Coherent stray light measurement device and method for space gravitational wave detection

Abstract

The present invention belongs to the field of optical systems, and specifically relates to a coherent stray light measurement device and method for space gravitational wave detection. The main purpose is to solve the technical problem that the existing stray light measurement device is mainly for incoherent stray light and cannot effectively identify and control coherent stray light. The device includes a laser light source, a first fiber coupler, a second fiber coupler, a first acousto-optic modulator, a second acousto-optic modulator, a first collimator, a second collimator, a third collimator, a first beam splitter, a second beam splitter, a first photodetector, a second photodetector, a third photodetector, a scattering mirror, a phase-locked amplifier and a spectrum analyzer. The present invention can accurately capture and characterize the coherent characteristics of stray light, provide key data support for high-precision interferometric measurement, enable the measuring device to effectively identify and measure coherent stray light, and significantly improve the accuracy and reliability of interferometric measurement.

Description

Technical Field

[0001] The present invention relates to a coherent stray light measuring device and method, and in particular to a coherent stray light measuring device and method for space gravitational wave detection. Background Art

[0002] The Tianqin Project, a space gravitational wave detection project led by my country, aims to detect low-frequency gravitational waves in the frequency range of 0.1mHz to 1Hz through laser interferometry technology. The Tianqin Project uses three satellites to form an equilateral triangle configuration, with each side about 100,000 kilometers, forming a large-scale space interferometer. A Michelson interferometer is formed between the three satellites. Each satellite is a transceiver. Since the light source transmits and receives the same optical path, the backward stray light generated by the transmitting light source will inevitably enter the receiver optical device to produce crosstalk. Part of the stray light has the same or similar phase relationship as the original light beam, that is, coherent stray light. The characteristics of coherent stray light include fixed phase, frequency and amplitude, which enables coherent stray light to interfere with the main beam, resulting in phase shift or instability of the interference signal, which in turn leads to measurement errors and noise. Traditional stray light measurement devices are mainly aimed at incoherent stray light and cannot effectively identify and measure coherent stray light.

[0003] Therefore, developing a device and method that can effectively measure coherent stray light is of great significance to improving the performance of space gravitational wave detection systems. Summary of the invention

[0004] The purpose of the present invention is to solve the technical problem that the existing stray light measurement devices are mainly for incoherent stray light and cannot effectively identify and measure coherent stray light, and to provide a coherent stray light measurement device and method for space gravitational wave detection.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is:

[0006] A coherent stray light measurement device for space gravitational wave detection, which is special in that:

[0007] It includes a laser light source, a first fiber coupler, a second fiber coupler, a first acousto-optic modulator, a second acousto-optic modulator, a first collimator, a second collimator, a third collimator, a first beam splitter, a second beam splitter, a first photodetector, a second photodetector, a third photodetector, a scattering mirror, a phase-locked amplifier and a spectrum analyzer;

[0008] The output end of the laser light source is connected to the input end of the first optical fiber coupler;

[0009] The input ends of the first acousto-optic modulator and the second acousto-optic modulator are respectively connected to the first output end and the second output end of the first optical fiber coupler, and are used to modulate the frequencies of the respective input laser beams to their respective target values;

[0010] An output end of the second acousto-optic modulator is connected to an input end of the second optical fiber coupler;

[0011] The first collimator and the second collimator are respectively connected to the output end of the first acousto-optic modulator and the first output end of the second fiber coupler;

[0012] The first beam splitter is arranged on the output light path of the first collimator, with the laser beam output by the first collimator as a reference, the first photodetector is arranged on the reflected light path of the first beam splitter, the second beam splitter is arranged on the transmitted light path of the first beam splitter and is located on the output light path of the second collimator, and the second photodetector and the third photodetector are arranged on the reflected light path and the transmitted light path of the second beam splitter respectively;

[0013] The input end of the third collimator is connected to the second output end of the second optical fiber coupler, and the scattering mirror is arranged on the output optical path of the third collimator to generate coherent stray light and reflect it to the first beam splitter;

