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

Abstract

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

Description

Technical Field

[0001] This application relates to the field of laser interferometer technology, and in particular to a laser interferometer and a noise suppression method for suppressing angle-length coupling noise. Background Technology

[0002] When gravitational waves pass through, the distance between the test masses in the space-based gravitational wave detection satellite array changes. The laser interferometer reads this distance change and thus retrieves the gravitational wave signal. In space, satellites are subject to jitter due to non-conservative forces such as sporadic celestial events, solar radiation, cosmic rays, and interstellar magnetic fields. The test masses, however, are placed in a drag-free control system simulating a situation where they are not acted upon by any force other than gravity. In this case, the forces acting on the satellite and the test masses are inconsistent, causing jitter in the test masses. This jitter leads to an angular tilt in the measurement laser beam reflected from the test masses, introducing additional longitudinal optical path signals and generating angular coherent interference effects, i.e., angle-length coupling noise. Existing research indicates that among various noises affecting the accuracy of laser interferometry, angle-length coupling noise is the second largest noise source after shot noise.

[0003] Existing laser interferometers are not effective at suppressing angle-length coupled noise. Summary of the Invention

[0004] Therefore, it is necessary to provide a laser interferometer that can effectively suppress angle-length coupling noise in response to the above-mentioned technical problems.

[0005] In a first aspect, this application provides a laser interferometer for suppressing angle-length coupling noise. The laser interferometer includes a light source structure, an offset structure, a detection structure, and a control device. The control device is connected to the light source structure, the offset structure, and the detection structure. The light source structure emits a laser beam under the control of the control device. The offset structure includes a test mass positioned on the output optical path of the laser beam, capable of reflecting 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 positioned on the optical path of the reflected laser beam to perform beam combining processing to obtain a first combined laser beam. The noise suppression structure is positioned on the optical path of the first combined laser beam to perform noise suppression on the first combined laser beam to obtain a second combined laser beam. The first photodetector receives the second combined laser beam and performs photoelectric conversion on it to obtain a first detection result. The control device adjusts the noise suppression structure according to the first detection result until the first detection result meets a preset requirement.

[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 a multi-degree-of-freedom adjustable optical plate. The two rotatable optical wedges are used to generate deflection at any angle within a certain cone angle in space. The multi-degree-of-freedom adjustable optical plate is used to compensate for the positional offset caused by the angular offset of the first combined laser beam. The imaging system is used to image the rotation axis of the test quality 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 generation unit, a lock-in amplifier, and an adjustment structure. The signal generation unit is used to generate a displacement signal based on a displacement signal generation method and a first detection result. The displacement signal generation method is either a four-channel arithmetic average method or a four-channel weighted average 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 lock-in amplification result.

[0008] In one embodiment, the lock-in amplifier is specifically used to perform frequency doubling demodulation on the displacement signal to determine the 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 lock-in amplification result until the first lock-in amplification result is minimized.

[0009] In one embodiment, the lock-in amplifier is specifically used to perform first-harmonic demodulation on the displacement signal to determine the 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 lock-in amplification result until the second lock-in 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; the control device is also used to compare the first detection result with the second detection result.

[0012] Secondly, this application also provides a noise suppression method, comprising:

[0013] The system controls the laser beam emitted from the light source structure; it controls the rotation of the test mass in the offset structure to cause the laser beam passing through the test mass to produce angular or axial linear displacement; it adjusts the laser beam combining element to combine the laser beam passing through the test mass with another laser beam to generate a first combined laser beam; it performs noise suppression on the first combined laser beam according to the noise suppression structure to determine a second combined laser beam; it performs photoelectric conversion on the second combined laser beam according to the first photoelectric sensor to determine a first detection result; and it adjusts 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. The displacement signal generation method is either a four-signal arithmetic average method or a four-signal weighted average method. The displacement signal is demodulated to determine the phase-locked amplification result. 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 based on the second photoelectric sensor to determine a second detection result; and comparing the first detection result with the second detection result.

