected by an electric cable 20, and guide the detection signal from the detector to the control unit 14. On the other hand, the control unit 14 and the laser light source unit 10 are configured by being connected by an electric cable 21. As shown in FIG. 1, the laser light source unit 10 in this embodiment includes a laser diode 24, a Peltier element 25, a collimator lens 26, an optical isolator 27, and an objective lens 28.

The laser diode 24 of the light emission source is provided with a Peltier element (heating and / or cooling element) 25 and a temperature sensor (not shown), and the control unit 14 to be described later.
It is controlled to maintain a constant temperature by the temperature controller. On the other hand, the laser diode 24 receives a frequency modulation current from the control unit 14 described later via the electric cable 21, and emits the frequency-modulated laser light.

The modulated laser light is collimated by a collimator lens 26, passes through an optical isolator 27 that prevents reflected light, and is condensed by an objective lens 28.
It is incident on the optical fiber 16. The modulated laser light is
It is guided to the detector main body 11 via this optical fiber 16. Next, the structure of the detector body will be described. As shown in FIG. 2, the detector body 11 has an opening 13 formed in the lower surface of the body case 12, and the leaf spring 3 is formed in the opening 13.
1 and a probe 32 that is movable up and down. A reflecting mirror 33 is fixed on the line of motion of the probe. The reflecting mirror formed on the probe may be a separate mirror fixed as described above, or may be directly mirror-finished on the probe to form a mirror.

The laser light guided to the detector body 11 is
The collimated lens 35 collimates the light, and the optical axis L
₁Split into two different directions with the upper beam splitter 36
To be done. Then, one of the laser beams is
The optical path is bent by the mirror 34 and the optical axis L₂Said reflection on
The mirror 33 is illuminated and the other is the optical axis L.₁Optical axis L orthogonal to ₃
Optically illuminates the reference mirror 37 arranged above.
Place the system. The photodiode 38 has an optical axis L.₃Up
The beam splitter 36 and the reference mirror 37.
And place it.

The optical path changing mirror 34 is provided in the detector body.
Optical axis L is not essential for configuration₁And L ₂Placed coaxially
Good. That is, the optical axis L is not provided without the optical path changing mirror.₁of
Reflector 3 in which the laser beam is directly formed on the probe 32
The detector body may be configured so that it illuminates 3. E
The diode 38 is connected to the main body cable via an electric cable 39.
Connected to the removable connector 40 attached to
ing. The electric cable 20 is detected via the connector 40
Connector 4 that can be connected to and detached from the main body 11
It is connected to the control unit 14 via 1. Photodaio
The detection signal photoelectrically converted by the battery 38 is output from the main case 12.
In order to facilitate connection with the control unit 14 described later.
Is.

As described above, the optical axis L ₂ of the object light optical system in the detector body is arranged so as to be substantially on the line of motion of the probe 32. On the other hand, the control unit 14, as shown in FIG.
Mainly a sawtooth wave or triangular wave generator 50, a temperature controller 51, a bandpass filter 52, a waveform shaper 53,
54, frequency multiplication circuits 56 and 57, a gate circuit 58, and an up / down counter 60.

The principle of measurement in the surface profile measuring apparatus configured as described above will be described using a sawtooth wave modulation current. FIG. 3 shows a block diagram of the control unit. The sawtooth wave or triangular wave generator 50 outputs a sawtooth wave modulation current Sa (FIG. 4A) having a period T _S (frequency f _s , angular frequency ω _s ) to the laser diode (light source unit) and the waveform shaper 54. To do. The sawtooth wave or triangular wave generator 50 outputs a sawtooth wave modulation current Sa having a modulation width smaller than that of the bias current as shown in FIG.

The laser diode has a sawtooth wave modulation current Sa.
The oscillation frequency and the emission intensity are modulated by. The laser diode is provided with a heating and / or cooling element (Peltier element) 25 and a temperature sensor, and the temperature controller 51 heats and / or cools the temperature detected by the temperature sensor to a constant value. The element (Peltier element) 25 is controlled. This suppresses the wavelength change due to the temperature change of the laser diode and improves the measurement accuracy.