[0014] The first photodetector, the second photodetector and the third photodetector are respectively used to convert the optical signals received by them into electrical signals;

[0015] The input end of the phase-locked amplifier is connected to the output ends of the first photodetector, the second photodetector and the third photodetector respectively, and is used to receive the electrical signals output by the first photodetector, the second photodetector and the third photodetector, and demodulate the electrical signals to extract the phase information therein;

[0016] The input end of the spectrum analyzer is connected to the output end of the lock-in amplifier, and is used to receive the demodulated electrical signal output by the lock-in amplifier and analyze the frequency components in the electrical signal to extract the frequency and amplitude information of the coherent stray light.

[0017] Furthermore, the output end of the laser light source and the input end of the first fiber coupler, the input ends of the first acousto-optic modulator and the second acousto-optic modulator and the first output end and the second output end of the first fiber coupler, the first collimator and the second collimator and the output end of the first acousto-optic modulator and the first output end of the second fiber coupler, and the third collimator and the second output end of the second fiber coupler are respectively connected through polarization-maintaining optical fibers.

[0018] Further, the first photodetector, the second photodetector and the third photodetector are all photodiodes.

[0019] Furthermore, the frequencies of the laser beams modulated by the first acousto-optic modulator and the second acousto-optic modulator are different, the first acousto-optic modulator is used to modulate the frequency of its input laser beam to 50 Hz, and the second acousto-optic modulator is used to modulate the frequency of its input laser beam to 51 Hz;

[0020] The wavelength of the laser light source is 1064nm.

[0021] At the same time, the present invention also provides a coherent stray light measurement method for space gravitational wave detection, which is based on the aforementioned coherent stray light measurement device for space gravitational wave detection, and is special in that it includes the following steps:

[0022] Step 1, start the laser light source, and guide the laser light beam emitted by the laser light source to the first optical fiber coupler, divide the laser light beam into two paths through the first optical fiber coupler, and then guide them to the input ends of the first acousto-optic modulator and the second acousto-optic modulator respectively;

[0023] Step 2, modulating the frequencies of the respective input laser beams to their respective target values ​​through the first acousto-optic modulator and the second acousto-optic modulator, and then dividing the second acousto-optic modulator into two paths through the second fiber coupler, and guiding one path to the second collimator;

[0024] Step 3, emitting the laser beam outputted by the first acousto-optic modulator to the first beam splitter through the first collimator, and then reflecting a part of the laser beam to the first photodetector through the first beam splitter, and transmitting another part of the laser beam to the second beam splitter;

[0025] The laser beam received by the collimator is emitted to the second beam splitter, and then the laser beam is transmitted to the second photodetector through the second beam splitter, and is reflected to the third photodetector at the same time;

[0026] Step 4: The first photodetector, the second photodetector and the third photodetector respectively convert the received optical signals into electrical signals, and transmit them to the lock-in amplifiers respectively;

[0027] Step 5: demodulating the input electrical signal through a lock-in amplifier to extract the phase information of the laser beam when no coherent stray light is added, and outputting the demodulated electrical signal to a spectrum analyzer;

[0028] Step 6: Analyze the frequency components in the demodulated electrical signal by a spectrum analyzer, and extract the frequency and amplitude information of the laser beam when no coherent stray light is added;

[0029] Step 7, emitting another laser beam outputted by the second fiber coupler to a scattering mirror through a third collimator, scattering the laser beam through the scattering mirror to form coherent stray light, and reflecting the light to the first beam splitter, and then transmitting the coherent stray light to the first photodetector through the first beam splitter, and reflecting the light to the second beam splitter at the same time, and then reflecting the light to the second photodetector through the second beam splitter, and transmitting the light to the third photodetector at the same time;

[0030] Step 8, extracting the phase, frequency and amplitude information of the laser beam after adding the coherent stray light in the same manner as steps 4 to 6;

[0031] Step 9: According to the phase, frequency and amplitude information of the laser beam before and after the coherent stray light is added, the intensity of the coherent stray light is obtained to complete the measurement.

