Laser interferometer for suppressing angle-length coupled noise and noise suppression method

Abstract

The invention relates to a laser interferometer for suppressing angle-length coupling noise and a noise suppression method, the laser interferometer comprises a light source structure, an offset structure, a detection structure and a control device, and the control device is connected with the light source structure, the offset structure and the detection structure; the light source structure is used for emitting laser beams under the control of the control device; the offset structure comprises a test mass, the test mass is arranged on an emergent light path of the laser beam and can reflect the laser beam, and the test mass can be driven by the control device to rotate; the detection structure comprises a laser beam combining element, a noise suppression structure and a first photoelectric detector; and the control device is used for adjusting the noise suppression structure according to the first detection result until the first detection result meets a preset requirement. The laser interferometer can effectively improve the noise suppression effect.

Description

Technical Field

[0001] The present application relates to the technical field of laser interferometers, and in particular to a laser interferometer for suppressing angle-length coupling noise and a noise suppression method. Background Art

[0002] When a gravitational wave passes, the distance between the test masses in an array of space-based gravitational wave detection satellites changes. Laser interferometers read this distance change and use it to invert the gravitational wave signal. In space, satellites vibrate due to non-conservative forces such as celestial events, solar radiation, cosmic rays, and interstellar magnetic fields. The test masses themselves are placed in a drag-free control system, simulating a situation where they are free from all forces except gravity. The forces acting on the satellites are inconsistent with those on the test masses, causing the test masses to vibrate. This causes the measurement laser beam reflected from the test masses to tilt at an angle, introducing additional longitudinal optical path signals and generating angular coherence interference effects, known as angle-length coupling noise. Existing research indicates that among the various noise sources that affect laser interferometry accuracy, angle-length coupling noise is the second-largest source, after shot noise.

[0003] Existing laser interferometers have poor suppression effect on angle-length coupling noise. Summary of the Invention

[0004] Based on this, it is necessary to provide a laser interferometer that can effectively suppress angle-length coupling noise to address the above technical problems.

[0005] In the first aspect, the present application provides a laser interferometer for suppressing angle-length coupling noise, the laser interferometer including a light source structure, an offset structure, a detection structure and a control device, the control device being connected to the light source structure, the offset structure and the detection structure; the light source structure is used to emit a laser beam under the control of the control device; the offset structure includes a test mass, the test mass is arranged on the output optical path of the laser beam, and can reflect the laser beam, and the test mass can rotate under the drive of the control device; the detection structure includes a laser beam combining element, a noise suppression structure and a first photodetector; wherein, the laser beam combining element is arranged on the optical path of the reflected laser beam, and is used to combine the reflected laser beam to obtain a first combined laser beam, the noise suppression structure is arranged on the optical path of the first combined laser beam, and is used to suppress noise on the first combined laser beam to obtain a second combined laser beam, the first photodetector is used to receive the second combined laser beam, and perform photoelectric conversion on the second combined laser beam to obtain a first detection result; the control device is used to adjust the noise suppression structure according to the first detection result until the first detection result meets the preset requirements.

[0006] In one embodiment, the noise suppression structure includes an imaging system and an angle deflection system. The angle deflection system includes two rotatable optical wedges and an optical plate adjustable in multiple degrees of freedom. The two rotatable optical wedges are used to generate deflections at any angle within a certain cone angle in space; the optical plate adjustable in multiple degrees of freedom is used to compensate for the position offset caused by the angular offset of the first combined laser beam; and the imaging system is used to image the rotation axis of the test mass at the center of the first photodetector.

[0007] In one embodiment, the first photodetector is a four-quadrant detector, and the control device includes a signal generating unit, a phase-locked amplifier and an adjustment structure; the signal generating unit is used to generate a displacement signal based on a displacement signal generating method and a first detection result, and the displacement signal generating method is a four-channel signal arithmetic averaging method or a four-channel signal weighted averaging method; the phase-locked amplifier is used to demodulate the displacement signal and determine the phase-locked amplification result; the adjustment structure is used to adjust the noise suppression structure according to the phase-locked amplification result.

[0008] In one embodiment, the phase-locked amplifier is specifically used to perform double frequency demodulation on the displacement signal to determine a first phase-locked amplification result; the adjustment structure is specifically used to adjust the axial position of the first photodetector and the imaging system according to the first phase-locked amplification result until the first phase-locked amplification result is minimized.

[0009] In one embodiment, the phase-locked amplifier is specifically used to perform one-time frequency demodulation on the displacement signal to determine a second phase-locked amplification result; the adjustment structure is specifically used to adjust the angles of two rotatable optical wedges in the angle deflection system according to the second phase-locked amplification result until the second phase-locked amplification result is minimized.

[0010] In one embodiment, the adjustment structure is further configured to adjust the optical plate in the angle deflection system according to the difference between the amplitudes of the four quadrant signals corresponding to the first detection result, until the difference between the amplitudes of the four quadrant signals corresponding to the first detection result meets a preset difference threshold.

