Array focusing laser differential interference measurement system

Abstract

The invention discloses an array type focused laser differential interference measurement system, relates to the technical field of fluid mechanics measurement, and aims to solve the problem of how to improve the FLDI measurement efficiency and ensure the measurement precision at the same time. An emission light path generates multiple paths of light splitting pairs by using a diffractive optical element; a multi-path optical fiber array receiving system is arranged at the tail end of the receiving optical path and comprises a plurality of groups of receiving terminals, each group of receiving terminals comprises a three-dimensional coordinate frame, a photoelectric detector and an optical fiber probe, a rigid connecting rod is fixedly connected to a moving part of the three-dimensional coordinate frame, and the optical fiber probe is fixedly connected with the rigid connecting rod; the positions of the rigid connecting rods of the multiple groups of receiving terminals are respectively adjusted, so that the positions of the receiving ends of the multiple optical fiber probes are respectively in one-to-one correspondence with the final imaging focus positions of the multiple paths of light in the receiving light path; the device is simple in structure and ingenious in conception, the measurement efficiency can be remarkably improved, and meanwhile it can be guaranteed that multiple paths of optical signals are respectively and accurately received, so that the measurement accuracy is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of fluid mechanics measurement, and in particular to an array-type focused laser differential interferometry measurement system. Background Art

[0002] Ground wind tunnel test is one of the important means to study hypersonic aerodynamics, and it is of great significance to the study of hypersonic aerodynamics. However, due to the extreme environment of high inflow velocity, high inflow total temperature, and even the risk of high-speed impact of metal oxide particles in hypersonic wind tunnels, the test technology of hypersonic flow field is relatively scarce, which has hindered the study of related issues to a certain extent. As a measuring instrument based on the principle of optical interference, focused laser differential interferometry (FLDI) has the characteristics of non-intrusiveness and high time resolution, and has been widely used in the measurement of hypersonic flow fields (such as hypersonic boundary layer transition, hypersonic turbulent boundary layer, hypersonic free flow disturbance, and supersonic jet noise radiation, etc.).

[0003] Existing focused laser differential interferometry measurement systems all include a transmitting optical path and a receiving optical path. The transmitting optical path includes a coherent light source generator, a concave lens, a polarizer, a prism, and a convex lens arranged in sequence, wherein the coherent light source generator is used to emit a beam of parallel laser light with the same phase and consistent polarization direction, the concave lens is used to diverge the parallel laser beams of each channel into conical laser beams, the polarizer is used to filter out nonlinear polarized interference light in the conical laser beams of each channel, the prism is used to separate the linear polarized light of each channel into two polarized light beams with the same intensity and perpendicular polarization directions according to the principle of double refraction, the convex lens is used to focus the two separated light beams with perpendicular polarization directions in each channel into two separated focal points, and the two separated focal points of each channel are in the focusing area; the receiving optical path includes a convex lens, a prism, and a polarizer arranged in sequence, wherein the convex lens is used to refocus the laser beam diverged after passing through the focusing area, the prism is used to merge the two separated light beams of each splitting pair, and the polarizer is used to mix the merged light beams so that the mixed light beams can perform phase interference. Traditional methods acquire data through a single laser beam and interference pattern, but their efficiency and accuracy are limited when measurements of large areas or complex structures are required.

[0004] At present, there have been related studies to improve the FLDI measurement efficiency. For example, in the invention patent application with publication number CN111426446A, entitled A Multi-channel Focusing Laser Differential Interferometer, it is disclosed that a single laser beam emitted by a single laser is divided into multiple laser beams using a beam splitter group and a corresponding reflector group, and then focused at multiple measuring points. Therefore, density pulsation information of multiple measuring points in the flow field can be obtained simultaneously each time, which greatly reduces the number of experiments, improves the test efficiency of the wind tunnel, and saves test costs. However, this beam splitting method will disperse the focus points into multiple points, requiring multiple sets of equipment to complete the measurement. Not only may optical components such as lenses bring more errors, further leading to a reduction in measurement accuracy, but the equipment footprint and cost will also increase exponentially.

