CN111043991A - Straightness measuring interferometer system without nonlinear error and measuring method - Google Patents
Straightness measuring interferometer system without nonlinear error and measuring method Download PDFInfo
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- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/26—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes
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- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
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Abstract
The invention provides a linearity measuring interferometer system without nonlinear error and a measuring method. The heterodyne light source adopts light emitted by a monostable frequency laser light source, the polarization direction of the light is divided into two beams of light by a spectroscope, and the two beams of light are changed into two spatially separated beams of light with different frequencies after respectively passing through two acousto-optic modulators. The two beams of light are divided into four spatially symmetric beams of light that propagate in parallel after passing through a Koesters prism. The four light beams pass through an interferometer system consisting of a half wave plate, a combined polarization beam splitter prism, a quarter wave plate, a wedge angle prism and a wedge surface reflector, when the wedge angle prism generates horizontal direction linearity displacement, the optical path information (or called phase information) of two beams of measuring light is changed, and the linearity error of the wedge angle prism can be obtained by comparing the phase difference change of the two beams of measuring light signals. The method provided by the invention can realize high-precision measurement of tiny straightness accuracy errors.
Description
Technical Field
The invention relates to the technical field of micro-nano measurement, in particular to a high-precision measurement interferometer with a small straightness error and a measurement method.
Background
Advanced manufacturing technology has become a key research object in manufacturing industry as one of the priority subjects of the national outline of long-term scientific and technical development. At present, the displacement control precision in various precision positioning devices is generally in the nanometer level, and in high-performance precision numerical control machine tools and three-coordinate measuring machines, the displacement measurement precision reaches a few nanometers, even below 1 nanometer. The ever increasing demands on the accuracy of the displacement mean that various deviations in the displacement process must be measured and controlled precisely. In the measurement of errors with multiple degrees of freedom, straightness errors refer to offset in the direction perpendicular to a motion axis, influence on positioning accuracy of a high-precision displacement table is the most direct, and the straightness errors are very important content in the mechanical manufacturing industry.
At present, a plurality of detection methods for straightness errors are applied, and the detection methods are mainly based on laser collimation and laser interference. The measuring precision is mainly limited by the detection precision of a position detector and the direction drift of a laser light source based on a measuring scheme of laser collimation; the system utilizes a differential plane interferometer, combines the combination of wedge prism and wedge surface reflection to form a four-beam system with geometric space symmetry, and utilizes a phase meter with the resolution of 2 pi/3600 to realize the linearity error detection with the measurement resolution reaching the nanometer level. But due to the phenomenon of frequency aliasing in the system, a nonlinear error exists in a measurement result, and the error can reach tens of nanometers or even tens of nanometers, so that the detection accuracy of the straightness error is severely limited. Therefore, the importance of inventing a linearity measuring interferometer without nonlinear error is not negligible.
In the interferometer system described in the invention with publication number CN104613902A, the non-orthogonality of the light emitted from the light source or the light leakage of the beam splitter prism of two different frequencies causes the frequency aliasing phenomenon, so that the measured optical signal has the non-linear error, which can reach tens of nanometers or even more.
Disclosure of Invention
1. Objects of the invention
The invention provides a linearity measuring interferometer system without nonlinear error and a measuring method, which can eliminate the nonlinear error and obtain the measuring precision of nanoscale linearity error.
2. The technical scheme adopted by the invention
The invention discloses a linearity measuring interferometer system without nonlinear error, which comprises a heterodyne light source system and a linearity measuring interferometer system;
the heterodyne light source system comprises a frequency stabilized laser, a beam splitter prism, a two-stage acousto-optic modulator, a two-stage light shielding element and a multi-stage right-angle prism;
the frequency stabilized laser is divided into two beams of light after passing through the light splitter, and then is regulated by the acousto-optic modulator, and two beams of parallel light with different frequencies and separated in space are emitted through the multistage right-angle prism;
a straightness measuring interferometer system, comprising: the device comprises a Koesters prism, a half wave plate, a combined beam splitter prism, a quarter wave plate, a right-angle prism, a combined wedge-surface reflector, a first two-stage photoelectric receiver and a second two-stage photoelectric receiver;
two beams of parallel light beams pass through a Koesters prism, a half wave plate, a combined beam splitter prism, a quarter wave plate, a right-angle prism, a combined wedge angle prism and a combined wedge surface reflector;
when the combined wedge-angle prism generates linearity displacement in the horizontal direction, the optical paths of two beams of light with different frequencies change, so that the phase difference between two measurement signals changes, and the linearity error can be obtained by measuring the phase difference information.
