CN114414837A - Non-contact laser speed measurement system based on Taeman-Green interferometer - Google Patents

Abstract

The invention discloses a non-contact laser speed measurement system based on a Tyman-Green interferometer, wherein a first lens, a quarter wave plate, a polarization beam splitter, a beam splitter prism and a first reflector are sequentially arranged on a light path vertical to an object to be measured from near to far, a beam expander and a laser are sequentially arranged on the light path below the beam splitter prism from near to far, a second reflector is arranged on the light path above the beam splitter prism, a second lens and a first photoelectric detector are sequentially arranged on the light path below the polarization beam splitter from near to far, a third lens and a charge coupling element are sequentially arranged on the light path above the polarization beam splitter from near to far, and the size of a light spot falling on the object to be measured is the same as that of a light spot falling on the charge coupling element. The invention realizes the coaxial structure of two emergent lights and avoids the separation of two beams of lights in the cross-interface measurement.

Description

A Non-contact Laser Velocimetry System Based on Taiman-Green Interferometer

technical field

The invention relates to the field of laser speed measurement, in particular to a non-contact laser speed measurement system based on a Taiman-Green interferometer.

Background technique

Laser velocimetry is the measurement of the speed of an object by means of a laser. There are two basic principles for determining the speed using optical technology. One is based on measuring the Doppler frequency shift of the scattered particles of the target, and the other is the time-of-flight method, that is, measuring The time it takes for a particle to traverse a certain spatial interval. The velocity of the measured object is determined using Doppler shift and time of flight, respectively. With the development of science and technology, the traditional measurement equipment can no longer meet the needs of the current situation, and has been gradually eliminated, and the laser speed sensor has been widely used, it is of great significance in many fields of measurement.

Existing laser Doppler velocimeters mainly use the double beam-double scattering mode, and the double beam differential mode laser Doppler velocimetry system requires the detection light to be strictly intersected at the point to be measured, which leads to the opto-mechanical stability of such systems. The requirements are extremely high. When used in some harsh environments (underwater high-pressure environment, cross-interface measurement and environment with certain interface fluctuations, etc.), the detection light is prone to non-intersection at the point to be measured, such as measuring deep-sea hydrothermal fluids. At the flow rate, with the increase of seawater pressure, the deformation of the light window of the pressure chamber makes it difficult for the double beams to keep crossing in the hydrothermal velocity detection, which will eventually lead to measurement failure. The interval and direction of the interference fringes are fixed and cannot be adjusted with the change of the particle size of the measured object and the change of the direction of the measured speed.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies of the prior art, and to provide a Tyman-Green interference based method that can avoid the problem that the probe light cannot cross at the point to be measured, has good stability, and can measure the velocity of particles in different directions and sizes. The non-contact laser velocimetry system of the instrument.

The purpose of this invention is to realize through the following technical solutions:

A non-contact laser velocimetry system based on a Taiman-Green interferometer, comprising a laser, a beam expander, a beam splitting prism, a No. 1 mirror, a No. 2 mirror, a polarization beam splitter, a quarter-wave plate, Charge-coupled element, No. 1 photodetector, No. 1 lens, No. 2 lens, No. 3 lens, on the optical path perpendicular to the object to be measured, the No. 1 lens and the quarter-wave are arranged in order from near to far from the object to be measured. A beam splitter, a polarizing beam splitter, a beam splitting prism, a No. 1 reflector, a beam expander and a laser are arranged in order from near to far away from the beam splitting prism on the optical path below the beam splitting prism, and two beam splitters are arranged on the optical path above the beam splitting prism. No. 1 mirror, set the No. 2 lens and No. 1 photodetector in order from near to far from the polarizing beam splitter on the optical path below the polarizing beam splitter, and set the No. The third lens and the charge-coupled element are arranged in sequence at the far and far ends, wherein the size of the light spot falling on the object to be tested is the same as the size of the light spot falling on the charge-coupled element.