The modulated laser light output from the laser diode 24 passes through the collimator lens 26, the optical isolator 27, and the objective lens 28, and the optical fiber 1
It is condensed at the tip of 6 and guided through the optical fiber 16 into the detector body. Since the laser light source unit 10 and the detector body 11 are optically connected to each other by the optical fiber 16 having the removable optical connectors 16A and 16B, the connection and removal are easy.

The laser light that has entered the detector body is collimated by the collimator lens 35, and is split into two different directions by the beam splitter 36 arranged on the optical axis L ₁ . That is, one laser beam has an optical axis L
Reflector 3 attached to the movable probe placed on ₂
And the other laser beam is reflected by the reference mirror 37 arranged on the optical axis L ₃ orthogonal to the optical axis L ₁ .

The laser beams reflected by the reference mirror 37 and the reflecting mirror 33 are reflected by the beam splitter 36.
Superposed by. The reflecting mirror 33 mounted on the motion line of the probe follows the change in the shape of the surface of the object to be measured W and moves up and down integrally with the probe, and the laser beam reflected by the reflecting mirror 33. (Object light) and the reference mirror 3
There is a time delay corresponding to the moving distance of the reflecting mirror 33 with respect to the laser beam (reference light) reflected by 7, and both frequencies are different. Therefore, heterodyne interference occurs between the reference light and the object light.

The interference signal is received by the photodiode 38, photoelectrically converted into the electric signal, and the electric cables 39, 2 are transmitted.
It is sent to the control unit 14 via 0. The control unit processes the interference signal and calculates the moving distance of the probe, that is, the surface shape of the measured object. The frequency and phase of the signal Se (FIG. 4 (C)) detected by the photodiode 38 are
It is proportional to the optical path distance difference D between the reference mirror 37 and the reflecting mirror 33 attached to the probe. The level of the signal Se is influenced by the change in emission intensity due to the frequency modulation of the laser diode 24 and the reflectance of the reflecting mirror 33.

In the present invention, the influence of the change in the emission intensity of the laser diode 24 is removed from the signal detected by the photodiode 38 based on the following principle.
First, the modulation of the oscillation frequency of the laser diode and the modulation of the emission intensity will be described. Figure 4 shows the laser diode.
When a sawtooth wave modulation current Sa (t) having a period T _s and a modulation width Δi as shown in (A) is input, the oscillation angular frequency ω (t) and the emission intensity I (t) of the laser diode are also modulated in a sawtooth shape. Be done
(See FIGS. 4B and 4C).

Here, one modulation period (-T _s / 2≤t≤T)
_s / 2), the sawtooth wave modulation current Sa (t) is given by the following expression: Sa (t) = i ₀ + Δi · t / T _s = i ₀ + α _i · t (1) ω (t) and emission intensity I (t)
Is the following equation: ω (t) = ω ₀ + Δω · t / T _s = ω ₀ + k _wi · α _i · t (2) I (t) = I ₀ + ΔI · t / T _s = I ₀ + k _Ii・ It can be written as α _i · t (3).

However, the definitions of i ₀ , ω ₀ , Δi, Δω, and ΔI are shown in FIG. Further, α _i = Δi / T _s (current modulation rate) k _wi = Δω / Δi (modulation constant of oscillation angular frequency) k _Ii = ΔI / Δi (modulation constant of emission intensity)

Next, the interference signal detected by the photodiode 38 will be described. Beam splitter 36
The emission intensity of the laser diode 24 reaching
And However, η is a constant determined by the coupling rate of the laser light to the optical fiber 16. If the intensity of the reflected light (reference light) of the reference mirror 37 is I _r (t) and the reflected light (object light) of the reflector 33 attached to the probe is I ₀ (t), then I _r (t ), I ₀ (t) are as follows: I _r (t) = β _r ηI (t) (4) I ₀ (t) = β ₀ ηI (t) (5) . However, β _r and β ₀ are reflection coefficients.

The reference light and the object light undergo heterodyne interference, and the interference signal Se detected by the photodiode 38 is detected.
(t) is given by the following equation. Se (t) = K · ηI (t) × _{[β r + β 0 +2 (β} r β 0) 1/2 cos (ω b t + φ b) ] ... (6) where, K is the photoelectric conversion of the photodiode 38 , Ω _b ,
φ _b is the angular frequency and phase of the beat signal, and is expressed by the following equation, ω _b = 2Δω / T _S τ (7) φ _b = ω ₀ τ (8) In Expressions (7) and (8), τ is the time delay between the reference light and the object light, as shown in FIG.