[0011] In one embodiment, the detection structure further includes a second photodetector, which is used to perform photoelectric conversion on the first combined laser beam to obtain a second detection result; and the control device is further used to compare the first detection result with the second detection result.

[0012] In a second aspect, the present application also provides a noise suppression method, comprising:

[0013] Control the light source structure to emit a laser beam; control the rotation of the test mass in the offset structure to cause the laser beam passing the test mass to produce angular displacement or axial linear displacement; adjust the laser beam combining element to combine the laser beam passing the test mass with another laser beam to generate a first combined laser beam, perform noise suppression on the first combined laser beam according to the noise suppression structure, determine the second combined laser beam, perform photoelectric conversion on the second combined laser beam according to the first photoelectric sensor, and determine a first detection result; adjust the noise suppression structure according to the first detection result until the first detection result meets the preset requirements.

[0014] In one embodiment, a displacement signal is generated based on a displacement signal generation method and a first detection result, wherein the displacement signal generation method is a four-channel signal arithmetic averaging method or a four-channel signal weighted averaging method; the displacement signal is demodulated to determine a phase-locked amplification result; and the noise suppression structure is adjusted according to the phase-locked amplification result.

[0015] In one embodiment, the method further includes: performing photoelectric conversion on the first combined laser beam according to a second photoelectric sensor to determine a second detection result; and comparing the first detection result with the second detection result.

[0016] The above-mentioned laser interferometer and noise suppression method for suppressing angle-length coupling noise include a light source structure, an offset structure, a detection structure and a control device, and the control device is connected to the light source structure, the offset structure and the detection structure; the light source structure is used to emit a laser beam under the control of the control device; the offset structure includes a test mass, the test mass is arranged on the output optical path of the laser beam, and can reflect the laser beam, and the test mass can rotate under the drive of the control device; the detection structure includes a laser beam combining element, a noise suppression structure and a first photodetector; wherein, the laser beam combining element is arranged on the optical path of the reflected laser beam, and is used to combine the reflected laser beam to obtain a first combined laser beam, the noise suppression structure is arranged on the optical path of the first combined laser beam, and is used to suppress the noise of the first combined laser beam to obtain a second combined laser beam, and the first photodetector is used to receive the second combined laser beam and perform photoelectric conversion on the second combined laser beam to obtain a first detection result; the control device is used to adjust the noise suppression structure according to the first detection result until the first detection result meets the preset requirements. By controlling the test mass to rotate, the laser beam passing through the test mass produces angular displacement or axial linear displacement, thereby generating an optical path change and introducing a noise signal. The first combined laser beam is subjected to noise suppression by the noise suppression structure. At the same time, the noise suppression structure is continuously adjusted according to the noise suppression result, which can effectively improve the noise suppression effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following briefly introduces the drawings required for use in the embodiments or related technical descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 Schematic diagram of the principle of angle-length coupled lever effect in laser interferometer;

[0019] Figure 2 Schematic diagram of the principle of angle-length coupled piston effect in laser interferometer;

[0020] Figure 3 Schematic diagram of the structure of a laser interferometer for suppressing angle-length coupling noise in one embodiment;

[0021] Figure 4 Schematic diagram showing the optical path comparison of a laser beam in a laser interferometer according to an embodiment;

[0022] Figure 5 FIG. 4 is a flow chart of a noise suppression method in one embodiment.

[0023] Description of reference numerals:

[0024] 310: Light source structure; 320: Offset structure; 321: Half-wave plate; 322: Polarization beam splitter cube; 323: Quarter-wave plate; 324: Reflector; 10: Test mass; 330: Detection structure; 331: Laser beam combining element; 332: First photodetector; 333: Imaging system; 334: Angle deflection system; 335: Second photodetector; 340 Control device; 350: Beam splitter cube. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0027] It will be understood that the terms "first," "second," etc., used herein may be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish a first element from another element. For example, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor without departing from the scope of this application. The first resistor and the second resistor are both resistors, but they are not the same resistor.

[0028] It can be understood that the “connection” in the following embodiments should be understood as “electrical connection”, “communication connection”, etc. if there is transmission of electrical signals or data between the connected circuits, modules, units, etc.

[0029] It is understood that “at least one” refers to one or more, “a plurality” refers to two or more, and “at least a portion of an element” refers to a portion or all of an element.

[0030] As used herein, the singular forms "a," "an," and "the" may also include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include," "comprising," "having," and the like specify the presence of stated features, integers, steps, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof. Furthermore, the term "and / or" as used in this specification includes any and all combinations of the relevant listed items.

[0031] When a gravitational wave passes, the distance between test masses in a gravitational wave detection satellite changes. Laser interferometers read this distance change, thereby inverting the gravitational wave signal. A test mass is an object used for measurement or testing in an experiment. It can be a mirror, a sample, or any other object whose displacement needs to be precisely measured. In gravitational wave detectors, optical interferometers, or precision measurement experiments, a test mass is a target object whose displacement needs to be precisely measured.

