Vortex polarimeter and measurement method

Abstract

The invention relates to the technical field of polarimeters, in particular to a vortex polarimeter and a measuring method, and the vortex polarimeter comprises a polarization state generator, a first diaphragm, a polarization analyzer, a 4F imaging system and a computer; the polarization state generator is used for converting a light beam into a linear polarization vortex light beam, a to-be-measured optical rotation solution is placed on an emergent light path of the polarization state generator, the first diaphragm is mounted on an incident light path of the to-be-measured optical rotation solution, and the polarization analyzer is mounted on the emergent light path of the to-be-measured optical rotation solution; the linear polarization vortex light beam passes through a to-be-detected optical rotation solution and then enters the polarization analyzer, the 4F imaging system is installed on an emergent light path of the polarization analyzer, and the 4F imaging system is used for imaging the polarization analyzer and sending a collected polarized light image to the computer for analysis. According to the vortex polarimeter, the transmission-type optical path is adopted and combined with the 4F imaging system, the accuracy of optical rotation measurement is effectively improved, the detection work of the to-be-detected optical rotation solution with the large concentration can be achieved, and in addition, the vortex polarimeter is simple in structure and low in cost.

Description

Technical Field

[0001] The present invention relates to the technical field of polarimeters, and in particular to a vortex polarimeter and a measuring method. Background Art

[0002] Polarimeter is an instrument for measuring the optical rotation of a substance. By measuring the optical rotation of a sample, the concentration, content and purity of the substance can be analyzed and determined. It is widely used in pharmaceutical, drug testing, sugar, food, spices, monosodium glutamate, chemical, petroleum and other industrial production. It can also be used in scientific research and teaching departments for laboratory analysis or process quality control.

[0003] Existing polarimeters, such as the vortex polarimeter provided by publication number CN116438445A, use a multi-wavelength light beam with a polarization state and / or phase state that varies in azimuth to focus the vortex light beam on the sample to be tested within a wide range of incident angles to detect sample characteristics; this prior art uses reflective signal processing, but for solutions with high concentrations, since the reflected signal is weak, this prior art has the problem of low detection accuracy when facing solutions with high concentrations; in addition, the overall structure of the vortex polarimeter is complex and the cost is high.

[0004] Based on this, how to achieve accurate measurement of the optical rotation of solutions with high concentrations and reduce costs is a technical problem that urgently needs to be solved. Summary of the invention

[0005] The object of the present invention is to provide a vortex polarimeter and a measuring method, which adopts a transmission optical path and combines a 4F imaging system to solve the technical problem of how to accurately measure the optical rotation of a solution with a relatively high concentration and reduce the cost.

[0006] The present invention is implemented by the following technical scheme: a vortex polarimeter, comprising a polarization state generator, a first aperture, an analyzer, a 4F imaging system and a computer;

[0007] The polarization state generator is used to convert a light beam into a linearly polarized vortex light beam. The optically active solution to be measured is placed on the exit light path of the polarization state generator. The first aperture is installed on the incident light path of the optically active solution to be measured. The analyzer is installed on the exit light path of the optically active solution to be measured. The linearly polarized vortex light beam passes through the optically active solution to be measured and then enters the analyzer. The 4F imaging system is installed on the exit light path of the analyzer. The 4F imaging system is used to image the analyzer and send the collected polarized light image to a computer for analysis.

[0008] According to a preferred embodiment, the polarization state generator includes a first polarizer, a quarter wave plate, a vortex wave plate and a second polarizer, the first polarizer is used to modulate the light beam into linearly polarized light, the quarter wave plate is installed on the output light path of the first polarizer, and is used to convert the linearly polarized light into a circularly polarized light beam, the vortex wave plate is installed before the second polarizer, and is used to convert the circularly polarized light into a circularly polarized vortex light beam, and the second polarizer is used to convert the circularly polarized vortex light beam into a linearly polarized vortex light beam.

[0009] According to a preferred embodiment, the 4F imaging system includes a first convex lens, a second convex lens and a second aperture, the polarizer is installed at the focal position of the first convex lens, the second aperture is installed at the Fourier plane position of the 4F imaging system, and the second convex lens is installed on the incident light path of the CCD sensor image plane.

[0010] According to a preferred embodiment, the focal lengths of the first convex lens and the second convex lens are both 125 mm.

[0011] According to a preferred embodiment, it also includes a light source that generates the light beam, and a collimating beam expander is installed on the output light path of the light source, and the collimating beam expander is installed on the incident light path of the polarization state generator, so that the light beam emitted by the light source is expanded and converted into parallel light and emitted into the polarization state generator.