[0032] Further, in step 9, the following formula is used to calculate the intensity ΔI of the coherent stray light at the first photodetector based on the phase, frequency and amplitude information of the laser beam before and after the coherent stray light is added to the electrical signal output by the first photodetector: PD1 :

[0033]

[0034] The following formula is used to calculate the intensity ΔI of the coherent stray light at the second photodetector based on the phase, frequency and amplitude information of the laser beam before and after the coherent stray light is added to the electrical signal output by the second photodetector: PD2 :

[0035]

[0036] The following formula is used to calculate the intensity ΔI of the coherent stray light at the third photodetector based on the phase, frequency and amplitude information of the laser beam before and after the coherent stray light is added to the electrical signal output by the third photodetector: PD3 :

[0037]

[0038] Where: I PD1，stray ,I PD2，stray and I PD3，stray are the light intensities of the mixed light beams at the first photodetector, the second photodetector and the third photodetector when coherent stray light is added; I PD1，no stray ,I PD2，no stray and I PD3，no stray are the light intensities of the laser beam at the first photodetector, the second photodetector and the third photodetector respectively when no coherent stray light is added; t A and tB are the transmission coefficients of the first beam splitter and the second beam splitter, respectively; and are the forward and reverse reflection coefficients of the first beam splitter, respectively; and are the forward and reverse reflection coefficients of the second beam splitter respectively; a1, a2 and a3 are the amplitudes of the light beams at the first collimator, the second collimator and the third collimator respectively; ω1, ω2 and ω3 are the frequencies of the light beams at the first collimator, the second collimator and the third collimator respectively; φ1, φ2 and φ3 are the phases of the light beams at the first collimator, the second collimator and the third collimator respectively; T is time.

[0039] The beneficial effects of the present invention are:

[0040] 1. The present invention conducts in-depth analysis and measurement of the coherent characteristics of stray light, breaking through the limitation that traditional stray light measurement devices are limited to incoherent stray light. By designing a special coherent stray light measurement device, the coherent characteristics of stray light can be accurately captured and characterized, providing key data support for high-precision interferometry, enabling the measurement device to effectively identify and measure coherent stray light, significantly improving the accuracy and reliability of interferometry.

[0041] 2. The present invention combines the signal processing technology of the phase-locked amplifier and the spectrum analyzer to achieve accurate quantitative measurement of the coherent stray light interference results. This method can not only monitor the frequency, amplitude and phase of the coherent stray light in real time, but also accurately evaluate its impact on the interference signal, providing a scientific basis and feedback mechanism for the accurate measurement of coherent stray light, helping to optimize the space interferometer settings, ensuring the accuracy of the interferometric measurement and the stability of the optical system, and providing important technical support for high-precision interferometric measurements such as space gravitational wave detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of working process 1 (without loading coherent stray light) in an embodiment of a coherent stray light measurement device for space gravitational wave detection of the present invention, wherein a phase-locked amplifier and a spectrum analyzer are not shown in the figure;

[0043] Figure 2 This is a schematic diagram of working process 2 (coherent stray light has been loaded) in an embodiment of a coherent stray light measurement device for space gravitational wave detection of the present invention, wherein a phase-locked amplifier and a spectrum analyzer are not shown in the figure;

[0044] Figure 3 The present invention is a flow chart of an embodiment of a coherent stray light measurement method for space gravitational wave detection.

[0045] In the figure: 1-laser light source, 2-first fiber coupler, 3-first acousto-optic modulator, 4-second acousto-optic modulator, 5-second fiber coupler, 6-first collimator, 7-third collimator, 8-second collimator, 9-first beam splitter, 10-second beam splitter, 11-first photodetector, 12-second photodetector, 13-third photodetector, 14-scattering mirror, 15-polarization-maintaining fiber;

[0046] The direction indicated by the arrow is the direction of optical signal transmission. DETAILED DESCRIPTION

[0047] In order to make the purpose, advantages and features of the present invention more clear, the following is a further detailed description of a coherent stray light measurement device and method for space gravitational wave detection proposed by the present invention in combination with the accompanying drawings and specific embodiments. According to the following specific embodiments, the advantages and features of the present invention will be more clear.

