CN113175867B - Sine phase modulation laser interferometer and carrier generation and signal demodulation method - Google Patents
Sine phase modulation laser interferometer and carrier generation and signal demodulation method Download PDFInfo
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
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- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
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- G01B9/02083—Interferometers characterised by particular signal processing and presentation
Abstract
The invention discloses a sinusoidal phase modulation laser interferometer and a carrier generation and signal demodulation method, wherein a high-frequency sound wave is utilized to enable a gas-liquid interface to generate a high-frequency liquid surface sound wave, reference light of a homodyne interferometer is incident to the gas-liquid interface, and the high-frequency liquid surface sound wave modulates the phase of the reference light to realize the generation of homodyne interference signal phase carriers; the method can solve the problems that the prior PGC demodulation method needs to realize high-frequency sinusoidal phase modulation on the reference arm of the homodyne interferometer, and expensive devices are needed for realizing the high-frequency sinusoidal phase modulation. The invention adopts an Arctan demodulation algorithm based on real-time normalization to eliminate the influence of carrier phase delay caused by low-frequency capillary waves on the liquid surface and carrier modulation depth change caused by power fluctuation of an electroacoustic transducer on a demodulation result.
Description
Technical Field
The invention relates to the technical field of laser interferometry, in particular to a sinusoidal phase modulation laser interferometer and a carrier generation and signal demodulation method.
Background
For the laser interferometry, phase demodulation of the interference signal must be implemented to achieve resolution on the order of nanometers of the measured displacement. The demodulation of the interference signal phase must obtain the orthogonal interference signal pair through the optical path or the signal processing algorithm, and currently, three methods are commonly used to obtain the orthogonal interference signal pair: a heterodyne interferometer and a specific signal processing algorithm are used; combining a homodyne interferometer with a polarization spectroscope, and obtaining orthogonal signals by adopting two photoelectric detectors; a homodyne interferometer with sinusoidal phase modulation and a specific signal processing algorithm are used. The former two methods are greatly influenced by the polarization state of the light source or the performance of the polarizer, and the phase demodulation result of the interference signal always has nonlinear error which is difficult to eliminate.
The PGC demodulation does not need to use a polarization device, uses a photoelectric detector to receive interference signals, and does not have the problem of unequal gains or non-ideal orthogonality of double detectors; generally, it has a larger dynamic demodulation range and higher demodulation sensitivity. The PGC demodulation method finally realizes the solution of the phase of the interference signal by using a DCM algorithm or an Arctan algorithm.
The PGC-DCM method has lower harmonic distortion, but the demodulation result is easily affected by light intensity disturbance and fringe contrast; although the PGC-Arctan demodulation algorithm is not influenced by strong light disturbance and fringe contrast, the two methods are influenced by carrier phase delay and carrier modulation depth calculation deviation. Meanwhile, the modulation depth of the PGC-Arctan demodulation algorithm needs to be accurately adjusted to 2.63rad, and J is guaranteed 1 (C) And J 2 (C) So as to meet the requirements of low harmonic distortion and high stability. However, it is very difficult to adjust the modulation depth to 2.63rad accurately, and it is not an optimal value in terms of both demodulation error and signal-to-noise ratio.
In addition, the PGC demodulation method needs to utilize devices such as an electro-optic modulator or an acousto-optic modulator to realize high-frequency sinusoidal phase modulation on a reference arm of a homodyne interferometer, so that an interference signal generates a phase carrier; however, these devices are expensive, and the driving equipment thereof often costs high, which greatly increases the cost of the whole measuring system.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a sinusoidal phase modulation laser interferometer.
The invention discloses a sinusoidal phase modulation laser interferometer, which sequentially comprises the following components in the direction of an optical path: he — Ne laser, polarizing plate, and spectroscope;
a measuring mirror is arranged on one side of a reflection light path of the spectroscope, and an optical filter and a photoelectric detector are sequentially arranged on the other side of the reflection light path of the spectroscope, wherein the photoelectric detector is connected with a computer through a data acquisition card;
a liquid container is arranged on a transmission light path of the spectroscope, and an electroacoustic transducer is arranged in the liquid container; the sound wave radiated by the electroacoustic transducer generates a high-frequency liquid surface sound wave on the liquid surface, the reference light is incident to the liquid surface and returns to the spectroscope after being modulated by the high-frequency liquid surface sound wave.