[0012] According to a preferred embodiment, the light source is a HE-NE laser.

[0013] According to a preferred embodiment, the polarization state generator, the first aperture, the analyzer and the 4F imaging system are coaxially arranged and installed at the same height.

[0014] The present invention also provides a detection method using the vortex polarimeter as described above, comprising the following steps:

[0015] Step A, turn on the equipment, including the light source and the CCD sensor;

[0016] Step B, adjusting the polarizer and the analyzer so that their polarization states are orthogonal to each other, and the angle of the analyzer is recorded as θ0;

[0017] Step C, placing the optically active solution to be tested on the outgoing light path of the polarization state generator, receiving the polarized light image through the CCD sensor and sending the polarized light image to the computer for light intensity analysis, adjusting the angle of the analyzer according to a preset light intensity threshold to minimize the light intensity, and the angle of the analyzer at this time is recorded as θ1;

[0018] Step D: The optical rotation of the optically active solution to be measured is θ i =θ1-θ0.

[0019] The technical solutions of a vortex polarimeter and a measuring method provided by the present invention have at least the following advantages and beneficial effects: (1) The vortex polarimeter adopts a transmission optical path and is combined with a 4F imaging system, which effectively improves the accuracy of optical rotation measurement; (2) For optically active solutions with high concentrations to be measured, by adopting linearly polarized vortex light, the measurement error is low, which further improves the accuracy of optical rotation measurement; (3) The vortex polarimeter has a simple structure and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of the optical path of the vortex polarimeter provided in Example 1 of the present invention;

[0021] Figure numerals: 1-HE-NE laser, 2-collimating beam expander, 3-first polarizer, 4-1 / 4 wave plate, 5-vortex wave plate, 6-second polarizer, 7-first aperture, 8-optically active solution to be measured, 9-polarizer, 10-first convex lens, 11-second aperture, 12-second convex lens, 13-CCD sensor, 14-computer. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0023] Example 1

[0024] Figure 1 Schematic diagram of the optical path of the vortex polarimeter provided in the embodiment of the present invention. Figure 1 As shown, the vortex polarimeter includes a light source, a collimating beam expander 2, a polarization state generator, a first aperture 7, an analyzer 9, a 4F imaging system and a computer 14.

[0025] In some embodiments, the light source is a laser, such as a solid laser, a gas laser, a liquid laser, a semiconductor laser, etc. Specifically, in this embodiment, a HE-NE laser 1 is used, that is, the HE-NE laser 1 is used as a light source to provide a stable, scatter-free and high-precision light beam. In this embodiment, a collimating beam expander 2 is installed on the output light path of the HE-NE laser, and the collimating beam expander 2 is installed on the incident light path of the polarization state generator, so that the light beam emitted by the HE-NE laser 1 is expanded and converted into parallel light, and finally injected into the polarization state generator.

[0026] In some embodiments, the polarization state generator can be generated by a combination of a spiral phase plate and a half-wave plate, and the polarization state generator is used to convert a light beam into a linearly polarized vortex light beam. For the optically active solution 8 to be measured with a relatively high concentration, by using the linearly polarized vortex light, the measurement error is low, and the accuracy of the optical rotation measurement is further improved. Specifically in this embodiment, the optically active solution 8 to be measured is placed on the outgoing light path of the polarization state generator, and a first aperture 7 is further installed on the incident light path of the optically active solution 8 to be measured, and the number and direction of the linearly polarized vortex light beam entering the optically active solution 8 to be measured are controlled by the first aperture 7 to achieve stray light filtering. Specifically in this embodiment, the first aperture 7 is selected as an aperture aperture to limit the solid angle of the linearly polarized vortex light beam, and the aperture aperture is used to block the stray light so that it cannot enter the subsequent light path.

[0027] Specifically in this embodiment, the polarization state generator includes a first polarizer 3, a quarter wave plate 4, a vortex wave plate 5 and a second polarizer 6. The first polarizer 3 is used to modulate the light beam into linear polarized light; the quarter wave plate 4 is installed on the output light path of the first polarizer 3, and is used to convert the linear polarized light into a circularly polarized light beam; specifically in this embodiment, the quarter wave plate 4 is made of birefringent material, and by precisely controlling the thickness, a phase difference of π / 2 radians is generated when the light beam passes through, thereby converting the linear polarized light into circularly polarized light; the vortex wave plate 5 is installed before the second polarizer 6, and is used to convert the circularly polarized light into a circularly polarized vortex light beam; specifically in this embodiment, the vortex wave plate 5 is based on an N-BK7 glass substrate and a liquid crystal polymer birefringent material, and is supported by a light-controlled orientation process, presenting a sandwich structure of "front and rear glass substrates and an intermediate LCP functional film layer"; when the incident light is circularly polarized light, the vortex wave plate 5 can generate a circularly polarized vortex light beam with a spiral phase wavefront; the second polarizer 6 is used to convert the circularly polarized vortex light beam into a linearly polarized vortex light beam.

