[0018] The device consists of three parts, including the light source beam splitting optical path part 1, the measuring optical path part 2 and the receiving signal part 3 with a phase difference of 90°. In the light source splitting optical path 1, a beam splitting prism 1-2, a right-angle mirror 1-3, an acousto-optic modulation 1-4 and 1-5, collimator 1-6 and 1-7, the incident light source is divided into two beams of laser beams with frequency difference, and enter the measurement optical path part 2; the measurement optical path part 2 is respectively put into the polarization beam splitter prism 2-1, 2-2 and 2-8, depolarizing beamsplitter prism 2-10, right-angle mirror 2-9, 1/4 wave plate 2-3 and 2-7, measured mirror 2-5 and reference reflection After mirrors 2-4 and 2-6 reflect twice to realize the optical multiplier, they are received by the photoelectric receiver 2-11; the received signal part 3 with a phase difference of 90° is sequentially placed into a 1/2 wave plate 3-1 and a beam splitting prism 3- 2. 1/4 wave plate 3-3, beam splitting prism 3-3, polarizing plates 3-5 and 3-6 and photoelectric receivers 3-7 and 3-8.
[0019] The beam-splitting prism 1-2 in the light source beam-splitting optical path part 1 is a depolarizing beam-splitting prism.
[0020] The two beams of light separated by the dichroic prism 1-2 respectively enter the AOMs 1-4 and 1-5 with frequency differences, and select the first-order diffracted lights of the two AOMs to generate two beams with fixed frequency differences linearly polarized light.
[0021] Acousto-optic modulators 1-4 and 1-5, collimators 1-6 and 1-7 are followed by polarization beamsplitter prisms 2-1, 2-2 and 2-8, depolarization beamsplitter prisms 2-10, 1/ 4 wave plates 2-3 and 2-7, so that the two beams of light separated by the light source are incident on the measuring mirror 2-5 and the reference mirrors 2-4 and 2-6 twice to obtain the beat frequency signal of the reference light.
[0022] The acousto-optic modulators 1-4 and 1-5 modulate two beams of laser light with different optical frequencies, and the polarization beam splitter 2-1 after the collimators 1-6 and 1-7 separates the light of each frequency into vibration states Two beams of linearly polarized light perpendicular to each other, in which lasers with different frequencies and the same polarization direction beat each other to obtain the reference signal of the dual-frequency interferometer.
[0023] The fast axis of the 1/4 wave plate 2-3 is placed at an angle of 45°, the incident linearly polarized light becomes circularly polarized light after passing through the 1/4 wave plate 2-3, and after being reflected by the mirrors 2-4 and 2-5, After passing through the 1/4 wave plate 2-3 again, it is converted into linearly polarized light perpendicular to the vibration direction of the incident ray polarized light, passes through the polarization beam splitter 2-8, and then passes through the reference mirror 2-6 and the measuring mirror 2-5 , to achieve an optical quadruple pass.
[0024] The receiving signal part 3 with a phase difference of 90° obtains two beams of linearly polarized light with the same polarization direction from the polarization beam splitter 2-1, and one beam of linearly polarized light is converted into a polarized beam with the original polarization by the 1/2 wave plate 3-1. The linearly polarized light that is perpendicular to each other is converted into two beams of circularly polarized light with the opposite direction of rotation through the 1/4 wave plate 3-3, and then divided into two beams of circularly polarized light that are mixed with the opposite direction of the polarization state through the depolarization beam splitter 3-4 Polarized light, two beams of light are received by photoelectric receivers 3-7 and 3-8 through polarizers 3-5 and 3-6 respectively.
[0025] The fast axis of the 1/2 wave plate 3-1 is placed at an angle of 45° so that the incident linearly polarized light passes through the 1/2 wave plate 3-1 and becomes linearly polarized light perpendicular to the original polarization state.
[0026] The fast axis of the 1/4 wave plate 3-3 is placed at an angle of 45°, so that the incident linearly polarized light becomes circularly polarized light after passing through the 1/4 wave plate 3-3.
[0027] The optical axes of the two polarizers 3-5 and 3-6 are placed at an angle of 45° to achieve a reference signal phase difference of 90°.