[0016] The aforementioned laser interferometer and noise suppression method for suppressing angle-length coupling noise includes a light source structure, an offset structure, a detection structure, and a control device. The control device is connected to the light source structure, the offset structure, and the detection structure. The light source structure emits a laser beam under the control of the control device. The offset structure includes a test mass, which is positioned on the output 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 positioned 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 positioned on the optical path of the first combined laser beam and is used to suppress noise in the first combined laser beam to obtain a second combined laser beam. The first photodetector receives the second combined laser beam and performs photoelectric conversion on it to obtain a first detection result. The control device adjusts the noise suppression structure according to the first detection result until the first detection result meets a preset requirement. By controlling the rotation of the test mass, the laser beam passing through the test mass will produce angular displacement or axial linear displacement, thereby generating optical path change and introducing noise signal. The noise suppression structure suppresses the noise of the first combined laser beam. At the same time, by continuously adjusting the noise suppression structure according to the noise suppression results, the noise suppression effect can be effectively improved. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments or related technologies of this application, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram illustrating the principle of the angle-length coupling lever effect in a laser interferometer.

[0019] Figure 2 This is a schematic diagram illustrating the principle of the angle-length coupled piston effect in a laser interferometer.

[0020] Figure 3 This is a schematic diagram of a laser interferometer for suppressing angle-length coupling noise in one embodiment;

[0021] Figure 4 This is a schematic diagram comparing the optical paths of a laser beam in a laser interferometer in one embodiment;

[0022] Figure 5 This is a flowchart illustrating a noise suppression method in one embodiment.

[0023] Explanation of reference numerals in the attached figures:

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

[0025] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0027] It is 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 one element from another. For example, without departing from the scope of this application, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0028] It is understood that the term "connection" in the following embodiments should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have electrical signal or data transmission with each other.

[0029] It is understandable that "at least one" refers to one or more, and "multiple" refers to two or more. "At least a part of an element" refers to part or all of an element.

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

[0031] When gravitational waves pass through, the distance between test masses in a gravitational wave detection satellite changes. A laser interferometer reads this distance change and thus retrieves the gravitational wave signal. The test mass is the object used for measurement or testing in the experiment. It can be a mirror, a sample, or any other object requiring precise measurement. In gravitational wave detectors, optical interferometers, or precision measurement experiments, the test mass is the target object whose displacement needs to be precisely measured.

[0032] In space, satellites are subject to jitter due to non-conservative forces such as celestial events, solar radiation, cosmic rays, and interstellar magnetic fields. The test mass, however, is placed in a drag-free control system simulating a situation where it is not acted upon by any force other than gravity. In this case, the forces acting on the satellite and the test mass are inconsistent, causing jitter in the test mass. This jitter leads to an angular tilt in the measurement laser beam reflected from the test mass, introducing additional longitudinal optical path signals and generating angular coherent interference effects, i.e., angle-length coupling noise. Existing research shows that among various noises affecting the accuracy of laser interferometry, angle-length coupling noise is the second largest noise source after shot noise. Its essence is that changes in the beam's angle cause changes in its length, even though the system may not have undergone any displacement change. Coupling noise caused solely by changes in geometric relationships is called geometric angle-length coupling noise.

[0033] Geometric angle-length coupling noise can be divided into the "lever effect" of coupling 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. For example... Figure 1 The diagram shows the principle of the coupling lever effect caused by the coincidence of the rotation axis and the reflection center. Point A represents the rotation axis and reflection center of the test quality, and S represents the light source. Let AB1 represent the distance from the reflection point of the test mass 10 to the photosensitive surface 20 of the photodetector, and AB2 represent the distance from the reflection center to the photosensitive surface 20 of the photodetector after the test mass has rotated by an angle γ around its axis. The distance from the reflection center to the photosensitive surface 20 of the photodetector can be represented by d. level Unified representation, Let be the tilt angle of the photosensitive surface 20 of the photodetector, where the coupling lever effect can be determined by AB2-AB1. For example... Figure 2 The diagram illustrates the coupling piston effect caused by the misalignment of the rotation axis and the reflection center. Point O represents the rotation axis of the test mass, and A1 and A2 represent the reflection centers of the test mass at different rotation angles. lat d is the lateral distance between the axis of rotation and the reflection point. long is the longitudinal distance between the rotation axis and the reflection point. When all offset angles are small, the coupling result OPD caused by these two effects is... This can be represented as:

[0034]

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

[0036] Currently, imaging systems can be used to suppress angle-length coupling. The principle is that the rotation axis of the test mass is imaged onto the center of the detector. According to Fermat's principle, the optical path reaching the detector is the same regardless of the rotation angle, thus suppressing angle-length coupling. However, a standalone imaging system can only suppress second-order coupling; its effect on first-order coupling is poor, and it can only suppress it by adjusting the first-order coefficients, such as by adjusting the offset position d. lat and corner This can be achieved by setting the parameters to zero as much as possible, but this requires precise calculations and is not easy to implement. In other words, existing laser interferometers are not very effective at suppressing angle-length coupled noise.