[0028] Furthermore, the analyzer 9 is installed on the outgoing light path of the optically active solution 8 to be measured, and the linearly polarized vortex light beam enters the analyzer 9 after passing through the optically active solution 8 to be measured. The analyzer 9 is used to detect the polarization state of the linearly polarized vortex light beam after transmitting the optically active solution 8 to be measured. The 4F imaging system is installed on the outgoing light path of the analyzer 9, and the 4F imaging system is used to image the analyzer 9 and realize the function of spatial frequency filtering; it should be noted that the 4F imaging system forms a clear image on the output plane by performing Fourier transform and inverse Fourier transform, and sends the collected polarized light image to the computer 14 for light intensity analysis, which can effectively reduce the noise in the imaging and enhance the characteristics; the vortex polarimeter adopts a transmission light path and combines the 4F imaging system, which effectively improves the accuracy of optical rotation measurement.

[0029] In summary, the vortex polarimeter provided in this embodiment improves the accuracy of optical rotation measurement, and has a simple overall structure and reduced costs.

[0030] Example 2

[0031] This embodiment further describes the 4F imaging system based on the technical solution provided in Embodiment 1:

[0032] In this embodiment, the 4F imaging system includes a first convex lens 10, a second convex lens 12 and a second aperture 11; the analyzer 9 is installed at the focal position of the first convex lens 10, and the first convex lens 10 converts the spatial distribution of the input image into the frequency domain distribution by performing Fourier transform; the second aperture 11 is installed at the Fourier plane position of the 4F imaging system to limit the aperture and direction of the imaging beam; the second convex lens 12 is installed on the incident light path of the image plane of the CCD sensor 13, and the second convex lens 12 converts the frequency domain distribution back to the time domain distribution by performing inverse Fourier transform, and finally forms a clear image on the image plane of the CCD sensor 13. In some embodiments, for the optically active solution 8 to be measured is a glucose solution, the focal lengths of the first convex lens 10 and the second convex lens 12 are both 125 mm.

[0033] Example 3

[0034] This embodiment is based on the technical solution provided in Embodiment 1, and further describes the arrangement and installation of the polarization state generator, the first aperture 7, the analyzer 9 and the 4F imaging system:

[0035] In this embodiment, in order to further simplify the overall structure of the vortex polarimeter, the polarization state generator, the first aperture 7, the analyzer 9 and the 4F imaging system are coaxially arranged and installed at equal heights.

[0036] Example 4

[0037] This embodiment provides a detection method based on the technical solution provided in any one of Examples 1 to 4. The detection method uses a vortex polarimeter provided in any one of Examples 1 to 4.

[0038] In this embodiment, the detection method includes the following steps:

[0039] Step A, turn off the indoor light source, test the indoor background light through the light intensity analysis software, and obtain the initial background light intensity;

[0040] Step B, turning on the device, including the light source and the CCD sensor 13;

[0041] Step C, adjusting the polarizer and the analyzer 9 so that their polarization states are orthogonal to each other, and the angle of the analyzer 9 is recorded as θ0;

[0042] Step D: Place the optically active solution 8 to be tested on the outgoing light path of the polarization state generator, receive the polarized light image through the CCD sensor 13 and send the polarized light image to the computer 14 for light intensity analysis. -3 Adjust the angle of the polarizer 9 to minimize the light intensity. At this time, the angle of the polarizer 9 is recorded as θ1;

[0043] Step E: The optical rotation of the optically active solution 8 to be measured is θ i =θ1-θ0.

[0044] The following is an explanation of the test results based on the linearly polarized vortex light detection provided in this embodiment:

[0045] When the concentration of glucose solution is 0.300 g / mL and the optical path length of the solution is L=2.0 dm, the test results are shown in Table 1 below:

[0046] Table 1. Optical rotation measurement results when the concentration is 0.300 g / mL and L is 2.0 dm

[0047]

[0048] It can be seen from Table 1 above that the average measured optical rotation is 31.622°, the theoretical optical rotation is 31.620°, the relative average error of the measured optical rotation is 0.070%, and the standard deviation is 0.024°.