[0005] In view of the above experience, if the split light control is completed in only one set of equipment, since the propagation directions of each light beam in the convergence area are not parallel, the spacing and height of the receiving end signal will also have certain deviations, resulting in distorted measurement results. Therefore, an array-type focused laser differential interferometry measurement system is urgently needed to solve this problem. Summary of the invention

[0006] A common solution in existing array-type focused laser differential interferometry systems is to use diffraction optical elements (DOE) to split the light in the transmission light path to multiply the amount of simultaneous measurements. However, multi-path light brings new problems. In the receiving light path, since the multi-path light signals are actually focused on a spherical focal plane rather than a focal plane, this will cause the optical signal receiving device to be unable to accurately receive the multi-path light signals, especially the two outermost light signals. It is difficult to achieve a good signal-to-noise ratio, and the measurement accuracy is difficult to guarantee. The above problems are not solved by the current array-type focused differential interferometry measurement system.

[0007] The object of the present invention is to provide an array-type focused laser differential interferometry measurement system to solve the problem of how to improve the FLDI measurement efficiency while ensuring the measurement accuracy.

[0008] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: an array-type focused laser differential interferometry measurement system, comprising a transmitting light path and a receiving light path. After the transmitting light path diverges the coherent light into a cone, the diffraction optical element is used to generate a multi-path split light pair, and then the nonlinear polarized interference light in the cone light beam is filtered out through a polarizer; a multi-path optical fiber array receiving system is arranged at the tail end of the receiving light path, which comprises a plurality of groups of receiving terminals, each group of receiving terminals comprises a three-dimensional coordinate frame, a photodetector and an optical fiber probe, a rigid connecting rod is fixedly connected to the moving part of the three-dimensional coordinate frame, the receiving end of the optical fiber probe is fixedly connected to the rigid connecting rod on the outside, and the receiving end faces parallel to the optical axis direction of the convex lens, the rigid connecting rods of the plurality of groups of receiving terminals are adjusted in position respectively, so that the receiving end positions of the plurality of optical fiber probes correspond one by one to the final imaging focus positions of the multi-path light in the receiving light path, and the optical fiber probes of each group of receiving terminals are respectively connected to the photodetectors of each group.

[0009] The photodetector is relatively large. If multiple photodetectors are used directly, the adjustment space is limited and it can only be applied to the multiple sets of equipment mentioned in the above background technology. After adopting the above typewriter-type connecting rod structure multi-channel optical fiber array receiving system of the present invention, since the optical fiber probes are respectively fixed on rigid connecting rods connected to different three-dimensional coordinate frames, each optical fiber probe can be driven by the rigid connecting rod to accurately adjust the position individually, so that the receiving ends of all optical fiber probes fall on the spherical focal plane where the multi-channel optical signals are focused, and each optical signal is accurately received, thereby ensuring the measurement accuracy.

[0010] Preferably, the receiving optical path also includes a mounting seat, a plurality of slide rails are provided at the upper end thereof, the direction of the slide rails is parallel to the optical axis direction of the convex lens of the receiving optical path, and the three-dimensional coordinate frame and photoelectric detector of each group of receiving terminals are positionably slidably connected to a slide rail.

[0011] Preferably, the emission light path includes a coherent light source generator, a concave lens, a diffractive optical element, a polarizer, a Wollaston prism, and a convex lens arranged in sequence, wherein the diffractive optical element divides the conical light beam diverged by the concave lens into multiple light paths, and then filters out interference light through the polarizer; the Wollaston prism divides each linear polarization into two linear polarizations with a certain separation angle, mutually perpendicular polarization directions and equal light intensities; and the convex lens converges the divergent light beams in the observation area to form 6 pairs of separate focal points.

[0012] Preferably, the receiving optical path includes a convex lens, a Wollaston prism, a polarizer, a concave lens, and a multi-channel optical fiber array receiving system arranged in sequence, wherein the concave lens is used to adjust the actual focal length of the receiving end.

