CN101140222A - Spectrometer system and method for measuring whole optical parameter including turbidity dielectric materials - Google Patents

Abstract

A spectrograph system and a method measure all optical parameters of turbid medium materials. The system comprises a computer respectively connected with a light source, a monochrometer, a sampling device and a signal measuring device. Wherein, lights emitted by the light source are projected to the sampling device through the monochrometer and a light path. Light signals from the sampling device are transmitted to the signal measuring device connected with the computer through the light path. In addition, the method obtains, inputs and calculates error values of actual light signals and measured light signals on all wavelengths of set bands to acquire and input sample system parameters, thus entering into a subprogram for refractive index calculation. Input sample optical parameters compares difference between light signals of actual measuring and calculated light signals. As the difference is less than the measuring error value, it is necessary to calculate and output other optical parameter spectrum of the sample. Otherwise, the light signal is returned to a subprogram of optical transmission theoretical calculation. The measuring system of the present invention brings great convenience and accurately measures all optical parameters of light signals and all materials including turbid medium materials.

Description

Spectrometer system and method for determining all optical parameters of turbid medium material

Technical Field

The invention relates to a spectrometer system and a method. And more particularly to a spectrometer system and method for accurately measuring all optical parameters of a material, including a turbid medium, that can be used to accurately measure optical signals and optical parameters.

Background

The spectrum is a function relationship of optical parameters and light wavelengths, and different materials have different spectra and reflect the characteristics of the materials. The determination of the characteristic spectra of materials, the analysis and the study are referred to as spectroscopy. A spectrometer is one of material analysis instruments widely used in various industries based on the principle of spectroscopy. In any spectrometer, it is necessary to process the measured optical signal to obtain optical parameters based on a mathematical physical model that accurately describes the interaction of light with a material. Among the spectrometers, the absorption spectrometer (spectrophotometer) that measures the optical attenuation coefficient spectrum of materials from the ultraviolet to the infrared spectral region is one of the most commonly used spectrometers.

In general, the interaction between light and material can be divided into two categories, absorption and scattering. If the material scatters light strongly, it is called optically turbid medium. Many materials are optically turbid media, such as ceramics, non-transparent plastics, milk, paints, cell suspension liquids, water or oils or other solutions contaminated or having suspended particles, soft tissues of humans, animals and plants, etc. Light absorption and light scattering occur in turbid media in the presence of light interacting with materials, and the spatial and temporal distribution of the interaction is of a random nature. In this case, the energy propagation and distribution of light in the material is a complex boundary condition problem, and needs to be described and solved by an accurate mathematical physical model. The optical model of turbid media, which is widely used at present, is the radiation transport theory, which defines the optical parameters of materials as absorption coefficients, scattering coefficients and scattering phase functions. The absorption coefficient represents the average number of times a photon is absorbed per unit propagation distance within a material and is generally related to the type, concentration, size, shape, etc. of different components or particles within the material. While the scattering coefficient and scattering phase function represent the probability distribution of the average number of times a photon is scattered per unit propagation distance within the material and the scattering angle. Where a form of scattering phase function is known, such as a Henyey-Greenstein phase function, the scattering phase function may be determined by one or more scalar parameters. Hanny-Greenstein phase function is determined by a scalar parameter, called anisotropy parameter, defined as the mean value of the cosine of the scattering angle, as discussed in detail in the references (e.g., Z.Song, K.Dong, X.H. Hu, and J.Q.Lu. "Monte Carlo Simulation of converting Laser Beams amplification in Biological Tissues", applied Optics, vol.38, pp.2944-2949 (1999)).

In addition to the above Optical parameters, the Optical Refractive index of a material is also an Optical parameter, which can be generally determined by the Fresnel formula of the boundary coupling condition of electromagnetic waves between materials of different properties, and the detailed discussion of the references can be found (e.g., H. Ding, J.Q.Lu, K.M.Jacobs, X.H.Hu., "Determination of reflective industries of porous Skin Tissues and Intralipid at 8 wall hs beta. 325and 1557 nm", journal of the Optical Society of America A, vol.22, pp.1151-1157 (2005)). If we assume that the scattering phase function of a material can be described by the Hanny-Green Stent phase function, the scattering phase function can be uniquely determined by each anisotropy parameter. For a macroscopically homogeneous turbid medium material, the absorption and scattering interactions of the material on light can be fully described according to 4 parameters defined by the radiation transmission theory and fresnel equations, namely, the absorption coefficient, scattering coefficient, anisotropy parameter and refractive index, and are referred to herein as all optical parameters or all optical parameters. These 4 optical parameters typically vary with the wavelength of the light and are therefore a function of the wavelength, referred to herein as the overall optical parameter spectrum.

The attenuation coefficient mentioned above may be defined as the sum of the absorption coefficient and the scattering coefficient. The optical model on which the currently used absorption spectrometer is based is Beer-Lambert law, which is an approximation of the radiation transmission theory. Therefore, the spectrometer cannot respectively measure the absorption coefficient, the scattering coefficient and other optical parameters, and has limited analysis capability on materials, such as an absorption medium (such as black ink) and a scattering medium (such as milk white) with the same attenuation coefficient cannot be distinguished. And the whole optical parameter spectrum of the measured material can greatly improve the capability of the spectrometer for analyzing and researching materials including turbid media.

