High-precision detection device and detection method for laser power and fluctuation thereof

Abstract

The invention discloses a high-precision detection device for laser power and fluctuation thereof, and the device comprises a to-be-detected laser, and the to-be-detected laser outputted by the to-be-detected laser passes through a plurality of polarization splitting prisms, a Faraday rotator, a plurality of lambda / 4 wave plates, a broken-line-shaped reflector array, and a first torsional pendulum reflector and a second torsional pendulum reflector on a swing rod. Multiple actions on the swing rod are realized, and the incident laser to be measured is separated from the finally emergent laser to be measured; the deflection of the swing rod is measured by irradiating an angle measurement reflector in the center of the swing rod with measurement laser, and the swing rod is restored to an initial angle by using control laser. The invention also discloses a high-precision detection method for the laser power and the fluctuation thereof, the oscillating bar is kept at an initial angle by using the control laser, and the optical power of the laser to be detected and the fluctuation of the optical power are reflected in real time by the optical power of the control laser. According to the invention, the resolution level is considered while the wide range is ensured, the measurement efficiency and the measurement precision are improved, and the detection of the laser power with a high signal-to-noise ratio is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of precision measurement, and particularly relates to a high-precision detection device for laser optical power and its fluctuation, and also relates to a high-precision detection method for laser optical power and its fluctuation. Background Art

[0002] The high-precision measurement of laser optical power and its fluctuation is an important topic in the technical field of precision measurement. For example, because of its extremely high potential displacement and angle measurement accuracy, a laser interferometer is an important part of various precision measurement systems. A laser interferometer gravitational wave detector is a direct means to detect gravitational waves. However, because the gravitational wave signal is very weak and various noises are very strong, there are extremely high requirements for the sensitivity of the laser interferometer. Among them, for the laser light source of the interferometer, not only the output power should be large, but also good optical power stability is required. Especially in the lower frequency band required for detecting gravitational wave signals, a higher relative stability of optical power is needed. Therefore, the accurate measurement and evaluation of the optical power and its fluctuation of the laser are very important.

[0003] The measurement of laser optical power and its fluctuation has received attention very early. In order to evaluate the laser optical power, various different solutions have been proposed at home and abroad. The common ones include using a photodiode to sample and measure the optical power, and using a precision elastic structure to sense the radiation pressure, etc. The former is simple and convenient, but it will lose light energy, is not suitable for the measurement of high-power laser optical power, and is limited by the background current noise of the photodiode and the noise of the amplifier circuit in high-precision measurement and the measurement of low-frequency fluctuations; the latter has received attention because its measurement process does not absorb the energy of light and can be monitored in real time in the optical path.

[0004] In the solution of using a precision elastic structure to sense the radiation pressure: Stimler proposed a test method that converts the photon momentum into the deflection angle of the elastic structure. However, due to inconvenient testing, poor practicability, and the inability to superimpose the light pressure fluctuation effect, it was not popular at that time. Ryger proposed a laser radiation power meter based on a double-spring mechanical structure, and obtained the measured laser power by converting the radiation pressure into the displacement of the measurement plate; Artusio-Glimpse proposed to improve the measurement result accuracy by non-coherently amplifying the radiation pressure through multiple reflections. The optical power measurement accuracy of the above two solutions depends very much on the modeling accuracy between them and the light pressure. In addition, there are also Williams et al. who developed a portable high-radiation power meter by using a simple commercial force sensor as the measurement element, but it is only applicable to strong light measurement, and the accuracy and resolution are poor.

[0005] In addition, it is possible to improve the measurement accuracy of laser optical power by combining an optical resonator for multiple reflections in the prior art. However, in order to achieve the relevant goals, there are extremely high requirements for the length control of the optical cavity, which is difficult to achieve in practice.

[0006] For the measurement of the light pressure of high-power lasers, in the prior art, a high-precision balance is used to achieve it. However, the accuracy of this method of measurement usually cannot be guaranteed, and the measurement uncertainty is relatively high. It is impossible to achieve the measurement of gravitational wave detection, etc., which requires both high power and high-stability lasers.

[0007] In view of the deficiencies of the existing solutions, the present invention proposes a precision laser optical power measurement device that combines a polarization optical path, multiple reflections of a zigzag mirror array, and a torsion pendulum system. While ensuring a large measurement range, this device is also very sensitive to fluctuations in light pressure. This device has the characteristics of high optical power resolution, a large measurement range, and simple operation. Summary of the Invention

[0008] The purpose of the present invention is to provide a high-precision detection device for laser optical power and its fluctuations, and also provide a high-precision detection method for laser optical power and its fluctuations, aiming at the above problems existing in the prior art.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] A high-precision detection device for laser optical power and its fluctuations includes a laser to be measured. The laser to be measured output by the laser to be measured is sequentially converted into a first linearly polarized state by an inclined first polarization beam splitter prism and a Faraday rotator, and then sequentially passes through a second polarization beam splitter prism and a first λ / 4 wave plate and is reflected by a first torsion pendulum mirror near one end of a swing rod, and is converted into a second linearly polarized state again after passing through the first λ / 4 wave plate.

[0011] The laser to be measured in the second linearly polarized state is sequentially reflected by the second polarization beam splitter prism, an intermediate component, reflected by a third polarization beam splitter prism and passes through a second λ / 4 wave plate, and is reflected by a second torsion pendulum mirror near the other end of the swing rod and is converted into a first linearly polarized state again after passing through the second λ / 4 wave plate. Then, it sequentially passes through the third polarization beam splitter prism in transmission, is reflected by a third optical path mirror, passes through the third polarization beam splitter prism again in transmission and passes through the second λ / 4 wave plate in transmission, and is reflected by the second torsion pendulum mirror for the second time.