[0032] In space, satellites experience jitter due to non-conservative forces such as celestial events, solar radiation, cosmic rays, and interstellar magnetic fields. However, the test mass itself is placed in a drag-free control system, simulating a situation free from all forces except gravity. The forces acting on the satellite and the test mass are inconsistent, causing the test mass to vibrate. This causes the measurement laser beam reflected from the test mass to tilt at an angle, introducing additional longitudinal optical path signals and generating angular coherent interference effects known as angle-length coupling noise. Existing research indicates that among the various noise sources affecting laser interferometry accuracy, angle-length coupling noise is the second-largest source after shot noise. Essentially, this noise is caused by changes in the beam's length due to changes in its angle, even though the system may not have undergone any displacement changes. Coupling noise caused solely by changes in geometric relationships is called geometric angle-length coupling noise.

[0033] The geometric angle-length coupling noise can be divided into the coupling "lever effect" caused by the coincidence of the rotation axis of the test mass and the reflection center of the laser beam on the test mass, and the additional coupling "piston effect" caused by the misalignment of the rotation axis of the test mass and the reflection center. Figure 1 The figure shows the principle diagram of the coupling lever effect caused by the coincidence of the rotation axis and the reflection center, where point A is the rotation axis and the reflection center of the test mass, S is the light source, is the angle at which the light beam is incident on the test mass 10. The line segment AB1 can represent the distance from the reflection point of the light beam on the test mass 10 to the photosensitive surface 20 of the photodetector. The line segment AB2 can represent the distance from the reflection center of the light beam to the photosensitive surface 20 of the photodetector after the test mass rotates about the rotation axis by an angle γ. The distance from the reflection center to the photosensitive surface 20 of the photodetector can be expressed as d level Unified said, is the tilt angle of the photodetector photosensitive surface 20, wherein the coupling lever effect can be determined by AB2-AB1. Figure 2 The figure shows the principle diagram of the coupled piston effect caused by the misalignment of the rotation axis and the reflection center. Point O is the rotation axis of the test mass, A1 and A2 are the reflection centers of the test mass at different rotation angles, and d lat is the lateral distance between the axis of rotation and the reflection point, d long is the longitudinal distance between the axis of rotation and the reflection point. When the offset angles are small, the coupling result OPD ( ) can be expressed as:

[0034]

[0035] Among them, there are first-order and second-order terms in the coupling according to the change of the rotation angle.

[0036] Currently, an imaging system can be used to suppress angle-length coupling. The principle is to image the rotation axis of the test mass at the center of the detector. According to the Fermat principle, the optical path reaching the detector at different rotation angles is the same, thus suppressing angle-length coupling. However, a single imaging system can only suppress second-order coupling and has poor effect on first-order coupling. The only way to suppress this is by adding the first-order term coefficients, such as the offset position d lat and corners This is done by setting the parameters to zero as much as possible, which requires precise calculation and is not easy to achieve. In other words, existing laser interferometers are not very effective in suppressing angle-length coupled noise.

[0037] In view of this, an embodiment of the present application provides a laser interferometer that can effectively suppress angle-length coupling noise.

[0038] In an exemplary embodiment, Figure 3 As shown, the laser interferometer for suppressing angle-length coupling noise includes a light source structure 310 , an offset structure 320 , a detection structure 330 and a control device 340 , and the control device 340 is connected to the light source structure 310 , the offset structure 320 and the detection structure 330 .

[0039] Optionally, the light source structure 310 is used to emit a laser beam under the control of the control device 340 .

[0040] Optionally, the light source structure 310 may include a laser, an optical isolator, a fiber coupler, a polarization-maintaining single-mode fiber, a fiber collimator, and a polarizer. The polarization-maintaining single-mode fiber is used for optical filtering, and the polarizer is used to adjust the laser beam into polarized light, which can facilitate subsequent optical path processing. For example, the polarizer can adjust the laser beam to p-polarization.

[0041] Illustratively, the light source structure can emit a collimated fundamental mode Gaussian beam with a specific polarization. The embodiment of the present application does not limit the wavelength of the laser beam and can be determined according to actual conditions. For example, when performing gravitational wave detection, the emitted laser beam can be a continuous laser with a wavelength of 1064 nm.

[0042] Optional, such as Figure 3 As shown, the laser interferometer further includes a beam splitter cube 350, which is disposed between the light source structure and the offset structure. The beam splitter cube is used to split the laser beam emitted by the light source structure into a reflected beam and a transmitted beam, and to allow the reflected beam to enter the offset structure.

[0043] A beamsplitter cube is an optical component that splits an incident light beam into two beams of a specific ratio. It consists of two right-angle prisms, one of which has a beam-splitting coating on its inclined surface, and the two prisms are then cemented together.

