A method for measuring the absorption coefficient of a medium and the reflectivity of any material in the medium

Abstract

The present invention discloses a method for measuring the absorption coefficient of a medium and the reflectivity of any material in the medium. The method for measuring the absorption coefficient of a medium and the reflectivity of an inner wall comprises: 1) selecting a detector whose inner wall is a highly reflective material and setting a small opening on the inner wall, and the detector is filled with the medium to be measured; 2) using a light source to illuminate through a microhole to collect a light signal waveform; fitting to obtain the effective attenuation length of light in the detector; 3) changing the size of the reflection area; repeating step 2) to obtain the effective attenuation length in reflection areas of different sizes; 4) fitting the absorption length of the medium and the reflectivity of the inner wall according to the formula λ'=1 / (1 / λ‑ln(f1*(1‑ε)) / L). The method for measuring the reflectivity of any material in the medium comprises: 1) fixing the reflection area of ​​the above device; 2) respectively measuring the effective attenuation lengths λ1 and λ2 of light in the detector when there is no reflective material at the opening and when the opening is covered with any material; 3) obtaining the reflectivity of any material covered in the medium according to the formula #imgabs0# or #imgabs1# and the measured parameters.

Description

Technical Field

[0001] The invention relates to a method for measuring a medium absorption coefficient and a reflectivity of any material in the medium. The absorption coefficient of the medium and the reflectivity of any material in the medium are measured by measuring light intensity attenuation. Background Art

[0002] The attenuation of light intensity along the propagation direction in the medium is caused by the absorption and scattering of light by the medium. Due to the influence of scattering, commercially available instruments such as spectrophotometers can measure the attenuation factor of light in the medium, but cannot measure the absorption coefficient after removing the scattering effect. The measurement of the reflectivity of materials in the medium is affected by the absorption of the medium, which is also a technical problem at home and abroad. Most metrological institutions at home and abroad do not have mature technical instruments to provide accurate measurements.

[0003] Starting from the first principle, the present invention has developed a series of innovative methods for measuring the optical parameters of detectors based on the absorption, reflection and propagation principle of light in a detector whose inner wall is a reflective material. The present invention proposes a method based on the first principle and derives a formula for simulation and proof. The developed method proves that the same device can be used to measure the absorption coefficient of the medium and the reflectivity of any material in the medium, filling the technical gap at home and abroad. Summary of the invention

[0004] The purpose of the present invention is to provide a method for measuring the absorption coefficient of a medium and the reflectivity of any material in the medium. The present invention uses a detector whose inner wall is a highly reflective material and whose reflective area can be adjusted in size, and sets a signal collector and a light source through microholes on the inner wall. The detector is provided with a small opening that can cover the material to be tested with any reflectivity. The photosensitive element collects the signal change in the detector after being irradiated by pulsed light, and measures the waveform signal of the signal size changing with time when the reflective area is of different sizes and there is no reflective material at the opening and when the opening is covered with the material to be tested, respectively. The absorption coefficient of light in the medium and the reflectivity of any type of material in the medium are measured using a simple and novel method.

[0005] The technical solution of the present invention is:

[0006] A method for measuring the absorption coefficient of a medium and the reflectivity of an inner wall of a detector in the medium, the steps comprising:

[0007] 1) A detector with a highly reflective inner wall is selected, and a signal collector and a light source are set through microholes on the inner wall. The size of the light reflection area can be adjusted (for example, the height of the reflection area of ​​a cylindrical cavity or a rectangular cavity can be changed by adjusting the distance between the upper and lower reflection surfaces). A small opening is set on the reflection surface, and the detector is filled with the medium to be tested;

[0008] 2) using a selected pulse light source to illuminate the reflection area of ​​the detector, using the signal collector to collect the optical signal waveform, and fitting the collected signal waveform to obtain the effective attenuation length of the light in the detector;

[0009] 3) changing the size of the reflection area (such as the height of the reflection area), repeating step 2), and measuring the effective attenuation length of light in the detector when the reflection area has different sizes;