[0012] The laser to be measured reflected by the second torsion pendulum mirror for the second time passes through the second λ / 4 wave plate and is converted into a second linearly polarized state, and then sequentially passes through reflection by the third polarization beam splitter prism, an intermediate component, reflection by the second polarization beam splitter prism, and a first λ / 4 wave plate, is reflected by the first torsion pendulum mirror for the second time and is converted into a first linearly polarized state after passing through the first λ / 4 wave plate in transmission, and then sequentially passes through the second polarization beam splitter prism in transmission and the Faraday rotator and is reflected by the first polarization beam splitter prism to an external system.

[0013] The measurement laser output by the angle measurement unit is reflected back to the angle measurement unit by an angle measurement mirror at the center of the swing rod.

[0014] As described above, the first polarization beam splitter prism is placed obliquely at a 45° rotation around the optical axis of the laser to be measured with respect to the second and third polarization beam splitter prisms. At the same time, the Faraday rotator also rotates the polarization direction of the laser to be measured by 45°, and the rotation direction of the first polarization beam splitter prism is opposite to the rotation direction of the Faraday rotator for the polarization state of the laser to be measured.

[0015] As described above, the first pendulum mirror and the second pendulum mirror are respectively close to both ends of the pendulum rod and are respectively located on opposite sides of the pendulum rod; the angle-measuring mirror is located on the central side wall of the pendulum rod, and the angle-measuring mirror and the first pendulum mirror are in the same plane, or the angle-measuring mirror and the second pendulum mirror are in the same plane.

[0016] As described above, the first linear polarization state is the P polarization state, and the second linear polarization state is the S polarization state.

[0017] As described above, the first pendulum mirror includes a first pendulum end folded mirror array, and a first experimental platform end folded mirror array is arranged on the base of the experimental platform opposite to the first pendulum end folded mirror array; the second pendulum mirror includes a second pendulum end folded mirror array, and a second experimental platform end folded mirror array is arranged on the base of the experimental platform opposite to the second pendulum end folded mirror array; the first pendulum end folded mirror array, the first experimental platform end folded mirror array, the second pendulum end folded mirror array, and the second experimental platform end folded mirror array each include a plurality of sequentially connected mirror units, and each mirror unit includes two reflecting surfaces that are 90° to each other.

[0018] As described above, the top of the center in the length direction of the pendulum rod is connected to the bottom end of the suspension wire, the top end of the suspension wire is connected to the rotary table, the rotary table is arranged on the top of the torsion pendulum frame, and the torsion pendulum frame is arranged on the base of the experimental platform.

[0019] As described above, a vacuum chamber is further provided on the base of the experimental platform, and the pendulum rod and the suspension wire are both located in the vacuum chamber.

[0020] As described above, the intermediate assembly includes a second optical path mirror and a first optical path mirror.

[0021] The laser to be measured with the second linear polarization state obtained by the laser to be measured passing through the first λ / 4 wave plate for the second time is reflected by the second polarization beam splitter prism, reflected by the first optical path mirror, reflected by the second optical path mirror, reflected by the third polarization beam splitter prism, and transmitted through the second λ / 4 wave plate, and then reflected by the second pendulum mirror and converted into the laser to be measured with the first linear polarization state by passing through the second λ / 4 wave plate again.

[0022] The second linearly polarized test laser obtained after the test laser reflected by the second torsional mirror for the second time passes through the second λ / 4 waveplate is reflected by the third polarization beam splitter prism, reflected by the second optical path mirror, reflected by the first optical path mirror, reflected by the second polarization beam splitter prism, and transmitted through the first λ / 4 waveplate, and then enters the first torsional mirror for the second time.

[0023] As described above, the high-precision detection device for laser optical power and its fluctuation further includes a control laser, and the control laser emitted by the control laser is parallel to the plane where the test laser is located; the incident point of the control laser on the swing rod and the second torsional mirror are both within the same half swing rod area bounded by the center of the swing rod, and the incident point of the control laser on the swing rod and the second torsional mirror are respectively located on the opposite sides of the swing rod; or the incident point of the control laser on the swing rod and the first torsional mirror are both within the same half swing rod area bounded by the center of the swing rod, and the incident point of the control laser on the swing rod and the first torsional mirror are respectively located on the opposite sides of the swing rod.

[0024] The high-precision detection method for laser optical power and its fluctuation uses the high-precision detection device for laser optical power and its fluctuation as described above.

[0025] When performing open-loop detection on the optical power of the test laser, the following steps are included:

[0026] After turning on the test laser, whenever the maximum difference in the oscillation of the deflection angle of the measurement laser is greater than the open-loop detection measurement laser angle threshold, turn on the control laser. After the maximum difference in the oscillation of the deflection angle of the measurement laser is less than or equal to the open-loop detection measurement laser angle threshold, turn off the control laser, and then obtain the deflection angle of the measurement laser in the stable state of the swing rod.

[0027] When performing closed-loop detection on the optical power of the test laser, the following steps are included:

[0028] After turning on the test laser, when the test laser acts on the swing rod to cause the swing rod to deflect, the control laser outputs the control laser and continuously acts on the swing rod; at the same time, the measurement signal output by the angle measurement unit is sent to the power control port of the control laser through the feedback control unit of the control laser, so that the swing rod returns to the initial angle, and the initial angle of the swing rod is the angle when the swing rod is not affected by the test laser; the optical power of the control laser and the fluctuation of the optical power of the control laser can reflect the optical power of the test laser and the fluctuation of the optical power of the test laser in real time.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] Existing light pressure measurement devices can often only be used to measure one of low-energy and high-energy lasers, and it is often impossible to ensure both resolution and range at the same time. The present invention takes into account the level of resolution while ensuring a large range.