Further, Koesters prism: the device comprises triangular prisms with symmetrical sizes, wherein the right-angle sides AC of the two triangular prisms are the same in length and are glued together, a layer of polarization light splitting film is plated on a gluing surface, incident light rays comprise horizontally polarized light p light and vertically polarized light s light, the p light is transmitted when being incident on the polarization light splitting film, and is horizontally emitted after being reflected by an AD surface; the s light is reflected when being incident on the polarization beam splitting film, and then is horizontally emitted after being reflected by the AB surface.
Further, the quarter wave plate: when the optical axis direction and the vibration direction form an angle of 45 degrees, when the incident light is linearly polarized light, the emergent light is circularly polarized light, if the linearly polarized light passes through the quarter wave plate in a reciprocating manner, the polarization direction is changed by 90 degrees, namely the linearly polarized light is originally horizontal polarized light, and after passing through the quarter wave plate in a reciprocating manner, the horizontally polarized light is changed, and in the same way, the vertically polarized light is originally vertical polarized light and after passing through the quarter wave plate in a reciprocating manner, the horizontally polarized light is changed.
Further, the half wave plate: when the optical axis direction and the vibration direction form an angle of 45 degrees, the incident light is horizontally polarized light and is changed into vertically polarized light after passing through.
A measurement method of linearity measurement interferometer without nonlinear error, wherein the included angle between the polarization direction of laser emitted by a frequency stabilized laser of a heterodyne light source system and the horizontal direction is 45 degrees or circularly polarized light, the frequency is f, the laser is divided into two beams of light by a beam splitter prism, and the polarization state and the frequency of the two beams of light are not changed; the two beams of light respectively pass through two acousto-optic modulators, the driving frequencies of the two acousto-optic modulators are respectively f1 and f2, the zero-order diffraction light is respectively shielded by a light shielding element, and the emergent light frequency of the + 1-order diffraction light or the-1-order diffraction light is respectively changed into f + f1 and f + f2 or f-f1 and f-f 2; after being reflected by the multistage right-angle prism, the two beams of light are emitted in parallel, and the frequency difference of the two beams of light is f1-f 2.
Further, the straightness measuring interferometer system: parallel light with a certain frequency difference comprises a first light beam and a second light beam;
the light beam is divided into two beams of linearly polarized light with different frequencies and mutually vertical polarization directions through a Koesters prism, the two beams of linearly polarized light are respectively represented as vertically polarized light and horizontally polarized light, and the horizontally polarized light is converted into vertically polarized light II after passing through a half wave plate; the vertically polarized light and the vertically polarized light II are incident to the combined beam splitter prism and are reflected at the upper part of the light surface, the reflected light is the first reflected light and the second reflected light respectively, after being reflected by the right-angle prism, the reflected light is the third reflected light and the fourth reflected light, the reflected light is incident to the combined beam splitter prism again and is reflected at the upper part of the light surface, and the emergent light is the fifth reflected light and the sixth reflected light respectively;
the other light beam is the same as the first light beam and passes through a Koesters prism, a half-wave plate and a combined beam splitter prism;
the difference is that the light is transmitted at the lower part of the light surface, the transmitted light is transmitted light I and transmitted light II after passing through the quarter-wave plate, the polarization state is changed into circularly polarized light, two beams of emergent light beams have certain deflection angles after being refracted by the combined wedge-angle prism, and the emergent light beams respectively enter the combined wedge-surface reflector and return to the original path.