[0044] Optionally, the beam splitter cube can be divided into a non-polarization beam splitter cube and a polarization beam splitter cube. In the embodiment of the present application, the beam splitter cube is taken as an example as a non-polarization beam splitter cube, which can split the laser beam into a reflected beam and a transmitted beam.

[0045] Optionally, the offset structure 320 includes a test mass 10 , which is disposed on an outgoing optical path of the laser beam and can reflect the laser beam. The test mass 10 can rotate under the drive of the control device 340 .

[0046] Optional, such as Figure 3 As shown, taking the laser beam as p-polarized light as an example, the offset structure 320 further includes a half-wave plate 321, a polarization beam splitter cube 322, a quarter-wave plate 323 and a reflector 324. The polarization beam splitter cube 322 can reflect s-polarized light and transmit p-polarized light.

[0047] For example, Figure 3 As shown, in the embodiment of the present application, the optical path of the laser beam in the offset structure 320 can be: after the laser beam passes through the beam splitter cube 350, the corresponding reflected light beam enters the offset structure 320, and is converted into s-polarized light through the half-wave plate 321, and then reflected by the polarization beam splitter cube 322, passes through the 1 / 4 wave plate 323 to the test mass 10, and is reflected by the test mass 10 and passes through the 1 / 4 wave plate 323 again. At this time, since the laser beam passes through the 1 / 4 wave plate 323 twice, it is converted into p-polarized light, is transmitted through the polarization beam splitter cube 322 to reach the reflector 324, and enters the detection structure 330 after being reflected by the reflector 324.

[0048] The control device 340 can perform sinusoidal modulation of a certain amplitude on the test mass 10. , so that the test mass can rotate at a specific frequency.

[0049] Optionally, the detection structure 330 includes a laser beam combining element 331 , a noise suppression structure, and a first photodetector 332 .

[0050] Among them, the laser beam combining element 331 is arranged on the optical path of the reflected laser beam, and is used to combine the reflected laser beam to obtain a first combined laser beam. The noise suppression structure is arranged on the optical path of the first combined laser beam, and is used to suppress the noise of the first combined laser beam to obtain a second combined laser beam. The first photodetector 332 is used to receive the second combined laser beam and perform photoelectric conversion on the second combined laser beam to obtain a first detection result.

[0051] Optional, such as Figure 3 As shown, the noise suppression structure includes an imaging system 333 and an angle deflection system 334 .

[0052] For example, Figure 3As shown, the optical path of the laser beam in the detection structure 330 is: the laser beam entering the detection structure 330 is combined by the laser beam combining element 331 to obtain a first combined laser beam, the first combined laser beam is transformed into a second combined laser beam after passing through the imaging system 333 and the angle deflection system 334, and the second combined laser beam is received by the first photodetector 332.

[0053] Optionally, the imaging system 333 is used to image the rotation axis of the test mass 10 at the center of the first photodetector 332. At this time, due to the Fermat principle, the displacement change caused by the angle offset is the same as when there is no offset, and the noise signal can be suppressed. That is, the optical path of the light beams with different rotation angles reaching the first photodetector remains unchanged. In this way, even if the test mass shakes at an angle, the optical path will not change, and thus no additional noise signal will be introduced.

[0054] Exemplarily, the imaging system can be a dual-lens imaging system or a four-lens imaging system, for example, a dual-lens imaging system composed of a convex lens and a concave lens, a dual-lens imaging system composed of a double convex lens, or a four-lens imaging system composed of a convex lens-concave lens-concave lens-convex lens. The embodiments of the present application do not limit this.

[0055] Optionally, the angle deflection system 334 can produce an angle offset for the first combined laser beam to compensate for the beam position offset caused by the angle offset of the rotation of the test mass, thereby adjusting the first-order coupling coefficient to zero and effectively suppressing the first-order angle-length coupling noise.

[0056] Optionally, the control device 340 is configured to adjust the noise suppression structure according to the first detection result until the first detection result meets a preset requirement.

[0057] The first detection result may be a noise signal, and the preset requirement may be that the noise signal is minimized.

[0058] Optionally, the imaging system 333 and the angle deflection system 334 can be adjusted according to the first noise signal, and the first detection results corresponding to the adjusted imaging system 333 and the angle deflection system 334 can be repeatedly obtained, so that the angle-length coupling noise can be accurately and effectively suppressed.