Since I (t) in equation (6) can be expressed by equation (3), if (k _Ii ·
α _i · t) is smaller than I _0, and the following equation is given: I ₀ >> | k _Ii · α _i · t _max | = k _Ii · α _i · T _s / 2 = k _Ii (Δi / T _s ) If (T _s / 2) = k _Ii · Δi / 2 = ΔI / 2 (9) is satisfied, (k _Ii · α _i · t) can be ignored. Then, in this case, the above equation (6) is expressed by the following equation: Se (t) ≈K · ηI ₀ [β _r + β ₀ +2 (β _r β ₀ ) ^1/2 cos (ω _b t + φ _b )] ... (10) is obtained, and by cutting the DC component (β _r + β ₀ ), the following equation (11) can be obtained.

[0029] Se (t) = A · cos (ω b t + φ b) ... (11) However, in order to satisfy the above expression (9) may be as follows. (1) Increase I ₀ . (2) Reduce Δi. (3) _Reduce k _Ii .

The above (1) and (2) increase the bias current i ₀ in the modulation current Sa (t) shown in the equation (1),
This means reducing the modulation width Δi. Also, k _{Ii in} (3) cannot be changed freely due to the inherent characteristics of the laser diode, but k _Ii is small and
Select a laser diode with a large _wi and use it.

In the present embodiment, as described above, the sawtooth wave or triangular wave generator 50 has the sawtooth wave modulation current S having a small modulation width with respect to the bias current as shown in FIG. 4 (A).
As a result, the interference signal Se detected by the photodiode 38 is so small that the change in the emission intensity due to the frequency modulation of the laser diode 24 is negligible as shown in FIG. 4C.

Now, referring to FIG. 3, the photodiode 38
The interference signal Se detected by is output to the bandpass filter 52. The bandpass filter 52 has a center frequency f _s and a bandwidth Δν (for example, f _s / 10), extracts the component of f _s from the input signal Se, and waveform-shapes the extracted signal Sf (FIG. 4D). Output to the device 53.
The waveform shaper 53 converts the input signal Sf into a rectangular wave signal Sg (FIG. 4 (E)), and the frequency multiplier 56 outputs the signal Sg.
Magnification of the frequency of g set in advance (m = 2 in FIG. 4)
So that the signal becomes a pulse signal.
Sg ′ is output to the input G ₁ of the gate circuit 58 (FIG. 4).
(See (G) and (H)).

On the other hand, the waveform shaper 54 converts the sawtooth wave modulation current Sa input from the sawtooth wave or triangle wave generator 50 into a rectangular wave signal Sb (FIG. 4 (B)), and the frequency multiplication circuit 57 uses this. The frequency of the signal Sb is multiplied by the frequency multiplication circuit 56.
Multiplied by the same multiplication factor, and the multiplied signal (pulse signal)
Sb ′ is output to the input G ₂ of the gate circuit 58 (see FIG. 4).
(See (F)).

The gate circuit 58, the input G ₁ 'and enter G ₂ of the pulse signal Sb' pulse signal Sg create a new pulse signal by the frequency difference, and outputs the up input U or down input D of the up-down counter 60 . Therefore, the up / down counter 60 integrates the frequency difference between the pulse signal Sb 'and the pulse signal Sg'. By the way, when the DUT is stopped, the frequency of the pulse signal Sg ′ output from the frequency multiplication circuit 56 is the reference pulse signal Sb ′ output from the frequency multiplication circuit 57.
, And the count value of the up / down counter 60 does not change, but when the DUT moves, the signal Sg output from the waveform shaper 53 due to the Doppler frequency shift (the pulse output from the frequency multiplication circuit 56) Signal S
The frequency of g ') changes.

That is, when the object to be measured moves away, the reflecting mirror 33 moves together with the probe in the direction away from the object,
The frequency of the pulse signal Sg 'increases (see FIG. 4 (G)), and the frequency of the pulse signal Sg' decreases as the object to be measured moves toward (see FIG. 4 (H)). Therefore, the difference between the pulse numbers of the pulse signal Sb ′ and the pulse signal Sg ′ corresponds to the moving speed and moving direction of the measured object, and the integrated value of the difference between the pulse numbers corresponds to the moving amount of the measured object. Accordingly, the moving distance of the measured object can be measured based on the amount of increase or decrease in the count value of the up / down counter 60 when the measured object is moved from a certain position to another position.