[0048] See also Figure 1 The present embodiment is a coherent stray light measuring device for space gravitational wave detection, which mainly includes a laser light source 1, a first fiber coupler 2, a second fiber coupler 5, a first acousto-optic modulator 3, a second acousto-optic modulator 4, a first collimator 6, a second collimator 8, a third collimator 7, a first beam splitter 9, a second beam splitter 10, a first photodetector 11, a second photodetector 12, a third photodetector 13, a scattering mirror 14, and Figure 1 The lock-in amplifier and spectrum analyzer are shown in FIG.

[0049] Among them, the wavelength of the laser light source 1 is 1064nm. The output end of the laser light source 1 is connected to the input end of the first fiber coupler 2 through a polarization-maintaining fiber 15, and the input ends of the first acousto-optic modulator 3 and the second acousto-optic modulator 4 are respectively connected to the first output end and the second output end of the first fiber coupler 2 through the polarization-maintaining fiber 15. The first acousto-optic modulator 3 and the second acousto-optic modulator 4 are used to modulate the frequency of their respective input laser beams to their respective target values, and the target values ​​of the two are different. In this embodiment, according to the requirements of the use conditions, the first acousto-optic modulator 3 is set to modulate the frequency of its input laser beam to 50Hz, and the second acousto-optic modulator 4 is set to modulate the frequency of its input laser beam to 51Hz; in other embodiments of the present invention, those skilled in the art can make specific settings as needed. The output end of the second acousto-optic modulator 4 is connected to the input end of the second fiber coupler 5 through a polarization-maintaining fiber 15, the first collimator 6 and the second collimator 8 are respectively connected to the output end of the first acousto-optic modulator 3 and the first output end of the second fiber coupler 5 through the polarization-maintaining fiber 15, and the third collimator 7 is connected to the second output end of the second fiber coupler 5 through the polarization-maintaining fiber 15.

[0050] The first beam splitter 9 is disposed on the output optical path of the first collimator 6. For the convenience of description, the relative positions of the first photodetector 11, the first beam splitter 9, the second beam splitter 10, the second photodetector 12 and the third photodetector 13 are defined below with reference to the laser beam output by the first collimator 6:

[0051] The first photodetector 11 is arranged on the reflected light path of the first beam splitter 9, the second beam splitter 10 is arranged on the transmitted light path of the first beam splitter 9 and the output light path of the second collimator 8, and the second photodetector 12 and the third photodetector 13 are arranged on the reflected light path and the transmitted light path of the second beam splitter 10, respectively.

[0052] The scattering mirror 14 is arranged on the output light path of the third collimator 7 , and coherent stray light is generated by the rough surface of the scattering mirror 14 and reflected to the first beam splitter 9 .

[0053] In this embodiment, the first photodetector 11, the second photodetector 12 and the third photodetector 13 are all photodiodes. The first photodetector 11, the second photodetector 12 and the third photodetector 13 convert their received optical signals into electrical signals respectively; the input end of the phase-locked amplifier is connected to the output end of the first photodetector 11, the second photodetector 12 and the third photodetector 13 respectively, receives the electrical signals output by the first photodetector 11, the second photodetector 12 and the third photodetector 13, and demodulates the electrical signals to extract the phase information therein; the input end of the spectrum analyzer is connected to the output end of the phase-locked amplifier, receives the demodulated electrical signal output by the phase-locked amplifier, and analyzes the frequency components in the electrical signal to extract the frequency and amplitude information of the coherent stray light.