[0059] The above-mentioned laser interferometer and noise suppression method for suppressing angle-length coupling noise include a light source structure, an offset structure, a detection structure and a control device, and the control device is connected to the light source structure, the offset structure and the detection structure; the light source structure is used to emit a laser beam under the control of the control device; the offset structure includes a test mass, the test mass is arranged on the output optical path of the laser beam, and can reflect the laser beam, and the test mass can rotate under the drive of the control device; the detection structure includes a laser beam combining element, a noise suppression structure and a first photodetector; wherein, the laser beam combining element is arranged on the optical path of the reflected laser beam, and is used to combine the reflected laser beam to obtain a first combined laser beam, the noise suppression structure is arranged on the optical path of the first combined laser beam, and is used to suppress the noise of the first combined laser beam to obtain a second combined laser beam, and the first photodetector is used to receive the second combined laser beam and perform photoelectric conversion on the second combined laser beam to obtain a first detection result; the control device is used to adjust the noise suppression structure according to the first detection result until the first detection result meets the preset requirements. By controlling the rotation of the test mass, the laser beam passing through the test mass undergoes angular or axial displacement, thereby generating a change in optical path and introducing noise signals. The noise suppression structure includes an imaging system and an angle deflection system. Through the imaging system, even if the test mass vibrates, the optical path of the laser beam reaching the first photodetector does not change, effectively suppressing the noise signal of the first combined laser beam. The angle deflection system adjusts the angle at which the laser beam enters the first photodetector to compensate for the beam position offset caused by the angular displacement of the test mass, further suppressing the noise signal. At the same time, by continuously adjusting the noise suppression structure based on the noise suppression results, the noise suppression effect can be effectively improved.

[0060] In an exemplary embodiment, Figure 3 As shown, optionally, the angle deflection system 334 includes two rotatable optical wedges and an optical plate adjustable in multiple degrees of freedom, the two rotatable optical wedges are used to generate deflection at any angle within a certain cone angle in space; the optical plate adjustable in multiple degrees of freedom is used to compensate for the position offset caused by the angular offset of the first combined laser beam; the imaging system 333 includes a convex lens and a concave lens, and the imaging system is used to image the rotation axis of the test mass at the center of the first photodetector.

[0061] Optional, such as Figure 4 As shown, it is a schematic diagram of the optical path of the laser beam after passing through the test mass and the noise suppression structure. The two laser beams are combined by the laser beam combining element 331 to form heterodyne interference, where one laser beam 41 is reflected by the test mass 10, and the other laser beam 42 is not reflected by the test mass 10.

[0062] Due to the rotation of the test mass 10, 401 is the optical path of the first combined laser beam incident on the first photodetector 332 without passing through the noise suppression structure, and additional angle-length coupling will be generated at this time; 402 is the optical path of the second combined laser beam incident on the first photodetector 332 after only passing through the imaging system 333. At this time, light beams of different angles can all reach the center of the first photodetector 332 through the same optical path, and the noise signal can be suppressed; 403 is the optical path of the second combined laser beam incident on the first photodetector 332 after passing through the imaging system 333 and the angle deflection system 334. At this time, light beams of different angles can all reach the center of the first photodetector 332 through the same optical path, and at the same time, a beam inclination will be formed when incident on the first photodetector 332, which is used to compensate for the beam position offset caused by the angular offset of the laser beam due to the rotation of the test mass. In this way, the first-order coupling coefficient can be adjusted to zero, and the first-order angle-length coupling noise can be effectively suppressed.

[0063] In an exemplary embodiment, optionally, the first photodetector 332 is a four-quadrant detector, and the control device 340 includes a signal generating unit, a phase-locked amplifier and an adjustment structure; the signal generating unit is used to generate a displacement signal based on a displacement signal generating method and a first detection result, and the displacement signal generating method is a four-channel signal arithmetic averaging method or a four-channel signal weighted averaging method; the phase-locked amplifier is used to demodulate the displacement signal and determine the phase-locked amplification result; the adjustment structure is used to adjust the noise suppression structure according to the phase-locked amplification result.

[0064] A four-quadrant detector is a photoelectric detection device consisting of four photodiodes with identical performance arranged in rectangular coordinates. It converts incident light signals into electrical signals and determines the position and intensity of the incident light by comparing the output signals of the four quadrants.

[0065] Optionally, the displacement signal LPS is determined by the arithmetic average method of the four signals AP It can be expressed by the following formula:

[0066]

[0067] in, to They are the output signals of the four quadrants of the first photodetector respectively.

[0068] Optionally, the displacement signal LSP is determined by the weighted average method of the four-way signal LPF It can be expressed by the following formula:

[0069]

[0070] in, to are the weighting parameters of the output signals of the four quadrants of the first optical detector.

[0071] The process of adjusting the noise suppression structure according to the phase-locked amplification result is described in detail below.

[0072] Optionally, a phase-locked amplifier is specifically used to perform double frequency demodulation on the displacement signal to determine a first phase-locked amplification result; an adjustment structure is specifically used to adjust the axial position and imaging system of the first photodetector according to the first phase-locked amplification result until the first phase-locked amplification result is minimized.

[0073] Optionally, the lock-in amplifier's process for performing double-frequency demodulation on the displacement signal may include: modulating the displacement signal onto a carrier of known frequency to form a modulated signal; due to some physical mechanism, a signal also exists at double the carrier frequency; setting the lock-in amplifier's reference frequency to double the carrier frequency; multiplying the doubled frequency signal by the reference signal; and removing high-frequency components through a low-pass filter to obtain a demodulated DC signal. The reference signal has the same frequency as the displacement signal.