[0013] Another technical solution provided by the present invention is an application of an array-type focused laser differential interferometry measurement system in hypersonic flow field measurement, which is used to multiply the measurement efficiency while ensuring the measurement accuracy.

[0014] Another technical solution provided by the present invention is a multi-path light receiving method for a focused laser differential interferometer measurement system. According to the number of light beams received by the receiving light path, an equal number of fiber optic probes are set, and each fiber optic probe is fixed on a different position adjustment device. According to the specific imaging focus of each light beam, the receiving end position of each fiber optic probe is adjusted to correspond to each imaging focus position one by one. Each fiber optic probe is connected to a photodetector for converting light intensity information into electrical signals and transmitting them to a data processing and analysis system.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. The array-type focused laser differential interferometry measurement system has a simple structure and ingenious design. By adopting array design and focused laser differential interferometry technology, it can achieve high-precision and synchronous measurement of multiple measuring points in a small area to meet the needs of accurate detection of complex structures or small changes; through multi-point synchronous acquisition, it significantly improves the measurement speed and efficiency, reduces the time consumption of single-point measurement, thereby improving the work efficiency of the overall system and indirectly saving measurement costs.

[0017] 2. This array-type focused laser differential interferometry measurement system effectively solves the spatial limitation problems in optical path arrangement and signal acquisition in an extremely small measurement area through innovative fiber probe layout and three-dimensional control mechanism, ensuring the efficient operation of the measurement system in confined space.

[0018] 3. The array-type focused laser differential interferometry measurement system can adjust multiple points separately, ensuring that each light is received at the actual imaging focus, which can improve the reliability of the data and the measurement accuracy of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The principle comparison between the conventional solution and the array solution of Example 1 is shown;

[0020] Figure 2 Schematic diagram of the three-dimensional structure of the measurement system of Example 1 of the present invention;

[0021] Figure 3 This is a schematic diagram of the three-dimensional structure of a multi-channel optical fiber array receiving system according to Embodiment 1 of the present invention;

[0022] Figure 4 Schematic diagram of the positional relationship of the optical elements of Example 1. The three-dimensional coordinate frame in the figure is only a schematic diagram of the position.

[0023] In the figure: 1. three-dimensional coordinate frame; 2. rigid connecting rod; 3. photoelectric detector; 4. optical fiber probe; 5. mounting base. DETAILED DESCRIPTION

[0024] See also Figures 1 to 4 In the array-type focused laser differential interferometry measurement system of the present invention, after the coherent light is diverged into a cone, the emission light path first uses a diffractive optical element to generate a multi-path split light pair, and then passes through a polarizer to filter out the nonlinearly polarized interference light in the cone light beam;

[0025] After proposing the above improvement plan, in the actual array-type focused laser differential interference optical path installation process, due to the deviation of lens installation, the spacing and height of the signal appearing at the receiving end also have certain deviations, which will lead to inaccurate measurement results. On this basis, we continue to study how to solve the measurement accuracy problem;

[0026] In order to avoid distortion of measurement results caused by certain deviations in the spacing and height of the signals at the receiving end due to the propagation directions of the light beams in the convergence area not being parallel, the improvement idea of ​​the present invention for the receiving end is to find the position of the optical signal in real time. Therefore, the device receiving the optical signal needs to be able to achieve precise three-dimensional control to solve the problem of synchronous acquisition of multiple points.

[0027] Faced with the challenge of small measurement intervals and tiny signal spacing, we used extremely delicate fiber optic probes, which were fixed to a three-dimensional coordinate frame by rigid metal connecting rods to achieve precise three-dimensional control. This layout enables us to effectively arrange the probes in a small space and ensure accurate reception of optical signals. The row of photodetectors and independent connection of the fiber optic probes further ensure synchronous acquisition and accurate detection of signals.