[0010] 4) According to the formula λ'=1 / (1 / λ-ln(f1*(1-ε)) / L), the corresponding points of the effective attenuation length λ' and the parameter (such as height) of the change of the size of the reflection area are fitted to obtain the absorption length λ (the inverse of the absorption coefficient) of the medium in the reflection cavity and the average reflectivity f1 of the inner wall of the detector outside the opening area. The corresponding points of λ' and L can also be fitted to obtain λ and f1. Where, λ'

[0011] In order to obtain the effective attenuation length of light in reflection areas of different sizes by fitting the collected light signal waveform, ε is the ratio of the opening area to the inner wall area of ​​the reflection area corresponding to different sizes of the reflection area, and L is the average optical path (average reflection step) of a single reflection of the light in reflection areas of different sizes, which can be calculated by 4*(reflection area volume) / (reflection area inner wall area), or obtained by Geant4 simulation or measured by the method in patent ZL201710397900.8.

[0012] The present invention also provides a method for measuring the reflectivity of any material in a medium

[0013] 1) A detector with a highly reflective inner wall and a small opening is selected, and a signal collector and a light source are arranged through the microholes on the inner wall. The detector is filled with the above medium (the device described in the above method and the measured medium absorption length λ can be directly used);

[0014] 2) irradiating the detector with a selected pulse light source, collecting the optical signal waveform with the signal collector, and obtaining the effective attenuation length λ1 of the photon in the reflection area of ​​the detector according to the collected signal waveform;

[0015] 3) Covering the opening with the material to be tested, irradiating the detector with the light source, collecting the light signal waveform with the signal collector, and obtaining the effective attenuation length λ2 of the photon in the reflection area of ​​the detector according to the collected signal waveform;

[0016] 4) Calculate the reflectivity f2 of the material to be tested covering the opening according to the size of the detector, the ratio ε of the opening area to the inner wall area of ​​the reflection zone, and the measured λ1, λ2 and the medium absorption length λ.

[0017] In step 4), according to the formula Calculate the reflectivity f2 of the material to be tested in the medium; wherein L is the average optical path (average reflection step length) of a single reflection of the light in the detector, which can be calculated by 4*(reflection area volume) / (reflection area inner wall area), or can be obtained by simulation or measured by the method in patent ZL201710397900.8.

[0018] The present invention provides a second method for measuring the reflectivity of any material in a medium

[0019] 1) A detector whose inner wall is made of highly reflective material and has a small opening is selected, and a signal collector and a light source are set through the microholes on the inner wall. The detector is filled with the above medium (the device described in the above method and the measured medium absorption length λ and the average reflectivity f1 of the inner wall of the medium except the opening can be directly used);

[0020] 2) Covering the opening with the material to be tested, irradiating the detector with the light source, collecting the optical signal waveform with the signal collector, and obtaining the effective attenuation length λ2 of the photon in the detector according to the collected signal waveform;

[0021] 3) Calculate the reflectivity f2 of the material to be tested covering the opening according to the size of the detector, the ratio ε of the opening area to the inner wall area of ​​the reflection zone, and the measured f1, λ2 and λ.

[0022] In step 3), you can also use the formula Calculate the reflectivity f2 of the material to be tested in the medium; wherein L is the average optical path length (average reflection step length) of a single reflection of the light in the detector, which can be calculated by 4*(reflection area volume) / (reflection area inner wall area), or can be obtained by simulation or measured by the method in patent ZL201710397900.8.

[0023] Further, using N*e -t / τ Exponential fitting is used to obtain the waveform of the collected signal size changing with time to obtain the attenuation factor τ of the number of photons with time. The attenuation factor is multiplied by the speed of light to obtain the effective attenuation length of the photon in the detector; or the waveform of the collected signal size changing with time is multiplied by the speed of light to obtain the waveform changing with distance, and then N*e -t / λ’ The effective attenuation length λ' is obtained by fitting; wherein N, τ, and λ' are all parameters that can be directly fitted, and are respectively the number of photoelectrons collected by the signal collector at the initial moment of fitting, the effective attenuation time, and the effective attenuation length.