The modulation current waveform is not limited to the sawtooth wave, but a triangular wave may be used. When a triangular wave is used, the doubled sensitivity can be obtained by inverting the phase of the folded portion and adding it to the first half portion. Next, the maximum velocity of the measurement surface that can measure displacement will be described. Interference signal S detected by photodiode 38
As described above, e can be expressed by the equation (10), and the signal Sf (t) output from the bandpass filter 52 can be expressed by the following equation: Sf (t) = B · cos (ω _S t + φ _b ) ... (12)

Now, considering the case where the measurement surface moves at a speed v from the initial distance D ₀ and the distance D can be expressed as D = D ₀ + vt (13), the equation (12) is given by Sf (t) = B · cos {2π [(f _s + Δf _D ) t + 2D ₀ / λ ₀ ]} (14) Here, Δf _D is the Doppler frequency shift due to the movement of the measurement surface and can be expressed by the following equation.

Δf _D = 2v / λ ₀ (15) On the other hand, in order to obtain Sf (t) from the bandpass filter 52, Δf _D is the band width Δν of the bandpass filter 52.
It needs to be smaller. Therefore, the maximum moving speed v _max of the measurement surface on which the displacement can be measured is as follows. _{v max = λ 0/2 ·} Δν ... as shown in (16) (16), to increase the maximum moving speed v _max, it is necessary to increase the bandwidth .DELTA..nu of the bandpass filter 52. In the embodiment, the bandpass filter 52
Although the center frequency of the f _s, the signal Se output from the photodiode 38, because it is continuously modulated with a period T _S, is a periodic function of period _{T S, f s, 2f s} ,
, Nf _s , ..., Each frequency component is included. Now, the center band-pass filter of the frequency nf _s, when to extract the component of the frequency nf _s, equation (12), Sf (t) = B · cos (nω S t + φ b) = B · cos [2π (nf _s + Δf _D ) t]. Then, Δν is 1/10 of the center frequency nf _s
When set to, formula (16), and _{v max = λ 0/2 ·} Δν = λ 0/2 · nf s / 10 ... (17). Therefore, the maximum speed can be increased by increasing n and f _s .

By the way, the oscillation frequency of the laser diode 24 is
When the wave number is linearly modulated by the drive current, the drive current
Frequency f_sIs the upper limit of the modulation characteristic of the laser diode 24.
Limited by sex. On the other hand, a bandpass filter
The intensity of the frequency component extracted by
sin 〔(ω_b−nω_S) T_S/ 2] / [(ω_b-N
ω _S) T_S/ 2]. The value of the sink function is
ω_b= Nω_S, The maximum value becomes 1, and ω_bAnd nω_S
Sharply decreases according to the difference between
And the strength of the output signal of the bandpass filter 52 is small.
And the waveform shaper 53 does not output an accurate pulse signal.
It becomes impossible to measure.

Although the value of n is limited under the above conditions, a large n can be obtained by increasing the angular frequency ω _b of the beat signal. In order to increase the angular frequency ω _b , the frequency modulation width of the laser diode 24 may be increased or the optical path distance difference may be increased. The embodiment of FIG. 7 uses an optical fiber 74 instead of the electric cable 20 of the embodiment of FIG. 1, and the same or similar members in the embodiment of FIG. The description is omitted.

The light receiving portion of the detector main body shown in FIG. 7 is composed of a reflection mirror 71 for optical path conversion and an objective lens 72, and a photoelectric conversion element is provided in the control portion.
It is configured to be connected by an optical fiber 74 which is detachable by an optical connector. In the surface profile measuring apparatus configured as described above, the respective laser beams reflected by the reference mirror 37 and the reflecting mirror 33 provided on the motion line of the probe are superposed by the beam splitter 36, and Heterodyne interference occurs with the object light. The above process is similar to that described in the embodiment of FIG.