[0031] In the prior art, in order to separate the reflected light and the incident light, there is generally an incident angle. When the laser of the present invention acts on the torsion pendulum, it is usually normal incidence, and the incident light and the reflected light can be separated. Compared with the prior art, the influence of the variable of the angle is reduced.

[0032] In addition, by rotating and finely adjusting the suspension wire of the torsion pendulum, the equilibrium position of the working state of the torsion pendulum is always restored to the starting state to eliminate the measurement system error caused by the rotation of the torsion pendulum.

[0033] The present invention uses a control laser beam to achieve damping and control of the torsion pendulum, improving the measurement efficiency and measurement accuracy. By using the measurement signal to perform feedback control on the power of the control laser, high-precision closed-loop testing of the optical power fluctuation can be achieved, and continuous measurement of the optical power fluctuation of the laser to be measured can be realized.

[0034] The optical path transmission structure, the torsion pendulum mirror or the zigzag mirror array are exquisitely arranged in a certain order to form a multi-reflection structure for polarized laser, amplifying the coupling effect between the optical power of the laser to be measured and the torsion pendulum, and realizing the detection of the laser power and its fluctuation with high signal-to-noise ratio.

[0035] The optical power measurement accuracy of the present invention does not depend on the modeling accuracy between the optical power and the optical pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a schematic structural diagram of the detection device of the present invention;

[0037] Figure 2 is a schematic diagram of the torsion pendulum system;

[0038] Figure 3 is a schematic diagram of the zigzag mirror array;

[0039] Figure 4 is a schematic diagram of the change in the polarization state of the laser to be measured in the device of the present invention. (a) is a schematic diagram of the change in the polarization state of the laser to be measured from passing through the first polarization beam splitter prism to being incident on the third optical path mirror, and (b) is a schematic diagram of the change in the polarization state of the laser to be measured from being reflected by the third optical path mirror to the final output;

[0040] Among them, 1 - base; 2 - vacuum chamber; 3 - laser to be measured; 4 - first polarization beam splitter prism; 5 - Faraday rotator; 6 - second polarization beam splitter prism; 7 - first λ / 4 wave plate; 8 - pendulum system; 801 - pendulum frame; 802 - rotary table; 803 - suspension wire; 804 - pendulum rod; 805 - first pendulum mirror; 806 - second pendulum mirror; 807 - angle measurement mirror; 9 - first optical path mirror; 10 - second optical path mirror; 11 - third polarization beam splitter prism; 12 - second λ / 4 wave plate; 13 - third optical path mirror; 14 - angle measurement unit; 15 - control laser; 1001 - first pendulum end folded mirror array; 1002 - first experimental platform end folded mirror array. Detailed implementation manner

[0041] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0042] Embodiment 1

[0043] The high-precision detection device for the laser optical power and its fluctuation of the present invention has a structure as Figure 1 shown, and includes an experimental platform, a laser 3 to be measured, an optical path transmission structure, a pendulum system 8 and an angle measurement unit 14. By introducing polarization beam splitters (including the first polarization beam splitter prism 4, the second polarization beam splitter prism 6 and the third polarization beam splitter prism 11) with different reflection and transmission characteristics for the laser to be measured in different polarization states, a set of specific and feasible implementation optical paths are designed, so that the laser to be measured undergoes multiple interactions of normal incidence and reflection in the pendulum system 8, so that the measurement effect is amplified, thereby improving the test signal-to-noise ratio of the optical power of the laser to be measured. The specific structural settings are as follows:

[0044] The experimental platform includes a base 1, and the laser 3 to be measured, an optical path transmission structure, a pendulum system 8 and an angle measurement unit 14 are arranged on the base 1.

[0045] The pendulum system 8 is as Figure 2As shown, it includes a swing rod 804. A first torsional pendulum mirror 805 and a second torsional pendulum mirror 806 are respectively fixed at both ends of the swing rod 804 close to the swing rod 804, and the first torsional pendulum mirror 805 and the second torsional pendulum mirror 806 are respectively located on opposite sides of the swing rod 804; an angle measuring mirror 807 is fixed on the central side wall of the swing rod 804. The angle measuring mirror 807 and the first torsional pendulum mirror 805 are in the same plane, or the angle measuring mirror 807 and the second torsional pendulum mirror 806 are in the same plane; the top of the center in the length direction of the swing rod 804 is connected to the bottom end of the suspension wire 803, and the top end of the suspension wire 803 is connected to the turntable 802. The turntable 802 is arranged on the top of the torsional pendulum frame 801, and the torsional pendulum frame 801 is arranged on the base 1 of the experimental platform, so that the swing rod 804 is suspended under the suspension wire 803.

[0046] The optical path transmission structure includes: a first polarization beam splitter prism 4, a Faraday rotator 5, a second polarization beam splitter prism 6, a first λ / 4 wave plate 7, a first optical path mirror 9, a second optical path mirror 10, a third polarization beam splitter prism 11, a second λ / 4 wave plate 12 and a third optical path mirror 13. The test laser output by the test laser 3 is reflected multiple times on the first torsional pendulum mirror 805 and the second torsional pendulum mirror 806 through the optical path transmission structure, so as to achieve the effect of amplifying the measurement effect.