[0037] In view of this, embodiments of this application provide a laser interferometer that can effectively suppress angle-length coupling noise.

[0038] In one exemplary embodiment, such as 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. 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, an optical fiber coupler, a polarization-maintaining single-mode fiber, an optical 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 to polarized light, which can facilitate subsequent optical path processing. For example, the polarizer can adjust the laser beam to p-polarization.

[0041] For example, the light source structure can emit a collimated fundamental mode Gaussian beam with a specific polarization. The wavelength of the laser beam is not limited in the embodiments of this application and can be determined according to the actual situation. For example, when performing gravitational wave detection, the emitted laser beam can be a continuous laser with a wavelength of 1064nm.

[0042] Optional, such as Figure 3 As shown, the laser interferometer also 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 from the light source structure into a reflected beam and a transmitted beam, and to make the reflected beam enter the offset structure.

[0043] A beam splitter cube is an optical element that splits an incident light beam into two beams with a specific ratio. A beam splitter cube consists of two right-angle prisms, one of which has a beam-splitting film coated on its inclined surface, and the two prisms are then glued together.

[0044] Optionally, the beam splitter cube can be divided into a non-polarized beam splitter cube and a polarized beam splitter cube. In this embodiment, taking the non-polarized beam splitter cube as an example, the laser beam can be divided into a reflected beam and a transmitted beam.

[0045] Optionally, the offset structure 320 includes a test mass 10, which is set in the 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 also 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, such as Figure 3 As shown in the embodiment of this application, the optical path of the laser beam in the offset structure 320 can be as follows: after the laser beam passes through the beam splitter cube 350, the corresponding reflected beam enters the offset structure 320, passes through the half-wave plate 321 and is converted into s-polarized light, then is reflected by the polarization beam splitter cube 322, passes through the quarter-wave plate 323 to the test quality 10, is reflected by the test quality 10 and passes through the quarter-wave plate 323 again. At this time, since the laser beam passes through the quarter-wave plate 323 twice, it is converted into p-polarized light, passes through the polarization beam splitter cube 322 and reaches the reflector 324, and after being reflected by the reflector 324, it enters the detector structure 330.

[0048] The control device 340 can apply a sinusoidal modulation of the test mass 10 to a certain amplitude. In this way, the test quality can be rotated 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] The laser beam combining element 331 is disposed 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 disposed on the optical path of the first combined laser beam and is used to suppress noise in 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, such as Figure 3As shown, the optical path of the laser beam in the detection structure 330 is as follows: the laser beam entering the detection structure 330 is combined by the laser beam combining element 331 to obtain the first combined laser beam. The first combined laser beam is transformed into the second combined laser beam after passing through the imaging system 333 and the angle deflection system 334. 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 Fermat's principle, the displacement change caused by the angle shift is the same as when there is no shift, which can suppress the noise signal. That is, the optical path of the beam reaching the first photodetector at different rotation angles remains unchanged. In this way, even if the test mass experiences angle jitter, the optical path will not change, thus not introducing additional noise signals.

[0054] For example, the imaging system can be a dual-lens imaging system or a four-lens imaging system. For instance, it can be a dual-lens imaging system composed of a convex lens and a concave lens, or a dual-lens imaging system composed of two convex lenses, or a four-lens imaging system composed of a convex lens-concave lens-concave lens-convex lens. The embodiments of this application do not limit this.

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

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

[0057] The first detection result can be a noise signal, and the preset requirement is 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 result corresponding to the adjustment of the imaging system 333 and the angle deflection system 334 can be repeatedly acquired. This can accurately and effectively suppress the angle-length coupling noise.

