CN101750143B - Integrated optical interference three-dimensional vibration monitor - Google Patents

Abstract

An integrated optical interference three-dimensional vibration monitor includes a laser, and along the forward direction of the laser output light beam are a first lens, a beam splitter, an aperture and a measuring reflector on the same optical axis in sequence. The measuring reflector is fixed on the surface of the object to be monitored, and outside the coherent light output surface of the beam splitter prism are a second lens, a third lens and a photodetector in sequence to form a detection system. The present invention integrates the main part of the optical path into a single beam splitter prism, and has a simple structure, stable and reliable. In addition, the two waves that interfere are both derived from the divergent light emitted by the laser after passing through the lens, and are therefore both spherical waves, which can realize three-dimensional monitoring of optical interference that distinguishes the vibration of the object to be measured from the vibration of the measuring light path.

Description

Integrated optical interference three-dimensional vibration monitor

technical field

The invention relates to a motion monitor, in particular to an integrated optical interference three-dimensional vibration monitor.

Background technique

The low-frequency vibration of mechanical structures generally has the characteristics of slow attenuation, large amplitude and difficult vibration isolation. In a large-scale optical precision mechanical platform, low-frequency vibration passing through optical components will have a non-negligible impact on the beam propagating in it, so it is very important to effectively monitor the vibration of the optical platform.

The traditional optical interferometry method uses two-beam interference, one of which is used as a reference beam, and the other is used as a measurement beam. The change of interference fringes is detected by a photodetector to reflect the vibration of the object. For example, the measurement method mentioned in the article "Laser Interferometry Technology Principle and Application of Mechanical Vibration Measurement", on the one hand, the two waves for interference are plane waves, which can only reflect the two-dimensional information of the vibration of the object, and cannot effectively reflect the three-dimensional information of the object Vibration; on the other hand, during the measurement process, no measures such as locking the laser beam are taken, which may cause interference fringes to change due to the vibration of the optical path itself, thereby affecting the interference to the monitoring of the measured object, that is to say, the effective area cannot be Divide the vibration of the measured object and monitor the vibration of the optical path.

Therefore, in order to achieve practical measurement, there are two aspects that need to be paid attention to: on the one hand, there is no good solution to achieve vibration separation; on the other hand, to achieve three-dimensional monitoring of object vibration, multiple platforms are usually used now It is relatively complex and impractical to carry out measurements, such as the method mentioned in the paper "Novel Active Isolation System with 3D Laser Interferometer and Piezoelectric Displacement Actuator".

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art, and provide an integrated optical interference three-dimensional vibration monitor, which can realize three-dimensional monitoring of optical interference that distinguishes between the vibration of the measured object and the vibration of the measurement optical path.

Technical solution of the present invention is as follows:

An integrated optical interference three-dimensional vibration monitor, including a laser, along the forward direction of the output beam of the laser is a first lens with the same optical axis, a beam splitting prism, a diaphragm, and a measuring reflector, and the measuring reflector is fixed on On the surface of the object to be monitored, the angle between the beam-splitting surface of the beam-splitting prism and the optical axis is 45°, and the beam-splitting surface of the beam-splitting prism divides the laser beam input from the incident surface into reflected light and transmitted light, In the dichroic prism, the periphery of the side opposite to the incident surface is coated with a total reflection film, and a light hole is left in the middle, and the beam of the transmitted light passes through the light hole and the diaphragm and directly hits the measuring reflector In order to detect the light beam, the reflective surface of the dichroic prism is coated with a total reflection film. The reflected light is called the reference beam after being reflected by the reflective surface, and the side opposite to the reflective surface is the coherent light output surface. The coherent light output surface of the dichroic prism is followed by a second lens, a third lens and a photodetector to form a detection system.

After passing through the first lens, the light emitted by the laser is incident on the beam splitting prism in the form of divergent light, and the incident light is divided into two beams by the beam splitting surface: reflected light and transmitted light. The reflected light beam is used as the reference light, and after being reflected by the side coated with the total reflection film, it returns directly to the splitting surface. The transmitted light is further divided into two parts:

The light beam located at the periphery is affected by the reflective film coated around this side, and is directly reflected back to the splitter surface. After meeting with the reference beam, the light beam is shrunk through two lenses, and finally irradiated on the photodetector to form outer ring interference fringes; The beam located in the inner ring passes through the middle aperture and the diaphragm, is reflected by the measuring mirror, and then returns to the beam splitting surface, and interferes with the middle part of the reference beam to form an inner ring fringe on the photodetector.