The detection light due to this interference has its optical path bent by the reflection mirror 71 for optical path conversion, is condensed by the condenser lens 72, and is incident on the end face of the optical fiber 74 formed of a single mode fiber. The optical path changing reflection mirror 71 is not essential in the configuration. The detection light sent to the control unit via the optical fiber 74 is photoelectrically converted and processed in the control unit. The principle of measurement in the controller is similar to that of the embodiment shown in FIGS. In the embodiment of FIG. 1, the detection light was converted into an electric signal in the detector body and sent to the control unit via an electric cable, but in the embodiment of FIG. 7, the detection light is sent through an optical fiber. Since it is sent to the control unit and photoelectrically converted in the control unit, it is more resistant to electrical noise than the embodiment of FIG. 1, and there is no problem of frequency response delay due to the electric cable, and high speed response is achieved. Is advantageous.

In the embodiment shown in FIG. 1 and the embodiment shown in FIG. 7, the laser light source section 10 and the control section 14 are described as being independent of each other, but as shown by the imaginary lines in FIGS. The light source unit and the control unit may be integrated. As a scanning method at the time of measurement, the detector main body 11 may be fixed and the object to be measured W may be moved, or conversely,
The object to be measured W may be fixed and the detector main body 11 may be moved for scanning.

In the embodiment according to the present invention, since the polarization of the laser beam is not used, unlike the interferometer using the polarization, the polarization element, the polarization beam splitter, etc. are not required, and the optical system is simplified. There is. Further, the detector main body 11, the light source unit 10 and the control unit 14 are connected to the optical connector 16
It is easy to attach / detach each other via A, 16B and the connectors 40, 41, and the entire apparatus can be made compact with a simple optical system.

[0045]

As described above, according to the displacement measuring apparatus of the present invention, it is possible to construct the interference optical system by the reflecting mirror provided on the moving line of the probe. Since the moving distance of the tentacle is optically measured, the measurement can be performed with high accuracy and excellent noise resistance, and the device can be made compact with a simple optical system.

Further, for the detection of the displacement, the Doppler frequency shift due to the movement of the reflecting mirror integrated with the probe is used to calculate this by an electric signal, so that the sensitivity calibration is not necessary, The displacement of the surface shape of the measured object can be measured in real time with high sensitivity, high accuracy, and high speed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the overall configuration of an embodiment of the present invention.

2 is an enlarged explanatory view of a detector main body portion of the apparatus shown in FIG.

FIG. 3 is a block diagram showing an embodiment of a control unit in the shape measuring apparatus according to the present invention in FIG.

4 (A) to 4 (H) are signal waveform diagrams output from the respective units of FIG. 3 when a sawtooth wave modulation current is used.

5A to 5C are waveform diagrams showing a modulation current of a sawtooth wave input to a laser diode, an oscillation angular frequency of the laser diode and an emission intensity generated by the modulation current, respectively.

FIG. 6 is a waveform diagram showing oscillation angular frequency and emission intensity change of object light and reference light when a sawtooth wave modulation current is used.

FIG. 7 is a schematic view of a main part showing another embodiment of the present invention.

[Explanation of symbols]

 10 ... Laser light source section 11 ... Detector main body section 12 ... Main body case 14 ... Control section 16, 74 ... Optical fiber 20, 21, 39 ... Electric cable 32 ... Probe 33 ... Reflecting mirror 34 ... Optical path changing mirror 36 ... Beam Splitter 37 ... Reference mirror 38 ... Photodiodes 40, 41 ... Connector

Claims (2)

[Claims] 1. A laser light source section for generating a frequency-modulated laser beam, a probe movably supported in the direction of unevenness of a measured section to be measured, and a movement line of the probe. A reflecting mirror configured on the probe, and split the laser beam introduced from the laser light source unit,
One of the divided laser beams is radiated to the reflecting mirror to obtain reflected light through an object light optical system that is aligned with the motion line of the probe, and at the same time, the other laser beam is radiated to a reference reflecting mirror. To obtain reflected light, a heterodyne interference optical system that interferes with both reflected light, and receive the interference light generated by the heterodyne interference optical system, a photoelectric conversion unit that converts the received optical interference signal into an electrical signal, A surface shape measuring apparatus comprising: a control unit that calculates a displacement amount of a probe based on a detection signal of a photoelectric conversion unit and controls frequency modulation of the laser light source. 2. The surface profile measuring apparatus according to claim 1, wherein the detection light is sent to the control unit by using an optical fiber and is electrically converted in the control unit.