[0047] The angle measuring unit 14 is used to output the measurement laser to the angle measuring mirror 807 and measure the angle between the measurement laser reflected by the angle measuring mirror 807 and the measurement laser emitted by the angle measuring unit 14. When the test laser acts on the first torsional pendulum mirror 805 and the second torsional pendulum mirror 806, the swing rod 804 will deflect. By observing the angle fluctuation of the reflected measurement laser, the deflection angle fluctuation of the swing rod 804 can be fed back, so as to convert the light pressure fluctuation of the test laser into the deflection angle fluctuation of the measurement laser, and the power value of the test laser can be obtained by converting the deflection angle value of the measurement laser. To facilitate detecting the angle between the incident direction and the reflected direction of the measurement laser, the angle measuring mirror 807 is not perpendicular to the incident direction of the measurement laser, and there is a small angle between the vertical direction of the angle measuring mirror 807 and the incident direction of the measurement laser.

[0048] The specific optical paths of the test laser and the measurement laser are as follows:

[0049] The laser 3 to be measured outputs the laser to be measured. The optical power of the laser to be measured and the optical power fluctuation of the laser to be measured are the quantities to be measured. The laser to be measured is sequentially converted into the laser to be measured in the first linearly polarized state through the first polarization beam splitter prism 4 and the Faraday rotator 5. The first polarization beam splitter prism 4 is placed at a 45° deflection along the vertical direction of the optical axis, and the Faraday rotator 5 is set to rotate the polarization state of the laser to be measured by 45°; the laser to be measured in the first linearly polarized state sequentially passes through the second polarization beam splitter prism 6 and the first λ / 4 wave plate 7 and then is incident on the first pendulum mirror 805; in this embodiment, the first linearly polarized state is the p-polarized state. For the laser to be measured in the p-polarized state, the inclined laser to be measured in the p-polarized state passes through the first polarization beam splitter prism 4 placed obliquely, and then is converted into the laser to be measured in the p-polarized state through the Faraday rotator 5. The laser to be measured in the p-polarized state passes through the second polarization beam splitter prism 6 and the first λ / 4 wave plate 7 and is reflected by the first pendulum mirror 805, as Figure 4 shown in (a) of FIG. 1, so that the laser to be measured makes the first normal incidence and reflection with the pendulum rod 804;

[0050] The laser to be measured reflected by the first pendulum mirror 805 is converted into the laser to be measured in the second linearly polarized state after passing through the first λ / 4 wave plate 7 for the second time. The laser to be measured in the second linearly polarized state is sequentially reflected by the second polarization beam splitter prism 6, the intermediate component (in this embodiment, the intermediate component includes the first optical path mirror 9 and the second optical path mirror 10, and the laser to be measured in the second linearly polarized state reflected by the second polarization beam splitter prism 6 is sequentially reflected by the first optical path mirror 9 and the second optical path mirror 10), reflected by the third polarization beam splitter prism 11, and transmitted through the second λ / 4 wave plate 12 and then is incident on the second pendulum mirror 806; in this embodiment, the second linearly polarized state is the s-polarized state. The laser to be measured reflected by the first pendulum mirror 805 becomes the laser to be measured in the s-polarized state after passing through the first λ / 4 wave plate 7 for the second time. The laser to be measured in the s-polarized state is reflected by the second polarization beam splitter prism 6 to achieve the purpose of beam splitting, and then sequentially passes through the first optical path mirror 9 and the second optical path mirror 10 to change the optical path direction, which is used to lead the optical path of the laser to be measured in the s-polarized state to the other side of the pendulum rod 804. At this time, the laser to be measured in the s-polarized state passes through the third polarization beam splitter prism 11 and the second λ / 4 wave plate 12 and is incident on the second pendulum mirror 806, so that the laser to be measured makes the second normal incidence and reflection with the pendulum rod 804;

[0051] The second linearly polarized state of the laser to be measured reflected by the second swing mirror 806 passes through the second λ / 4 wave plate 12 and is converted into the first linearly polarized state of the laser to be measured, and then is transmitted through the third polarization beam splitter prism 11 and reflected by the third optical path mirror 13. The first linearly polarized state of the laser to be measured reflected by the third optical path mirror 13 passes through the third polarization beam splitter prism 11 and the second λ / 4 wave plate 12 in sequence, and then is reflected by the second swing mirror 806 for the second time; in this embodiment, the s-polarized state of the laser to be measured reflected by the second swing mirror 806 passes through the second λ / 4 wave plate 12 for the second time and is converted into the p-polarized state of the laser to be measured (when ignoring the reflection loss, the theoretical light pressure obtained by the swing rod 804 reaches F = 4P0 / C, where P0 is the optical power of the laser to be measured and C is the speed of light). The p-polarized state of the laser to be measured converted by the second λ / 4 wave plate 12 is transmitted through the third polarization beam splitter prism 11 and acts on the third optical path mirror 13 for reflection, and then passes through the third polarization beam splitter prism 11 and the second λ / 4 wave plate 12 again and is reflected by the second swing mirror 806 again, as Figure 4 shown in (b) of

[0052] The laser to be measured reflected by the second swing mirror 806 for the second time passes through the second λ / 4 wave plate 12 and is converted into the second linearly polarized state of the laser to be measured again, and then passes through the third polarization beam splitter prism 11 for reflection, the intermediate component (i.e., the reflection of the second optical path mirror 10 and the reflection of the first optical path mirror 9), the second polarization beam splitter prism 6 for reflection, and the first λ / 4 wave plate 7 for transmission, and then is incident on the first swing mirror 805 for the second time; in this embodiment, the laser to be measured reflected by the second swing mirror 806 for the second time passes through the second λ / 4 wave plate 12 and is converted into the s-polarized state of the laser to be measured again, and then is reflected by the third polarization beam splitter prism 11, the second optical path mirror 10, the first optical path mirror 9, the second polarization beam splitter prism 6, and transmitted through the first λ / 4 wave plate 7 in sequence, and then acts on the first swing mirror 805 again, so that the laser to be measured and the swing rod 804 have the 4th normal incidence and reflection; at this time, the theoretical light pressure obtained by the swing rod 804 reaches F = 8P0 / C;