[0059] The aforementioned laser interferometer and noise suppression method for suppressing angle-length coupling noise includes a light source structure, an offset structure, a detection structure, and a control device. The control device is connected to the light source structure, the offset structure, and the detection structure. The light source structure emits a laser beam under the control of the control device. The offset structure includes a test mass, which is positioned on the output 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 positioned 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 positioned on the optical path of the first combined laser beam and is used to suppress noise in the first combined laser beam to obtain a second combined laser beam. The first photodetector receives the second combined laser beam and performs photoelectric conversion on it to obtain a first detection result. The control device adjusts the noise suppression structure according to the first detection result until the first detection result meets a preset requirement. By controlling the rotation of the test mass, the laser beam passing through the test mass undergoes angular or axial displacement, thereby introducing noise signals due to changes in optical path. The noise suppression structure includes an imaging system and an angle deflection system. Through the imaging system, even when the test mass fluctuates, the optical path of the laser beam reaching the first photodetector remains unchanged, effectively suppressing the noise signal of the first combined laser beam. The angle deflection system adjusts the angle of the laser beam incident on the first photodetector to compensate for the beam position shift caused by the angular deviation of the test mass, further suppressing the noise signal. Simultaneously, by continuously adjusting the noise suppression structure based on the noise suppression results, the noise suppression effect can be effectively improved.

[0060] In one exemplary embodiment, such as Figure 3 As shown, optionally, the angle deflection system 334 includes two rotatable optical wedges and an optical plate adjustable with 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 with multiple degrees of freedom is used to compensate for the positional offset caused by the angle offset of the first combined laser beam. The imaging system 333 includes a convex lens and a concave lens. The imaging system is used to image the rotation axis of the test quality at the center of the first photodetector.

[0061] Optional, such as Figure 4 The diagram shows the optical path of the laser beam after passing through the test quality and noise suppression structure. The two laser beams are combined by the laser beam combining element 331 to form heterodyne interference. One laser beam 41 is reflected by the test quality 10, while the other laser beam 42 is not reflected by the test quality 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, which will generate additional angle-length coupling; 402 is the optical path of the second combined laser beam incident on the first photodetector 332 after passing through the imaging system 333. At this time, beams at different angles can reach the center of the first photodetector 332 through the same optical path, which can suppress the noise signal; 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, beams at different angles can reach the center of the first photodetector 332 through the same optical path. At the same time, a beam tilt angle will be formed when incident on the first photodetector 332, which is used to compensate for the beam position shift caused by the angular shift of the laser beam due to the rotation of the test mass. This can adjust the first-order coupling coefficient to zero and effectively suppress the first-order angle-length coupling noise.

[0063] In one exemplary embodiment, optionally, the first photodetector 332 is a four-quadrant detector, and the control device 340 includes a signal generation unit, a lock-in amplifier, and an adjustment structure; the signal generation unit is used to generate a displacement signal based on a displacement signal generation method and a first detection result, wherein the displacement signal generation method is a four-channel signal arithmetic average method or a four-channel signal weighted average 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 lock-in amplification result.

[0064] The four-quadrant detector is a photoelectric detection device consisting of four identical photodiodes arranged in a Cartesian coordinate system. It converts incident light signals into electrical signals and determines the position and intensity of the incident light by comparing the output signals in the four quadrants.

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

[0066]

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

[0068] Optionally, the displacement signal LSP is determined according to the four-signal weighted average method. LPF This can be expressed by the following formula:

[0069]

[0070] in, to These are the weighted parameters of the output signals in the four quadrants of the first photodetector.

[0071] The following is a detailed explanation of the process of adjusting the noise suppression structure based on the lock-in amplification results.

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

[0073] Optionally, the process of demodulating the displacement signal using a lock-in amplifier (LPA) at its second harmonic frequency can include: modulating the displacement signal onto a carrier wave of a known frequency to form a modulated signal; due to some physical mechanisms, there is also a signal at the second harmonic frequency of the carrier wave; setting the LPA's reference frequency as the second harmonic frequency of the carrier wave; multiplying the second harmonic signal with the reference signal; and removing high-frequency components using a low-pass filter to obtain the demodulated DC signal. Here, the reference signal is a signal with the same frequency as the displacement signal.