[0028] In the light source splitting device 1, the laser light emitted by the He-Ne laser 1-1 with high frequency stability and high degree of polarization is divided into two beams of light through the depolarization beam splitter prism 1-2, and one beam of light is reflected by the depolarization beam splitter prism 1-2 To the acousto-optic modulator 1-4, a beam of light is transmitted by the depolarizing beam splitter prism 1-2, and the transmitted light is reflected by the right-angle prism 1-3 to the acousto-optic modulator 1-5, and two laser beams with the same polarization state pass through the acousto-optic After the modulator 1-5 is diffracted, the first-order diffracted light becomes two laser beams with the same polarization state and different frequencies. A collimated laser beam is used to change the vibration direction of the electric vector of the light by rotating the collimator 1-6 and 1-7, so that the vibration direction of the electric vector is the same as image 3 The polarization axis of the polarizing beam splitter 2-1 (the polarization axis is perpendicular to the interference table) is 45°.
[0029] The measuring optical path part 2 is an optical device for realizing an optical quadruple pass.
[0030] The optical device for realizing the optical quadruple pass includes three polarizing beam splitting prisms 2-1, 2-2, 2-8 and a depolarizing beam splitting prism 2-10. At the polarizing beam splitting prism 2-1, the light beam L is decomposed into intensity equal vertical and horizontal two orthogonal linearly polarized components L V and L H. Reference beam L V Reflected by the polarizing beam splitting surface to the receiving optical path of the reference signal, the L transmitted by the polarizing beam splitting prism 2-1 HTwo beams of laser light enter next polarizing beam splitter 2-2, because the light of the polarization state transmitted through polarizing beam splitting prism 2-1 is all transmitted through polarizing beam splitting prism 2-2, enters 1/4 wave plate 2-3, because 1 The fast axis of the /4 wave plate 2-3 is 45° different from the optical axis direction of the transmitted light of the polarizing beam splitter prism 2-2, so the incident linearly polarized light becomes circularly polarized light after passing through the 1/4 wave plate 2-3, different The circularly polarized light of the frequency is respectively incident on the reference mirror 2-4 and the measuring mirror 2-5, and after being reflected by the reference mirror 2-4 and the measuring mirror 2-5, it returns according to the original optical path and passes through the 1/4 wave plate After 2-3, the polarization direction changes from circularly polarized light to linearly polarized light and the vibration direction is perpendicular to the incident direction of the incident linearly polarized light. Due to the change of polarization state, the linearly polarized light that returns to the polarization beam splitter 2-2 is polarized The light-splitting surface of the beam-splitting prism 2-2 is fully reflected, and after being incident on the polarization beam-splitter 2-8, it is still fully reflected by the light-splitting surface of the polarization beam-splitter 2-8, and becomes a circle after being incident on the 1/4 wave plate 2-7 Polarized light, in the same way, after the light of different frequencies is reflected by the reference mirror 2-6 and the measuring mirror 2-5, it passes through the 1/4 wave plate 2-7 again, and is completely transmitted by the light-splitting surface of the polarization beam splitter prism 2-8. It is reflected by the right-angle reflector 2-9 to the depolarizing beam splitting prism 2-10, and after being respectively reflected by the beam splitting surface and the reflecting surface of the depolarizing beam splitting prism 2-10, two laser beams of different frequencies meet, and the signal carrying the measurement information is received by the photoelectric Receiver 2-11 receives.
[0031] Figure 4 In order to realize the phase difference of 90° by the optical method, the receiving signal part 3 is used.
[0032] After two beams of reference light with the same vibration direction and different frequencies enter the receiving signal part 3 with a phase difference of 90°, one beam of frequency light is directly incident on the polarization beam splitter prism 3-2 and is reflected by the beam splitting surface, and the other beam of frequency laser light passes through a 1 The /2 wave plate 3-1 is incident to the polarization beam splitter 3-2, wherein the feature of the 1/2 wave plate 3-1 is that the included angle between the fast axis of the wave plate and the X-axis direction is 45°, so that the 1/2 The polarization states of the laser at the frequency of the wave plate 3-1 and the laser at another frequency are perpendicular to each other, so that the linearly polarized light passing through the 1/2 wave plate 3-1 is transmitted and polarized on the beam-splitting plane of the polarization beam splitter prism 3-2 The reflection surface of the reflective coating of the beam splitting prism 3-2 is reflected. After the two beams meet at the polarization beam splitting prism 3-2, they enter the 1/4 wave plate 3-3 to form two beams of circularly polarized light with opposite rotation directions, and then pass through The depolarization beam splitter 3-4 enters the polarizer 3-5 and the polarizer 3-6 respectively after being split by the depolarization beam splitter 3-4, and the feature of the polarizer 3-5 and the polarizer 3-6 is that two polarizers The direction of the optical axis of the plate differs by 45°, so that the phase difference of the two beams of light passing through the polarizer 3-5 and the polarizer 3-6 is 90°, and is received by the receiver 3-7 and the receiver 3-8 respectively .