Furthermore, two beams of light returned from the original path are sequentially and twice passed through the quarter-wave plate, the polarization state is changed into vertical polarized light, the vertical polarized light is reflected at the smooth surface of the lower part of the combined beam splitter prism, the vertical polarized light is reflected at the light splitting surface of the upper part of the combined beam splitter prism, the vertical polarized light is reflected by the quarter-wave plate, the combined wedge angle prism and the combined wedge surface reflector again, the polarization direction is changed into horizontal polarized light due to the twice passed through the quarter-wave plate, the horizontal polarized light is transmitted at the light splitting surface of the upper part of the combined beam splitter prism, and the first two-stage photoelectric receiver receives the fifth reflected light and the sixth reflected; the two-stage photoelectric receiver II receives the light beam III and the light beam IV and converts the light beams into a measurement signal II; and then the phase meter performs phase comparison to obtain straightness error information geometrically.
Further, in the straightness measuring interferometer, light beams propagate through a wedge angle prism, wherein α is a wedge angle, β is a refraction angle, at the beginning of measurement, a light propagation light path is formed, if the wedge angle prism is displaced in the x direction by d, the left light Beam1 is outwards shifted by d, and the right light Beam2 is inwards shifted by d, because the total path of light propagation does not change, but the distance traveled by the Beam1 in the wedge angle prism is increased by AA, the distance traveled in the air is reduced by BB, and the refractive index of the wedge angle prism is larger than that of the air, the optical path length of the Beam1 is increased, and similarly, the distance traveled by the Beam2 in the wedge angle prism is reduced, the distance traveled in the air is increased, the optical path length of the Beam2 is reduced, and the absolute value of the optical path change amount of the Beam2 is equal to the absolute value of the optical path change amount of the Beam1, and the sign is opposite.
Further, assuming that L is the variation of the path of the light Beam1 in the wedge prism, it can be obtained:
because two beams of light pass through the wedge angle prism 4 times in sequence, the total optical path difference can be expressed as:
wherein n represents the refractive index of the wedge angle prism, and 1 represents the refractive index of air; the relationship between the optical path change and the phase difference Δ Φ can be expressed as:
wherein λ is the wavelength of the incident light, and formula (2) is substituted into formula (3) to obtain:
the straightness error d obtained after the form conversion is as follows:
3. advantageous effects adopted by the present invention
(1) In the invention, the light with different frequencies does not have frequency aliasing in the transmission process, two beams of light with different frequencies emitted by the heterodyne light source are spatially separated, and aliasing is not generated in the transmission process inside the interferometer, so that the nonlinear error can be fundamentally eliminated, the measurement precision of the invention can be improved by one order of magnitude, and the measurement stroke and the range are larger.
(2) The invention can be applied to high-precision numerical control machine tools, machining centers and various precision positioning motion devices, although the straightness error is generally small, the measurement precision requirement is better than 5nm, the wedge angle of the wedge angle prism is set to be 1 degree, the resolution of the phase meter is 0.1 degree, the measurement resolution of the straightness error is about 1.7nm, the measurement stroke is determined by the width of the wedge surface reflection prism and generally does not exceed 3m, the measurement range depends on the width of the wedge angle prism, and generally can reach 10 mm.
Drawings
FIG. 1 is a schematic diagram of the splitting of a Koesters prism in a non-linear error measurement interferometer;
FIG. 2 is a schematic view of the ray propagation of a combined beam splitting prism in a non-nonlinear error measurement interferometer;
FIG. 3 is a schematic diagram of the light path of a light beam propagating in a wedge prism;
FIG. 4 is a schematic diagram of an heterodyne light source system in a non-nonlinear error measurement interferometer;
FIG. 5 is a schematic diagram of a straightness measuring interferometer system in the non-linearity error measuring interferometer.
Detailed Description
The technical solutions in the examples of the present invention are clearly and completely described below with reference to the drawings in the examples of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without inventive step, are within the scope of the present invention.
The present invention will be described in further detail with reference to the accompanying drawings.