As a further improvement of the invention, the method also comprises the following steps: 1/4 slide glass;
the 1/4 slide is disposed between the polarizer and the beam splitter to prevent measurement return light and reference return light from returning to the laser.
As a further improvement of the invention, the method also comprises the following steps: a signal generator and a power amplifier;
the signal generator is connected with the power amplifier, the power amplifier is connected with the electroacoustic transducer and is used for driving the acoustic wave radiated by the electroacoustic transducer to generate a high-frequency liquid surface acoustic wave on the liquid surface; and the signal generator and the power amplifier are connected with the computer through the data acquisition card.
The invention also discloses a carrier generation and signal demodulation method based on the sine phase modulation laser interferometer, which comprises the following steps:
the elliptically polarized light output by the He-Ne laser is changed into linearly polarized light after passing through the polaroid; after passing through the spectroscope, the linearly polarized light is divided into measuring light and reference light; the measuring light returns to the spectroscope through the measuring mirror, the reference light enters the liquid surface, and returns to the spectroscope after being subjected to high-frequency liquid surface acoustic wave modulation;
the returned measuring light and the reference light are converged to form an optical interference mixing signal; the optical interference mixing signal is received by the photoelectric detector after passing through the optical filter and converts an optical signal into an electric signal; and the data acquisition card transmits the electric signal to the computer for phase demodulation.
As a further improvement of the present invention, the phase demodulation method includes:
obtaining the amplitude of each frequency component of the interference signal by FFT;
extracting effective interference signal low-frequency components according to the frequency spectrum threshold value, and calculating the sum of the amplitudes of the low-frequency components;
extracting effective frequency shift components of the interference signal according to a frequency spectrum threshold value, and calculating the sum of the amplitudes of the frequency shift components;
recording the ratio of the sum of the amplitudes of the low-frequency components to the sum of the amplitudes of the frequency shift components as an attenuation ratio;
obtaining a carrier modulation depth based on the attenuation ratio look-up table;
the acquired carrier signals are subjected to 90-degree phase shift to obtain orthogonal signals;
after frequency mixing and low-pass filtering are carried out on two paths of orthogonal carrier signals and interference signals, two paths of signals are obtained:
obtaining carrier phase delay based on the two paths of signals;
and 3, normalizing the orthogonal signal in real time based on the carrier modulation depth and the carrier phase delay, and then demodulating the phase of the interference signal.
Compared with the prior art, the invention has the beneficial effects that:
the invention utilizes the high-frequency sound wave to enable the gas-liquid interface to generate the high-frequency liquid surface sound wave, the reference light of the homodyne interferometer is incident to the gas-liquid interface, and the high-frequency liquid surface sound wave modulates the phase of the reference light, so that the carrier generation of homodyne interference signals is realized, and the method is a novel low-cost phase carrier generation method; the problem that the existing PGC demodulation method needs to realize high-frequency sinusoidal phase modulation on the reference arm of the homodyne interference meter, and expensive devices are needed for realizing the high-frequency sinusoidal phase modulation can be solved;
the method adopts an Arctan demodulation algorithm based on real-time normalization to eliminate the influence of carrier phase delay caused by low-frequency capillary waves on the liquid surface and carrier modulation depth change caused by power fluctuation of an electroacoustic transducer on a demodulation result; the vibration can be accurately demodulated when the modulation depth is not 2.63rad, and the invention can realize the interference signal with the modulation depth range of 0-3 rad and good interference effect.
Drawings
FIG. 1 is a schematic structural diagram of a sinusoidal phase modulation laser interferometer according to an embodiment of the present invention;
fig. 2 is a flowchart of a carrier modulation depth estimation method according to an embodiment of the present invention;
fig. 3 is a flowchart of a carrier phase delay estimation method according to an embodiment of the present invention;
fig. 4 is a flowchart of a phase demodulation method based on real-time normalization according to an embodiment of the present invention.
