A coherent detection method of rotational Doppler effect based on multi-mode reception

Abstract

The present invention relates to the field of photoelectric detection and signal processing technology, and specifically discloses a method for coherent detection of the rotational Doppler effect based on multi-mode reception, comprising: using a fundamental mode Gaussian beam at the transmitting end to illuminate a rotating object, and performing amplitude and spiral phase modulation on the Gaussian detection beam through the rotating object to form a scattered light field; using a vortex beam as a reference light, beating the fundamental mode component in the scattered light of the reference light with each OAM mode in the received echo signal light of the rotating object, mapping the different OAM modes in the echo signal light to the rotational Doppler spectrum, and realizing multi-mode reception of the echo signal light. The present application improves the energy utilization rate of the echo signal during rotational Doppler effect measurement, converts the single peak in the time-frequency domain of traditional rotational Doppler effect measurement into multiple peaks, facilitates cross-validation and adaptive extraction of detection results, and helps promote the practical application of rotational Doppler effect remote sensing.

Description

Technical Field

[0001] The present invention relates to the technical field of photoelectric detection and signal processing, and in particular to a rotational Doppler effect coherent detection method based on multi-mode reception. Background Art

[0002] The linear Doppler effect is a change in the frequency of a wave caused by the relative linear motion between the wave source and the observer. This effect, caused by linear motion in a Cartesian coordinate system and related to the linear momentum of the wave, is widely used in atmospheric measurements, object identification, motion monitoring, and other fields. When there is relative rotational motion between the wave source and the observer, a Doppler effect, the rotational Doppler effect, also occurs. This effect is the counterpart of the linear Doppler effect on a rotating object. It is caused by rotational motion in a polar coordinate system and is related to the angular momentum of the wave. Just as the linear Doppler effect requires a change in the linear momentum of the wave, the rotational Doppler effect requires a change in its angular momentum. In classic rotational Doppler effect measurements, a vortex beam is typically used as the probe beam. This is a special beam carrying orbital angular momentum, with a spiral wavefront and a central phase singularity. The rotational Doppler frequency shift signal is detected by exploiting the angle between the direction of the beam's Poynting vector and the beam's propagation direction. However, the vortex light source increases the complexity of the entire system. At the same time, in order to ensure detection sensitivity, it is often necessary to use a vortex beam with a large topological charge as the detection beam. The topological charge and the far-field divergence angle of the vortex beam are positively correlated, which makes the detection sensitivity and detection distance mutually restricted.

[0003] Current methods for measuring the rotational Doppler effect based on receiver-side modulation only receive a single, specific orbital angular momentum mode in the scattered light field of a rotating object, regardless of the type of probe beam emitted. While using an array detector can separate different orbital angular momentum modes to different detector locations, the limited frame rate prevents detection of high-frequency information, making it unsuitable for rotational Doppler effect remote sensing applications. According to mode decomposition theory, the scattered light field can be decomposed into multiple orbital angular momentum modes. Receiving only a single mode results in the loss of other modes, which in turn significantly wastes echo energy and, to some extent, negates the advantage of using a Gaussian light source in lidar, which offers higher echo energy than a vortex light source due to its smaller divergence angle. In rotational Doppler effect remote sensing applications, this significantly reduces detection range. Furthermore, in actual measurements, atmospheric turbulence can cause the proportions of individual orbital angular momentum modes to fluctuate, further reducing the signal-to-noise ratio. Therefore, achieving multimode reception of orbital angular momentum modes during receiver-side modulation has become a pressing challenge in practical rotational Doppler effect remote sensing. Summary of the Invention

[0004] To achieve the purpose of the present invention, the present application provides a method for coherent detection of the rotational Doppler effect based on multimode reception, comprising: step S1: irradiating a rotating object with a fundamental mode Gaussian beam at a transmitting end, and performing amplitude and spiral phase modulation on the Gaussian detection beam through the rotating object to form a scattered light field;

[0005] Step S2: At the receiving end, a vortex beam is used as a reference beam. The fundamental mode component of the scattered light of the reference beam beats with the various OAM modes in the received echo signal light of the rotating object. The different OAM modes in the echo signal light are mapped to the rotational Doppler spectrum to achieve multimode reception of the echo signal light.

[0006] In some specific embodiments, step S1 further includes:

[0007] A fundamental mode Gaussian beam is used as a detection beam to illuminate a rotating object. The scattered signal light modulated by the rotating object includes orbital angular momentum modes of different orders.