Example 1
The invention provides a linearity measurement interferometer system without nonlinear error, which is a heterodyne light source system and comprises a frequency stabilized laser 1, a beam splitter prism 2, a first-stage acousto-optic modulator 3, a second-stage acousto-optic modulator 6, a first light shielding element 4, a second light shielding element 7, a first right-angle prism 5, a second right-angle prism 8 and a third right-angle prism 9, wherein the first-stage acousto-optic modulator 3 and the second-stage acousto-optic modulator 6 are arranged in parallel; referring to fig. 5, a straightness measuring interferometer system includes: a Koesters prism 20, a half wave plate 21, a combined beam splitter prism 22, a quarter wave plate 24, a right angle prism 23, a combined wedge angle prism 25, a combined wedge surface reflector 26, a first two-stage photoelectric receiver 27 and a second two-stage photoelectric receiver 28;
the optical device Koesters prism comprises triangular prisms with symmetrical sizes, the right-angle sides AC of the two triangular prisms are the same in length and are glued together, a layer of polarization light splitting film is plated on a gluing surface, the light splitting principle of the optical device Koesters prism is shown in figure 1, incident light comprises horizontally polarized light p light and vertically polarized light s light, wherein the p light is transmitted when being incident on the polarization light splitting film and horizontally exits after being reflected by an AD surface; the s light is reflected when being incident on the polarization beam splitting film, and then is horizontally emitted after being reflected by the AB surface.
When the optical axis direction and the vibration direction form an angle of 45 degrees, the emergent light is circularly polarized light when the incident light is linearly polarized light, if the linearly polarized light passes through the quarter wave plate back and forth, the polarization direction changes by 90 degrees, namely the original horizontally polarized light passes through the quarter wave plate back and forth and is changed into vertically polarized light, and similarly, the vertically polarized light is changed into horizontally polarized light after passing through the quarter wave plate back and forth.
When the optical axis direction and the vibration direction form an angle of 45 degrees, the incident light is horizontally polarized light and is changed into vertically polarized light after passing through the half wave plate.
The invention utilizes the acousto-optic modulator to generate two beams of parallel light with different frequencies, the two beams of parallel light are spatially separated, the light beams pass through an interferometer system consisting of a Koesters prism, a half-wave plate, a combined beam splitter prism, a quarter-wave plate, a right-angle prism, a combined wedge angle prism and a combined wedge surface reflector, when the combined wedge angle prism generates straightness displacement in the horizontal direction, the optical paths of the two beams of light with different frequencies change, so that the phase difference between a measurement signal I and a measurement signal II changes, and the straightness error can be obtained by measuring the phase difference information. The invention aims to provide a linearity measuring interferometer without nonlinear error, because the nonlinear error is caused by aliasing of optical path information carried by light with different frequencies, two beams of light with different frequencies emitted by a heterodyne light source in the system are spatially separated, and aliasing is not generated in the internal propagation process of the interferometer, so the nonlinear error can be eliminated fundamentally.
The structure of the linearity error measurement interference is described in detail below with reference to the accompanying drawings.
By using the laser beam five 10 emitted by the frequency stabilized laser 1, the included angle between the polarization direction of the laser beam five 10 and the horizontal direction is 45 degrees or circularly polarized light, the frequency is f, the laser beam is divided into two beams of light through the light splitting prism 2, the two beams of light are shown as a beam six 11 and a beam seven 15, and the polarization states and the frequencies of the beam six 11 and the beam seven 15 are not changed. The light beam six 11 passes through the acousto-optic modulator 3 with the driving frequency f1 respectively, wherein the frequency of the emergent light of + 1 st order diffraction light or-1 st order diffraction light 13 is changed into f + f1 or f-f1, and the first zero order diffraction light 12 is shielded by the shielding element 4; the light beam seven 15 passes through the second-stage acousto-optic modulator 6 with the driving frequency of f2 respectively, wherein the frequency of the emergent light of the light beam nine 17 is changed into f + f2 or f-f2, and the second 16 zeroth-order diffracted light is blocked by the second light blocking element 7. The + 1 st order diffraction light or-1 st order diffraction light 13 is reflected by the first right-angle prism 5 and then horizontally emitted, and is expressed as light beam eight 14; beam nine 17 is reflected by the second right angle prism 8 as beam ten 18, beam ten 18 is reflected by the third right angle prism 9 and exits horizontally as beam eleven 19, beams eight 14 and eleven 19 are parallel to each other, and the difference between the frequencies of the two beams is f1-f 2.