[0024] Furthermore, it is recommended that the ratio ε of the area of ​​the opening to the inner wall area of ​​the detector be less than 5%.

[0025] Furthermore, there is no specific requirement for the reflectivity of the inner wall of the high-reflectivity material. In order to increase the data acquisition efficiency, it is recommended that the reflectivity of the high-reflectivity material of the inner wall body is greater than 90%, and it is not a pure mirror reflective material.

[0026] Furthermore, there is no specific requirement for the absorption length of the medium, but the larger the absorption length, the greater the inner wall reflectivity or the larger the detector size is required to achieve better measurement accuracy.

[0027] Furthermore, there is no specific requirement for the size and shape of the detector, but for different absorption, scattering lengths and reflectivities, detectors of different sizes can achieve better measurement accuracy.

[0028] The present invention is based on the reflection and absorption attenuation principle of photons in a detector whose inner wall is made of highly reflective material and has an opening. The method developed by the present invention proves that the detection device whose inner wall is made of reflective material as described above can realize the measurement of the medium absorption coefficient and the reflectivity of any material in the medium. The absorption length of light in the medium and the reflectivity of the material in the medium depend on the wavelength of light and the properties of the medium and material, and are parameters that are difficult to measure directly. The attenuation of light intensity along the propagation direction of light in the medium is caused by the absorption and scattering of light by the medium. The scattering length of light refers to the distance traveled by the number of photons in the propagation direction of light due to scattering to become 1 / e. The absorption length of light refers to the distance traveled by the number of photons due to absorption by the medium to become 1 / e, and the reciprocal of the light absorption length is the absorption coefficient. The photons generated by the pulsed light are fully mixed after multiple reflections in the detector. The average distance L (average optical path for a single reflection, or average reflection step length) traveled by the photons for each reflection can be approximately calculated based on the volume and area of ​​the reflection area, or can be measured according to the methods in Patents ZL201710398214.2 and ZL201710397900.8 or obtained through Geant4 simulation. The inventors have proved through Geant4 simulation that if the scattering length of the medium in the detector is greater than the size of the detector, the effect of scattering on the average optical path for a single reflection is very small. The scattering length of ultrapure water is more than 100 meters, and the scattering length of most transparent or translucent media reaches several meters or more than 100 meters. The size can be designed to achieve that when the detector is filled with these media, the average optical path for a single reflection of light in the detector is calculated by 4*(volume) / (inner wall area). The distance corresponding to the movement of a photon with a light speed of v in the detector for t time is x=v*t, and the number of reflections of the photon is x / L. Photons in the detector are mainly attenuated by the absorption of the inner wall of the detector and the absorption of the medium inside the detector. After the single-wavelength pulse LED light is irradiated in the detector, the photons are reflected and mixed multiple times in the detector, and the number of photons decays exponentially with time and distance. A photomultiplier tube (PMT) is used to collect the light signal in the detector through the microhole on the inner wall of the detector. The attenuation factor of the signal size received by the PMT over time reflects the attenuation factor of the total number of photons in the detector over time, which is expressed as N*e-t / τ Exponential fitting is used to obtain the waveform of the signal size collected by the PMT that changes with time to obtain the attenuation factor τ of the number of photons over time, and multiply it by the speed of light to convert time into distance to obtain the effective attenuation length λ' of the photons in the detector. The waveform of the signal size that changes with time can also be multiplied by the speed of light to obtain the waveform that changes with the flight distance and then N*e -x / λ’ The effective attenuation length λ' is obtained by fitting. Assuming that there are N0 photons of a specific wavelength in the detector at a certain moment, the medium absorption length corresponding to this wavelength is λ, and the total reflectivity of the inner wall is f, then the number of photons caused by the absorption of the inner wall of the detector after N0 photons move x distance becomes N0*(f) x / L , N0 photons move x distance, and the number of photons becomes N0*e simply due to the absorption of the medium -x / λ . Under the combined action, the number of photons remaining after N0 photons move x distance in the detector is N0*e -x / λ *(f) x / L , which can also be expressed by the effective attenuation length λ' as N0*e -x / λ’ Then e -x / λ’ =e -x / λ *(f) x / L (i.e., Formula 1), is transformed into 1 / λ'=1 / λ-ln(f) / L (i.e., Formula 2). If the absorption length of the medium inside the detector is λ, the inner wall of the detector has an opening or black body with a proportion of ε, and the average reflectivity of the remaining area is f1, and all photons are absorbed when they hit the opening or the inner wall of the black body, then the total reflectivity f of the inner wall of the detector is f1 multiplied by its proportion of the inner wall (1-ε), then Formula 2 becomes 1 / λ'=1 / λ-ln(f1*(1-ε)) / L (i.e., Formula 3). If the inner wall of the detector has an area reflectivity of f2 with a proportion of ε, and the average reflectivity of the remaining area is f1, then the total reflectivity of the inner wall of the detector is f1*(1-ε)+f2*ε, then Formula 2 becomes 1 / λ'=1 / λ-ln(f1*(1-ε)+f2*ε) / L (i.e., Formula 4).