[0008] In some specific embodiments, step S2 includes:

[0009] At the receiving end, a vortex beam is used as the reference light, and the different orbital angular momentum modes in the scattered signal light are mapped to the rotational Doppler spectrum by utilizing the principle of coherence between the fundamental mode components of the scattered signal light and the reference light.

[0010] In some specific embodiments, step S1 further includes:

[0011] When using a fundamental mode Gaussian beam for detection, the detection beam is determined according to the following formula:

[0012] ;

[0013] in, represents the three coordinates in cylindrical coordinates, Indicates time, represents the initial intensity of the Gaussian beam, represents the wave vector, Indicates the angular frequency.

[0014] In some specific embodiments, the scattered light field formed after the probe beam is irradiated on the rough surface of the rotating object is determined according to the light field function of the probe beam and the object modulation function:

[0015] ;

[0016] in, It represents the reflectivity coefficient of a point on the rough surface in the direction from the point to the receiving end. represents the order of the spiral pattern on the surface of the object, for The complex amplitude of the order spiral mode is , is the angular velocity of the object.

[0017] Beneficial effects of the above technical solution:

[0018] The technical solution proposed in this application is highly compatible and applicable to a wide range of scenarios. A simple modification of the existing linear Doppler LiDAR receiver can enable it to measure the rotational Doppler effect. Furthermore, this method remains applicable under extreme conditions, such as high-speed rotation. Using laser as the detection medium, it boasts long transmission distances, fast response speeds, and minimal environmental impact, offering broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 A schematic flow chart of a method for coherent detection of the rotational Doppler effect based on multi-mode reception provided by one embodiment of the present invention;

[0021] Figure 2 A schematic structural diagram of a rotational Doppler effect coherent detection system based on multi-mode reception provided by one embodiment of the present invention;

[0022] Figure 3 A schematic diagram of a detection optical path of a rotational Doppler effect coherent detection system based on multi-mode reception provided by one embodiment of the present invention;

[0023] Figure 4 A schematic diagram of experimental results of a rotational Doppler effect coherent detection system based on multi-mode reception is provided in accordance with an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0025] Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar symbols throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0026] Example 1

[0027] An embodiment of the present invention provides a method for coherent detection of the rotating Doppler effect based on multi-mode reception, referring to Figure 1 Shown, including:

[0028] Step S1: a fundamental mode Gaussian beam is used to illuminate a rotating object at the transmitting end, and the Gaussian detection beam is modulated in amplitude and spiral phase by the rotating object to form a scattered light field.

[0029] In a specific embodiment of the present invention, step S1 further includes:

[0030] A fundamental mode Gaussian beam is used as a detection beam to illuminate a rotating object. The scattered signal light modulated by the rotating object includes orbital angular momentum modes of different orders.

[0031] In a specific embodiment of the present invention, step S1 further includes:

[0032] When using a fundamental mode Gaussian beam for detection, the detection beam is determined according to the following formula:

[0033] ;

[0034] in, represents the three coordinates in cylindrical coordinates, Indicates time, represents the initial intensity of the Gaussian beam, represents the wave vector, Represents the angular frequency.

[0035] In a specific embodiment of the present invention, the scattered light field formed after the probe beam is irradiated on the rough surface of the rotating object is determined according to the probe beam light field function and the object modulation function:

[0036] ;

[0037] in, It represents the reflectivity coefficient of a point on the rough surface in the direction from the point to the receiving end. represents the order of the spiral pattern on the surface of the object, for The complex amplitude of the order spiral mode is , is the angular velocity of the object.

[0038] Specifically, the linearly polarized Gaussian beam emitted by the laser is divided into two paths. One path is used as a detection beam to irradiate the rotating object. The signal light field modulated and reflected by the rotating object enters the 50:50 splitter prism again. The other path generates linearly polarized single-state vortex light after passing through a quarter-wave plate, a vortex wave plate and a polarizer. After the reference light interacts with the target, only the fundamental mode is selected. The two are coherently mixed in the 50:50 splitter prism to scatter the signal light and the fundamental mode component of the vortex reference light. After being converged by a lens and filtered by a pinhole, it is transmitted to the photodetector. After Fourier transform, the multi-mode rotational Doppler signal is extracted in a single Fourier spectrum.

[0039] Step S2: At the receiving end, the vortex beam is used as the reference light. The fundamental mode component in the scattered light of the reference light beats with the various OAM modes in the received echo signal light of the rotating object. The different OAM modes in the echo signal light are mapped to the rotational Doppler spectrum, realizing multi-mode reception of the echo signal light.