Compared with the prior art, the present invention has the advantages and effects that the monitoring of the optical path itself and the monitoring of the measured object are independent of each other. The interference fringes in the outer ring are formed by the interference of reflected light from the two sides of the beam splitting prism itself, and do not contain any information of the measured object, so it only reflects the information of the optical path itself. If the outer ring fringes change, it means that the measurement optical path is vibrating. The interference fringes of the inner ring are formed by the interference of the light returned from the measuring mirror and the reference light, so it can reflect the vibration condition of the object. Since the change of the measurement optical path will also cause the change of the inner ring, the change of the inner ring stripes cannot correctly reflect the vibration of the measured object when the outer ring and the inner ring change at the same time. Only when the measurement optical path is kept still, that is, the outer ring fringe does not change, can the change of the inner ring fringe completely reflect the vibration of the measured object. Simultaneously, the present invention integrates the main optical path into a single beam splitting prism, which has a simple structure, is stable and reliable. In addition, the two interfering waves are both derived from the divergent light emitted by the laser after passing through the lens, so they are both spherical waves, which can realize three-dimensional monitoring of optical interference that distinguishes between the vibration of the measured object and the vibration of the measurement optical path.

Description of drawings

Fig. 1 is a device schematic diagram of the present invention;

Fig. 2 is the optical path schematic diagram of the embodiment of the present invention;

Fig. 3 is a principle diagram of the three-dimensional monitoring of the present invention.

Detailed ways

The present invention will be further described below in conjunction with drawings and embodiments.

It can be seen from Fig. 1 that the integrated optical interference three-dimensional vibration monitor of the present invention includes a laser 1, and is characterized in that along the advancing direction of the output beam of the laser 1, there are successively a first lens 2, a dichroic prism 3, and an aperture 8 on the same optical axis. And measuring reflector 9, described measuring reflector 9 is fixed on the surface of object 10 to be monitored, and the included angle between the beam-splitting surface of described beam-splitting prism 3 and described optical axis is 45 °, and the angle of this beam-splitting prism 3 The beam splitting surface divides the laser beam input from the incident surface into reflected light and transmitted light. The periphery of the side opposite to the incident surface in the beam splitting prism 3 is coated with a total reflection film 5, 7, and a light hole 6 is left in the middle. , the light beam that passes through the light hole 6 and the diaphragm 8 and directly hits the measuring mirror 9 in the transmitted light is the detection beam, and the reflective surface 4 of the dichroic prism 3 is coated with a total reflection film, and the reflected light is passed through The reflection of the reflective surface 4 is referred to as a reference beam, and the side opposite to the reflective surface 4 is a coherent light output surface. Outside the coherent light output surface of the dichroic prism 3 are the second lens 11 and the third lens in sequence. 12 and photodetector 13 and constitute a detection system.

The specific monitoring method of the present invention will be described below in conjunction with FIG. 2 . In this embodiment, the laser 1 is a He-Ne laser.

The light emitted by the laser 1 passes through the first lens 2 and then irradiates the incident surface of the dichroic prism 3 in the form of a divergent light beam. The dichroic prism 3 splits the incident light into reflected light and transmitted light through the dichroic surface.

Wherein the reflected light part, that is, the light beam between the light rays 16 and 17 , after being reflected by the total negative surface 4 of the dichroic prism 3 , directly reaches the interference area. This portion of light exists between rays 18 and 19 as reference light.

The transmitted light part can be divided into two parts:

Wherein the light beams located in the periphery, that is, the light beams between the light rays 14 and 20 and the light beams between 15 and 23, after being reflected by the total reflection films 5 and 7, are reflected by the light splitting surface of the optical prism 3 and directly reach the interference area. This part of the light, which exists between the light rays 24 and 25 and between 28 and 29, interferes with the reference light to form outer ring interference fringes, which are used to monitor the vibration of the light path itself.

The other part of the transmitted light, that is, the transmitted light located in the inner ring, that is, the light between the light rays 21 and 22, passes through the aperture 6 and the aperture 8, then reaches the measuring reflector 9, and then reflects back to the dichroic prism 3, After being reflected by the beam-splitting surface of the beam-splitting prism 3, it meets the reference beam and reaches the interference area to form a measuring beam. This part of light is located between the light rays 26 and 27 and also interferes with the reference light to form inner interference fringes for monitoring the vibration of the measured object. It is worth noting that the light beams located between the light rays 20 and 21 and the light beams between the light rays 22 and 23 are partly because the surface of the aperture 8 is a diffuse reflection surface, and the light beams are diffusely reflected, and partly after being reflected by the measuring mirror 9 Blocked by the diaphragm 8, they are not reflected back to the photodetector 13, as shown by the ray 30. In this way, a part of blanks will be formed between the inner ring interference fringes and the outer ring interference fringes, that is, the part between the light rays 26 and 25 and 27 and 28, so that the two parts of the interference fringes can be clearly distinguished.