[0029] Take a cylindrical detector with a reflective material as an example, assuming that the radius of the upper cover and lower base of the detector is r, the upper cover can be moved to change the height of the reflection area, the lower base has an opening area of ​​δ, and the signal collector and light source are set through the microholes on the inner wall. When the height of the reflection area is h, the ratio of the opening area to the inner wall area is δ / (2*π*r*r+2*π*r*h), and the average optical path of a single reflection is calculated as 2*r*h / (r+h) based on 4*V / S. When the absorption length of the medium in this detector is λ, Formula 3 can also be expressed as 1 / λ'=1 / λ-ln(f1*(1-(δ / (2*π*r*r+2*π*r*h)) / (2*r*h / (r+h))(i.e. Formula 5). First, the height of the detector reflection area is set to h1, the pulse light is irradiated inside, the optical signal waveform is collected by the signal collector, and the effective attenuation length λ1 is obtained by fitting. The height of the detector reflection area is changed, and the above measurement process is repeated to obtain the effective attenuation length at different detector heights. By fitting the corresponding points of the effective attenuation length with respect to the height of the reflection area using Formula 5, the absorption length λ of the medium and the reflectivity f1 of the inner wall of the detector can be fitted at the same time. The height of the detector reflection area is set to h1, cover the opening with the material to be tested of any reflectivity, use the selected light source to illuminate the detector, use the signal collector to collect the optical signal waveform, and fit to obtain the effective attenuation length λ2 of the photon in the detector. When the detector height is h1, the ratio of the opening area to the inner wall of the detector ε=δ / (2*π*r*r+2*π*r*h1), and the average optical path of a single reflection is calculated according to 4*V / S as L=2*r*h1 / (r+h1). According to Formula 3 and Formula 4, 1 / λ1=1 / λ-ln(f1*(1-ε) / L, and 1 / λ2=1 / λ-ln(f1*(1-ε+f2*ε) / L. Then the formula deformation calculation shows that the reflectivity of the material covered at the opening is: (i.e. Formula 6) or (i.e., Formula 7). That is, by measuring the attenuation of light intensity over time at different heights of the reflection cavity and when there is no reflective material at the opening and when the material to be tested is attached to the opening, the absorption length of the medium and the reflectivity of any material in the medium can be measured.

[0030] This method is applicable to any shape of detector that can measure volume and area. Through Geant4 simulation verification, the method was verified using cylindrical detectors and rectangular detectors respectively, and it can achieve good measurement accuracy.