Preferably, the No. 1 lens and the No. 2 lens are lenses of the same specification, and the distance between the No. 1 lens and the object to be measured is equal to the distance between the No. 2 lens and the CCD.

Preferably, a collimator is provided between the laser and the beam expander.

Preferably, it also includes a No. 4 lens and a detector array, the No. 4 lens and the detector array are arranged in order from near to far from the object to be measured, and the detector array includes at least one No. 2 photodetector.

The beneficial effects of the present invention are:

(1) The non-contact laser velocimetry system based on the Taiman-Green interferometer realizes the coaxial structure of the two outgoing beams. In the cross-interface measurement, the phenomenon of separation of the two beams is avoided, and it is suitable for various harsh environments. It has a wide range of applications and high measurement stability.

(2) By adjusting the positions of the No. 1 mirror and No. 2 mirror, the direction and spacing of the interference fringes can be changed, so as to realize the measurement of particle velocities in different directions and sizes.

(3) Multi-point simultaneous speed measurement can be realized by setting the detector array.

Description of drawings

Fig. 1 is the overall structure schematic diagram of the present invention;

Figure 2 is a graph of the speed and signal-to-noise ratio varying with the rotational speed;

Figure 3 is a graph of frequency and speed varying with rotational speed;

Figure 4 is a graph of frequency and signal-to-noise ratio as a function of the number of stripes;

In the figure, 1-laser, 2-collimator, 3-beam expander, 4-beam splitting prism, 5-1 mirror, 6-2 mirror, 7-polarization beam splitter, 8-quarter One wave plate, 9-No.1 lens, 10-Object to be tested, 11-No.2 lens, 12-No.1 photodetector, 13-No.3 lens, 14-Charge coupled element, 15-No.4 lens, 16 - Photodetector number two.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present invention.

Referring to Figures 1-4, the present invention provides a technical solution:

A non-contact laser velocimetry system based on a Taiman-Green interferometer, comprising a laser 1, a beam expander 3, a beam splitting prism 4, a No. 1 mirror 5, a No. 2 mirror 6, a polarization beam splitter 7, and a fourth One-wave plate 8, charge-coupled element 14, No. 1 photodetector 12, No. 1 lens, No. 2 lens 11, No. 3 lens 13, on the optical path perpendicular to the object to be tested 10, the distance from the object to be measured 10 is closer The first lens 9, the quarter-wave plate 8, the polarizing beam splitter 7, the beam splitting prism 4, and the first reflector 5 are arranged in turn, and the distance from the beam splitting prism 4 on the optical path under the beam splitting prism 4 The beam expander 3 and the laser 1 are arranged in turn, and the second reflector 6 is arranged on the optical path above the beam splitting prism 4, and the polarizing beam splitter 7 is arranged on the optical path below the polarizing beam splitter 7 from near to far. The No. 2 lens 11 and the No. 1 photodetector 12 are arranged on the optical path above the polarizing beam splitter 7 from the polarizing beam splitter 7 in order from near to far away. The size of the light spot falling on the object to be tested 10 is the same as the size of the light spot falling on the charge-coupled element 14, which ensures the accuracy of the measurement result.

Further, a collimator 2 is provided between the laser 1 and the beam expander 3 . The light emitted by the laser 1 is collimated and then enters the beam expander 3 in parallel.