[0054] See also Figure 3 The specific implementation steps of the coherent stray light measurement method for space gravitational wave detection in this embodiment are as follows:

[0055] 1. Start the laser light source 1 and the beam splitting path

[0056] See also Figure 1 First, start the 1064nm laser light source 1. After the laser beam output by the laser light source 1 is stable, guide the laser beam to the first fiber coupler 2. The first fiber coupler 2 divides the laser beam into two paths, one path is transmitted to the first acousto-optic modulator 3, and the other path is transmitted to the second acousto-optic modulator 4.

[0057] 2. AOM settings

[0058] Radio frequency signals are input into the first AOM 3 and the second AOM 4 to modulate the frequency of the laser beam. The first AOM 3 modulates the frequency of the laser beam to ω1 = 50 Hz, and the second AOM 4 modulates the frequency of the laser beam to ω2 = 51 Hz.

[0059] In order to ensure the accuracy of the frequency of the modulated laser beam, the stability of the RF signal must be ensured.

[0060] 3. Interference beam formation

[0061] After the first acousto-optic modulator 3 outputs its modulated laser beam, it is collimated by the first collimator 6; after the second acousto-optic modulator 4 outputs its modulated laser beam, it is divided into two paths by the second fiber coupler 5, and one of the paths is guided to the second collimator 8 for collimation by the second collimator 8. The first collimator 6 and the second collimator 8 can collimate the laser beam into a free space beam, so that the laser beam remains parallel, thereby reducing beam divergence and improving the accuracy of interferometric measurement.

[0062] The first arm laser beam generated by the first collimator 6 passes through the first beam splitter 9, wherein a portion of the reflected laser beam enters the first photodetector 11, and the other portion of the transmitted laser beam enters the second beam splitter 10. The second arm laser beam generated by the second collimator 8 passes through the second beam splitter 10, wherein a portion of the transmitted laser beam enters the second photodetector 12, and the other portion of the reflected laser beam enters the third photodetector 13.

[0063] In the absence of coherent stray light, the laser beam E1 and the laser beam E2 emitted by the first collimator 6 and the second collimator 8 can be expressed as:

[0064]

[0065] Wherein: a1 and a2 are the amplitudes of the laser beams at the first collimator 6 and the second collimator 8, respectively; ω1 and ω2 are the frequencies of the laser beams at the first collimator 6 and the second collimator 8, respectively; φ1 and φ2 are the phases of the laser beams at the first collimator 6 and the second collimator 8, respectively; j is an imaginary unit; and T is time.

[0066] The Fresnel coefficient is used to describe the reflection and transmission of light at the interface of different optical media, setting the reflection coefficient r and the transmission coefficient t:

[0067] r 2 +t 2 =1

[0068] Use t A ,t Bdenote the transmission coefficients of the first beam splitter 9 and the second beam splitter 10, respectively, denote the forward and reverse reflection coefficients of the first beam splitter 9, respectively, denote the forward and reverse reflection coefficients of the second beam splitter 10 respectively.

[0069] The light intensity received by the first photodetector 11 and the second photodetector 12 can be expressed as the difference frequency interference result of two laser beams with different frequencies ω1 and ω2:

[0070] The light intensity I received by the first photodetector 11 PD1 , no stray It can be expressed as:

[0071]

[0072] The light intensity I received by the second photodetector 12 PD2，no stray It can be expressed as:

[0073]

[0074] At this time, due to the injection of incoherent stray light, the third photodetector 13 only measures the nominal light beam, and the received light intensity I PD3，no stray It can be expressed as:

[0075]

[0076] 4. Introduction of coherent stray light

[0077] See also Figure 2 , the other laser beam outputted by the second fiber coupler 5 is collimated by the third collimator 7, and then the collimated laser beam is guided to the rough surface of the scattering mirror 14, and coherent stray light is generated on the surface. The coherent stray light E3 can be expressed as:

[0078]

[0079] These coherent stray lights E3 are introduced into the optical path through the first beam splitter 9 and are respectively loaded onto the first photodetector 11 , the second photodetector 12 and the third photodetector 13 .