[0031] Compared with the prior art, the present invention has the following positive effects:

[0032] This method cleverly achieves the measurement of the absorption coefficient of the medium and the reflectivity of any material in the medium by a simple and novel method. When all optical parameters are unknown, the conditions available in an ordinary laboratory can be used to build a device to measure the absorption coefficient of the medium and the reflectivity of any material in the medium. It can also be extended to study the reflective properties of the material to be tested when there is a certain distance between the material to be tested and the opening. The measurement method of the present invention is simple to operate and has a novel principle, and has great application value. The present invention has great application value in detector development and calibration, reflectivity and absorption length measurement, properties of materials in the medium, composition and biological properties of the medium, content of impurities in the medium and substance concentration, etc., and can provide conveniently operated instruments and analysis methods for more accurate deterministic research in these fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The figure is a flow chart of the method of the present invention.

[0034] Figure 2 To simulate the change of the number of photons received by the PMT over time after the pulsed LED light is irradiated in the detector, the black thick line segment is N0*e -t / τ Function fitting results.

[0035] Figure 3 To simulate the change of effective attenuation length with detector height when a cylindrical cavity with a diameter of 50 cm and heights of 20 cm, 40 cm and 60 cm respectively is filled with water with an absorption length of 20 meters, the inner wall is made of a material with a reflectivity of 98% and the top opening is 15 cm*10 cm. The thick black line segment is the fitting result of the function using formula five.

[0036] Figure 4 To simulate the change of the number of photons received by the PMT over time after the pulsed LED light is irradiated in the detector, when the cylindrical cavity with a diameter of 50 cm and a height of 60 cm is filled with water with an absorption length of 20 meters, the inner wall is made of a material with a reflectivity of 98% and the upper opening of 15 cm*10 cm is covered with a material with a reflectivity of 10%. The black thick line segment is N0*e -t / τ2 Function fitting results.

[0037] Figure 5 To simulate the change of the number of photons received by the PMT over time after the pulsed LED light is irradiated in the detector, when a cylindrical cavity with a diameter of 50 cm and a height of 60 cm is filled with water with an absorption length of 20 meters, the inner wall is made of a material with a reflectivity of 98% and the upper opening of 15 cm*10 cm is covered with a material with a reflectivity of 50%. The black thick line segment is N0*e -t / τ2 Function fitting results.

[0038] Figure 6 To simulate the change of the number of photons received by the PMT over time after the pulsed LED light is irradiated in the detector, when the cylindrical cavity with a diameter of 50 cm and a height of 60 cm is filled with water with an absorption length of 20 meters, the inner wall is made of a material with a reflectivity of 98% and the upper opening of 15 cm*10 cm is covered with a material with a reflectivity of 90%. The black thick line segment is N0*e -t / τ2 Function fitting results. DETAILED DESCRIPTION

[0039] The specific implementation method takes the following simulation verification scheme as an example:

[0040] Simulate a cylindrical cavity with a diameter of 50cm and a height of 80cm. The inner wall of the detector is made of Tyvek material with a reflectivity of 98%. Inside the detector is water with an absorption length of 20 meters and a refractive index of 1.33. The upper Tyvek has a microhole with a diameter of 1cm for the photomultiplier tube cathode surface to receive photons. The lower Tveyk is fixed and has an opening of 15cm*10cm. Each simulation generates 100,000 photons within 10ns. The number of photons received per unit time by the photomultiplier tube changes with time. The starting point of time is when the event is generated. Set different random numbers for multiple simulations to improve the statistics. Figure 2 The change of the number of photons received by the PMT over time when the Tyvek cover is 60cm high and there is no reflective material at the opening. The thick black line is N0*e -t / τ1 The effective decay time obtained by function fitting is 31.76ns, and multiplying it by the speed of light gives an effective decay length of 7.159m. The effective decay length of light in the detector is obtained by simulation fitting when the height of the Tyvek cover is 20cm, 40cm, and 60cm. Figure 3 The horizontal axis is the detector height, and the vertical axis is the effective attenuation length obtained by simulating and fitting the PMT waveform at different heights. Figure 3 The black line in the middle is fitted using Formula 5, which gives a water absorption length of 19.75 meters and a reflectivity of 98% on the inner wall of the detector, both of which are highly consistent with the values ​​put in the simulation.