Determining the full spectrum of an optical parameter of a material requires providing a broad spectrum of incident light to illuminate a sample of the material and then measuring the scattered light signal outside the sample at different directions and locations at the same wavelength as the incident light. Light is absorbed during the propagation of a material, causing the disappearance of light or photons and the change of the direction of photon propagation due to scattering. The spatial and temporal distribution of absorption and scattering interactions in a material is generally random, with statistical characteristics determined by the optical parameters of the material. The random nature of light scattering causes randomness in the directional and positional distribution of the light emerging from the sample in three dimensions, which makes it difficult to measure the scattered light signal of a material assay. The currently reported measurement methods include a method of measuring diffuse reflected light and diffuse transmitted light signals using an integrating sphere, and a method of measuring the distribution of reflected light signals using a separate detector or an array detector. The disadvantages of these methods are either the complexity of the measuring system or the inability to accurately determine the optical signal and the optical parameters. For a detailed discussion, reference is made to the literature (e.g., C.Chen, J.Q.Lu, H.Ding, K.M.Jacobs, Y.Du, and X.H.Hu, "A primary method for determining the degree of optical parameters of nucleic samples and applications to intrasliding beta 550 and 163nm," Optics Express, vol.14, pp.7420-7435 (2006)).

Disclosure of Invention

The technical problem to be solved by the invention is to provide a spectrometer system and a method for accurately measuring all optical parameters of materials including turbid media, wherein the spectrometer system is simple in measuring system and can be used for accurately measuring optical signals and optical parameters.

The technical scheme adopted by the invention is as follows: a spectrometer system and method for determining all optical parameters of a material comprising a turbid medium.

Wherein, survey including the whole optical parameter's of turbid medium material spectrometer system includes: a light source section, a monochromator section, a light path section, a sample device section, a signal measuring section, and a computer section; wherein, the computer part used for controlling and data processing and calculating is connected with light source part, monochromator part, sample apparatus part, and signal measuring part separately; the light emitted by the light source part is injected into the sample device part through the monochromator part and the light path part; the optical signal emitted from the sample device section passes through the optical path section to the signal measuring section connected to the computer section.

The sample device part comprises a sample turntable used for adjusting the incident angle of incident light entering the sample and a sample box arranged on the sample turntable and internally provided with the sample.

The light source part comprises a light source and an optical modulator, wherein a control end of the light source is connected with the computer part through a cable, and an output light beam of the light source passes through the monochromator part, the optical modulator and the light splitting sheet and then enters the sample device part as a monochromatic incident light beam.

The light source is obtained by a continuous spectrum incoherent broad spectrum light source, and the irradiation light wavelength of the light source is continuously distributed in a set spectrum domain.

The light source in the light source part can also be composed of a plurality of lasers as coherent light sources, the output light beam wavelength is in a discrete form, and monochromatic output light can be directly obtained to the light path part.

The incident beam may have a diameter of 1 mm to 100 mm.

The monochromator part consists of a beam focusing collimation light path and a spectrum light splitting device.

The light path part comprises: a first curved reflector at the output end of the monochromator part for collimating the light beam, a beam splitter at the light reflecting side of the first curved reflector, and a reflector for receiving the collimated transmitted light beam of the sample in the sample device part; a second curved mirror for focusing on the reflected light side of the mirror, and a slit or aperture for receiving the reflected light from the second curved mirror.

The signal measuring part comprises: a photodetector that receives a diffusely reflected light beam of the sample; a photoelectric detector positioned at one side of the beam splitter and used for receiving the reflected light beam reflected by the mirror; a photodetector that receives the diffusely transmitted beam of light of the sample; a photodetector positioned at one side of the slit emergent light; and the signal processing circuit receives and processes the optical signals of the photodetectors and then sends the optical signals to the computer part.

The method of the invention for a spectrometer system for determining all optical parameters including turbid medium materials comprises the following stages:

a method for a spectrometer system for determining all optical parameters of a material comprising a turbid medium, comprising the following stages:

the first stage is as follows: acquiring input and calculating actual measurement optical signals and measurement error values on all wavelengths in a set waveband, and acquiring and inputting sample system parameters;

and a second stage: entering a refractive index calculation subprogram in the calculation program, and calculating and determining the refractive indexes of the sample on all wavelengths in the set waveband to obtain a refractive index spectrum of the sample;

and a third stage: inputting an initial value of an optical parameter of a sample and adjusting the optical parameter value of the sample within a set wave band to enter a light transmission theory calculation subprogram in a calculation program to obtain a calculation optical signal;

a fourth stage: comparing the difference between the actually measured optical signal and the calculated optical signal at the set wavelength;

and a fifth stage: in the comparison of the fourth stage, when the difference is smaller than the measurement error value, outputting all optical parameter spectrums of the sample, otherwise, returning to the third stage;

the obtaining input and calculating the measured optical signals at all wavelengths within the set band is: the ratio of the reflected light to the incident light intensity is the specular reflectance, the ratio of the diffuse reflected light intensity to the incident light intensity is the diffuse reflectance, the ratio of the collimated transmitted light to the incident light intensity is the collimated transmittance, and the ratio of the diffuse transmitted light intensity to the incident light intensity is the diffuse transmittance.