[0053] The laser to be measured that has been reflected for the second time by the first swing mirror 805 is transmitted through the first λ / 4 wave plate 7 and converted into the laser to be measured in the first linear polarization state. The laser to be measured in the first linear polarization state is transmitted through the second polarization beam splitter prism 6 and then converted into the laser to be measured in the inclined second linear polarization state by the Faraday rotator 5, and is reflected by the first polarization beam splitter prism 4 and output to the external system. In this embodiment, the laser to be measured after the fourth reflection is transmitted through the first λ / 4 wave plate 7 and the second polarization beam splitter prism 6 in sequence and then converted into the laser to be measured in the inclined s polarization state by the Faraday rotator 5, and is reflected by the first polarization beam splitter prism 4 to achieve separation from the initially incident laser to be measured. The optical power and fluctuation of the outgoing laser beam reflected by the first polarization beam splitter prism 4 are accurately measured by the swing system 8 and can be used for subsequent high-precision research;

[0054] Meanwhile, the angle measurement unit 14 outputs the measurement laser to the angle measurement mirror 807. The measurement laser reflected by the angle measurement mirror 807 returns to the angle measurement unit 14. The combination of the angle measurement mirror 807 and the angle measurement unit 14 is used to detect the angle change of the swing rod 804. The angle measurement unit 14 is an optical lever system or an autocollimator, etc. The optical pressure F on the optical pressure action point by the laser to be measured can be calculated by the following formula: F = Kθ / L F , where K is the torsional stiffness of the suspension wire, L F is the distance from the optical pressure action point to the swing rotation center. The optical pressure action point is the point where the laser to be measured is incident on the first swing mirror 805 or the second swing mirror 806; θ is the deflection angle of the swing rod.

[0055] Further, in order to enable the optical path of the laser to be measured to continuously propagate along the reflecting surface of the first pendulum mirror 805 or the second pendulum mirror 806 after incidence, so as to achieve the purpose of more reflections, the present invention introduces four folded mirror arrays to further amplify the optical pressure received by the pendulum system 8, thereby improving the sensitivity of optical effect detection. The four folded mirror arrays are respectively a first pendulum end folded mirror array 1001, a first experimental platform end folded mirror array 1002, a second pendulum end folded mirror array, and a second experimental platform end folded mirror array. The specific settings are as follows: The first pendulum mirror 805 includes the first pendulum end folded mirror array 1001, and the first experimental platform end folded mirror array 1002 is arranged on the base 1 of the experimental platform opposite to the first pendulum end folded mirror array 1001; the second pendulum mirror 806 includes the second pendulum end folded mirror array, and the second experimental platform end folded mirror array is arranged on the base 1 of the experimental platform opposite to the second pendulum end folded mirror array; the first pendulum end folded mirror array 1001, the first experimental platform end folded mirror array 1002, the second pendulum end folded mirror array, and the second experimental platform end folded mirror array each include a plurality of sequentially connected mirror units, and each mirror unit includes two reflecting surfaces that are perpendicular to each other. The laser to be measured incident on the mirror unit is sequentially reflected by the two reflecting surfaces in the mirror unit and then exits into the opposite mirror unit. The transmission direction of the laser to be measured incident on the same mirror unit is parallel and opposite to the transmission direction of the laser to be measured exiting, so that the laser to be measured is repeatedly reflected between the opposite folded mirror arrays. In this embodiment, the first pendulum end folded mirror array 1001, the first experimental platform end folded mirror array 1002, the second pendulum end folded mirror array, and the second experimental platform end folded mirror array each include 3 sequentially connected mirror units, as Figure 3 shown. Through the above settings, the number of specular reflections of the laser to be measured on the first pendulum mirror 805 or the second pendulum mirror 806 is extended from 2 times to 6 times. In this way, the laser to be measured will have a total of 12 specular incidences and specular reflections with the pendulum rod 804. At this time, the theoretical optical pressure obtained by the pendulum rod 804 reaches F = 24P0 / C. Generally, when each folded mirror array on the pendulum rod 804 includes N mirror units, the theoretical optical pressure of the laser to be measured on the pendulum rod 804 reaches F = 8NP0 / C. Compared with the scheme of stimler, the measurement effect is amplified by 4N times, thus greatly improving the signal-to-noise ratio and accuracy of the measurement.

[0056] The deflection angle of the measurement laser is twice the deflection angle of the pendulum rod 804. The optical power P of the laser to be measured measured by the present invention 测 is: θ 光θ represents the deflection angle of the measurement laser, and N is the number of mirror units in each zigzag mirror array.

[0057] At this time, if the loss of the laser during reflection is considered, and the loss caused by the reverse of the propagation direction of the laser each time it is reflected remains unchanged, the optical power of the laser to be measured can be expressed as:

[0058]

[0059] θ 光 θ represents the deflection angle of the measurement laser, and N is the number of mirror units in each zigzag mirror array. λi represents the reflectivity when the propagation direction of the light is reversed for the i-th time, and n represents the number of times the light is reflected when the laser to be measured interacts with the torsion pendulum for the i-th time.