[0040] In a specific embodiment of the present invention, step S2 includes:

[0041] At the receiving end, a vortex beam is used as the local oscillator light, and the different orbital angular momentum modes in the scattered signal light are mapped to the rotational Doppler spectrum by utilizing the principle of coherence between the fundamental mode components of the scattered signal light and the reference light.

[0042] In terms of signal energy utilization, by using a vortex beam as a reference light at the receiving end, the different orbital angular momentum patterns in the scattered signal light are mapped to the rotational Doppler spectrum, which greatly improves the utilization of the echo signal.

[0043] Specifically, when a fundamental mode Gaussian beam is used for detection, the detection beam can be expressed as:

[0044] (1)

[0045] in, represents the three coordinates in the cylindrical coordinates of the detection beam, Indicates time, represents the initial intensity of the Gaussian beam, represents the wave vector, Indicates the angular frequency.

[0046] In actual detection, rotating objects are often composed of rough surfaces, which modulate the amplitude and phase of the detection beam. The modulation function of the rough surface on the beam can be expressed as:

[0047] (2)

[0048] in, It represents the reflectivity coefficient of a point on the rough surface in the direction from the point to the receiving end. represents the order of the orbital angular momentum mode on the surface of the object, for The complex amplitude of the orbital angular momentum mode is , which can be expressed as:

[0049] (3)

[0050] When an object moves at an angular velocity During rotation, the phase modulation function adds an angular variable that varies with time and is expressed as:

[0051] (4)

[0052] The scattered light field formed when the probe beam hits the rough surface of the rotating object can be expressed as the product of the probe beam light field function and the object modulation function:

[0053] (5)

[0054] It can be seen that the scattered light field modulated by the rotating object contains many OAM modes of different orders, carrying different rotational Doppler frequency shifts. The LG beam, as an OAM eigenmode, is a set of orthogonal and complete basis vectors in the Hilbert space, forming a complete infinite-dimensional foundation. With the increase of the topological charge, the difficulty of receiving higher-order modes gradually increases. Considering the influence of the aperture of the receiving system, only a limited number of OAM modes of the scattered light field can be received by the receiving system. In order to ensure the receiving efficiency of the receiving system, the detection beam should be irradiated onto the rotating object in a collimated state, so that each OAM mode of the scattered light field has a small far-field divergence angle to ensure the number of OAM modes in the scattered light field entering the receiving system. The OAM mode received by the receiving system can be expressed as:

[0055] (6)

[0056] It can be seen that there are The mode passes through the receiving system. At this time, we use a vortex beam as the reference beam, which can be expressed as:

[0057] (7)

[0058] in, is the initial intensity of the vortex beam, is the topological charge of the vortex beam.

[0059] Similarly, the scattered light field formed when the reference beam is irradiated on the rough surface of a rotating object can be expressed as the product of the reference beam light field function and the object modulation function:

[0060] (8)

[0061] If the reference beam is focused with a small spot size and a large far-field divergence angle to illuminate a rotating object, then each OAM mode in the scattered light field modulated by the rotating object will have a large far-field divergence angle, and the higher-order modes will be dissipated. Only the fundamental mode beam, i.e., the component with OAM=0, can return to the receiving system, which can be expressed as:

[0062] (9)

[0063] The detection light and the reference light are modulated by the rotating object and then reflected. They coherently interact on the detector, and the resulting photocurrent can be expressed as:

[0064] (10)

[0065] in, It represents the responsivity of the detector. It can be seen that the photocurrent caused by the signal contains three parts, namely the DC term, the beat frequency signal between different modes of the signal light, and the beat frequency signal between the signal light and the local oscillator light. Since the intensity of the local oscillator light is much greater than the intensity of the signal light, the beat frequency signal between different modes of the signal light can be ignored. The intermediate frequency signal of the photocurrent can be approximately expressed as:

[0066] (11)

[0067] It can be seen that if Without changing the sign, each OAM mode corresponds to the beat frequency shift one by one, so the present application successfully realizes the multi-mode reception of RDE signals in the scattered light field of the rotating object.

[0068] Specifically, a vortex beam is used as the reference light, and the fundamental mode component in the scattered light of the reference light beats with the various OAM modes in the received echo signal light of the rotating object, mapping the different OAM modes in the echo signal light to the rotating Doppler spectrum, thereby realizing multi-mode reception of the echo signal light.