In the figure:
1. a He-Ne laser; 2. a polarizing plate; 3. a beam splitter; 4. a measuring mirror; 5. a reflector; 6. a liquid surface acoustic wave; 7. an optical filter; 8. a photodetector; 9. a data acquisition card; 10. a computer; 11. a signal generator; 12. a power amplifier; 13. an electroacoustic transducer; 14. 1/4 slide(s).
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
The invention is described in further detail below with reference to the following drawings:
as shown in fig. 1, the present invention provides a sinusoidal phase modulation laser interferometer, comprising: He-Ne laser 1, polaroid 2, spectroscope 3, measuring mirror 4, reflector 5, liquid surface acoustic wave 6, optical filter 7, photoelectric detector 8, data acquisition card 9, computer 10, signal generator 11, power amplifier 12, electroacoustic transducer 13 and 1/4 slide 14; wherein, the first and the second end of the pipe are connected with each other,
the laser light path of the He-Ne laser 1 is sequentially connected with a polaroid 2 and a spectroscope 3, and furthermore, an 1/4 glass slide 14 can be additionally arranged between the polaroid 2 and the spectroscope 3 and is used for preventing measurement return light and reference return light from returning to the He-Ne laser 1 to influence the stability of the laser; the invention arranges a measuring mirror 4 on the reflected light path of a spectroscope 3, an optical filter 7 and a photoelectric detector 8 are arranged on the transmitted light path of the returned light of the measuring mirror 4 through the spectroscope 3 in sequence, and the photoelectric detector 8 is connected with a computer 10 through a data acquisition card 9. The invention is sequentially provided with a reflector 5 and a liquid container on a transmission light path of a spectroscope 3, wherein an electroacoustic transducer 13 is arranged in the liquid container, a signal generator 11 is connected with a power amplifier 12, the power amplifier 12 is connected with the electroacoustic transducer 13, the signal generator 11 and the power amplifier 12 are used for driving sound waves radiated by the electroacoustic transducer 13 to generate high-frequency liquid surface sound waves 6 on the liquid surface, and the liquid surface sound waves 6 are used for modulating reference light; the signal generator 11 and the power amplifier 12 are both connected with the computer 10 through the data acquisition card 9.
The phase carrier generation method of the invention comprises the following steps:
the elliptically polarized light output by the He-Ne laser 1 is changed into linearly polarized light after passing through the polaroid 1; after passing through the spectroscope 3, the linearly polarized light is divided into measuring light and reference light; the measuring light returns to the spectroscope 3 through the measuring mirror 4, the reference light enters the liquid surface through the reflector 5, and returns to the spectroscope 3 after being modulated by the high-frequency liquid surface acoustic wave 6; the returned measuring light and the reference light are converged to form an optical interference mixing signal; the optical interference mixing signal is received by a photoelectric detector 8 after passing through an optical filter 7, and the photoelectric detector 8 converts the optical signal into an electric signal; the data acquisition card 9 transmits the acquired electric signals to the computer 10 for phase demodulation.
The phase demodulation method implemented on the computer 10 comprises the following steps:
obtaining the amplitude of each frequency component of the interference signal by FFT;
extracting effective low-frequency components of the interference signal according to a frequency spectrum threshold value, and calculating the sum of the amplitudes of the low-frequency components;
extracting effective frequency shift components of the interference signal according to a frequency spectrum threshold value, and calculating the sum of the amplitudes of the frequency shift components;
recording the ratio of the sum of the amplitudes of the low-frequency components to the sum of the amplitudes of the frequency shift components as an attenuation ratio;
obtaining the modulation depth of the carrier based on the attenuation ratio table look-up;
the acquired carrier signals are subjected to 90-degree phase shift to obtain orthogonal signals;
after frequency mixing and low-pass filtering are carried out on two paths of orthogonal carrier signals and interference signals, two paths of signals are obtained:
obtaining carrier phase delay based on the two paths of signals;
and 3, carrying out real-time normalization on the orthogonal signal based on the carrier modulation depth and the carrier phase delay, and then carrying out phase demodulation on the interference signal.