[0049] When the glucose solution concentration is 0.3 g / mL and L=0.6 dm, the test results are shown in Table 2 below:

[0050] Table 2. Optical rotation measurement results when the concentration is 0.3 g / mL and L is 0.6 dm

[0051]

[0052] It can be seen from Table 2 above that the average measured optical rotation is 9.486°, the theoretical optical rotation is 9.490°, the relative average error of the measured optical rotation is 0.126%, and the standard deviation is 0.012°.

[0053] The comparison results of the optical rotation test of different light source types are shown in Table 3 below:

[0054] Table 3. Comparison of optical rotation measurements of different light source types

[0055]

[0056] The relative error comparison results of different light source types are shown in Table 4 below:

[0057] Table 4. Comparison of relative errors of different light source types

[0058]

[0059] The experimental results show that: under the same conditions, linearly polarized vortex light significantly improves the accuracy of optical rotation measurement. In particular, when L = 2.0dm, the relative error of linearly polarized vortex light is only 0.070%, which is much lower than the 0.152% of He-Ne laser, indicating that linearly polarized vortex light has a significant advantage in improving the accuracy of optical rotation measurement.

[0060] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A vortex polarimeter, characterized in that It comprises a polarization state generator, a first aperture (7), an analyzer (9), a 4F imaging system and a computer (14); The polarization state generator is used to convert a light beam into a linearly polarized vortex light beam. The optically active solution (8) to be measured is placed on the exit light path of the polarization state generator. The first aperture (7) is installed on the incident light path of the optically active solution (8) to be measured. The analyzer (9) is installed on the exit light path of the optically active solution (8) to be measured. The linearly polarized vortex light beam passes through the optically active solution (8) to be measured and then enters the analyzer (9). The 4F imaging system is installed on the exit light path of the analyzer (9). The 4F imaging system is used to image the analyzer (9) and send the collected polarized light image to a computer (14) for analysis.

2. The vortex polarimeter according to claim 1, wherein The polarization state generator comprises a first polarizer (3), a quarter wave plate (4), a vortex wave plate (5) and a second polarizer (6); the first polarizer (3) is used to modulate a light beam into linearly polarized light; the quarter wave plate (4) is installed on an exit light path of the first polarizer (3) and is used to convert the linearly polarized light into circularly polarized light; the vortex wave plate (5) is installed before the second polarizer (6) and is used to modulate the circularly polarized light into a circularly polarized vortex light beam; and the second polarizer (6) is used to convert the circularly polarized vortex light beam into a linearly polarized vortex light beam.

3. The vortex polarimeter according to claim 1, wherein The 4F imaging system comprises a first convex lens (10), a second convex lens (12) and a second aperture (11); the polarizer (9) is installed at the focal position of the first convex lens (10); the second aperture (11) is installed at the Fourier plane position of the 4F imaging system; and the second convex lens (12) is installed on the incident light path of the image plane of the CCD sensor (13).

4. The vortex polarimeter according to claim 3, wherein: The focal lengths of the first convex lens (10) and the second convex lens (12) are both 125 mm.

5. The vortex polarimeter according to claim 1, wherein It also includes a light source for generating the light beam, wherein a collimating beam expander (2) is installed on the outgoing light path of the light source, and the collimating beam expander (2) is installed on the incident light path of the polarization state generator, so that the light beam emitted by the light source is expanded and converted into parallel light and incident on the polarization state generator.

6. The vortex polarimeter according to claim 5, characterized in that The light source is a HE-NE laser (1).

7. The vortex polarimeter according to claim 1, wherein: The polarization state generator, the first aperture (7), the analyzer (9) and the 4F imaging system are coaxially arranged and installed at equal heights.

8. A detection method using the vortex polarimeter according to any one of claims 1 to 7, characterized in that: The steps include: Step A, turning on the device, including the light source and the CCD sensor 13; Step B, adjusting the polarizer and the analyzer 9 so that their polarization states are orthogonal to each other, and the angle of the analyzer 9 is recorded as θ0; Step C, placing the optically active solution 8 to be tested on the outgoing light path of the polarization state generator, receiving the polarized light image through the CCD sensor 13, and sending the polarized light image to the computer 14 for light intensity analysis, adjusting the angle of the analyzer 9 according to the preset light intensity threshold to minimize the light intensity, at this time the angle of the analyzer 9 is recorded as θ1; Step D: The optical rotation of the optically active solution 8 to be measured is θ i =θ1-θ0.

Images