The first beam 29 is divided into two linearly polarized lights with different frequencies and mutually perpendicular polarization directions through a Koesters prism 20, the linearly polarized lights are respectively represented as a vertically polarized light 31 and a horizontally polarized light 32, the horizontally polarized light 32 is changed into a vertically polarized light after passing through a half wave plate 21, and emergent light is a vertically polarized light two 33. The vertically polarized light 31 and the vertically polarized light 33 enter the combined beam splitter prism 22, are reflected at the upper part light surface 22a, are reflected as a first reflected light 37 and a second reflected light 39 respectively, are reflected by the right-angle prism 23, are reflected as a third reflected light 38 and a fourth reflected light 40, enter the combined beam splitter prism 22 again, and are reflected at the upper part light surface 22a, and are emergent lights as a fifth reflected light 53 and a sixth reflected light 55 respectively;
the second light beam 30 is divided into two linearly polarized light beams with different frequencies and mutually perpendicular polarization directions through the koestirs prism 20, the linearly polarized light beams are respectively represented as a third light beam 34 vertical polarized light and a fourth light beam 36 horizontal polarized light, the third light beam 34 is changed into vertical polarized light after passing through the half wave plate 21, and emergent light is a fifth light beam 35. The fifth light beam 35 and the fourth light beam 36 enter the combined beam splitter prism 22, are transmitted at the lower light surface portion 22b, are respectively a sixth light beam 41 and a seventh light beam 42, pass through the quarter-wave plate 24, pass through the first transmitted light 43 and the second transmitted light 44, are changed into circularly polarized light in polarization state, are refracted by the combined wedge angle prism 25, exit the eighth light beam 45 and the ninth light beam 46 with certain deflection angles, enter the combined wedge surface reflector 26 respectively, and return in the original path. The returned light beam passes through the quarter-wave plate 24 twice in sequence, the polarization state of the returned light beam is changed into vertical polarized light, the returned light beam is reflected at the lower light surface 22b of the combined beam splitter prism 22 and then reflected at the upper light splitting surface 22a, the emitted light beam is represented as a tenth light beam 47 and an eleventh light beam 48, the emitted light beam passes through the quarter-wave plate 24 again respectively, the third transmitted light beam 49 and the fourth transmitted light beam 50 are transmitted, the polarization state of the returned light beam is changed into circularly polarized light, the circularly polarized light beam is refracted by the combined wedge angle prism 25, the emitted twelfth light beam 51 and the emitted thirteenth light beam 52 have certain deflection angles, and the light beams enter the combined wedge surface reflector 26 respectively and return to. Because the two-time transmission passes through the quarter-wave plate 24, the polarization direction is changed into horizontal polarized light, the horizontal polarized light is transmitted at the combined beam splitter prism 22 and the upper light splitting surface 22a, the transmitted light is the light beam three 54 and the light beam four 56 respectively, and the reflected light five 53 and the reflected light six 55 are received by the two-stage photoelectric receiver one 27 and are converted into a measurement signal one; the two-stage photoelectric receiver two 28 receives the light beam three 54 and the light beam four 56 and converts the light beams into a measurement signal two. And then the phase meter performs phase comparison to obtain straightness error information geometrically.
The calculation principle of the straightness measuring interferometer is described in detail below:
FIG. 3 is a schematic diagram of the Beam propagation through a wedge prism, where α is the wedge angle and β is the refraction angle, at the beginning of the measurement, the light propagation path is shown by a dashed line, if the wedge prism is shifted in the x direction by d, the left Beam BEAM1 is shifted outward and the right Beam BEAM2 is shifted inward by d, as shown by a solid line, the total path of the light propagation does not change, but the Beam1 propagates inside the wedge prism with increased distance AA, the distance of the Beam propagating inside the air is decreased by BB, the wedge prism is made of k9 glass with a refractive index of 1.516, the refractive index of the air is about 1, the optical path of the Beam1 is increased, the distance of the Beam2 propagating inside the wedge prism is decreased, the distance of the Beam propagating inside the air is increased, and the Beam2 has decreased, the amount of the change of the Beam2 is equal to the absolute value of the change of the Beam1, and the sign of the optical path is opposite.