[0060] In the above optical path transmission structure, the spot of the measurement laser will deflect as the swing rod 804 deflects. After multiple reflections of the laser to be measured, the spot on the second torsion pendulum mirror 806 will approach the rotation center of the swing rod 804. Then, the laser to be measured acts on the swing rod 804 twice again, and the outgoing direction of the laser to be measured will be on the same horizontal line as the incident direction of the laser to be measured but in the opposite direction. Therefore, the rotation of the swing rod 804 will not separate the incident laser to be measured and the outgoing laser to be measured. The present invention achieves the purpose of beam splitting by placing the first polarization beam splitter prism 4 at an angle of 45°, in cooperation with the Faraday rotator 5 that can change the polarization direction of the laser to be measured: the laser to be measured is perpendicularly incident on the incident surfaces of the first polarization beam splitter prism 4, the second polarization beam splitter prism 6, and the third polarization beam splitter prism 11 respectively. However, since the first polarization beam splitter prism 4 rotates 45° around the optical axis of the laser to be measured relative to the second polarization beam splitter prism 6 and the third polarization beam splitter prism 11, the first polarization beam splitter prism 4 allows the laser to be measured in the inclined first polarization state to pass through the first polarization beam splitter prism 4, and the laser to be measured in the inclined second polarization state is reflected (the polarization state of the laser to be measured can be adjusted so that the laser to be measured is in the inclined first polarization state, thereby maximizing the energy of the laser to be measured passing through the first polarization beam splitter prism 4). In this embodiment, the inclined first polarization state is the inclined p polarization state, and the laser to be measured in the inclined p polarization state has a 45° angle with the laser to be measured in the p polarization state (for example, the laser to be measured in the inclined p polarization state deflects 45° counterclockwise compared to the laser to be measured in the p polarization state, corresponding to the rotation angle of the Faraday rotator 5 for the laser to be measured being 45° clockwise; the laser to be measured in the inclined p polarization state can also deflect 45° clockwise, corresponding to the rotation angle of the Faraday rotator 5 for the laser to be measured being 45° counterclockwise). In this embodiment, the inclined second polarization state is the inclined s polarization state, and the laser to be measured in the inclined s polarization state is perpendicular to the laser to be measured in the inclined p polarization state. The laser to be measured in the inclined p polarization state passes through the Faraday rotator 5 and rotates 45° (such as rotating 45° clockwise) to obtain the laser to be measured in the p polarization state. Subsequently, multiple reflections are used to improve the sensitivity of the torsion pendulum system 8. When the laser to be measured is reflected for the second time by the first torsion pendulum mirror 805, it passes through the first λ / 4 wave plate 7 and returns to the p polarization state, and then passes through the Faraday rotator 5 again and rotates 45° (such as rotating 45° clockwise) to be converted into the inclined s polarization state. Then, when it passes through the first polarization beam splitter prism 4 again, it is reflected by the first polarization beam splitter prism 4, thereby being separated from the incident laser to be measured. That is, the first polarization beam splitter prism 4 is placed at an angle of 45° with respect to the second polarization beam splitter prism 6 and the third polarization beam splitter prism 11 around the optical axis of the laser to be measured, and at the same time, the Faraday rotator 5 also rotates the polarization direction of the laser to be measured by 45°, and the rotation direction of the first polarization beam splitter prism 4 and the rotation direction of the Faraday rotator 5 for the polarization state of the laser to be measured are opposite, thereby realizing the separation of the incident laser to be measured and the outgoing laser to be measured.That is, the deflection state of the laser to be measured passes through the first polarization beam splitter prism 4 and is rotated by 45° by the Faraday rotator 5 to become a p-polarized state. After passing through a round of reflection, the p-polarized laser to be measured returns and passes through the Faraday rotator 5 again, and then has a phase difference of 90° from the original obliquely p-polarized laser to be measured, thus achieving the purpose of beam splitting.

[0061] Further, when the swing rod 804 of the torsion pendulum system 8 is stationary, the incident point of the laser on the swing rod 804 remains unchanged, and the optical path of the laser to be measured reflected back by the first torsion pendulum mirror 805 for the second time always overlaps with the optical path of the initially incident laser to be measured. When the swing rod 804 deflects, the spot of the laser to be measured incident on the second torsion pendulum mirror 806 will move, but the change in the spot position of the incident laser acting on the first torsion pendulum mirror 805 can be ignored. Taking the swing rod 804 rotating 1 mrad from the position perpendicular to the transmission direction of the laser to be measured as an estimate, the change in the spot position of the first torsion pendulum mirror 805 is about 50 nm and can be ignored, while the change in the spot position at the second torsion pendulum mirror 806 is about 1 mm, which will cause a 0.5% measurement system error. To eliminate the above measurement system error, the present invention fine-tunes the angle of the turntable 802, and the turntable 802 readjusts the swing rod 804 to the initial position through the suspension wire 803, thereby eliminating the measurement system error caused by the rotation of the swing rod 804. To accurately control the rotation angle of the swing rod 804, the turntable 802 is a motor.

[0062] Further, when performing high-precision measurements, to avoid the disturbance of the air to the swing rod 804 and the scattering of the laser power, a vacuum chamber 2 is provided on the base 1 of the experimental platform, and the swing rod 804 and the suspension wire 803 need to be located inside the vacuum chamber 2; the vacuum chamber 2 provided in this embodiment is as Figure 1 shown, the laser to be measured 3 and the angle measurement unit 14 are located outside the vacuum chamber 2, the optical path transmission structure and the torsion pendulum system 8 are located inside the vacuum chamber 2, the laser to be measured output by the laser to be measured 3 passes through the first light passing port of the vacuum chamber 2 and is incident on the first polarization beam splitter prism 4, the measurement laser output by the angle measurement unit 14 passes through the second light passing port of the vacuum chamber 2 and is incident on the angle measurement mirror 807, the measurement laser reflected by the angle measurement mirror 807 returns to the angle measurement unit 14 through the second light passing port, and in the vacuum chamber 2, the laser to be measured reflected by the first polarization beam splitter prism 4 after multiple interactions with the swing rod 804 exits the vacuum chamber 2 through the third light passing port of the vacuum chamber 2.