[0080] 5. Signal detection

[0081] The first photodetector 11, the second photodetector 12 and the third photodetector 13 convert the received optical signal into an electrical signal. The first photodetector 11 and the second photodetector 12 mainly detect the interference signal, while the third photodetector 13 detects the mixed signal of the coherent stray light and the main light beam.

[0082] The light intensity I received by the first photodetector 11 after injecting coherent stray light PD1，stray The expression is:

[0083]

[0084] After expansion, we can get:

[0085]

[0086] The light intensity I received by the second photodetector 12 after injecting coherent stray light PD2，stray The expression is:

[0087]

[0088] The light intensity I received by the third photodetector 13 after injecting coherent stray light PD3，stray The expression is:

[0089]

[0090] 6. Signal analysis

[0091] The electrical signals output by the first photodetector 11, the second photodetector 12 and the third photodetector 13 are respectively input to the phase-locked amplifier. The electrical signals output by the first photodetector 11, the second photodetector 12 and the third photodetector 13 are demodulated by the phase-locked amplifier to extract the phase information in the signal. The demodulated signal is then transmitted to the spectrum analyzer, which can detect the beat frequency signals related to the coherent stray light: (ω1-ω3) and (ω2-ω3) to analyze the frequency components in the signal and extract the frequency and amplitude information of the coherent stray light.

[0092] 7. Coherent stray light affects calculations

[0093] By comparing the electrical signals output by the first photodetector 11, the second photodetector 12 and the third photodetector 13 before and after the introduction of coherent stray light, the influence of coherent stray light on the interference signal is analyzed. In particular, the phase and amplitude changes of the interference signal output by the first photodetector 11 are analyzed in detail to determine the influence of the coherent stray light. Based on the data output by the spectrum analyzer and the lock-in amplifier, the physical characteristics of the coherent stray light, including its amplitude and phase, are inverted and calculated.

[0094] The intensity of coherent stray light at the first photodetector 11 is ΔI PD1 for:

[0095]

[0096] The second photodetector 12 is mainly used to monitor the other part of the interference signal, and together with the first photodetector 11, forms a reference signal pair. The second photodetector 12 receives the light signal from the interference path, which contains the relative change information of the two-arm interference light beams. By comparing and analyzing the signals of the second photodetector 12 and the first photodetector 11, the background noise and incoherent stray light interference can be further eliminated to ensure the stability and accuracy of the interference signal. In addition, the signal of the second photodetector 12 can also help detect the phase and amplitude changes introduced by the coherent stray light, providing a reference for evaluating the impact of the coherent stray light on the interference system.

[0097] The intensity ΔI of the coherent stray light at the second photodetector 12 PD2 for:

[0098]

[0099] The third photodetector 13 is specifically used to monitor the injected coherent stray light. It is located on the path of the injected coherent stray light and is used to measure the characteristics of the coherent stray light, such as the injected power, modulation frequency or phase change. Through the measurement of the third photodetector 13, the specific properties of the coherent stray light can be determined, which is crucial for evaluating its impact on the interference system. In addition, comparing and analyzing the measurement results of the third photodetector 13 with the signals of the first photodetector 11 and the second photodetector 12 can deeply reveal the impact mechanism of the coherent stray light on the interference signal.

[0100] The intensity ΔI of the coherent stray light at the third photodetector 13 PD3 for:

[0101]

[0102] At this point, the measurement of coherent stray light can be achieved.