[0069] Example 2

[0070] An embodiment of the present invention provides a rotational Doppler effect coherent detection system based on multi-mode reception, comprising:

[0071] A beam emitting module is configured to illuminate a rotating object with a fundamental mode Gaussian beam, and modulate the amplitude and spiral phase of the Gaussian probe beam through the rotating object to form a scattered light field.

[0072] The beam receiving module uses the vortex beam as the reference light, and the fundamental mode component in the scattered light of the reference light beats the various OAM modes in the received echo signal light of the rotating object, mapping the different OAM modes in the echo signal light to the rotational Doppler spectrum to achieve multi-mode reception of the echo signal light. In a specific embodiment of the present invention, the beam processing module is also used to:

[0073] A fundamental mode Gaussian beam is used as a detection beam to illuminate a rotating object. The scattered signal light modulated by the rotating object includes orbital angular momentum modes of different orders.

[0074] In a specific embodiment of the present invention, the beam scattering module is used to:

[0075] At the receiving end, a vortex beam is used as the local oscillator light, and the different orbital angular momentum modes in the scattered signal light are mapped to the rotational Doppler spectrum by utilizing the principle of coherence between the fundamental mode components of the scattered signal light and the reference light.

[0076] In a specific embodiment of the present invention, when a fundamental mode Gaussian beam is used for detection, the detection beam is determined according to the following formula:

[0077] ;

[0078] in, represents the three coordinates in cylindrical coordinates, Indicates time, represents the initial intensity of the Gaussian beam, represents the wave vector, Represents the angular frequency.

[0079] In a specific embodiment of the present invention, the scattered light field formed after the probe beam is irradiated on the rough surface of the rotating object is determined according to the probe beam light field function and the object modulation function:

[0080] ;

[0081] in, It represents the reflectivity coefficient of a point on the rough surface in the direction from the point to the receiving end. represents the order of the spiral pattern on the surface of the object, for The complex amplitude of the order spiral mode is , is the angular velocity of the object.

[0082] The present invention uses a fundamental mode Gaussian beam as a detection beam and a single-state vortex beam as a reference beam. The implementation object is a rotating object in space, as follows:

[0083] The optical path required for detection is as follows Figure 3 As shown, laser 1 first generates a narrow-linewidth linearly polarized Gaussian beam with a wavelength of 532 nm. This beam passes through a 10:90 beam splitter prism 2 and is split into two beams. One beam, serving as the probe beam, passes through a 50:50 beam splitter prism 9 and illuminates a rotating object 8 simulated by a DMD. The signal light field, modulated and reflected by the rotating object, reenters the 50:50 beam splitter prism 9. The other beam, serving as the reference beam, is reflected by a reflector 3 onto a quarter-wave plate 4. By adjusting the fast-axis orientation of the quarter-wave plate 4, the polarization state of the beam incident on the vortex half-wave plate 5 can be adjusted. Thus, the sign and polarization state of the single-state vortex beam are selected and prepared, and then the circular polarization state of the reference beam is adjusted to the linear polarization state consistent with the detection beam using the linear polarizer 6, and finally reflected into the 50:50 dichroic prism 9 through the reflector 7, and the fundamental mode components of the scattered signal light and the scattered light of the reference light are coherently mixed in the 50:50 dichroic prism 9, converged by the lens 10 and filtered by the pinhole 11, and transmitted to the photodetector 12, and after Fourier transformation, the multimode rotation Doppler signal is extracted in a Fourier spectrum. In the experiment, the present application uses DMD to simulate the rotating object, and uses the polarization maintenance characteristics of the DMD to prevent the scattered light field of the rotating object from depolarizing. By loading different simulated rotating phase holograms on the DMD, the OAM component and proportion in the reflected light field are quantitatively adjusted. In the experiment, the present application loads on the object to A total of 10 modes of spiral phase holograms.