[0063] Furthermore, to improve the measurement efficiency, reduce the amplitude of the back-and-forth rotation of the swing rod 804 to suppress measurement errors, and improve the measurement accuracy, the detection device of the present invention further includes a control laser 15. The control laser emitted by the control laser 15 is parallel to the plane where the laser to be measured is located. The control laser emitted by the control laser 15 interacts with the swing rod 804 for damping and controlling the rotation of the swing rod 804 (that is, the incident point of the control laser on the swing rod 804 and the second torsion pendulum mirror 806 are both within the same half-swing rod area bounded by the center of the swing rod 804, and the incident point of the control laser on the swing rod 804 and the second torsion pendulum mirror 806 are respectively located on the opposite sides of the swing rod 804; or the incident point of the control laser on the swing rod 804 and the first torsion pendulum mirror 805 are both within the same half-swing rod area bounded by the center of the swing rod 804, and the incident point of the control laser on the swing rod 804 and the first torsion pendulum mirror 805 are respectively located on the opposite sides of the swing rod 804). The control laser 15 has two working modes:

[0064] Perform open-loop detection: After turning on the laser 3 to be measured, whenever the oscillation angle of the swing rod 804 is greater than the open-loop detection swing rod angle threshold (corresponding to the maximum difference in the oscillation of the deflection angle of the measurement laser being greater than the open-loop detection measurement laser angle threshold, and the maximum difference in the oscillation of the deflection angle of the measurement laser is the difference between the maximum and minimum values of the deflection angle of the measurement laser in a change cycle), turn on the control laser 15 to give the swing rod 804 a reaction force with the control laser, increase the damping of the torsion pendulum system 8, so that the swing rod 804 reaches a stable state as soon as possible. After the swing rod 804 tends to be stable or is stable, that is, the oscillation angle of the swing rod 804 is less than or equal to the open-loop detection angle threshold (corresponding to the maximum difference in the oscillation of the deflection angle of the measurement laser being less than or equal to the open-loop detection measurement laser angle threshold), turn off the control laser 15, and then obtain the deflection angle of the measurement laser in the stable state of the swing rod 804;

[0065] Perform closed-loop detection: After turning on the laser 3 to be measured, when the laser to be measured acts on the swing rod 804 causing the swing rod 804 to deflect, control the laser 15 to output control laser to continuously act on the swing rod 804 to give a reaction force to the swing rod 804. At the same time, the measurement signal output by the angle measurement unit 14 reaches the power control port of the control laser 15 through the feedback control unit of the control laser 15, realizing high-precision closed-loop suppression of the optical power fluctuation of the control laser 15, so that the swing rod 804 returns to the initial angle, excluding the interference of the rotation of the swing rod 804. The initial angle of the swing rod 804 is the angle when the swing rod 804 is not affected by the laser to be measured. When performing continuous optical power measurement, the optical pressure of the laser to be measured acts on the swing rod 804 causing the swing rod 804 to deflect. At the same time, the angle measurement unit 14 transmits the measurement signal carrying the deflection angle change information of the reflected measurement laser to the control laser 15, so that the control laser 15 adjusts the optical power of the control laser according to the angle change of the reflected measurement laser, making the swing rod 804 return to its original position. From the optical power of the control laser and the fluctuation of the optical power of the control laser, the optical power of the laser to be measured and the fluctuation of the optical power of the laser to be measured are reflected in real time.

[0066] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways to substitute, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A high-precision detection device for laser optical power and its fluctuation, including a laser to be measured (3), characterized in that, The laser to be measured (3) outputs the laser to be measured, which sequentially passes through an inclined first polarization beam splitter prism (4) and a Faraday rotator (5) to be converted into a first linearly polarized state, and sequentially passes through a second polarization beam splitter prism (6) and a first λ / 4 wave plate (7), and then is reflected by a first torsional mirror (805) near one end on a swing rod (804), and passes through the first λ / 4 wave plate (7) again to be converted into a second linearly polarized state; The laser to be measured in the second linearly polarized state sequentially passes through the reflection of the second polarization beam splitter prism (6), an intermediate component, the reflection of the third polarization beam splitter prism (11), and a second λ / 4 wave plate (12), and then is reflected by a second torsional mirror (806) near the other end on the swing rod (804) and passes through the second λ / 4 wave plate (12) again to be converted into a first linearly polarized state. Then, it sequentially passes through the transmission of the third polarization beam splitter prism (11), the reflection of a third optical path mirror (13), the second transmission of the third polarization beam splitter prism (11), and the transmission of the second λ / 4 wave plate (12), and is reflected by the second torsional mirror (806) for the second time; The laser to be measured reflected by the second torsional mirror (806) for the second time passes through the second λ / 4 wave plate (12) to be converted into a second linearly polarized state, and sequentially passes through the reflection of the third polarization beam splitter prism (11), an intermediate component, the reflection of the second polarization beam splitter prism (6), and the first λ / 4 wave plate (7), and then is reflected by the first torsional mirror (805) for the second time and passes through the transmission of the first λ / 4 wave plate (7) to be converted into a first linearly polarized state. Then, it sequentially passes through the transmission of the second polarization beam splitter prism (6) and the Faraday rotator (5) and is reflected by the first polarization beam splitter prism (4) to an external system; The measurement laser output by an angle measurement unit (14) is reflected back to the angle measurement unit (14) by an angle measurement mirror (807) at the center of the swing rod (804).

2. The high-precision detection device for laser optical power and its fluctuation according to claim 1, characterized in that The first polarization beam splitter prism (4) is inclined at a rotation of 45° around the optical axis of the laser to be measured relative to the second polarization beam splitter prism (6) and the third polarization beam splitter prism (11). At the same time, the Faraday rotator (5) also rotates the polarization direction of the laser to be measured by 45°, and the rotation direction of the first polarization beam splitter prism (4) is opposite to the rotation direction of the polarization state of the laser to be measured by the Faraday rotator (5).