Example (b):
the phase demodulation of the invention comprises the following specific research processes:
1. signal model
According to the acoustic theory, when the sound pressure of the sound wave incident on the liquid surface is p i Angular frequency of omega c At an initial phase of
Liquid surface acoustic wave instantaneous vibration displacement A generated by excitation saw (t) may be represented by the following formula:
where ρ represents the density of the liquid medium, c is the speed of sound in the liquid, and ρ c is the acoustic impedance of the liquid medium; from the equation (1), the amplitude of the liquid surface acoustic wave is determined by the incident sound pressure p i Angular frequency omega c And acoustic impedance pc of the liquid medium.
And modulating the reference light of the interferometer by using the liquid surface acoustic wave so that the interference signal generates a phase carrier. If the working wavelength lambda of the laser is determined, the modulation depth C of the carrier wave 0 Calculated from equation (2):
therefore, the control of the carrier modulation depth is easily achieved by adjusting the radiation power of the electroacoustic transducer.
Due to the influence of molecular thermal motion, air micro-disturbance and other factors, the liquid surface often contains low-frequency capillary waves with the scale of micrometer, and the frequency of the surface capillary waves is generally less than 2 Hz. On the one hand, the capillary wave causes a change in the phase delay of the carrier wave, and on the other hand, because its dimension is comparable to the wavelength of the incident laser beam, it also causes a certain degree of scattering of the incident laser beam, and also causes a slight fluctuation of the coherent component in the scattered light, which causes a change in the intensity of the interference signal. Under the influence of fluctuation of the power of the electroacoustic transducer, the amplitude of the liquid surface acoustic wave also fluctuates, so that the modulation depth of the carrier wave changes.
Thus, the output signal of a liquid surface acoustic wave generating phase carrier interferometer can be described by equation (3):
in the formula I 0 The signal is a direct current component, and the component can be filtered by utilizing alternating current coupling during signal sampling; i is 1 The amplitude of the alternating current component of the interference signal is influenced by capillary waves of the liquid surface and changes at low frequency; c 0 For carrier modulation depth, due to fluctuations in the power of the electroacoustic transducer and its drive, C 0 Slow changes also occur;
the phase difference caused by the vibration to be measured and the capillary wave on the liquid surface.
Can be represented by the following formula:
in the formula (I), the compound is shown in the specification,
to measure the initial phase difference of the light and the reference light, C 1 Modulation depth, ω, of the vibration being measured 1 In order to measure the angular frequency of the vibration,
is the initial phase of the measured vibration. C n Modulating depth, omega, for very low frequency capillary waves at liquid surfaces n Is the capillary wave angular frequency of the liquid surface,
is the initial phase of capillary wave on the surface of the liquid.
Complete phase
The measured vibration can be easily extracted by a high-pass filtering method after demodulation.
2. The phase demodulation method comprises the following steps:
because the change of the carrier phase delay caused by the capillary wave on the liquid surface and the change of the carrier modulation depth caused by the fluctuation of the power of the electroacoustic transducer are relatively slow, the carrier phase delay and the carrier modulation depth can be regarded as constants in a signal sampling period. According to the principle of PGC demodulation, the following orthogonal signal pairs can be obtained after mixing and low-frequency filtering the interference signal by using the first frequency multiplication carrier signal and the second frequency multiplication carrier signal:
in the formula (I), the compound is shown in the specification,
is the carrier phase delay, which is driven by the electro-acoustic transducer and the phase delay caused by the propagation of the acoustic wave in the medium. Influenced by capillary waves on the surface of the liquid, interference signal intensity I 1 At a low frequencyIn the context of the variations of (a),
also varied, carrier modulation depth C 0 Slow changes also occur. Therefore, the lissajous figure drawn by the two orthogonal signals is not an ideal circle or an ideal ellipse. The Arctan algorithm can eliminate the influence of interference signal intensity disturbance, and the Arctan algorithm is used for realizing phase difference
Also the carrier modulation depth C must be accomplished 0 And carrier phase delay
And (4) calculating.