The sample system parameters include: incident light parameters, sample and sample box shape parameters, and orientation parameters of the photoelectric detector relative to the sample box.

The refractive index calculation subprogram in the calculation program comprises the following steps:

the first step is as follows: setting the initial value of the sample refractive index on the incident light wavelength according to the sample system parameters, the sample box material refractive index on the set incident light wavelength and the actually measured function curve of the specular reflectivity and the incident angle;

the second step is that: obtaining a function curve of the calculated specular reflectivity and the incident angle according to a Fresnel equation;

the third step: comparing the calculated difference between the measured specular reflectivity and the incident angle curve, and repeating the second step by repeatedly adjusting the refractive index of the sample until the difference is smaller than the measurement error value;

the fourth step: and judging whether the refractive index spectrum is calculated on all wavelengths in the set wave band, returning to the first step if the refractive index spectrum is not calculated, outputting the sample refractive index spectrum if the refractive index spectrum is calculated, and returning to the main procedure.

The sample system parameters include: the area, direction and power distribution of the incident beam cross section, the shape parameters of the sample and the sample box, and the orientation parameters of the photodetector relative to the sample box.

The optical transmission theory calculation subprogram in the calculation program comprises the following steps:

the first step is as follows: inputting system parameters of a sample, and actually measuring absorption coefficients, scattering coefficients and initial set values of various anisotropic parameters in optical signals and optical parameters of the sample; input traced incident beam photon total number N₀ (ii) a Randomly determining the total photon traveling distance according to the set sample absorption coefficient;

the second step is that: determine if the number of tracked photons N is greater than 1? Determining the photon scattering angle, namely the travelling direction, and randomly determining the travelling free path of the photons; tracking the photon to the next scattering point;

the third step: is it determined whether the accumulated photon travel distance is greater than the total distance? Is a photon touching a sample boundary or sample box boundary? Is a photon spill out of the sample cell? And whether the photon was accepted by the detector;

the fourth step: calculating an optical signal; and judging whether the accumulated photon number N is larger than the total photon number N₀ ；

The fifth step: and outputting a calculation optical signal and returning to the main program.

The sample system parameters include: incident light parameters, sample and sample box shape parameters, and orientation parameters of the photoelectric detector relative to the sample box.

The spectrometer system and the method for measuring all optical parameters including the turbid medium material have the advantages of simple measuring system and convenient use, and can accurately measure optical signals and all optical parameters including the turbid material. The capability of the spectrometer for analyzing and researching materials including turbid media can be greatly improved.

Drawings

FIG. 1 is a schematic diagram of the spectrometer system of the present invention;

FIG. 2 is a schematic view of a sample device in an embodiment of the present invention;

FIG. 3 is a flow chart of the assay method of the present invention;

FIG. 4 is a flowchart of a refractive index calculation subroutine in the measuring method of the present invention;

FIG. 5 is a flowchart of a calculation subroutine of the optical transmission theory in the measuring method of the present invention.

Wherein:

1: light source 2: monochromator section

3: first curved mirror 4: optical modulator

5: a light splitting sheet 6: photoelectric detector

7: the photodetector 8: sample (I)

9: the sample turntable 10: photoelectric detector

11: the mirror 12: second curved reflector

13: slit or aperture 14: photoelectric detector

15: the signal processing circuit 16: computer part

17: output beam 18: output beam splitting

19: incident light beam 20: mirror-like reflected light beam

21: diffusely-reflected light beam 22: collimating the transmitted beam

23: diffuse light beam 24-32: signal and control cable

33: sample box

Detailed Description

The spectrometer system and the method for determining all optical parameters including the material of a turbid medium according to the invention will be described in detail with reference to the accompanying drawings and examples.

Accurate determination of all optical parameters of materials, including turbid media, requires measurement of reflected and transmitted light signals in different directions from the exit of the white sample. Specular reflected light is defined as reflected light propagating in a direction that satisfies the law of light reflection, while collimated transmitted light is light in the transmission direction unaffected by scattering. The diffuse reflection light and the diffuse transmission light are respectively defined as light with the propagation direction deviating from the reflection direction of the mirror and the collimation transmission direction under the condition that the light wavelength is unchanged, namely diffuse reflection light emitted from the sample incidence surface and diffuse transmission light emitted from the sample transmission surface.

As shown in fig. 1, the spectrometer system of the invention for determining all optical parameters of a material comprising a turbid medium comprises: a light source section, a monochromator section 2, a light path section, a sample device section, a signal measuring section, and a computer section 16; wherein, the computer part 16 for controlling, processing data and calculating is respectively connected with the light source part, the monochromator part 2, the sample device part and the signal measuring part; the light emitted by the light source part is emitted into the sample device part through the monochromator part 2 and the light path part; the optical signal emitted from the sample device section passes through the optical path section to the signal measuring section connected to the computer section 16.

The sample apparatus portion comprises a sample turntable 9 for adjusting the incident angle of incident light 19 into the sample 8 and the sample 8 disposed thereon. As shown in fig. 2, the control program in the computer 16 controls the sample stage 9 via the cable 27 to adjust the incident angle of the incident light 19 entering the sample 8, which is in the range of 0 to 80 degrees.