Claims

1. A coherent stray light measurement device for space gravitational wave detection, characterized in that: The invention comprises a laser light source (1), a first optical fiber coupler (2), a second optical fiber coupler (5), a first acousto-optic modulator (3), a second acousto-optic modulator (4), a first collimator (6), a second collimator (8), a third collimator (7), a first beam splitter (9), a second beam splitter (10), a first photodetector (11), a second photodetector (12), a third photodetector (13), a scattering mirror (14), a phase-locked amplifier and a spectrum analyzer; The output end of the laser light source (1) is connected to the input end of the first optical fiber coupler (2); the input ends of the first acousto-optic modulator (3) and the second acousto-optic modulator (4) are respectively connected to the first output end and the second output end of the first optical fiber coupler (2), and are used to modulate the frequencies of the respective input laser beams to their respective target values; the output end of the second acousto-optic modulator (4) is connected to the input end of the second optical fiber coupler (5); the first collimator (6) and the second collimator (8) are respectively connected to the output end of the first acousto-optic modulator (3) and the first output end of the second optical fiber coupler (5); The first beam splitter (9) is arranged on the output light path of the first collimator (6), taking the laser beam output by the first collimator (6) as a reference, the first photodetector (11) is arranged on the reflected light path of the first beam splitter (9), the second beam splitter (10) is arranged on the transmitted light path of the first beam splitter (9) and is also located on the output light path of the second collimator (8), and the second photodetector (12) and the third photodetector (13) are arranged on the reflected light path and the transmitted light path of the second beam splitter (10), respectively; The input end of the third collimator (7) is connected to the second output end of the second optical fiber coupler (5); the scattering mirror (14) is arranged on the output optical path of the third collimator (7) and is used to generate coherent stray light and reflect it to the first beam splitter (9); a part of the coherent stray light is transmitted to the first photodetector (11) through the first beam splitter (9); another part of the coherent stray light is reflected to the second beam splitter (10); the light is then reflected to the second photodetector (12) through the second beam splitter (10); and the light is transmitted to the third photodetector (13); The first photodetector (11), the second photodetector (12) and the third photodetector (13) are respectively used to convert the optical signals received by them into electrical signals; The input end of the phase-locked amplifier is respectively connected to the output ends of the first photodetector (11), the second photodetector (12) and the third photodetector (13), and is used to receive the electrical signals output by the first photodetector (11), the second photodetector (12) and the third photodetector (13), and demodulate the electrical signals to extract phase information therein; The input end of the spectrum analyzer is connected to the output end of the lock-in amplifier, and is used to receive the demodulated electrical signal output by the lock-in amplifier and analyze the frequency components in the electrical signal to extract the frequency and amplitude information of the coherent stray light.

2. The coherent stray light measurement device for space gravitational wave detection according to claim 1, characterized in that: The output end of the laser light source (1) and the input end of the first optical fiber coupler (2), the input ends of the first acousto-optic modulator (3) and the second acousto-optic modulator (4) and the first output end and the second output end of the first optical fiber coupler (2), the first collimator (6) and the second collimator (8) and the output end of the first acousto-optic modulator (3) and the first output end of the second optical fiber coupler (5), and the third collimator (7) and the second output end of the second optical fiber coupler (5) are respectively connected via polarization-maintaining optical fibers (15).

3. A coherent stray light measurement device for space gravitational wave detection according to claim 1 or 2, characterized in that: The first photodetector (11), the second photodetector (12) and the third photodetector (13) are all photodiodes.

4. The coherent stray light measurement device for space gravitational wave detection according to claim 3, characterized in that: The frequencies of the laser light beams modulated by the first acousto-optic modulator (3) and the second acousto-optic modulator (4) are different.

5. The coherent stray light measurement device for space gravitational wave detection according to claim 4, characterized in that: The first acousto-optic modulator (3) is used to modulate the frequency of its input laser beam to 50 Hz, and the second acousto-optic modulator (4) is used to modulate the frequency of its input laser beam to 51 Hz; The wavelength of the laser light source (1) is 1064 nm.