[0074] Optionally, the first phase-locked amplification result may include the amplitude of the demodulated DC signal, and the amplitude may represent the amplitude of the displacement signal.

[0075] Optionally, the adjustment structure can adjust the axial position and imaging system of the first photodetector according to the first phase-locked amplification result, and then reacquire the displacement signal and the first phase-locked amplification result after the phase-locked amplifier performs double frequency demodulation on the displacement signal. When the first phase-locked amplification result is minimum, it indicates that the axis of rotation of the test mass is imaged at the center of the first photodetector, and the second-order angle-length coupling noise can be effectively suppressed at this time.

[0076] Optionally, a phase-locked amplifier is specifically used to perform one-time frequency demodulation on the displacement signal to determine a second phase-locked amplification result; an adjustment structure is specifically used to adjust the angles of the two rotatable optical wedges in the angle deflection system 334 according to the second phase-locked amplification result until the second phase-locked amplification result is minimized.

[0077] Optionally, the process of the phase-locked amplifier demodulating the displacement signal by one frequency can include: modulating the displacement signal onto a carrier of a known frequency to form a modulation signal; the phase-locked amplifier multiplies the modulation signal with the reference signal, removes the high-frequency components through a low-pass filter, and obtains a demodulated DC signal.

[0078] Optionally, the second phase-locked amplification result may include the amplitude of the demodulated DC signal, and the amplitude may represent the amplitude of the displacement signal.

[0079] Optionally, the adjustment structure can adjust the angles of the two rotatable optical wedges in the angle deflection system 334 according to the second phase-locked amplification result, and then reacquire the displacement signal and the second phase-locked amplification result after the phase-locked amplifier demodulates the displacement signal by one frequency. When the second phase-locked amplification result is minimum, it indicates that the beam position offset caused by the angular offset of the laser beam due to the rotation of the test mass has been effectively compensated, thereby suppressing the first-order angle-length coupling noise.

[0080] Optionally, the adjustment structure is further configured to adjust the optical plate in the angle deflection system 334 according to the difference between the amplitudes of the four quadrant signals corresponding to the first detection result, until the difference between the amplitudes of the four quadrant signals corresponding to the first detection result meets a preset difference threshold.

[0081] The preset difference threshold is relatively small so that the amplitudes of the signals in the four quadrants are substantially the same.

[0082] Optionally, by adjusting the optical plate in the angle deflection system 334 so that the amplitudes of the four quadrant signals are approximately the same, when the laser beam is incident on the first photodetector, the spot position is the center position of the first photodetector, which can further suppress noise.

[0083] In an exemplary embodiment, the control device 340 further includes an oscilloscope, a phase meter, and a laser frequency stabilization unit. The oscilloscope is used to display the signal obtained by the first photodetection unit; the phase meter is used to calculate the phase of the heterodyne signal. The phase meter uses a phase-locked loop (PLL) phase meter design, which closely tracks phase changes as the phase changes. The laser frequency stabilization unit is used to stabilize the laser in the light source structure 310. It can lock the laser to a cavity or a molecular absorption line to form a stabilized laser, and can also lock one laser beam to another during laser light combination processing.

[0084] In an exemplary embodiment, Figure 3 As shown, the laser beam combining element 331 is a beam combining cube, which is used to combine the laser beam emitted by the offset structure 320 with another laser beam. The other laser beam is a modulated laser beam with a certain frequency difference emitted by the light source structure 310, or a laser beam emitted by other laser interferometers.

[0085] Optionally, when the other laser beam is a laser beam emitted by another laser interferometer, the laser interferometer has the same structure as the laser interferometer in the embodiment of the present application, and the other laser beam can be a transmitted beam of the laser beam emitted by the light source structure in the other laser interferometer after passing through the beam splitting cube.

[0086] Optionally, the current laser interferometer is the master interferometer, and the other laser interferometer is the slave interferometer. The laser frequency stabilization unit of the master interferometer is used to lock the laser to the molecular absorption spectrum or the ultra-stable cavity to form a stabilized laser, and the laser frequency stabilization unit of the slave interferometer is used to lock the slave laser beam to the master laser beam to form a responsive interferometer. At this time, the angle-length coupling noise on the slave interferometer can also be observed in the control device 340 of the master interferometer.

[0087] In an exemplary embodiment, Figure 3 As shown, the detection structure 330 also includes a second photodetector 335, which is used to perform photoelectric conversion on the first combined laser beam to obtain a second detection result; the control device 340 is also used to compare the first detection result with the second detection result.

[0088] Optionally, the optical signal received by the second photodetector 335 is an optical signal that has not passed through the noise suppression structure. The optical signal is converted into an electrical signal by the second photodetector 335, that is, a second detection result. By comparing the first detection result and the second detection result, the suppression effect of the noise suppression structure can be compared.