The light source part comprises alight source 1 and an external light modulator 4, thelight source 1 comprises a required power supply, a cooling device and an electric light source device, and the modulator 4 can modulate the intensity of light beams output by the light source in a mechanical, electrooptical or acousto-optic mode. Wherein, the control end of thelight source 1 is connected with the computer part 16 through the cable 25, and the output light beam 17 of thelight source 1 passes through the monochromator part 2, the light modulator 4 and the light splitting sheet 5and then enters the sample 8 in the sample device part as a monochromatic incident light beam 19.

Thelight source 1 is obtained by an incoherent broad-spectrum light source with a continuous spectrum, the irradiation light wavelength of the incoherent broad-spectrum light source is continuously distributed in a set spectral domain, and the output light of the broad-spectrum light source 1 can obtain a monochromatic output light beam through a monochromator 2.

The output beam 17 can be modulated in intensity by the modulator 4 in a frequency range from 0.1 Hz to 100 MHz for SNR purposes. The intensity of the output light from thelight source 1 and the modulation frequency of the modulator 4 can be controlled and selected by the control program in the computer 16 through the cables 25and 26. Another way of achieving an intensity modulation of the output light of thelight source 1 is by modulating the input current of the electric light source.

The light source part can also be composed of a plurality of semiconductor lasers as coherent light sources, the wavelength of the light irradiated by the light source part is a separation spectrum in a set spectral domain, and monochromatic output light 17 can be directly obtained to the first curved reflector 3 of the light path part without a monochromator 2.

The monochromator part 2 consists of an internal light beam focusing collimation light path and a spectrum light splitting device. The spectrum light-splitting device can be realized by a grating or a prism or a light filter plate.

In optical path order, the monochromator 2, as shown in fig. 1, is positioned between thelight source 1 and the sample 8, forming a monochromatic incident light beam 19, the wavelength of which is selectable by the monochromator 2 via cable 24 by a control program in computer 16. Another optical path of the present invention is realized by placing a monochromator 2 between a sample 8 and photodetectors 7, 22, 23, spectrally dispersing the signal light, and detecting the light signal by wavelength. In the case of multiple photodetectors, the latter approach requires multiple monochromators or mechanical rotation devices to switch different optical signals, and the spectrometer system may become more complex.

The light path part consists of a group of reflectors and a light splitting piece and comprises: a first curved mirror 3 for collimating the light beam at the output end of the monochromator section 2, a beam splitter 5 on the light-reflecting side of the first curved mirror 3, and a mirror 11 for receiving the collimated transmitted light beam 22 of the sample 8 in the sample device section; a second curved mirror 12 for focusing on the reflected light side of the mirror 11, and a slit 13 for receiving the reflected light of the second curved mirror 12.

The optical path section couples the light source output beam into the sample 8 and couples the collimated transmission signal light into the photodetector 14 through the spatial filter arrangement formed by the second curved mirror 12 and the slit 13. In addition, the light splitter 5and the photodetector 6 are used to monitor the intensity change of the light beam 17 outputted from the light source, and the incident light intensity can be indirectly measured by the fixed light intensity relationship between the light beam 18 and the incident light beam 19 of the sample 8. The incident beam 19 may have a diameter of between 1 mm and 100 mm.

The signal measuring part comprises: a linear array photodetector 7 that receives a diffusely-reflected light beam 21 of the sample 8; a separate photodetector 6 located at one side of the spectroscope 5 for receiving the specularly reflected light beam 20 for indirectly measuring the incident light intensity signal; a discrete photodetector 10 for receiving a diffuse transmitted light beam 23 from the sample 8 for measuring a diffuse transmitted light intensity signal; a discrete photodetector 14 located on the light emitting side of the slit 13 for measuring a collimated transmitted light intensity signal; the optical signals of the photodetectors 6, 7, 10, 14 are received, processed and sent to a signal processing circuit 15 of a computer portion 16. Wherein the linear array photodetector 7 is used to measure the intensity signals of the specularly reflected and diffusely scattered light as a function of the angle of incidence of the incident light 19 when the sample 8 is in different orientation positions as shown in fig. 1 and 2; discrete photodetector 6 is used to indirectly measure the incident light intensity signal, discrete photodetector 10 is used to measure the diffuse transmitted light intensity signal, and discrete photodetector 14 is used to measure the collimated transmitted light intensity signal. The optical signal is converted into an electric signal by each photodetector, amplified, sent to an amplifier and an analog-digital converter constituting the signal processing circuit 15 through signal cables 29, 30, 31, and 32, converted into a real-time optical signal, and sent to a computer program in the computer 16 for control and data processing and calculation through the signal cable 28.

The amplifier in the signal processing circuit 15 is usually a current-voltage conversion amplifying circuit composed of a low-noise high-precision instrument operational amplifier (such as AD8663 available from Analog Devices); the Analog-to-digital converter is an Analog-to-digital conversion integrated circuit composed of 16-bit or higher Analog-to-digital conversion integrated blocks (such as AD7693 manufactured by Analog Devices, inc.); the linear photodetector 7 is typically implemented with an array of 2 to 4096 (or more) photodetector pixels (e.g., S8865-128 from Hamamatsu corporation), and the spatial distribution of light intensity can be measured.

