A scanning sheet light generation system for 3DLIF

Abstract

The application belongs to the technical field of laser shaping, and discloses a scanning sheet light generating system for 3DLIF. The system comprises three modules, a first beam expanding and collimating module, a rotatable diaphragm and a second beam expanding module. The first beam expanding and collimating module is used for outputting collimated sheet light with a preset width. The rotatable diaphragm is provided with two slit bands on the outer circumference. Each slit band gradually rises along the circumferential direction and comprises a plurality of rectangular slits distributed continuously. The rectangular slits in the two slit bands are symmetric about the axis of the rotatable diaphragm. The collimated sheet light is incident from one of the rectangular slits, cut by the incident slit and emitted from the slit symmetric with the incident slit, and shaped into linear laser. The second beam expanding module is used for shaping the linear laser into scanning sheet laser with a diffusion angle. Through the application, the problems of complex structure, harsh installation requirement and non-parallel sheet light of the current sheet light source scanning system applied to 3DLIF technology are solved.

Description

A scanning sheet light generation system for 3DLIF Technical Field

[0001] This invention belongs to the field of laser shaping technology, and more specifically, relates to a scanning sheet light generation system for 3DLIF. Background Technology

[0002] Laser-induced fluorescence (LIF) is a flow field observation technique in fluid mechanics, specifically involving the visualization of flow fields and the measurement of concentration and temperature fields. It primarily utilizes a sheet light source to illuminate the flow field, then detects the fluorescence signals generated by excited fluorescent dyes within the flow field, enabling direct observation of fluid motion. Due to its significant advantages in observing flow field motion, LIF technology has been widely applied. Generally, LIF technology can observe fluid flow within a single plane of a flow field, thus basically meeting the requirements for measuring two-dimensional flow fields. However, when using LIF technology to explore complex three-dimensional flow phenomena, it is often like the blind men and the elephant, unable to provide a detailed understanding of the instantaneous three-dimensional flow characteristics. In light of these issues, researchers have proposed a scanning laser-induced fluorescence (3DLIF) technique. Its basic principle is similar to a CT scanner, acquiring flow field characteristics in multiple planes within a short time, and finally obtaining the three-dimensional information of the flow field through three-dimensional reconstruction technology.

[0003] Before building an experimental system based on 3DLIF technology, the illumination problem of the flow field needs to be solved, namely, achieving the scanning of sheet light at multiple spatial positions within the flow field to be measured. Currently, there are three main solutions internationally: the galvanometer scheme, the rotating drum scheme, and the rotating scanner scheme. However, all of these sheet light source scanning schemes have certain drawbacks. The galvanometer scheme is currently the most widely used, with a relatively simple overall system structure, but it suffers from the problem of the sheet light not being perfectly parallel, thus introducing errors into subsequent flow field reconstruction. While the rotating drum and rotating scanner schemes can obtain parallel sheet light, their system structures are more complex, and they have stringent requirements for the concentricity of the device and the installation angle. Due to these issues, all of these schemes are still in the research and experimental stage and have not yet entered the industrialization stage. Therefore, proposing a scanning scheme with a simple structure that enables the sheet light source to scan the measurement area in parallel is essential for improving the measurement accuracy and three-dimensional reconstruction of the flow field. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a scanning sheet light generation system for 3DLIF, which solves the problems of complex structure, demanding installation requirements and non-parallel sheet light in the current sheet light source scanning system applied to 3DLIF technology.

[0005] To achieve the above objectives, according to this invention, a scanning sheet light generation system for 3DLIF is provided. This system includes three modules: a first-stage beam expander and collimator module, a rotatable aperture, and a second-stage beam expander module.

[0006] The first-stage beam expander and collimator module is used to output collimator light of a preset width;

[0007] The rotatable aperture is located behind the first-stage beam expander and collimator module. It is cylindrical and has two slit bands on its outer circumference. Each slit band gradually rises along the circumference and includes multiple rectangular slits. The rectangular slits in the two slit bands are symmetrical about the axis of the rotatable aperture. The collimator light enters from one rectangular slit and exits from the symmetrical rectangular slit in the other slit band, thus shaping it into a line laser. When the rotatable aperture rotates along the axis, different rotation directions correspond to different scanning directions of the laser.

[0008] The second-stage beam expander module is located behind the rotatable aperture. The line laser emitted from the rotatable aperture is shaped into a scanning sheet laser with a diffusion angle after entering the second-stage beam expander module.

[0009] More preferably, the rectangular slits are evenly distributed on the circumference of the rotatable aperture, and the circumferential angle corresponding to each rectangular slit is 360° / 2N, where N is the total number of rectangular slits in a single slit band.