When working, the linearly polarized light is output from the laser 1, passes through the collimator 2 and the beam expander 3, and then reaches the semi-transparent and semi-reflective beam splitting prism 4, one of which is reflected by the beam splitting prism 4 to the No. The beam splitting prism 4 is incident on the second reflector 6 , and the two beams are reflected by the first reflector 5 and the second reflector 6 respectively and then merged at the beam splitter prism 4 , and form an interference beam and enter the polarization beam splitter 7 . Most of the interference light is focused on the object to be tested 10 by the No. 1 lens 9 after passing through the quarter-wave plate 8, and the scattered light of the particles of the object to be tested is collected by the No. 1 lens 9, and then passes through the quarter-wave plate 8. After being reflected by the polarization beam splitter 7 , the second lens 11 is focused on the first photodetector 12 , and a small part of the interference light is reflected by the polarization beam splitter 7 and collected by the third lens 13 and focused on the charge-coupled element 14 . The No. 1 photodetector 12 measures the frequency, the charge-coupled element 14 measures the fringe spacing, and the speed of the object to be measured is the frequency multiplied by the spacing. By adjusting the positions of the No. 1 mirror 5 and the No. 2 mirror 6, the measurement of the object to be measured 10 of different sizes and different measurement directions can be adapted.

In this embodiment, in order to ensure that the size of the light spot falling on the object to be tested 10 is the same as the size of the light spot falling on the charge-coupled element 14, and at the same time to ensure convenient operation, the first lens 9 and the second lens 11 use the same specification lens , and the distance between the No. 1 lens 9 and the object to be tested 10 is equal to the distance between the No. 2 lens 11 and the CCD 14 .

由频率f_D和条纹间距d得到的速度V如图2所示，每个值是三个重复的平均值。为了比较，理论速度也由旋转直径15.5mm和斩波器显示的旋转速度计算，两者重合较好。图2中还描述了不同速度下的信噪比(SNR)，SNR随着速度的增加而降低，此结论与双光束差动模式的激光多普勒测速系统基本一致，测量结果精确。In order to verify the feasibility of the velocimetry method, a non-contact laser velocimetry system based on the Taiman-Green interferometer was designed and built. The optical chopper with adjustable speed is selected as the object to be tested. The optical chopper is a precision instrument with stable speed and small jitter. The point on the chopper is used as the test point to measure the speed in the tangential direction of this point. The fringe direction was adjusted to be perpendicular to the linear velocity of the photo-chopper surface, and the fringe spacing observed using the CCD 14 was 6.4 μm. The number of stripes is 27. The scattered light on the target is collected by the No. 1 lens 9 , passes through the quarter-wave plate 8 , is reflected by the polarizing beam splitter prism 7 , and is focused by the No. 2 lens 11 to the No. 1 photodetector 12 . The purpose of the experiment is to measure the frequency f _D of the output signal of the No. 1 photodetector 12 as a function of the rotational speed, while

The velocity V obtained from the frequency f _D and the fringe spacing d is shown in Figure 2, and each value is the average of three replicates. For comparison, the theoretical speed is also calculated from the rotation diameter of 15.5mm and the rotation speed displayed by the chopper, and the two coincide well. Figure 2 also describes the signal-to-noise ratio (SNR) at different speeds. The SNR decreases with the increase of speed. This conclusion is basically consistent with the laser Doppler velocimetry system in the dual-beam differential mode, and the measurement results are accurate.

Further, it also includes a No. 4 lens 15 and a detector array. The No. 4 lens 15 and the detector array are arranged in order from near to far from the object to be tested 10, and the detector array includes at least one No. 2 photodetector 16. . The traditional double-beam differential mode speed measurement system can only measure the speed of one measurement point. On the basis of this scheme, adding a detector array can realize the measurement of multi-point speed on the object to be measured 10 (using multiple No. 2 photodetectors 16 to achieve multiple For point measurement, each No. 2 photodetector 16 can measure one point, and a certain number of No. 2 photodetectors 16 can be set according to requirements to measure the speed of a certain number of points). The frequency is measured by the No. 2 photodetector 16, the fringe spacing is measured by the charge-coupled element 14, and the speed of the object to be measured is the frequency multiplied by the spacing.