[0028] The specific method is: according to the number of received light beams, set an equal number of fiber optic probes, fix each fiber optic probe on a different position adjustment device, adjust the receiving end position of each fiber optic probe according to the specific imaging focus of each light beam, so that it corresponds to each imaging focus position, and each fiber optic probe is connected to a photodetector to convert light intensity information into electrical signals and transmit them to the data processing and analysis system. This innovation not only overcomes space limitations, but also optimizes the optical path design and improves the overall performance of the system.

[0029] See also Figure 3 A multi-channel optical fiber array receiving system is arranged at the tail end of the receiving optical path, which includes multiple groups of receiving terminals. Each group of receiving terminals includes a three-dimensional coordinate frame 1, a photodetector 3 and an optical fiber probe 4. A rigid connecting rod 2 is fixedly connected to the moving part of the three-dimensional coordinate frame 1. The receiving end of the optical fiber probe 4 is fixedly connected to the rigid connecting rod 2 on the outside, and the receiving end is oriented parallel to the optical axis direction of the convex lens. The rigid connecting rods 2 of the multiple groups of receiving terminals are adjusted in position respectively, so that the receiving end positions of the multiple optical fiber probes 4 correspond one by one to the final imaging focus positions of the multiple lights in the receiving optical path respectively, and the optical fiber probes 4 of each group of receiving terminals are connected to the photodetectors 3 of each group respectively.

[0030] like Figure 3 As shown, to facilitate fixation and adjustment, the receiving optical path may further include a mounting seat 5, the upper end of which is provided with a plurality of slide rails, the direction of the slide rails being parallel to the optical axis direction of the convex lens of the receiving optical path, and the three-dimensional coordinate frame 1 and the photoelectric detector 3 of each group of receiving terminals are positionably slidably connected with a slide rail. Specifically, tightening devices may be provided on both sides of the lower ends of the three-dimensional coordinate frame 1 and the photoelectric detector 3, which can be positioned by tightening. With the above structure, the cumbersomeness of adjustment can be effectively reduced, and the positioning of the three-dimensional coordinate frame can be facilitated.

[0031] The difference between the present invention and the common focusing laser differential interference system in terms of optical elements is that the emission optical path of the present invention includes a coherent light source generator, a concave lens, a diffraction optical element (DOE), a polarizer, a Wollaston prism, and a convex lens arranged in sequence, wherein the diffraction optical element divides the conical light beam diverged by the concave lens into multiple light paths, and then filters out the interference light through the polarizer, and the Wollaston prism divides each line of polarized light into two linear polarized lights with a certain separation angle, mutually perpendicular polarization directions and equal light intensity, and the divergent light beams are converged in the observation area through the convex lens to form 6 pairs of separated focal points.

[0032] The receiving optical path differs from an ordinary focusing laser differential interference system in that it includes a convex lens, a Wollaston prism, a polarizer, a concave lens arranged in sequence, and the above-mentioned multi-channel optical fiber array receiving system, wherein the concave lens is used to adjust the actual focal length of the receiving end.

[0033] In addition, some structures and devices in the present invention can be equivalently replaced while achieving the same function. For example, the above-mentioned Wollaston prism can also adopt other birefringent prisms with the same splitting angle, such as Sanderson prism, etc. The three-dimensional coordinate frame can also adopt a bracket that can also achieve independent multi-dimensional adjustment, such as a four-dimensional adjustment frame, etc.

[0034] The present invention can be applied to the measurement of hypersonic flow fields, and can multiply the measurement efficiency on the basis of ensuring the measurement accuracy, especially playing an important role in wind tunnel tests, and can be mainly applied to the field of aerospace. It is based on the traditional focused laser differential interferometry method, and by introducing array technology, it can achieve high-precision measurement of the aerodynamic characteristics of the aircraft surface. By simulating the airflow environment under different flight conditions in the wind tunnel, the system can accurately observe and record the surface deformation and airflow distribution of the aircraft under various aerodynamic conditions, thereby providing key data for the design optimization, aerodynamic performance evaluation and structural improvement of the aircraft, and ensuring that the aircraft can achieve optimal performance in actual flight. The application of the measurement system of the present invention is conducive to improving the efficiency and accuracy of wind tunnel tests.