3. Carrier modulation depth estimation, as shown in fig. 2;
using the bezier identity, equation (3) can be expanded to the sum of the harmonic terms. After the expansion, the characteristics of the amplitude of each frequency component can be observed, and if A (omega) is the amplitude of the frequency omega component, the frequency in the interference signal is N omega n The component amplitudes (a, b are integers) of (a) and (b) passing through (ω) c The amplitude after frequency shift is as shown in equation (7):
when C is present n When larger, function
And
the curves of (a) almost completely coincide, the function values are approximately equal, and follow C n The values of the two functions are increased continuously, and the difference value of the two functions is negligible relative to the function.
When C is n In large numbers, there is an approximate equality:
then the frequency in the interference signal is A (N omega) n ) And A (N ω) n +ω c ) The number of effective components, that is, the number of extractable components whose amplitudes can be clearly distinguished from noise, is also large. Noting the number of effective frequency components as N e And is set to an even number, so there are:
combining the formula (8), and dividing the two formulas in the formula (9) to obtain a ratio defined as an attenuation ratio R:
as can be seen from equation (10), the amplitude of the low-frequency component in the interference signal regularly attenuates or increases after frequency shift of the carrier, and the rate of attenuation or increase is determined by the modulation depth of the carrier. Further analysis shows that even if the phase of the interference signal contains more low-frequency vibration, the low-frequency component of the interference signal still meets the rule after the carrier frequency shift.
The Fourier spectrum of the interference signal is obtained by utilizing an FFT algorithm, and the actual capillary wave frequency of the liquid surface is extremely low and is often smaller than the frequency resolution, so that the actually calculated frequency spectrum of the interference signal is a continuous spectrum. FIG. 3 shows a practical Carrier Modulation Depth Estimation Algorithm (CMDEA), which uses FFT to obtain the amplitudes of the frequency components of the interference signal, and extracts the effective low-frequency component A (N ω) of the interference signal according to the spectral threshold n ) Calculating the sum of their amplitudes, denoted S low Then, the frequency shift component A (N ω) is calculated n +ω c ) Is recorded as S high (ii) a The ratio of the two values is recorded as the attenuation ratio R; then, a table look-up method is used to obtain the carrier modulation depth C 0 。
4. Carrier phase delay estimation, as shown in fig. 3;
the interference signal is recorded as S (t), and the liquid surface acoustic wave excitation signal is recorded as cos (omega) c t), the Carrier Phase Delay Estimation Algorithm (CPDEA) is shown in fig. 3: collecting a carrier signal cos (omega) from an oscillator c t) and obtaining an orthogonal signal sin (omega) after 90 DEG phase shift (phase shift can be carried out by Hilbert transform) c t); the two orthogonal carrier signals are mixed with an interference signal S (t), and after low-pass filtering, signals can be obtained:
dividing the two forms to obtain
And then, the Arctan module is utilized to realize the calculation of the carrier phase delay. The Arctan module in the figure includes the Arctan algorithm and median filtering, which is used to remove the computation noise. Due to the fact that
The variation of (a) is relatively slow, and to further eliminate random errors, the average of all calculated values in the observation period can be taken as the carrier phase delay used for normalization. In the system, the carrier phase delay caused by the propagation distance of the power amplifier, the transducer and the sound wave in water is small, and the carrier phase delay range [ -pi/2, pi/2 ] calculated by Arctan]The system requirement can be completely met, and the value range expansion is not required.
5. PGC-Arctan phase demodulation based on real-time normalization, as shown in fig. 4;
because the carrier modulation depth and the phase delay change slowly relative to the signal acquisition and processing speed, the change period is far longer than the signal acquisition period. Therefore, the carrier modulation depth and the carrier phase delay estimated in the previous observation period can be used for normalization of the orthogonal signals in the current observation period, so that real-time normalization of the orthogonal signal pair is realized.
Fig. 4 shows an interference signal phase demodulation algorithm based on real-time normalization, in which a CMDEA module is used for carrier modulation depth estimation, and a CPDEA module is used for carrier phase delay estimation. After the phase demodulation of the interference signal is finished, unwrapping operation is carried out, the unwrapping operation is divided by a coefficient (4 pi/lambda), and finally the measured nano vibration can be extracted by using a filtering method.