The functions of the control and data processing and calculation section of the present invention are implemented by the control program and calculation program in the computer 16.

The computer 16 stores a control program for the spectrometer. The control program controls the intensity of the output beam 17 of thelight source 1 via cable 25, the monochromator 2 via cable 24 and the wavelength of the output beam 17 and the incident beam 19, the modulation frequency of the light modulator 4 via cable 26 and the output beam 17 and the incident beam 19, and the orientation of the turntable 9 and the sample cell 33, i.e. the angle of incidence of the incident beam 19 in relation to the plane of incidence of the sample 8, via cable 27.

The computer program in computer 16 first stores the real-time optical signal as a function of time in the computer's memory system and then demodulates it by the signal processing program to improve the signal-to-noise ratio. The demodulation process of the signal processing program can be accomplished by fourier transform over time. The ratio of the intensity of the demodulated specular reflection light or diffuse reflection light to the intensity of the incident light is a specular reflectivity or a diffuse reflectivity, and the ratio of the intensity of the collimated transmission light or diffuse transmission light to the intensity of the incident light is a collimated transmittance or a diffuse transmittance. The functional relation between the specular reflectivity, the diffuse reflectivity, the collimation transmissivity and the diffuse transmissivity output by the signal processing program and the wavelength of incident light is used as an actually measured optical signal spectrum, namely an actually measured optical signal and stored in a computer storage system. The computer program within the computer 16 then determines the full optical parameter spectrum of the sample 8 from the stored measured optical signals and the input sample system parameters and other parameters.

As shown in fig. 3, the method of the invention for a spectrometer system for determining all optical parameters including the material of a turbid medium comprises the following stages:

the first stage is as follows: acquiring and inputting actual measurement optical signals and measurement error values on all wavelengths in the set waveband, and acquiring and inputting sample system parameters; the measured optical signal at the set wavelength is: the ratio of the reflected light to the incident light intensity is specular reflectance, or the ratio of the diffuse reflected light intensity to the incident light intensity is diffuse reflectance, the ratio of the collimated transmitted light to the incident light intensity is collimated transmittance, and the ratio of the diffuse transmitted light intensity to the incident light intensity is diffuse transmittance.

And a second stage: entering a refractive index calculation subprogram in the calculation program, and calculating and determining the refractive index of the sample on all wavelengths in a set wave band according to the functional relation between the specular reflectivity and the incident angle measured by the linear array photoelectric detector and the refractive index of the material of the sample box, namely obtaining a sample refractive index spectrum;

and a third stage: inputting an initial value of an optical parameter of a sample and adjusting the optical parameter value of the sample in a set waveband to enter a light transmission theory calculation subprogram in a calculation program to obtain a calculation optical signal; and obtaining a calculated optical signal at the set incident light wavelength according to the input sample system parameters and the initial values or set values of the absorption coefficient, the scattering coefficient and the anisotropy parameter in the sample optical parameters.

A fourth stage: comparing the difference between the actually measured optical signal and the calculated optical signal at the set wavelength;

the fifth stage: in the comparison of the fourth stage, when the difference is smaller than the measurement error value, the entire optical parameter spectrum of the sample is output, otherwise, the third stage is returned. The optical parameters of the sample are adjusted repeatedly and the third stage is repeated until the difference between the calculated optical signal and the measured optical signal is smaller than the measurement error value, and the optical parameter value of the sample at the set incident light wavelength is output.

The sample system parameters described above include: incident light parameters, sample and cartridge shape parameters, and orientation parameters of the photodetector relative to the cartridge.

As shown in fig. 1 and 2, the control software in computer 16 controls turret 9 via cable 27 to adjust the angle of incidence of incident light 19 into sample cell 8, which ranges from 0 degrees to 80 degrees. At two or more angles of incidence within the incident range, the intensity of the specularly reflected light is measured by the linear array photodetector 7 and the specularly reflected reflectance is obtained. According to the actually measured functional relation between the specular reflectivity and the incident angle, the refractive index of the sample and the corresponding refractive index spectrum can be determined by adjusting the refractive index value of the sample and fitting the calculated functional relation between the specular reflectivity and the incident angle obtained based on the Fresnel equation.

In the method of the present invention, the refractive index calculation subroutine in the calculation procedure includes the steps of:

the first step is as follows: setting an initial value for the sample refractive index at the incident light wavelength based on sample system parameters, the sample cell material (typically optical glass) refractive index at the set incident light wavelength, and the measured specular reflectance as a function of incident angle;

the second step is that: obtaining a function curve of the calculated specular reflectivity and the incidence angle according to a Fresnel equation;

the third step: comparing the difference between the calculated specular reflectivity and the actually measured incident angle curve, and repeatedly adjusting the refractive index of the sample to return to the second step until the difference is smaller than the measurement error value; namely, the difference between the calculated and actually measured specular reflectivity and the incidence angle curve is smaller than the preset value.

The fourth step: and judging whether the refractive index spectrum is calculated on all wavelengths in the set wave band, returning to the first step if the refractive index spectrum is not calculated, outputting the sample refractive index spectrum if the refractive index spectrum is calculated, and returning to the main procedure.