[0035] The present invention is further described below by way of examples. The following is only a reference example and is not intended to be a complete example or optimal solution. The data and structures therein should not be used as specific limitations on the technical solution of the present invention.

[0036] Embodiment 1:

[0037] The array focused laser differential interferometry system consists of Figures 1 to 4 As shown, the emission light path ( Figure 2 Center left) and receiving optical path ( Figure 2 The right side of the middle) consists of two parts.

[0038] 1) Emission light path. The helium-neon laser emits a parallel light beam with the same phase and polarization direction, which becomes a divergent conical light beam after passing through a concave lens. The light cone is divided into 6 light paths through a diffraction optical element (DOE). After passing through a polarizer, the interference light perpendicular to the polarization direction is filtered out, which improves the final interference effect. The light beam passes through a Wollaston prism. Based on the birefringence characteristics of the Wollaston prism, when the optical axis of the prism is 45° to the direction of polarized light, each line of polarized light is divided into 2 linear polarized lights (o light and e light) with a certain separation angle, perpendicular polarization directions and equal light intensity. The convex lens then converges the divergent light beam in the observation area (interacting with the sample to be tested in the test chamber), forming 6 pairs of separate focal points.

[0039] 2) Receiving optical path. After passing through the focusing area, the light beam diverges again, converges after passing through the convex lens, and passes through the second Wollaston prism. At this time, the light beams with a certain separation angle are merged into a beam of light with the same propagation direction. The laser beam passes through the polarizer, and the light intensity component in the parallel polarization direction is retained to form 6 terminal signals. The focal length is adjusted through the concave lens, and the 6 three-dimensional coordinate frames of the multi-channel fiber array receiving system are adjusted so that the receiving ends of the 6 fiber probes coincide with the imaging focus of the 6 optical signals. The 6 optical signals are accurately captured by the 6 optical fiber arrays, and then transmitted to the photoelectric detector for photoelectric conversion to generate electrical signals, which are then converted into digital signals through a high-frequency data acquisition card and analyzed and processed in real time by dedicated software to obtain the final measurement results.

[0040] In the transmitting optical path, the optical focusing "probe" can be adjusted by a manual vertical lifting platform and a manual precision translation platform to ensure accurate positioning of the optical path; in the receiving optical path, the optical "probe" can be flexibly adjusted by an electric translation platform and the three-dimensional coordinate frame of the present invention to ensure high precision and stability of the system.

[0041] The array-type measurement focusing laser differential interferometry measurement system of this embodiment has little modification on the basis of the original equipment, does not require multiple sets of optical elements, is easy to implement, and has significantly improved the measurement efficiency after being put into use. The measurement process of the traditional single-point measurement system is relatively slow. The new array-type measurement system can measure multiple points at the same time, greatly improving the speed of data acquisition.

[0042] The specific measurement time of the single-point measurement system depends on the complexity of the sample and the measurement accuracy requirements. Assuming that the traditional single-point measurement takes about 6 minutes to process a sample, the measurement efficiency and data accuracy are limited. After the introduction of the array measurement system, since the diffractive optical element in this embodiment is divided into 6 beam paths, the measurement time is shortened to one-sixth of the original time, that is, each sample only needs 1 minute to complete the measurement, and the measurement efficiency is increased by 6 times.

[0043] This array-type focused laser differential interferometry system uses a typewriter-type connecting rod structure multi-channel fiber array. Not only does it not cause the problem of reduced measurement accuracy due to multi-channel acquisition, but it also reduces measurement errors and improves data reliability by adjusting the receiving position of each light individually to ensure that it is at the actual focus. In addition, by configuring diffractive optical elements and multi-channel fiber array receiving systems, it can monitor multiple areas at the same time, thereby significantly improving measurement speed and spatial resolution. This advancement enables the system to more effectively obtain the aerodynamic characteristics of the aircraft surface in wind tunnel tests, meeting the needs of high-precision and high-efficiency measurements.