[0089] Optionally, a sinusoidally modulated signal can be used to drive the test mass 10, and the coupling coefficient, that is, the derivative of the coupling displacement with respect to the angular displacement of the test mass 10, can be determined based on the first detection result and the second detection result. Alternatively, the displacement signal can be modulated by a specific angle noise signal to drive the test mass 10, and the reduction of the noise floor can be determined based on the first detection result and the second detection result.

[0090] It is understood that the embodiments of the present application also provide a noise suppression method. The implementation solution provided by this method is similar to the implementation solution described in the above-mentioned laser interferometer. Therefore, the specific limitations in the noise suppression method embodiment provided below can be referred to the limitations of the laser interferometer above and will not be repeated here.

[0091] In an exemplary embodiment, a noise suppression method is provided, which is applied to the laser interferometer for suppressing angle-length coupling noise described in any of the above embodiments, such as Figure 5 As shown, the noise suppression method includes the following steps:

[0092] Step 501: Control the light source structure to emit a laser beam.

[0093] Optionally, the laser frequency stabilization can be performed by a laser frequency stabilization unit in the control device. If it is on the main satellite of the gravitational wave interferometer, that is, when it serves as a main interferometer, the laser frequency stabilization unit can lock the laser to the molecular absorption spectrum line or the ultra-stable cavity. If it is on the slave satellite of the gravitational wave interferometer, that is, when it serves as a slave satellite, the laser frequency stabilization unit can lock the slave laser to the main laser. Optionally, the locking uses a phase table to generate a phase error signal and uses PI control to perform locking.

[0094] Optionally, the control device may adjust the polarizer in the light source structure to make the outgoing laser beam p-polarized.

[0095] Step 502: Control the rotation of the test mass in the offset structure so that the laser beam passing through the test mass generates angular displacement or axial linear displacement.

[0096] Optionally, the control device can adjust the half-wave plate and the quarter-wave plate in the offset structure so that the laser beam passing through the half-wave plate is s-polarized and finally emerges as p-polarized after passing through the quarter-wave plate twice.

[0097] Optionally, the test quality can be sinusoidally modulated with a certain amplitude , controlling the rotation of the test mass in the offset structure so that the laser beam passing through the test mass produces angular displacement or axial linear displacement.

[0098] Step 503: Adjust the laser beam combining element so that the laser beam that has passed the test quality is combined with another laser beam to generate a first combined laser beam, perform noise suppression on the first combined laser beam according to the noise suppression structure, determine the second combined laser beam, perform photoelectric conversion on the second combined laser beam according to the first photoelectric sensor, and determine the first detection result.

[0099] Optionally, the control device may adjust the laser beam combining element to combine the laser beam reflected by the test mass and another laser beam to generate heterodyne interference, thereby obtaining a first combined laser beam.

[0100] Optionally, the first photodetector is a four-quadrant detector, and the control device also needs to adjust the positions of the imaging system and the first photodetector to obtain approximately the same amplitude of the four signals.

[0101] For example, the amplitudes of the four-channel signals may be determined by an oscilloscope and a phase meter in the control device.

[0102] Step 504: Adjust the noise suppression structure according to the first detection result until the first detection result meets the preset requirement.

[0103] Optionally, the first detection result may be a noise signal, and the preset requirement may be that the noise signal is minimized.

[0104] Optionally, the control device can generate a displacement signal based on a displacement signal generation method and a first detection result, the displacement signal generation method being a four-channel signal arithmetic averaging method or a four-channel signal weighted averaging method, and then demodulate the displacement signal based on the phase-locked amplifier in the control device to determine the phase-locked amplification result, and then adjust the noise suppression structure according to the phase-locked amplification result through the adjustment structure in the control device. The embodiments of the present application will not be repeated here.

[0105] Optionally, the adjustment structure can adjust the axial position and imaging system of the first photodetector according to the first phase-locked amplification result, and then reacquire the displacement signal and the first phase-locked amplification result after the phase-locked amplifier performs double frequency demodulation on the displacement signal. When the first phase-locked amplification result is minimum, it indicates that the axis of rotation of the test mass is imaged at the center of the first photodetector, and the second-order angle-length coupling noise can be effectively suppressed at this time.

[0106] Optionally, the adjustment structure can adjust the angles of the two rotatable optical wedges in the angle deflection system according to the second phase-locked amplification result, and then reacquire the displacement signal and the second phase-locked amplification result after the phase-locked amplifier demodulates the displacement signal by one frequency. When the second phase-locked amplification result is minimum, it indicates that the beam position offset caused by the angular offset of the laser beam due to the rotation of the test mass has been effectively compensated, thereby suppressing the first-order angle-length coupling noise.

[0107] Optionally, the adjustment structure can also adjust the optical plate in the angle deflection system based on the differences in the amplitudes of the four quadrant signals corresponding to the first detection result until the amplitudes of the four quadrant signals corresponding to the first detection result are approximately the same. In this case, when the laser beam enters the first photodetector, the spot position is at the center of the first photodetector, further suppressing noise.