As shown in fig. 4, the refractive index calculation subroutine described above is specifically as follows:

s1: inputting sample system parameters and sample box material refractive index;

s2: inputting a function curve of actually measured specular reflectivity and an incident angle;

s3: selecting the wavelength of incident light;

s4: setting an initial value of the refractive index of the sample at the selected wavelength of the incident light;

s5: calculating a function curve of the specular reflectivity and the incidence angle according to a Fresnel equation;

s7: comparing and calculating the difference between the actually measured reflectivity and the function curve of the incidence angle, if the difference is larger than a set value, entering S6, and otherwise, entering S8;

s6: adjusting the refractive index of the sample, and entering S5;

s8: storing the selected wavelength and the last determined refractive index of the sample;

s9: judging whether the stored wavelength number is equal to the wavelength number in the wavelength range needing to be measured, if so, entering S10, otherwise, entering S3;

s10: the subroutine is finished and a sample refractive index spectrum is output;

the sample system parameters described in the above-described refractive index calculation subroutine include: the area, direction and power distribution of the incident beam cross section, the shape parameters of the sample and the sample box, the orientation parameters of the photoelectric detector relative to the sample box and the like.

In the method of the present invention, the optical transmission theory calculation subroutine in the calculation program includes the following steps:

the first step is as follows: inputting system parameters of a sample, and actually measuring absorption coefficients, scattering coefficients and initial set values of various anisotropic parameters in optical signals and optical parameters of the sample; total number of photons N of incident beam to be traced₀ (ii) a Randomly determining the total photon traveling distance according to the set sample absorption coefficient;

the second step is that: determine if the number of tracked photons N is greater than 1? Determining the photon scattering angle, namely the travelling direction, and randomly determining the travelling free path of the photons; tracking the photons to a next scattering point;

the third step: is it determined whether the accumulated photon travel distance is greater than the total distance? Is a photon touching a sample boundary or sample box boundary? Is a photon spill out of the sample box? And whether the photon was accepted by the detector;

the fourth step: calculating an optical signal; and judging whether the accumulated photon number N is greater than the total photon number N₀ ；

The fifth step: and outputting a calculation optical signal and returning to the main program.

As shown in fig. 5, the optical transmission theory calculation subroutine is specifically as follows:

s1: inputting a total number of photons N representing the intensity of the incident beam₀

S2: inputting sample system parameters;

s3: the initial direction of travel of the photons is determined by their direction of incidence;

s4: setting the initial value of the number N of the tracked photons: n =1;

s5: randomly determining the total photon path according to the absorption coefficient;

s7: determine if the number of photons being tracked N is greater than 1? N is greater than 1, S8, otherwise S9

S8: after randomly determining a photon scattering angle, namely a traveling direction according to the scattering phase function, entering S9;

s9: randomly determining the free travel distance of photons according to the scattering coefficient;

s10: tracking the photons to a next scattering point;

s11: is it determined whether the accumulated photon travel distance is greater than the total distance? If yes, entering S12, otherwise, entering S13;

s12: judging that the photons are absorbed and entering S6;

s6: increasing the number N of the tracked photons by 1 and then entering S5;

s13: is it determined whether photons touch the sample boundary? If yes, entering S14, otherwise, entering S8;

s14: is the photon randomly determined to overflow the sample based on the boundary reflection coefficient calculated based on the fresnel equation? If so, entering S15, otherwise, returning to the sample medium according to the reflection direction and continuing to track, and then entering S8;

s15: is it judged whether it is accepted by the photodetector? If yes, entering S17, otherwise, entering S16;

s16: entering S6 after the escape of photons is judged;

s17: increasing the number of photons received by the photodetector by 1 and calculating and storing the corresponding optical signal (i.e. the number of photons received by the photodetector and N)₀ Ratio of (d);

s18: judging whether the number N of the tracked photons is larger than the total number N of the photons representing the incident beam₀ (ii) a If yes, entering S19, otherwise, entering S6;

s19: the subprogram is ended and a calculation optical signal is output;

the sample system parameters described in the above optical transmission theory calculation subroutine include: incident light parameters, sample and sample box shape parameters, and orientation parameters of the photodetector relative to the sample box.

The method of the invention for determining all optical parameters of a spectrometer system comprising a turbid medium material is further explained below

The core of the calculation program part of the determination method of the spectrometer system is an optical signal calculation method based on the radiation transmission theory in the turbid medium. The radiation transmission theory can be expressed as a calculus equation of a radiation transmission equation, and the boundary condition is based on a fresnel equation of a boundary condition of electromagnetic wave propagation. The time-independent form of the radiation transport equation can be expressed as follows

s·▽L(r，s)＝-(μ_a +μ_s )L(r，s)+μ_s ∫_4π p(s，s′)L(r，s′)dΩ′。

Where s is the unit vector in the direction of light propagation,. Represents the vector dot product operator,. Represents the vector gradient operator, r is the coordinate vector in three-dimensional space, L (r, s) is the luminous flux (optical power in a unit solid angle per unit area),_a as a function of the absorption coefficient,_s for the scattering coefficient, p (s, s ') is the scattering phase function (proportional to the probability of light scattering from the s' direction to the s direction),