[0041] Then the height of the upper cover Tyvek was fixed at 60cm, and the opening was covered with materials with reflectivity of 10%, 50% and 90% for simulation. According to the radius and height of the detector, the average optical path of a single reflection was calculated to be L = (2*(0.25*0.6) / (0.25+0.6)) = 0.35294m. Figure 4 When the opening is covered with 10% reflectivity material, the number of photons received by the PMT changes with time after the pulsed LED light shines in the detector. The black thick line segment is N0*e -t / τ2Function fitting obtains an effective attenuation time of 40.27ns, which is multiplied by the speed of light to obtain an effective attenuation length of 7.3338 meters. According to Formula 6, the reflectivity of the material covering the opening is calculated as f2 = ((exp(0.35294 / 19.75-0.35294 / 7.333793)-exp(0.35294 / 19.75-0.35294 / 7.159))) / ((0.1*0.15) / (3.14159*0.25*0.25*2+2*3.14159*0.25*0.6)) = 10.14%. Figure 5 When the opening is covered with 50% reflectivity material, the number of photons received by the PMT changes with time after the pulsed LED light shines in the detector. The black thick line segment is N0*e -t / τ2 Function fitting obtains the effective attenuation time of 36ns, which is multiplied by the speed of light to obtain the effective attenuation length of 8.1158m. According to Formula 6, the reflectivity of the material covering the opening is calculated as f2 = ((exp(0.35294 / 19.75-0.35294 / 8.1158)-exp(0.35294 / 19.75-0.35294 / 7.159))) / ((0.1*0.15) / (3.14159*0.25*0.25*2+2*3.14159*0.25*0.6)) = 50.28%. Figure 4 When the opening is covered with 90% reflectivity material, the number of photons received by the PMT changes with time after the pulsed LED light shines in the detector. The black thick line segment is N0*e -t / τ2 Function fitting results in an effective decay time of 40.27ns, which is multiplied by the speed of light to obtain an effective decay length of 9.0765m. According to Formula 6, the reflectivity of the material covering the opening is calculated as f2 = ((exp(0.35294 / 19.75-0.35294 / 9.0675)-exp(0.35294 / 19.75-0.35294 / 7.159))) / ((0.1*0.15) / (3.14159*0.25*0.25*2+2*3.14159*0.25*0.6)) = 89.97%.

[0042] This method still works if the material at the opening is replaced with a material with any reflectivity. This method still works if the material at the opening is changed from diffuse reflection to specular reflection, or the size of the opening is changed. This method still works if the absorption length and scattering length of the medium and the detector size are set to different values, but for different absorption and scattering lengths, detectors of different sizes and materials with different reflectivity on the inner wall can achieve better measurement accuracy.

[0043] Alternatives

[0044] There are no specific requirements for the shape of the detector and the way to change the size of the reflection area, as long as the volume and area can be measured and the data collection efficiency is high enough. There are no specific requirements for the absorption and scattering length of the medium, the size of the detector, and the reflectivity of the inner wall. It is suitable for most transparent or translucent media, but for different absorption and scattering lengths, materials with different detector sizes and different reflectivities of the inner wall can achieve better measurement accuracy. The high-reflective material of the inner wall can be mainly diffuse reflection or mainly specular reflection, not necessarily absolute specular reflection. There are no requirements for the reflectivity and reflection model of the material to be tested attached to the opening. Any reflectivity is acceptable, and diffuse reflection materials or specular reflection materials are acceptable. When there is no material at the opening, the measurement can also be replaced by covering with black material with negligible reflectivity. A photomultiplier tube can be used as a photosensitive probe to collect signals in combination with any instrument that can collect waveforms, or other types of photosensitive probes can be used.