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

[0075] Optionally, the adjustment structure can adjust the axial position of the first photodetector and the imaging system 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 frequency doubling demodulation on the displacement signal. When the first phase-locked amplification result is at its minimum, it indicates that the rotation axis image of the test quality is at the center of the first photodetector. At this time, the second-order angle-length coupling noise can be effectively suppressed.

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

[0077] Optionally, the process of demodulating the displacement signal by first-harmonic generation in the lock-in amplifier may include: modulating the displacement signal onto a carrier wave of a known frequency to form a modulated signal; multiplying the modulated signal with a reference signal in the lock-in amplifier; removing high-frequency components by passing a low-pass filter to obtain the demodulated DC signal.

[0078] Optionally, the second phase-locked amplification result may include the amplitude of the demodulated DC signal, which can characterize 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 at its minimum, it indicates that the beam position shift caused by the angular shift of the laser beam due to the rotation of the test quality has been effectively compensated, thereby suppressing the first-order angle-length coupling noise.

[0080] Optionally, the adjustment structure is also used 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 the preset difference threshold.

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

[0082] Optionally, by adjusting the optical plate in the angle deflection system 334, the amplitudes of the signals in the four quadrants are approximately the same. At this time, 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 displays the signal obtained by the first photodetector unit; the phase meter calculates the phase of the heterodyne signal, and the phase meter uses a phase-locked loop (PLL) phase meter design to closely track phase changes during phase transitions; the laser frequency stabilization unit stabilizes the laser in the light source structure 310, and can lock the laser onto the cavity or molecular absorption spectral line to form a frequency-stabilized laser, or lock one laser beam onto another laser beam during laser beam combining.

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

[0085] Optionally, when the other laser beam is a laser beam emitted from another laser interferometer, the laser interferometer has the same structure as the laser interferometer in the embodiments of this application. The other laser beam can be the transmitted beam after the laser beam emitted from the light source structure in the other laser interferometer passes 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 onto the molecular absorption spectral line or the ultra-stable cavity to form a frequency-stabilized laser. The laser frequency stabilization unit of the slave interferometer is used to lock the slave laser beam onto the master laser beam to form a response interferometer. In this case, the angle-length coupling noise on the slave interferometer can also be observed in the control device 340 of the master interferometer.

[0087] In one exemplary embodiment, such as 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 second photodetector 335 converts the optical signal into an electrical signal, which is the 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 quality 10, and the coupling coefficient, i.e. the derivative of the coupled displacement with respect to the angular displacement of the test quality 10, can be determined based on the first and second detection results. Alternatively, a displacement signal modulated by a specific angular noise signal can be used to drive the test quality 10, and the reduction of the noise floor can be determined based on the first and second detection results.

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

[0091] In one exemplary embodiment, a noise suppression method is provided, which is applied to a laser interferometer for suppressing angle-length coupled noise as 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 laser beam emitted from the light source structure.

[0093] Optionally, laser frequency stabilization can be performed using a laser frequency stabilization unit in the control device. If it is on the master satellite of the gravitational wave interferometer, i.e., when it is used as the master interferometer, the laser frequency stabilization unit can lock the laser onto the molecular absorption spectral line or the ultrastable cavity. If it is on the slave satellite of the gravitational wave interferometer, i.e. when it is used as the slave satellite, the laser frequency stabilization unit can lock the slave laser onto the master laser. Optionally, the locking is performed by generating a phase error signal using a phase table and using PI control.

[0094] Optionally, the control device can adjust the polarizer in the light source structure to make the emitted 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 produces angular displacement or axial linear displacement.

[0096] Optionally, the control device can adjust the half-wave plate and quarter-wave plate in the offset structure so that the laser beam passing through the half-wave plate is s-polarized and the final output beam after passing through two quarter-wave plates is p-polarized.

[0097] Optionally, the test quality can be sinusoidally modulated to a certain extent. The test mass in the offset structure is rotated to cause the laser beam passing through the test mass to produce angular or axial displacement.

[0098] Step 503: Adjust the laser beam combining element to combine the laser beam that has passed the quality test 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 to determine the second combined laser beam. Perform photoelectric conversion on the second combined laser beam according to the first photoelectric sensor to determine the first detection result.