[0010] More preferably, the height of the rectangular slit is w, and its relationship with the width of the collimating plate light output by the first-stage beam expander and collimator module is as follows:

[0011] Nw≤S

[0012] Where N is the total number of rectangular slits in a single slit band, and S is the width of the collimator light.

[0013] More preferably, the central axes of the first-stage beam expanding and collimating module, the rotatable aperture, and the second-stage beam expanding module are on the same straight line.

[0014] More preferably, the center of the rotatable aperture is hollow for heat dissipation.

[0015] More preferably, the first-stage beam expanding and collimating module includes a Powell prism and a plano-convex cylindrical mirror, wherein the Powell prism is disposed in front of the plano-convex cylindrical mirror for receiving laser light.

[0016] More preferably, the second-stage beam expander module is a plano-concave cylindrical mirror.

[0017] More preferably, the system further includes a laser and a motor, the laser being positioned in front of the first-stage beam expander and collimator module for emitting laser light, and the motor being used to drive the rotatable aperture to rotate.

[0018] More preferably, the two ends of the rotatable aperture are respectively provided with connecting parts for connecting the motor and the fixed bearing.

[0019] More preferably, the connecting portion for connecting the motor is frustum-shaped, and the connecting portion for connecting the bearing is T-shaped.

[0020] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0021] 1. The present invention employs a rotatable aperture, which consists of two stacked slit bands with multiple rectangular slits arranged in a stepped and symmetrical manner. By rotating the aperture, light rays can be emitted and scanned in a straight line. The scanning frequency of the light rays can be changed by adjusting the rotation speed of the aperture. The structure is simple and has low installation requirements, effectively solving the problems in existing 3DLIF technology.

[0022] 2. This invention can process rotating apertures with different numbers of sides as needed to obtain different numbers of scanning planes to meet actual usage requirements. Compared with existing solutions, it can obtain a better dwell time for sheet light, which is of positive significance for improving the acquisition of high signal-to-noise ratio images by subsequent 3DLIF system cameras.

[0023] 3. The scanning sheet light generation scheme of the present invention is not limited to the field of 3DLIF, but can also be applied to scanning particle image velocimetry (3DPIV) and other optical scanning fields. The present invention has a simple structure, low processing cost, and low installation requirements. It does not involve the rotation of optical components, thus ensuring high safety. Attached Figure Description

[0024] Figure 1 is a schematic diagram of the working principle of the rotatable aperture constructed according to a preferred embodiment of the present invention, wherein (a) is a schematic diagram of the structure and light shaping effect of the rotatable aperture, (b) is a structural unfolded diagram, and (c) is a timing diagram of the light position and time of the scanning sheet.

[0025] Figure 2 illustrates the working process of the 3DLIF scanning sheet light generation system constructed according to a preferred embodiment of the present invention, wherein (a) is a front view and (b) is a top view;

[0026] Figure 3 is a schematic diagram of the upper half of the rotatable aperture constructed according to a preferred embodiment of the present invention;

[0027] Figure 4 is a schematic diagram of the structure of the lower half of the rotatable aperture constructed according to a preferred embodiment of the present invention;

[0028] Figure 5 is a schematic diagram of the structure of the 3DLIF scanning sheet light generation system constructed according to a preferred embodiment of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0030] A scanning sheet light generation system for 3DLIF mainly consists of three parts: a first-stage beam expander and collimator module, a rotatable aperture module, and a second-stage beam expander module. Its schematic diagram is shown in Figure 2.

[0031] The first-stage beam expander and collimator module consists of a Powell prism and a plano-convex cylindrical mirror. Taking a laser with a Gaussian energy distribution as the incident light source as an example, the incident light with a cross-sectional diameter of d is homogenized and shaped by the Powell prism, and outputs a sheet light with a certain divergence angle and uniform spanwise energy distribution. Then, the plano-convex cylindrical mirror collimates the incident sheet light, and outputs a collimated sheet light with a width of S and a thickness of d.

[0032] A schematic diagram of the rotatable aperture is shown in Figure 1. In Figure 1(a), the structure and light shaping effect of the rotatable aperture are shown; in Figure 1(b), the unfolded structure of the rotatable aperture is shown; and in Figure 1(c), the timing diagram of the light position and time of the scanning sheet is shown. In this embodiment, the core component of the rotatable aperture is a regular polyhedral (2N) prism with rectangular slits symmetrically distributed in a stepped manner along the axis of the prism.