[0108] In an exemplary embodiment, the noise suppression method further includes performing photoelectric conversion on the first combined laser beam according to a second photoelectric sensor, determining a second detection result, and comparing the first detection result with the second detection result.

[0109] In the description of this specification, reference to the terms "some embodiments" or "other embodiments" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example.

[0110] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0111] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A laser interferometer for suppressing angle-length coupling noise, characterized in that: The laser interferometer includes a light source structure, an offset structure, a detection structure and a control device, wherein the control device is connected to the light source structure, the offset structure and the detection structure; The light source structure is used to emit a laser beam under the control of the control device; The offset structure includes a test mass, which is arranged on the outgoing optical path of the laser beam and can reflect the laser beam. The test mass can rotate under the drive of the control device; The detection structure includes a laser beam combining element, a noise suppression structure and a first photodetector; The laser beam combining element is provided on the optical path of the reflected laser beam, and is used to combine the reflected laser beam to obtain a first combined laser beam. The noise suppression structure is provided on the optical path of the first combined laser beam, and is used to suppress the noise of the first combined laser beam to obtain a second combined laser beam. The first photodetector is used to receive the second combined laser beam and perform photoelectric conversion on the second combined laser beam to obtain a first detection result. The control device is used to adjust the noise suppression structure according to the first detection result until the first detection result meets a preset requirement.

2. The laser interferometer according to claim 1, wherein: The noise suppression structure includes an imaging system and an angle deflection system. The angle deflection system includes two rotatable optical wedges and an optical plate adjustable in multiple degrees of freedom. The two rotatable optical wedges are used to generate deflection at any angle within a certain cone angle in space. The optical flat plate capable of being adjusted with multiple degrees of freedom is used to compensate for positional deviation caused by angular deviation of the first combined laser beam; The imaging system is used to image the rotation axis of the test mass at the center of the first photodetector.

3. The laser interferometer according to any one of claims 1 or 2, characterized in that: The first photodetector is a four-quadrant detector, and the control device includes a signal generating unit, a lock-in amplifier and an adjustment structure; The signal generating unit is configured to generate a displacement signal based on a displacement signal generating method and the first detection result, wherein the displacement signal generating method is a four-channel signal arithmetic averaging method or a four-channel signal weighted averaging method; The lock-in amplifier is used to demodulate the displacement signal and determine the lock-in amplification result; The adjustment structure is used to adjust the noise suppression structure according to the phase-locked amplification result.

4. The laser interferometer according to claim 3, characterized in that The lock-in amplifier is specifically used to perform double frequency demodulation on the displacement signal to determine a first lock-in amplification result; The adjustment structure is specifically used to adjust the axial position of the first photodetector and the imaging system according to the first phase-locked amplification result until the first phase-locked amplification result is minimum.

5. The laser interferometer according to claim 3, characterized in that: The lock-in amplifier is specifically used to perform one-time frequency demodulation on the displacement signal to determine a second lock-in amplification result; The adjustment structure is specifically used to adjust the angles of the two rotatable optical wedges in the angle deflection system according to the second phase-locked amplification result until the second phase-locked amplification result is minimized.

6. The laser interferometer according to claim 5, characterized in that The adjustment structure is further configured to adjust the optical plate in the angle deflection system according to the difference between the amplitudes of the four quadrant signals corresponding to the first detection result, until the difference between the amplitudes of the four quadrant signals corresponding to the first detection result meets a preset difference threshold.

7. The laser interferometer according to claim 1, characterized in that The detection structure further includes a second photodetector, wherein the second photodetector is configured to perform photoelectric conversion on the first combined laser beam to obtain a second detection result; The control device is further configured to compare the first detection result with the second detection result.

8. A noise suppression method, characterized in that: The method is applied to the laser interferometer for suppressing angle-length coupling noise according to any one of claims 1 to 7, comprising: Controlling the light source structure to emit a laser beam; Controlling the rotation of the test mass in the offset structure to cause an angular displacement or an axial linear displacement of the laser beam passing through the test mass; adjusting a laser beam combining element to combine the laser beam having the test quality with another laser beam to generate a first combined laser beam, performing noise suppression on the first combined laser beam according to a noise suppression structure, determining a second combined laser beam, performing photoelectric conversion on the second combined laser beam according to a first photoelectric sensor, and determining a first detection result; The noise suppression structure is adjusted according to the first detection result until the first detection result meets a preset requirement.

9. The method according to claim 8, characterized in that The first photodetector is a four-quadrant detector, and the adjusting the noise suppression structure according to the first detection result includes: generating a displacement signal based on a displacement signal generating method and the first detection result, wherein the displacement signal generating method is a four-channel signal arithmetic average method or a four-channel signal weighted average method; Demodulating the displacement signal to determine a phase-locked amplification result; The noise suppression structure is adjusted according to the phase-locked amplification result.

10. The method according to claim 9, characterized in that The method further comprises: performing photoelectric conversion on the first combined laser beam according to a second photoelectric sensor to determine a second detection result; The first detection result is compared with the second detection result.

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