[0044] This improvement reduces the subsequent processing and adjustment costs caused by reduced accuracy, and saves an average of 200,000 yuan in rework costs caused by reduced accuracy each year, reducing related labor costs and material waste. The use of the new system not only speeds up the measurement speed, but also improves the measurement accuracy and overall production efficiency. It can save about 300,000 yuan in labor costs each year, and due to the reduction in errors, the overall annual cost is expected to be reduced by about 500,000 yuan.

[0045] The above are only preferred embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope defined by the claims.

[0046] Matters not described in detail in the present invention, such as the conformity of the lens position relationship with the imaging theorem and the focal length of the lens, are all well-known technologies to those skilled in the art.

Claims

1. An array-type focused laser differential interferometry system, comprising a transmitting optical path and a receiving optical path, characterized in that: After the coherent light is diverged into a cone, the emission light path first uses a diffractive optical element to generate a multi-path split light pair, and then passes through a polarizer to filter out nonlinearly polarized interference light in the cone light beam; A multi-channel optical fiber array receiving system is arranged at the tail end of the receiving optical path, comprising a plurality of groups of receiving terminals, each group of receiving terminals comprising a three-dimensional coordinate frame (1), a photoelectric detector (3) and an optical fiber probe (4); a rigid connecting rod (2) is fixedly connected to the movable part of the three-dimensional coordinate frame (1); the receiving end of the optical fiber probe (4) is fixedly connected to the rigid connecting rod (2) on the outside, and the receiving end faces parallel to the optical axis direction of the convex lens; the rigid connecting rods (2) of the plurality of groups of receiving terminals are respectively adjusted in position, so that the receiving end positions of the plurality of optical fiber probes (4) correspond one-to-one to the final imaging focus positions of the multi-channel light in the receiving optical path; and the optical fiber probes (4) of each group of receiving terminals are respectively connected to the photoelectric detectors (3) of each group.

2. The array-type focused laser differential interferometry measurement system according to claim 1, characterized in that: The receiving optical path also includes a mounting seat (5), the upper end of which is provided with a plurality of slide rails, the direction of the slide rails being parallel to the optical axis direction of the convex lens of the receiving optical path, and the three-dimensional coordinate frame (1) and the photoelectric detector (3) of each group of receiving terminals are positionably slidably connected to a slide rail.

3. The array-type focused laser differential interferometry measurement system according to claim 1, characterized in that: The emission light path includes a coherent light source generator, a concave lens, a diffractive optical element, a polarizer, a Wollaston prism, and a convex lens which are arranged in sequence. The diffractive optical element divides the conical light beam diverged by the concave lens into multiple light paths, and then filters out interference light through the polarizer. The Wollaston prism divides each linear polarization into two linear polarizations with a certain separation angle, mutually perpendicular polarization directions and equal light intensity. The divergent light beams are converged in an observation area through the convex lens to form 6 pairs of separated focal points.

4. The array-type focused laser differential interferometry measurement system according to claim 1, characterized in that: The receiving optical path comprises a convex lens, a Wollaston prism, a polarizing plate, a concave lens, and a multi-channel optical fiber array receiving system arranged in sequence, wherein the concave lens is used to adjust the actual focal length of the receiving end.

5. Application of an array-type focused laser differential interferometry measurement system according to any one of claims 1 to 4 in hypersonic flow field measurement, characterized in that: Used to multiply measurement efficiency while ensuring measurement accuracy.

6. A multi-path light receiving method for a focused laser differential interferometry system, characterized in that: According to the number of light beams received by the receiving optical path, an equal number of fiber optic probes are set, and each fiber optic probe is fixed on a different position adjustment device. According to the specific imaging focus of each light beam, the receiving end position of each fiber optic probe is adjusted to correspond to each imaging focus position one by one. Each fiber optic probe is connected to a photodetector to convert the light intensity information into an electrical signal and transmit it to the data processing and analysis system.

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