[0033] When using a rotatable aperture, the input collimating light needs to be aligned with the prism axis on the same horizontal plane. Within a certain angular range... A rectangular aperture allows only a single slit of laser light to pass through, thus shaping the input sheet light into a cross-section of [missing information]. A line laser. As the aperture rotates, the collimated light is shaped by adjacent slits on the prism to produce outputs of the same size, with a horizontal spacing of [missing information]. The linear laser is a linear laser. Furthermore, since the intensity of the input beam is uniform along its width, the intensity distribution of the linear laser output after being cut by the rectangular slit is also essentially the same. The rectangular aperture is rotated by a high-speed motor. When the rotation direction of the rotatable aperture is clockwise, the scanning direction of the linear laser is positive, as shown by the solid arrow in Figure 1(a). When the rotation direction is counterclockwise, the scanning direction of the linear laser is negative, as shown by the dashed arrow in Figure 1(a). The rectangular slits are symmetrically distributed on the polygonal prism relative to the prism axis. Therefore, when the prism rotates one revolution, the flow field of the area under test can be scanned twice, and the size of the scanned area is... In fact, the working time of the slit directly corresponds to the dwell time of the sheet light at a certain spatial position. Sufficient dwell time is crucial for improving the camera's exposure and enhancing the signal-to-noise ratio of the image.

[0034] The dwell time and position of the scanning beam are shown in Figure 1(c). With a rotatable aperture rotation speed of n revolutions per minute, the working time for each slit is... seconds, that is, the residence time of each light element. As can be seen from the timing diagram, the dwell position changes in a stepped manner. Therefore, compared with existing international solutions, this solution can provide a superior dwell time for sheet light. Furthermore, the rotatable aperture has a simple structure, low manufacturing cost, and can be flexibly designed according to specific needs.

[0035] As shown in Figures 3 and 4, the rotatable aperture has connecting parts at both ends, used to connect the motor and the fixed bearing, respectively. The connecting part for the motor is designed in a frustum shape to reduce the overall weight of the device while ensuring structural reliability. The connecting part for the bearing is T-shaped.

[0036] Finally, the output scanning line laser undergoes final shaping by a plano-concave cylindrical mirror, resulting in a scanning sheet laser with a specific diffusion angle. Since the line laser scanning array passes parallel to the long axis of the plano-concave cylindrical mirror, the mirror provides the same shaping effect on the sheet laser output at each position, resulting in a uniform intensity distribution for each sheet laser.

[0037] The present invention will be further described below with reference to specific embodiments.

[0038] Example 1

[0039] A scanning sheet light generation system for 3DLIF mainly consists of three parts: a first-stage beam expander and collimator module, a rotatable aperture module, and a second-stage beam expander module. The device of this invention is described in detail below:

[0040] The laser used in this case is a high-energy green laser with a power of 40W. The emitted beam intensity distribution is Gaussian, and the diameter d is 4mm. The Powell prism has a diameter of 9mm, a divergence angle of 20°, and is made of K9 glass. K9 glass is a high-performance optical material with good refractive and light-transmitting properties, and is a common optical component material in China. The Powell prism is fixed using a V-shaped clamp, model PTS-25, which can hold cylindrical lenses with dimensions ranging from 0 to 25mm. The plano-convex cylindrical lens has dimensions of 60x30mm, a focal length of f of 100mm, and is model GLH15-60x30-100, made of uncoated K9 glass. The plano-concave cylindrical lens is fixed using an adjustable frame, model MALH-3P, which can hold rectangular lenses with lengths from 10 to 75mm. The two lens frames are connected and fixed to two slides on the same guide rail by support rods. By adjusting the distance between the two slides to 200mm, the input line laser is shaped into a collimated surface beam with a width of 20mm. The first-stage beam expander and collimator module is placed on the lifting platform for easy adjustment of coaxiality with other modules. Note that for Powell prisms with different divergence angles, a plano-convex cylindrical lens with the corresponding focal length needs to be selected for sheet beam collimation. Since the Powell prism is a non-circular lens, the collimation relationship between the two is relatively complex and can be selected after simulation using optical simulation software Zemax.

[0041] The rotatable aperture mainly consists of a polygonal prism with slits and a servo motor. A schematic diagram of the prism structure is shown below. This case uses a 24-faceted prism structure, enabling sheet light scanning at 12 adjacent spatial positions. The prism has a side width of 11.6mm, a height of 33mm, and a side-to-side distance of 88mm. To reduce the overall weight of the rotating component and enhance its heat exchange performance, the rotating component features a hollow design with a wall thickness of 6mm. There are 24 slits, each 10mm long and 1.5mm wide, allowing for the scanning of sheet light with a thickness of 18mm. The servo motor is model HYUM 0200-03-D14, with a speed adjustment range of 0-1000 rpm. To ensure a secure connection between the prism and the motor, a polygonal frustum structure is used at the top of the prism, with a motor shaft connection hole at the center of the frustum, secured with a keyway. The rotatable aperture module is 3D printed and coated with fire-retardant paint to prevent specular reflection of the laser. To reduce the lateral load on the motor shaft, a T-shaped shaft is designed on the other side of the prism and connected to the bearing housing. The bearing housing is a compact double-bearing type, model MT173 / 6905ZZ, with a bearing length of 35mm and a bore diameter of 35mm. The bearing housing is fixed to the T-shaped aluminum profile bracket by threaded installation and is placed coaxially with the prism.