6. A method for measuring coherent stray light for space gravitational wave detection, based on a coherent stray light measurement device for space gravitational wave detection according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1, starting a laser light source (1), and guiding the laser light beam emitted by the laser light source to a first optical fiber coupler (2), dividing the laser light beam into two paths through the first optical fiber coupler (2), and then guiding the two paths to the input ends of a first acousto-optic modulator (3) and a second acousto-optic modulator (4), respectively; Step 2, modulating the frequencies of the respective input laser beams to their respective target values ​​through the first acousto-optic modulator (3) and the second acousto-optic modulator (4), and then dividing the second acousto-optic modulator (4) into two paths through the second fiber coupler (5), and guiding one of the paths to the second collimator (8); Step 3, emitting the laser beam outputted by the first acousto-optic modulator (3) to the first beam splitter (9) through the first collimator (6), and then reflecting a part of the laser beam to the first photodetector (11) through the first beam splitter (9), while transmitting another part of the laser beam to the second beam splitter (10); The laser beam received by the laser beam is emitted to the second beam splitter (10) through the second collimator (8), and then the laser beam is transmitted to the second photodetector (12) through the second beam splitter (10), and is reflected to the third photodetector (13) at the same time; Step 4: The first photodetector (11), the second photodetector (12) and the third photodetector (13) respectively convert the received optical signals into electrical signals, and transmit them to the lock-in amplifiers respectively; Step 5: demodulating the input electrical signal through a lock-in amplifier to extract the phase information of the laser beam when no coherent stray light is added, and outputting the demodulated electrical signal to a spectrum analyzer; Step 6: Analyze the frequency components in the demodulated electrical signal by a spectrum analyzer, and extract the frequency and amplitude information of the laser beam when no coherent stray light is added; Step 7, emitting another laser beam outputted by the second optical fiber coupler (5) to a scattering mirror (14) through a third collimator (7), scattering the laser beam through the scattering mirror (14) to form coherent stray light, and reflecting the light to the first beam splitter (9), and then transmitting the coherent stray light to the first photodetector (11) through the first beam splitter (9), and at the same time reflecting the light to the second beam splitter (10), and then reflecting the light to the second photodetector (12) through the second beam splitter (10), and at the same time transmitting the light to the third photodetector (13); Step 8, extracting the phase, frequency and amplitude information of the laser beam after adding the coherent stray light in the same manner as steps 4 to 6; Step 9: According to the phase, frequency and amplitude information of the laser beam before and after the coherent stray light is added, the intensity of the coherent stray light is obtained to complete the coherent stray light measurement.

7. The coherent stray light measurement method for space gravitational wave detection according to claim 6, characterized in that: In step 9, the following formula is used to calculate the intensity ΔI of the coherent stray light at the first photodetector (11) based on the phase, frequency and amplitude information of the laser beam before and after the coherent stray light is added to the electrical signal output by the first photodetector (11): PD1 : The following formula is used to calculate the light intensity ΔI of the coherent stray light at the second photodetector (12) based on the phase, frequency and amplitude information of the laser beam before and after the coherent stray light is added to the electrical signal output by the second photodetector (12): PD2 : The following formula is used to calculate the intensity ΔI of the coherent stray light at the third photodetector (13) based on the phase, frequency and amplitude information of the laser beam before and after the coherent stray light is added to the electrical signal output by the third photodetector (13): PD3 : Where: I PD1，stray ,I PD2，stray and I PD3，stray are respectively the light intensities of the mixed light beams at the first photodetector (11), the second photodetector (12) and the third photodetector (13) when coherent stray light is added; I PD1，nostray ,I PD2，nostray and I PD3，nostray are respectively the light intensities of the laser beams at the first photodetector (11), the second photodetector (12) and the third photodetector (13) when no coherent stray light is added; t A and t B are the transmission coefficients of the first beam splitter (9) and the second beam splitter (10), respectively; and are respectively the forward and reverse reflection coefficients of the first beam splitter (9); and are respectively the forward and reverse reflection coefficients of the second beam splitter (10); a1, a2 and a3 are respectively the amplitudes of the light beams at the first collimator (6), the second collimator (8) and the third collimator (7); ω1, ω2 and ω3 are respectively the frequencies of the light beams at the first collimator (6), the second collimator (8) and the third collimator (7); φ1, φ2 and φ3 are respectively the phases of the light beams at the first collimator (6), the second collimator (8) and the third collimator (7); and T is time.

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