The invention has the advantages that:
the invention utilizes the high-frequency sound wave to enable the gas-liquid interface to generate the high-frequency liquid surface sound wave, the reference light of the homodyne interferometer is incident to the gas-liquid interface, and the high-frequency liquid surface sound wave modulates the phase of the reference light, so that the carrier generation of homodyne interference signals is realized, and the method is a novel low-cost phase carrier generation method; the problem that the existing PGC demodulation method needs to realize high-frequency sine phase modulation on the reference arm of the homodyne interference meter, and expensive devices are needed for realizing the high-frequency sine phase modulation can be solved;
according to the method, an Arctan demodulation algorithm is adopted to eliminate the influence of carrier phase delay caused by low-frequency capillary waves on a liquid surface and carrier modulation depth change caused by power fluctuation of an electroacoustic transducer on a demodulation result; the method can still accurately demodulate vibration when the modulation depth is not 2.63rad, and can realize interference signals with the modulation depth range of 0-3 rad and good interference effect.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (3)
1. A carrier generation and signal demodulation method based on a sine phase modulation laser interferometer is characterized in that,
the sine phase modulation laser interferometer sequentially comprises the following components in the direction of an optical path: he — Ne laser, polarizing plate, and spectroscope; a measuring mirror is arranged on one side of a reflection light path of the spectroscope, and an optical filter and a photoelectric detector are sequentially arranged on the other side of the reflection light path of the spectroscope, wherein the photoelectric detector is connected with a computer through a data acquisition card; a liquid container is arranged on a transmission light path of the spectroscope, and an electroacoustic transducer is arranged in the liquid container; the sound wave radiated by the electroacoustic transducer generates a high-frequency liquid surface sound wave on the liquid surface, the reference light is incident to the liquid surface and returns to the spectroscope after being modulated by the high-frequency liquid surface sound wave;
the method for generating the carrier wave comprises the following steps:
the elliptically polarized light output by the He-Ne laser is changed into linearly polarized light after passing through the polaroid; after passing through the spectroscope, the linearly polarized light is divided into measuring light and reference light; the measuring light returns to the spectroscope through the measuring mirror, the reference light enters the liquid surface, and returns to the spectroscope after being subjected to high-frequency liquid surface acoustic wave modulation; the returned measuring light and the reference light are converged to form an optical interference mixing signal; the optical interference mixing signal is received by the photoelectric detector after passing through the optical filter and converts an optical signal into an electric signal; the data acquisition card transmits the electric signal to the computer for phase demodulation;
the phase demodulation method comprises the following steps:
step 1, calculating the carrier modulation depth:
obtaining the amplitude of each frequency component of the interference signal by FFT;
extracting effective low-frequency components of the interference signal according to a frequency spectrum threshold value, and calculating the sum of the amplitudes of the low-frequency components;
extracting effective frequency shift components of the interference signal according to a frequency spectrum threshold value, and calculating the sum of the amplitudes of the frequency shift components;
recording the ratio of the sum of the amplitudes of the low-frequency components to the sum of the amplitudes of the frequency shift components as an attenuation ratio;
obtaining a carrier modulation depth based on the attenuation ratio look-up table;
step 2, calculating carrier phase delay:
the acquired carrier signals are subjected to 90-degree phase shift to obtain orthogonal signals;
after frequency mixing and low-pass filtering are carried out on two paths of orthogonal carrier signals and interference signals, two paths of signals are obtained:
obtaining carrier phase delay based on the two paths of signals;
and 3, normalizing the orthogonal signal in real time based on the carrier modulation depth and the carrier phase delay, and then demodulating the phase of the interference signal.
2. The carrier generation, signal demodulation method of claim 1 wherein the sinusoidal phase modulation laser interferometer further comprises: 1/4 slide glass;
the 1/4 slide is disposed between the polarizer and the beam splitter to prevent measurement return light and reference return light from returning to the laser.
3. The carrier generation, signal demodulation method of claim 1 wherein the sinusoidal phase modulation laser interferometer further comprises: a signal generator and a power amplifier;
the signal generator is connected with the power amplifier, the power amplifier is connected with the electroacoustic transducer and is used for driving the acoustic wave radiated by the electroacoustic transducer to generate a high-frequency liquid surface acoustic wave on the liquid surface; and the signal generator and the power amplifier are connected with the computer through the data acquisition card.
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