[0084] For example, using Figure 3 The optical path shown uses a fundamental mode Gaussian beam as the probe beam, and a beam of topological charge is used at the receiving end. The vortex beam is used as the local oscillator beam to detect the rotation speed The effect of this method before and after using the rotating object with a value of 100 is compared by adjusting the presence or absence of the local oscillation light. The received scattered light signal is used Figure 2 The analysis process is shown in the figure, and the experimental results are as follows Figure 4 As shown, (a) and (b) are the scattered light signal and Fourier spectrum when there is no vortex local oscillator light, respectively. (c) and (d) are the scattered light signal and Fourier spectrum when there is no vortex local oscillator light, respectively. It can be seen that when there is no local oscillator vortex light, the orbital angular momentum component in the scattered light field cannot be received, and no rotational Doppler frequency shift can be observed. Only the fundamental frequency scintillation signal and its higher harmonics of the light irradiating the object itself can be observed. After adding the vortex local oscillator light, the vortex local oscillator light Mode and object scattered light field carried to The sum of the topological charges between the modes is 17 to 26, and the frequency shift caused in the Fourier spectrum is a cluster of peaks with an interval of 100 Hz in the range from 1700 Hz to 2600 Hz. The ten different orbital angular momentum modes in the scattered light field correspond to different rotational Doppler shifts, and the difference in the rotational Doppler shifts of adjacent modes is exactly the mode difference. and object speed Thus, the present application realizes the multi-mode reception of the rotational Doppler signal and utilizes all orbital angular momentum modes carried in the scattered light field.

[0085] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

[0086] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the various embodiments can be referred to each other. The embodiments of the present invention are described with reference to the flowcharts and / or block diagrams of the methods, terminal devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing terminal device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing terminal device generate instructions for implementing the functions in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 These computer program instructions can also be stored in a computer-readable memory that can guide a computer or other programmable data processing terminal device to work in a specific way, so that the instructions stored in the computer-readable memory produce a product including an instruction device, which implements the functions specified in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 These computer program instructions can also be loaded onto a computer or other programmable data processing terminal device, so that a series of operation steps are executed on the computer or other programmable terminal device to produce a computer-implemented process, thereby providing instructions for implementing the process in the process. Figure 1 a process or multiple processes and / or boxes Figure 1The steps of the functions specified in one or more blocks. Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention. Finally, it should be noted that, in this document, relational terms such as first and second, etc. are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or terminal device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article, or terminal device. Without further limitation, an element defined by the phrase "comprising a..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes the element.

[0087] The method and apparatus provided by the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present invention.

[0088] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "example," "specific example," "a specific embodiment," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A rotational Doppler effect coherent detection method based on multimode reception, characterized in that: include: Step S1: using a fundamental mode Gaussian beam to illuminate a rotating object at the transmitting end, and performing amplitude and spiral phase modulation on the Gaussian beam through the rotating object to form a scattered light field; Step S2: At the receiving end, the vortex beam is used as a reference beam. The fundamental mode component in the scattered light of the reference beam beats with the various OAM modes in the received echo signal light of the rotating object. The different OAM modes in the echo signal light are mapped to the rotational Doppler spectrum to achieve multimode reception of the echo signal light. Step S2 includes: At the receiving end, a vortex beam is used as a reference light, and the different orbital angular momentum modes in the scattered signal light are mapped to the rotational Doppler spectrum by taking advantage of the coherence between the fundamental mode components of the scattered signal light and the reference light. When a fundamental mode Gaussian beam is used for detection, the detection beam is expressed as: in, represents the three coordinates in the cylindrical coordinates of the probe beam, t represents time, E0 represents the initial intensity of the Gaussian beam, k represents the wave vector, and ω represents the angular frequency; In actual detection, rotating objects are often composed of rough surfaces, which modulate the amplitude and phase of the detection beam. The modulation function of the rough surface on the beam is expressed as: in, Indicates the direction of a point on the rough surface pointing to the receiving end. When the object rotates at an angular velocity Ω, the phase modulation function will add an angular variable that changes with time, expressed as:

2. The method for coherent detection of the rotational Doppler effect based on multimode reception according to claim 1, wherein: Step S1 further includes: A fundamental mode Gaussian beam is used as a detection beam to illuminate the rotating object, so that the scattered signal light modulated by the rotating object includes orbital angular momentum modes of different orders.

3. The method for coherent detection of the rotational Doppler effect based on multimode reception according to claim 2, wherein: Step S1 further includes: When using a fundamental mode Gaussian beam for detection, the detection beam is determined according to the following formula: in, Represents the three coordinates in cylindrical coordinates, t represents time, E0 represents the initial intensity of the Gaussian beam, k represents the wave vector, and ω represents the angular frequency.

4. The method for coherent detection of the rotational Doppler effect based on multimode reception according to claim 1, wherein: The scattered light field is determined according to the detection beam light field function and the object modulation function as follows: in, It represents the reflectivity coefficient of a point on the rough surface in the direction of the receiving end, n represents the order of the spiral pattern on the surface of the object, a n (r,z) is the complex amplitude of the n-th order spiral mode and Ω is the angular velocity of the object.

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