3. The high-precision detection device for laser optical power and its fluctuation according to claim 1, characterized in that The first torsional mirror (805) and the second torsional mirror (806) are respectively close to both ends of the swing rod (804) and are respectively located on opposite sides of the swing rod (804); the angle measurement mirror (807) is located on the central side wall of the swing rod (804), and the angle measurement mirror (807) is in the same plane as the first torsional mirror (805), or the angle measurement mirror (807) is in the same plane as the second torsional mirror (806).

4. The high-precision detection device for laser optical power and its fluctuation according to claim 1, wherein The first linearly polarized state is a P polarization state, and the second linearly polarized state is an S polarization state.

5. The high-precision detection device for laser optical power and its fluctuation according to claim 1, characterized in that The first torsional pendulum mirror (805) includes a first torsional pendulum end folded mirror array (1001), and a first experimental platform end folded mirror array (1002) is arranged on the base (1) of the experimental platform opposite to the first torsional pendulum end folded mirror array (1001); the second torsional pendulum mirror (806) includes a second torsional pendulum end folded mirror array, and a second experimental platform end folded mirror array is arranged on the base (1) of the experimental platform opposite to the second torsional pendulum end folded mirror array; the first torsional pendulum end folded mirror array (1001), the first experimental platform end folded mirror array (1002), the second torsional pendulum end folded mirror array, and the second experimental platform end folded mirror array each include a plurality of sequentially connected mirror units, and each mirror unit includes two reflecting surfaces that are perpendicular to each other at 90°.

6. The high-precision detection device for laser optical power and its fluctuation according to claim 1, characterized in that The top of the center in the length direction of the swing rod (804) is connected to the bottom end of the suspension wire (803), the top end of the suspension wire (803) is connected to the rotary table (802), the rotary table (802) is arranged on the top of the torsional pendulum frame (801), and the torsional pendulum frame (801) is arranged on the base (1) of the experimental platform.

7. The high-precision detection device for laser optical power and its fluctuation according to claim 6, characterized in that, A vacuum chamber (2) is further arranged on the base (1) of the experimental platform, and the swing rod (804) and the suspension wire (803) are both located inside the vacuum chamber (2).

8. The high-precision detection device for laser optical power and its fluctuation according to claim 1, characterized in that, The intermediate assembly includes a second optical path mirror (10) and a first optical path mirror (9). The second linearly polarized state of the laser to be measured obtained by the laser to be measured passing through the first λ / 4 wave plate (7) for the second time passes through the second polarization beam splitter prism (6) by reflection, the first optical path mirror (9) by reflection, the second optical path mirror (10) by reflection, the third polarization beam splitter prism (11) by reflection, and the second λ / 4 wave plate (12) by transmission, and then is reflected by the second torsional pendulum mirror (806) and passes through the second λ / 4 wave plate (12) again to be converted into the first linearly polarized state of the laser to be measured. The second linearly polarized state of the laser to be measured obtained by the laser to be measured reflected by the second torsional pendulum mirror (806) for the second time passing through the second λ / 4 wave plate (12) passes through the third polarization beam splitter prism (11) by reflection, the second optical path mirror (10) by reflection, the first optical path mirror (9) by reflection, the second polarization beam splitter prism (6) by reflection, and the first λ / 4 wave plate (7) by transmission, and then is incident on the first torsional pendulum mirror (805) for the second time.

9. The high-precision detection device for laser optical power and its fluctuation according to claim 1, wherein It further includes a control laser (15), and the control laser emitted by the control laser (15) is parallel to the plane where the laser to be measured is located; the incident point of the control laser on the swing rod (804) and the second torsional pendulum mirror (806) are both located in the same half-swing rod area bounded by the center of the swing rod (804), and the incident point of the control laser on the swing rod (804) and the second torsional pendulum mirror (806) are respectively located on the opposite sides of the swing rod (804); or the incident point of the control laser on the swing rod (804) and the first torsional pendulum mirror (805) are both located in the same half-swing rod area bounded by the center of the swing rod (804), and the incident point of the control laser on the swing rod (804) and the first torsional pendulum mirror (805) are respectively located on the opposite sides of the swing rod (804).

10. A high-precision detection method for laser optical power and its fluctuation, using the high-precision detection device for laser optical power and its fluctuation according to claim 9, characterized in that when performing open-loop detection on the optical power of the laser to be measured, the following steps are included: After turning on the laser to be measured (3), whenever the maximum difference in the oscillation of the deflection angle of the measurement laser is greater than the open-loop detection measurement laser angle threshold, turn on the control laser (15). After the maximum difference in the oscillation of the deflection angle of the measurement laser is less than or equal to the open-loop detection measurement laser angle threshold, turn off the control laser (15), and then obtain the deflection angle of the measurement laser; when performing closed-loop detection on the optical power of the laser to be measured, the following steps are included: Turn on the laser to be measured (3). After the laser to be measured acts on the swing rod (804) to cause the swing rod (804) to deflect, the control laser (15) outputs a control laser to continuously act on the swing rod (804); at the same time, the measurement signal output by the angle measurement unit (14) reaches the power control port of the control laser (15) through the feedback control unit of the control laser (15), so that the swing rod (804) returns to the initial angle, and the initial angle of the swing rod (804) is the angle when the swing rod (804) is not affected by the laser to be measured; the optical power of the control laser and the fluctuation of the optical power of the control laser can reflect the optical power of the laser to be measured and the fluctuation of the optical power of the laser to be measured in real time.

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