representing the stereo angle integral for the s' direction for a total solid angle of 4 in three dimensions. Boundary value problems based on radiative transfer equations generally have two solutions: a numerical solution method and a statistical method represented by a monte carlo method. The numerical solution method is to convert the radiation transmission equation into a difference equation set and solve the difference equation set according to boundary conditions based on the Fresnel equation. The monte carlo method is an optical transmission process described by the radiation transmission equation, and uses a plurality of photons to represent an incident light beam, and calculates the travel orbit of each photon in the three-dimensional space. The travel trajectory of the photons is determined by a plurality of random variables which are randomly variedThe distribution function of the quantity is determined by the absorption coefficient, the scattering coefficient and the scattering phase function, respectively. The trajectory of the photons traveling near the boundary of the area under consideration is generally processed according to a boundary reflection coefficient formula calculated based on fresnel equations. After the calculation of the travel trajectory of all photons (hundreds of thousands or more) is completed, the statistical analysis is performed, and the ratio of the photons collected by the detection fiber to the total number of incident photons represents the calculated optical signal.

When electromagnetic waves representing light are incident on an interface between two different media, reflected light and transmitted light occur, and a fresnel equation is an equation obtained based on the boundary condition of the electromagnetic waves and can be used for calculating the mirror reflectivity of the light at the boundary according to the incident angle and the refractive indexes of the two media. For unpolarized incident light, it is used to calculate the specular reflectance R at the interface between an optically transparent medium (e.g. air, glass, etc.) and a turbid medium_cal () The Fresnel equation of

In the above formula, the incident angle, n₀ Is the refractive index of the optically transparent medium, n_r Is the real part of the refractive index of the turbid medium, n_i Is the imaginary part of the refractive index of the turbid medium,

FIG. 5 is a logic flow implementing the Monte Carlo method. The method is characterized in that the turbid medium is equivalent to a medium containing randomly distributed light absorption centers and light scattering centers, the concentrations of the light absorption centers and the light scattering centers are respectively related to the absorption coefficient and the scattering coefficient of the turbid medium, and the random distribution of the light absorption centers and the light scattering centers is reflected by the random distribution of the total path and the free path of photons. Before the Monte Carlo method calculation starts, the input of incident light parameter is neededSuch as the beam energy distribution and the incident direction and the number of photons N representing the incident beam₀ And optical parameters and boundary geometry parameters representing the sample. Because of Monte CarloThe method is a statistical method, the result of which contains statistical errors, so the number of photons N required to be tracked and calculated₀ Must be large enough to reduce the statistical error in the calculation to a sufficiently small value. But N is₀ Too much results in too long a calculation time. In general case of N₀ Between the power of 10 to the power of 4 and the power of 10 to the power of 9.

As shown in FIG. 5, the Monte Carlo calculation method requires the calculation of N₀ The incident photons are subjected to the tracking calculation of the traveling path of the incident photons in the sample one by one until the traveling of the photons is finished, namely the photons are either absorbed by the sample or overflow the sample (namely the photons escape). Before the start of the travel path tracking calculation for each photon, the monte carlo calculation procedure will determine the total path of the photons from the random distribution determined by the absorption coefficient of the sample and the free travel path length of the photons from the random distribution determined by the scattering coefficient of the sample. The first step in the photon tracking calculation is to track the photon along the initial travel direction to a location determined by its free travel path, assuming the photon is scattered at this location. A test will be made as to whether a photon is absorbed or spilled before it starts the next free path travel. If one of the above conditions is met, the travel path tracking calculation for the next photon is started. If none of the above conditions is met, the monte carlo calculation procedure determines the scattering angle, i.e. the direction of the next free path to be traveled, according to the scattering phase function of the sample (or according to the anisotropy parameter of the sample under the condition of determining the phase function form such as the hanny-grinstein scattering phase function), and then determines the free path length of the photon according to the random distribution determined by the scattering coefficient of the sample, so as to start the repeated calculation of the tracking of the traveling path of the photon until the traveling of the photon is finished. If a tracked photon is received by a photodetector (photodetectors 7, 10, 14 in fig. 1), the number of photons received by that photodetector is incremented by 1 as a calculation data record associated with calculating the optical signal. When the tracking calculation of a certain photon traveling path is finished, the Monte Carlo calculation program compares the accumulated number N of the tracked and calculated photons, if N is larger than N₀ If the Monte Carlo calculation is finished, otherwise, adding 1 to N and then carrying out calculation on the next oneThe incident photons begin the tracking calculation. When to N₀ After the tracking calculation of all the incident photons is completed, the accumulated photon number and N received by each photoelectric detector₀ The ratio is output from the Monte Carlo calculation procedure as a calculated optical signal corresponding to the measured optical signal.

The calculation determination routine described in fig. 3 is implemented by the refractive index calculation subroutine shown in fig. 4, the optical transmission theory calculation subroutine shown in fig. 5, and an iterative loop process. The input data required for the refractive index calculation subroutine are: sample system parameters, refractive index of the sample box material and a function relation between actually measured specular reflectivity and an incident angle; the sample system parameters comprise the area, direction and power distribution of the incident beam cross section, the shape parameters of the sample and the sample box, the orientation parameters of the photoelectric detector relative to the sample box, and the like. The input data required by the optical transmission theory calculation subroutine are as follows: sample system parameters, actually measured optical signals, sample refractive index spectrum and initial values of sample optical parameters; the measured optical signal includes diffuse reflectance, collimated transmittance, and diffuse transmittance at all wavelengths. The initial values of the sample system parameters and the sample optical parameters in the input data are input by a user through a user interface, and the actually measured optical signals and the sample refractive index spectrum are provided by the data processing and calculating program of the control and data processing and calculating part.