[0045] Although the specific embodiments of the present invention are disclosed for the purpose of illustration, the purpose is to help understand the content of the present invention and implement it accordingly, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the best embodiment, and the scope of the present invention is subject to the scope defined in the claims.

Claims

1. A method for measuring a medium absorption coefficient and a reflectivity of an inner wall of a detector in a medium, the steps comprising: 1) A detector with an inner wall made of a highly reflective material is selected and a microhole and a small opening are arranged on the inner wall; the area outside the opening and the outside of the detector are black and light-proof; the detector is filled with a medium to be tested; 2) using the selected light source to illuminate the detector reflection area through the microhole, using a signal collector to collect the light signal waveform through the microhole and send it to a data processing unit; the data processing unit obtains the effective attenuation length of the light in the detector reflection area according to the collected light signal waveform by fitting; 3) changing the size of the inner wall reflection area of ​​the detector; repeating step 2) to measure the effective attenuation length of light in the detector; repeating the measurement to obtain the effective attenuation length corresponding to reflection areas of different sizes; 4) According to the formula λ'=1 / (1 / λ-ln(f1*(1-ε)) / L), the absorption length λ of the medium to be measured in the detector and the reflectivity f1 of the inner wall of the detector except the opening area in the medium are fitted; wherein λ' is the effective attenuation length of the light in the reflection areas of different sizes obtained by the data processing unit according to the waveform of the collected light signal, ε is the ratio of the area of ​​the opening area to the area of ​​the inner wall of the reflection area when the reflection areas are of different sizes, and L is the average optical path of a single reflection of the light in the reflection areas of different sizes.

2. The method according to claim 1, characterized in that The size of the reflection area of ​​the detector is adjustable.

3. The method according to claim 2, characterized in that The micro holes and opening areas are on the reflective surface.

4. The method according to claim 1, characterized in that The average optical path length L of a single reflection can be calculated by 4*(reflection area volume) / (inner wall area of ​​the reflection area), and can also be obtained by simulation or actual measurement.

5. The method according to claim 1, characterized in that The reflective material of the inner wall of the detector is a non-pure specular reflective material.

6. A method for measuring the reflectivity of any material in a medium, the steps comprising: A) obtaining the absorption length λ of the medium to be measured in the detector by the method of claim 1; B) using the selected light source to illuminate the internal reflection area of ​​the detector through the microhole, using a signal collector to collect the light signal waveform through the microhole and send it to a data processing unit; the data processing unit obtains the effective attenuation length λ1 of the light in the detector according to the collected light signal waveform; C) Covering the opening area with the material to be tested, then using the selected light source to illuminate the internal reflection area of ​​the detector through the microhole, using a signal collector to collect the light signal waveform through the microhole and send it to a data processing unit; the data processing unit obtains the effective attenuation length λ2 of the light in the detector according to the collected light signal waveform; D) Calculate the reflectivity f2 of the material to be tested covering the opening according to the size of the detector, ε, and λ1, λ2, λ, and L.

7. The method according to claim 6, characterized in that According to the formula f2=(e L / λ-L / λ2 -e L / λ-L / λ 1) / ε calculates the reflectivity f2 of the material to be tested in the medium.

8. A method for measuring the reflectivity of any material in a medium, the steps comprising: a) using the method of claim 1 to obtain the absorption length λ of the medium to be measured in the detector and the reflectivity f1 of the inner wall of the detector except the opening area in the medium; b) Covering the opening with the material to be tested, then using the selected light source to illuminate the inner wall of the detector through the microhole, using a signal collector to collect the light signal waveform through the microhole and send it to a data processing unit; the data processing unit obtains the effective attenuation length λ2 of the light in the detector according to the collected light signal waveform; c) calculating the reflectivity f2 of the material to be tested covering the opening according to the size of the detector, ε, and f1, λ2, λ, and L.

9. The method according to claim 8, characterized in that According to the formula Calculate the reflectivity f2 of the material to be tested in the medium.

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