A three-dimensional micro-movement stage is used to move the optical chopper closer to or away from the focal point of the first lens 9 . The focal point is marked as 0, and in the direction close to the lens 9, the position is marked from 0.5 mm to 5.5 mm. The scattered light is collected by the No. 4 lens 15, the No. 4 lens 15 is placed obliquely behind the target, and the No. 2 photodetector 16 has a relatively large photosensitive surface. Figure 3 depicts the variation of frequency with velocity at different locations. The frequency increases approximately linearly with increasing velocity, a result consistent with a differential laser Doppler system. The frequency increases as the target gets closer to the focal point, because the closer to the focal point, the smaller the spot on the target. But the number of fringes does not change at different positions, so the fringe spacing becomes smaller and the frequency _fD becomes larger at the same speed. The speeds obtained at different positions are shown in Figure 3. The speed determined by the frequency and the fringe interval is proportional to the rotation speed, and the same speed measured at different positions is basically equal. Thus, the detector array can measure the velocity at different locations simultaneously. In Figure 4, the chopper is fixed at the position marked 0.5mm at 100 rpm. The number of stripes can be changed by adjusting the No. 1 mirror 5 and No. 2 mirror 6. As the number of stripes increases, the frequency increases, so we can select the appropriate number of stripes to obtain the appropriate signal frequency. The signal-to-noise ratios under different fringe numbers are also plotted in Figure 4. As the fringe numbers increase, the SNR first increases and then decreases. For a certain size of particles, a suitable fringe spacing is required to obtain a higher signal-to-noise ratio.

The above are only preferred embodiments of the present invention, and it should be understood that the present invention is not limited to the form disclosed herein, should not be construed as an exclusion of other embodiments, but may be used in various other combinations, modifications and environments, and Modifications can be made within the scope of the concepts described herein by virtue of the above teachings or skill or knowledge in the relevant field. However, modifications and changes made by those skilled in the art do not depart from the spirit and scope of the present invention, and should all fall within the protection scope of the appended claims of the present invention.

Claims (4)

1. A non-contact laser speed measurement system based on a Tyman-Green interferometer is characterized in that: the device comprises a laser (1), a beam expander (3), a beam splitter prism (4), a first reflector (5), a second reflector (6), a polarization beam splitter (7), a quarter wave plate (8), a charge coupling element (14), a photoelectric detector (12), a first lens, a second lens (11) and a third lens (13), wherein the first lens (9), the quarter wave plate (8), the polarization beam splitter (7), the beam splitter prism (4) and the first reflector (5) are sequentially arranged on a light path perpendicular to a to-be-detected object (10) from near to far away from the to-be-detected object (10), the beam expander (3) and the laser (1) are sequentially arranged on the light path below the beam splitter prism (4) from near to far from the beam splitter prism (4), the second reflector (6) is arranged on the light path above the beam splitter prism (4), the second lens (11), the second reflector (11) and the third reflector (13) are sequentially arranged on the light path below the polarization beam splitter prism (7) from near to far from the polarization beam splitter prism (7), And the first photoelectric detector (12) is sequentially provided with a third lens (13) and a charge coupling element (14) from near to far away from the polarization beam splitter (7) on an optical path above the polarization beam splitter (7), wherein the size of a light spot falling on the object to be detected (10) is the same as that of a light spot falling on the charge coupling element (14).

2. The system of claim 1 in which the laser system is a Taeman-Green interferometer based non-contact laser velocimetry system, wherein: the first lens (9) and the second lens (11) adopt lenses with the same specification, and the distance between the first lens (9) and the object to be measured (10) is equal to the distance between the second lens (11) and the charge coupling element (14).

3. The system of claim 1 in which the laser system is a Taeman-Green interferometer based non-contact laser velocimetry system, wherein: a collimator (2) is arranged between the laser (1) and the beam expander (3).

4. The system of claim 1 in which the laser system is a Taeman-Green interferometer based non-contact laser velocimetry system, wherein: still include No. four lens (15) and detector array, No. four lens (15) and detector array set gradually from near to far away apart from determinand (10), detector array includes No. two at least photoelectric detector (16).

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