Assuming that L is the variation of the path of the light Beam1 in the wedge prism, it can be obtained:
because two beams of light pass through the wedge angle prism 4 times in sequence, the total optical path difference can be expressed as:
where n represents the index of refraction of the wedge angle prism and 1 represents the index of refraction of air. The relationship between the optical path change and the phase difference Δ Φ can be expressed as:
wherein λ is the wavelength of the incident light, and formula (2) is substituted into formula (3) to obtain:
where λ is the wavelength of the incident light. Thus, it is possible to obtain:
the minimum resolution of the straightness error d is about 2.44nm when α =1 ° and the resolution of the phase meter is 2 pi/3600.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (9)
1. A straightness measuring interferometer system free of non-linearity errors, comprising: heterodyne light source system, straightness measuring interferometer system;
the heterodyne light source system comprises a frequency stabilized laser (1), a beam splitter prism (2), a two-stage acousto-optic modulator, a two-stage light shielding element and a multi-stage right-angle prism;
the frequency stabilized laser (1) is divided into two beams of light after passing through a light splitter, and then is adjusted by an acousto-optic modulator to emit two beams of parallel light with different frequencies and separated in space through a multistage right-angle prism;
a straightness measuring interferometer system, comprising: the device comprises a Koesters prism (20), a half wave plate (21), a combined beam splitter prism (22), a quarter wave plate (24), a right-angle prism (23), a combined wedge-angle prism (25), a combined wedge-surface reflecting mirror (26), a first two-stage photoelectric receiver (27) and a second two-stage photoelectric receiver (28);
two parallel light beams pass through a Koesters prism (20), a half wave plate (21), a combined beam splitter prism (22), a quarter wave plate (24), a right-angle prism (23), a combined wedge angle prism (25) and a combined wedge surface reflector (26);
when the combined wedge angle prism (25) generates linearity displacement in the horizontal direction, the optical paths of two beams of light with different frequencies change, so that the phase difference between two measurement signals changes, and the linearity error can be obtained by measuring the phase difference information.
2. The linearity measurement interferometer system without nonlinear error as recited in claim 1, characterized by a koestirs prism (20): the device comprises triangular prisms with symmetrical sizes, wherein the right-angle sides AC of the two triangular prisms are the same in length and are glued together, a layer of polarization light splitting film is plated on a gluing surface, incident light rays comprise horizontally polarized light p light and vertically polarized light s light, the p light is transmitted when being incident on the polarization light splitting film, and is horizontally emitted after being reflected by an AD surface; the s light is reflected when being incident on the polarization beam splitting film, and then is horizontally emitted after being reflected by the AB surface.
3. The linearity measurement interferometer system without nonlinear error of claim 1, characterized by a quarter-wave plate (24): when the optical axis direction and the vibration direction form an angle of 45 degrees, when the incident light is linearly polarized light, the emergent light is circularly polarized light, if the linearly polarized light passes through the quarter wave plate in a reciprocating manner, the polarization direction is changed by 90 degrees, namely the linearly polarized light is originally horizontal polarized light, and after passing through the quarter wave plate in a reciprocating manner, the horizontally polarized light is changed, and in the same way, the vertically polarized light is originally vertical polarized light and after passing through the quarter wave plate in a reciprocating manner, the horizontally polarized light is changed.
4. The linearity measurement interferometer system without nonlinear error of claim 1, characterized by a half wave plate (21): when the optical axis direction and the vibration direction form an angle of 45 degrees, the incident light is horizontally polarized light and is changed into vertically polarized light after passing through.
5. A method of measuring a straightness measuring interferometer system without nonlinear error as recited in any one of claims 1 to 4, wherein: the included angle between the polarization direction of the laser emitted by the frequency stabilized laser (1) of the heterodyne light source system and the horizontal direction is 45 degrees or circularly polarized light, the frequency is f, the laser is divided into two beams of light by the light splitting prism (2), and the polarization state and the frequency of the two beams of light are not changed; the two beams of light respectively pass through two acousto-optic modulators, the driving frequencies of the two acousto-optic modulators are respectively f1 and f2, the zero-order diffraction light is respectively shielded by a light shielding element, and the emergent light frequency of the + 1-order diffraction light or the-1-order diffraction light is respectively changed into f + f1 and f + f2 or f-f1 and f-f 2; after being reflected by the multistage right-angle prism, the two beams of light are emitted in parallel, and the frequency difference of the two beams of light is f1-f 2.