[0042] The secondary beam expander module mainly consists of a plano-concave cylindrical lens, model GCL-110311, with a diameter of 25.4mm, a focal length of f-25mm, and made of uncoated K9 glass. The plano-concave cylindrical lens is mounted inside a cylindrical sleeve, model SM1L10, with an SM1 thread engraved inside the sleeve, 25.4mm deep. Two threaded retaining rings secure the lens inside the sleeve. A clamp and optical support rod fix the sleeve in a coaxial position with the scanning sheet light. By adjusting and rotating the sleeve, the diffuser end of the plano-concave cylindrical lens is aligned parallel to the incident scanning line light, ultimately outputting parallel-emitting scanning sheet light.

[0043] Table 1 lists some parameters of the sheet light scanning system at three different rotation speeds. Figure 5 shows a physical image of the 3DLIF sheet light scanning system assembled based on the above components. The sheet light scanning results show that a relatively consistent intensity of the scanning sheet light was obtained. It should be noted that after adjustment, the aperture should generally be rotated first, and then the laser should be turned on, to prevent the high-energy laser from irradiating the aperture for a prolonged period and burning or damaging its structure. When shutting down the system, the laser should be turned off first, and then the motor should be turned off, to improve the safety of system operation.

[0044] Table 1. Optical scanning parameters at different rotation speeds

[0045]

[0046] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A scanning sheet light generation system for 3DLIF, characterized in that, The system comprises three modules: a first-stage beam expander and collimator module, a rotatable aperture, and a second-stage beam expander module. The first-stage beam expander and collimator module outputs collimating light of a preset width. The rotatable aperture, cylindrical in shape and positioned behind the first-stage beam expander and collimator module, has two slits on its outer circumference. Each slit gradually rises along the circumference and includes multiple rectangular slits. The rectangular slits in the two slits are symmetrical about the axis of the rotatable aperture. The collimating light enters from one rectangular slit and exits through the other slit. The laser beam is emitted from a rectangular slit symmetrical to the rotatable aperture, and thus shaped into a line laser. When the rotatable aperture rotates along its axis, different rotation directions correspond to different scanning directions of the laser. The second-stage beam expander is located behind the rotatable aperture. The line laser emitted from the rotatable aperture enters the second-stage beam expander and is shaped into a scanning sheet laser with a diffusion angle. The rectangular slits are evenly distributed on the circumference of the rotatable aperture, and the circumferential angle corresponding to each rectangular slit is 360° / 2N, where N is the total number of rectangular slits in a single slit band.

2. The scanning sheet light generation system for 3DLIF as described in claim 1, characterized in that, The height of the rectangular slit is w, and its relationship with the width of the collimating plate light output by the first-stage beam expander and collimator module is as follows: Nw ≤ S, where, N is the total number of rectangular slits in a single slit band, and S is the width of the collimator light.

3. A scanning sheet light generation system for 3DLIF as described in claim 1 or 2, characterized in that, The central axes of the first-stage beam expander and collimator module, the rotatable aperture, and the second-stage beam expander module are on the same straight line.

4. A scanning sheet light generation system for 3DLIF as described in claim 1 or 2, characterized in that, The center of the rotatable aperture is hollow for heat dissipation.

5. A scanning sheet light generation system for 3DLIF as described in claim 1 or 2, characterized in that, The first-stage beam expander and collimator module includes a Powell prism and a plano-convex cylindrical mirror. The Powell prism is positioned in front of the plano-convex cylindrical mirror and is used to receive laser light.

6. A scanning sheet light generation system for 3DLIF as described in claim 1 or 2, characterized in that, The second-stage beam expander module is a plano-concave cylindrical mirror.

7. A scanning sheet light generation system for 3DLIF as described in claim 1 or 2, characterized in that, The system also includes a laser and a motor. The laser is positioned in front of the first-stage beam expander and collimator module to emit laser light, and the motor is used to drive the rotatable aperture to rotate.

8. The scanning sheet light generation system for 3DLIF as described in claim 7, characterized in that, The rotatable aperture has connecting parts at both ends, which are used to connect the motor and the fixed bearing, respectively.

9. A scanning sheet light generation system for 3DLIF as described in claim 8, characterized in that, The connecting part for connecting the motor is frustum-shaped, and the connecting part for connecting the bearing is T-shaped.

Images