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

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

[0101] For example, the amplitude of four signals can be determined using 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 requirements.

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

[0104] Optionally, the control device can generate a displacement signal based on the displacement signal generation method and the first detection result. The displacement signal generation method is either the arithmetic average of four signals or the weighted average of four signals. Then, the displacement signal is demodulated based on the lock-in amplifier in the control device to determine the lock-in amplification result. Then, the noise suppression structure is adjusted according to the lock-in amplification result by the adjustment structure in the control device. The embodiments of this application will not be described in detail here.

[0105] Optionally, the adjustment structure can adjust the axial position of the first photodetector and the imaging system 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 frequency doubling demodulation on the displacement signal. When the first phase-locked amplification result is at its minimum, it indicates that the rotation axis image of the test quality is at the center of the first photodetector. At this time, the second-order angle-length coupling noise can be effectively suppressed.

[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 at its minimum, it indicates that the beam position shift caused by the rotation angle of the laser beam due to the test quality 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 according to the differences between the amplitudes of the signals in the four quadrants corresponding to the first detection result, until the amplitudes of the signals in the four quadrants corresponding to the first detection result are approximately the same. At this time, when the laser beam is incident on the first photodetector, the spot position is at the center position of the first photodetector, which can further suppress noise.

[0108] In an exemplary embodiment, the noise suppression method further includes performing photoelectric conversion on the first combined laser beam based on the 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, references to terms such as "some embodiments," "other embodiments," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.

[0110] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above 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 embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application. Therefore, the protection scope of this application should 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 disposed 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 disposed 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 disposed on the optical path of the first combined laser beam and is used to suppress noise in 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; 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 that can be adjusted with multiple degrees of freedom. The two rotatable optical wedges are used to generate a deflection at any angle within a certain cone angle in space. The optical plate that can be adjusted with multiple degrees of freedom is used to compensate for the positional shift caused by the angle shift of the first combined laser beam. The imaging system is used to image the test quality's rotating axis onto the center of the first photodetector.

2. The laser interferometer according to claim 1, characterized in that, The first photodetector is a four-quadrant detector, and the control device includes a signal generation unit, a lock-in amplifier, and an adjustment structure. The signal generation unit is used to generate a displacement signal based on the displacement signal generation method and the first detection result. The displacement signal generation method is either the arithmetic average of four signals or the weighted average of four signals. 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 lock-in amplification result.

3. The laser interferometer according to claim 2, characterized in that, The lock-in amplifier is specifically used to perform frequency-doubled demodulation on the displacement signal to determine the 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 minimized.

4. The laser interferometer according to claim 2, characterized in that, The lock-in amplifier is specifically used to perform first-harmonic demodulation on the displacement signal to determine the 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.

5. The laser interferometer according to claim 4, characterized in that, The adjustment structure is also used 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.

6. The laser interferometer according to claim 1, characterized in that, 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. The control device is also used to compare the first detection result with the second detection result.

7. A noise suppression method, characterized in that, The method is applied to the laser interferometer for suppressing angle-length coupling noise as described in any one of claims 1 to 6, comprising: Control the laser beam emitted from the light source structure; The test mass in the offset structure is rotated so that the laser beam passing through the test mass produces angular displacement or axial linear displacement. Adjust the laser beam combining element to combine the laser beam that has passed the test quality with another laser beam to generate a first combined laser beam. Suppress the noise of the first combined laser beam according to the noise suppression structure to determine the second combined laser beam. Perform photoelectric conversion on the second combined laser beam according to the first photoelectric sensor to determine the first detection result. The noise suppression structure is adjusted according to the first detection result until the first detection result meets the preset requirements.

8. The method according to claim 7, characterized in that, The first photodetector is a four-quadrant detector, and the adjustment of the noise suppression structure based on the first detection result includes: A displacement signal is generated based on the displacement signal generation method and the first detection result. The displacement signal generation method is either the arithmetic average of four signals or the weighted average of four signals. The displacement signal is demodulated to determine the phase-locked amplification result; The noise suppression structure is adjusted based on the lock-in amplification results.

9. The method according to claim 8, characterized in that, The method further includes: The second detection result is determined by performing photoelectric conversion on the first combined laser beam using the second photoelectric sensor. Compare the first detection result with the second detection result.

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