6. The method of measuring a straightness measuring interferometer system without nonlinear error as recited in claim 5, wherein the straightness measuring interferometer system: parallel light with a certain frequency difference comprises a first light beam (29) and a second light beam (30);
the light beam I (29) is divided into two linearly polarized light beams with different frequencies and mutually perpendicular polarization directions through a Koesters prism (20), the linearly polarized light beams are respectively represented as vertically polarized light (31) and horizontally polarized light (32), and the horizontally polarized light beams (32) are changed into vertically polarized light II (33) after passing through a half wave plate (21); the vertically polarized light (31) and the vertically polarized light II (33) enter the combined beam splitter prism (22), are reflected at the upper part light surface (22a), are respectively reflected light I (37) and reflected light II (39), are reflected by the right-angle prism (23), are reflected light III (38) and reflected light IV (40), enter the combined beam splitter prism (22) again, are reflected at the upper part light surface (22a), and are respectively reflected light V (53) and reflected light VI (55);
the other light beam (30) passes through a Koesters prism (20), a half-wave plate (21) and a combined beam splitter prism (22) like the light beam (29);
the difference is that the light is transmitted at the lower part light surface (22b), after passing through the quarter-wave plate (24), the transmitted light is transmitted light I (43) and transmitted light II (44), the polarization state is changed into circularly polarized light, after being refracted by the combined wedge angle prism (25), two beams of emergent light beams have certain deflection angles, and after being respectively incident to the combined wedge surface reflector (26), the emergent light beams return to the original path.
7. The method of claim 6, wherein the two beams of light returned from the original path are converted into vertically polarized light by passing through the quarter-wave plate (24) twice in sequence, reflected at the lower light-splitting surface (22b) of the combined beam splitter prism (22), reflected at the upper light-splitting surface (22a), reflected again by the quarter-wave plate (24), the combined wedge-angle prism (25) and the combined wedge-surface reflector (26), and converted into horizontally polarized light by passing through the quarter-wave plate (24), transmitted at the upper light-splitting surface (22a) of the combined beam splitter prism (22), and the transmitted light is the beam three (54) and the beam four (56), respectively, and the reflected light five (53) and the reflected light six (55) are received by the two-stage photo-electric receiver one (27), converting the signal into a first measurement signal; the two-stage photoelectric receiver II (28) receives the light beam III (54) and the light beam IV (56) and converts the light beams into a measurement signal II; and then the phase meter performs phase comparison to obtain straightness error information geometrically.
8. The method of measurement of a linearity measurement interferometer system without non-linearity errors of claim 6, characterized in that the linearity measurement interferometer:
the method comprises the steps that light beams are transmitted through a wedge-angle prism, wherein α is a wedge angle, β is a refraction angle, at the beginning of measurement, a light ray transmission light path is formed, if the wedge-angle prism is displaced in the x direction by d, a left light Beam1 is outwards shifted by d, and a right light Beam2 is inwards shifted by d, the total path of light ray transmission is unchanged, but the distance of Beam1 transmitted in the wedge-angle prism is increased by AA, the distance of Beam1 transmitted in the air is reduced by BB, the refractive index of the wedge-angle prism is larger than that of the air, the optical path of Beam1 is increased, and similarly, the distance of Beam2 transmitted in the wedge-angle prism is reduced, the distance of Beam2 is reduced, the absolute value of the optical path change amount of Beam2 is equal to the absolute value of the optical path change amount of Beam1, and the sign of the absolute value of the optical path change amount of Beam.
9. The method of measuring a straightness measuring interferometer system without nonlinear error according to claim 8, wherein:
assuming that L is the variation of the path of the light Beam1 in the wedge prism, it can be obtained:
because two beams of light pass through the wedge angle prism 4 times in sequence, the total optical path difference can be expressed as:
wherein n represents the refractive index of the wedge angle prism, and 1 represents the refractive index of air; the relationship between the optical path change and the phase difference Δ Φ can be expressed as:
wherein λ is the wavelength of the incident light, and formula (2) is substituted into formula (3) to obtain:
the straightness error d obtained after the form conversion is as follows:
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