It can be seen from Figure 2 that the two waves interfering are spherical waves, so three-dimensional monitoring can be realized. A brief description of this principle is given below.

For spherical waves, the phase function of the z=0 plane is:

(1)式可化简为：where (x _o , y _o , z _o ) is the center position of the spherical wave, let

(1) can be simplified as:

When the items containing 1/l _o ² in the square brackets are less than 1, use the binomial theorem to expand the formula (2), and under the condition of Fresnel approximation, ignore the items above 1/l _o ³ , we can get:

In the present invention, the two columns of spherical waves interfering on the photodetector 13 are formed by a series of reflections of the light between the light rays 14 and 15 . Therefore, it can be considered that there are equivalent virtual light sources, the interference fringes are formed by the spherical waves emitted by them, and the position of the virtual light source can be obtained by the reflection theorem.

Assuming that the positions of the reference light wave and the virtual light source of the measurement light wave are (x _R , y _R , z _R ), (x _o , y _o , z _o ), similarly, their phase functions on the detection surface can be written as:

Thus, the optical path difference function can be obtained as:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Because the optical path difference Δ=nλ at the peak intensity position, (n=0, ±1, ±2,...), substituting into (6) formula, the fringe equation can be obtained under the first-order approximation as:

${\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; x</span>}\frac{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; the\; y</span>}\frac{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; n\&lambda;</span>}\frac{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

Again, it shows that the interference fringes are a family of concentric circles, and the coordinates of the center of the circle are:

${\mathrm{<span\; class="notranslate">\; x</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}$ ${\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

The radius of curvature of the stripes is:

$\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; [</span>{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; n\&lambda;</span>}{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

When the measured object vibrates, the measuring mirror vibrates accordingly, causing the measuring light wave to change, which is equivalent to changing the position of the virtual light source. It can be seen from formulas (8) and (9) that the center position and radius of curvature of the interference fringes will eventually change. Moreover, it can be seen from FIG. 2 that when the measured object 10 vibrates in three directions as shown in the figure, no matter which direction will cause the position of the virtual light source to change, resulting in changes in the interference fringes. It is by using this point that three-dimensional monitoring cannot be realized by plane wave interference.

As shown in Figure 3, assuming that R and O are the virtual light sources of the reference light wave and the measurement light wave respectively, then when the measured object 10 vibrates in three directions as shown in Figure 2, it will cause the point O to change, and its change Quantities can finally be decomposed into the three directions of x, y, and z shown in Figure 3.

According to (8) and (9), when O vibrates along the z-axis direction, the center of the interference fringe does not change, only the radius of curvature changes. That is to say, when O moves in the positive direction along the z-axis, the interference fringes will shrink, and when O moves in the reverse direction, the fringes will expand. The same analysis shows that when O vibrates along the x(y) axis, the center of the interference fringes also vibrates along the x(y) axis, and the radius changes slightly. In this way, the three-dimensional monitoring of the measured object is finally realized.

It can be seen that the present invention realizes three-dimensional monitoring and the separation of optical path monitoring and vibration monitoring of the measured object, and has a simple structure, adopts single-block integration, and is stable and reliable.

Claims (1)

1. An integrated optical interference three-dimensional vibration monitor, comprising a laser (1), is characterized in that, along the advancing direction of the laser (1) output light beam, the first lens (2) and the beam splitting prism (3) of the same optical axis are successively ), diaphragm (8), measuring reflector (9), described measuring reflector (9) is fixed on the surface of the object to be monitored (10), the splitting surface of the described beam splitting prism (3) and the described The included angle of the optical axis of the beam splitting prism (3) is 45 °, and the laser beam input from the incident surface is divided into reflected light and transmitted light by the beam splitting surface of the beam splitting prism (3). A total reflection film (5, 7) is coated on the periphery of one side, and a light hole (6) is left in the middle of the side opposite to the incident surface, and the transmitted light passes through the light hole (6) and the diaphragm ( 8) and the light beam that directly shines on the measuring reflector (9) is a detection beam, and the reflective surface (4) of the dichroic prism (3) is coated with a total reflection film, and the reflected light passes through the described reflective surface (4). ) is called the reference beam after reflection, and the side opposite to the reflective surface (4) is the coherent light output surface, and outside the coherent light output surface of the dichroic prism (3) are the second lens (11), the third The lens (12) and the photodetector (13) together constitute a detection system.

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