According to these input data, the light transport theory calculation subroutine of the calculation program uses the Monte Carlo method to calculate the number of photons which represent the incident light energy and are collected by the photodetector after the photons are emitted from the sample in the computer model, and the ratio of the number of incident photons to the number of incident photons is defined as the calculated light signal output equivalent to the corresponding measured light signal. And the difference between the calculated and measured optical signals determines whether the optical transport theory calculation subroutine is finished or the calculation is reiterated. If the difference between the calculated and actually measured optical signals is smaller than a set value determined according to the experimental error of the actually measured optical signals, the initial value of the optical parameter of the sample is the correct optical parameter of the sample, and the optical transmission theory calculation subroutine is finished and is combined with the refractive index for storage, so that the optical parameters are all the optical parameters of the sample. If the difference between the calculated optical signal and the actually measured optical signal is larger than the set value, the optical transmission theory calculation subprogram enters an iterative loop process, namely the optical parameters of the measured sample are repeatedly adjusted and the optical signal is calculated by entering the optical transmission theory calculation subprogram part again until the difference between the calculated optical signal and the actually measured optical signal is smaller than the set value. The optical transport theory calculation subroutine described above will run at all wavelengths within the set wavelength band until a spectrum is obtained for all optical parameters of the sample within the set wavelength band.

The sample optical parameter adjustment process in the iterative loop process described above can be designed based on the following principle. Firstly, the modulation direction of an attenuation coefficient (which is the sum of an absorption coefficient and a scattering coefficient) is determined according to the difference of the measured and calculated collimation transmissivity in an optical signal: if the measured collimated transmission is greater than the calculated collimated transmission, the attenuation factor is decreased, otherwise the attenuation factor is increased. And then determining the modulation direction of the absorption coefficient according to the difference of the sum of the diffuse transmittance and the diffuse reflectance in the actually measured and calculated optical signal: if the sum of the actually measured diffuse transmittance and the diffuse reflectance is larger than the sum of the calculated diffuse transmittance and the calculated diffuse reflectance, the absorption coefficient is decreased, otherwise, the absorption coefficient is increased. Then, the modulation direction of the anisotropic coefficient is determined according to the difference between the ratios of the diffuse transmittance and the diffuse reflectance in the measured and calculated optical signals: if the ratio of the measured diffuse transmittance to the diffuse reflectance is larger than the ratio of the calculated diffuse transmittance to the diffuse reflectance, the anisotropy coefficient is increased, otherwise, the anisotropy coefficient is decreased.

Claims (16)

1. A spectrometer system for determining all optical parameters of a material comprising a turbid medium, comprising: a light source section, a monochromator section (2), a light path section, a sample device section, a signal measuring section, and a computer section (16); wherein, a computer part (16) for controlling, processing data and calculating is respectively connected with the light source part, the monochromator part (2), the sample device part and the signal measuring part; the light emitted by the light source part is emitted into the sample device part through the monochromator part (2) and the light path part; the optical signal emitted from the sample device section passes through the optical path section to the signal measuring section connected to the computer section (16).

2. A spectrometer system for determining all optical parameters including turbid medium materials according to claim 1, characterized in that the sample assembly part comprises a sample turntable (9) for adjusting the angle of incidence of the incident light into the sample and a sample box (33) arranged thereon, inside which the sample (8) is arranged.

3. A spectrometer system for determining all optical parameters including the material of a turbid medium according to claim 1, characterized in that the light source part comprises a light source (1) and a light modulator (4), wherein the control end of the light source (1) is connected to the computer part (16) via a cable (25), and the output light beam (17) of the light source (1) is passed through the monochromator part (2), the light modulator (4) and the beamsplitter (5) and is directed into the sample arrangement part as a monochromatic incident light beam (19).

4. A spectrometer system for determining all optical parameters including turbid medium materials according to claim 3, characterized in that the light source (1) is obtained from a continuous spectrum incoherent broad spectrum light source with a continuous distribution of the illuminating light wavelengths in a set spectral domain.

5. A spectrometer system for determining all optical parameters including the material of a turbid medium according to claim 3 characterized in that the light source (1) in the light source section may also be comprised of a plurality of lasers as coherent light sources with output beam wavelengths in discrete form for obtaining monochromatic output light (17) directly into the light path section.

6. A spectrometer system for determining all optical parameters of a material comprising a turbid medium according to claim 3, characterized in that the incident light beam (19) has a diameter of between 1 mm and 100 mm.

7. A spectrometer system for determining all optical parameters of a material comprising a turbid medium according to claim 1, characterized in that the monochromator part (2) is formed by a beam focusing collimating light path and a spectral splitting device.

8. A spectrometer system for determining all optical parameters of a material comprising a turbid medium according to claim 1, characterized in that the optical path section comprises: a first curved mirror (3) for collimating the light beam at the output of the monochromator section (2), a beam splitter (5) on the light-reflecting side of the first curved mirror (3), and a mirror (11) for receiving the collimated transmitted light beam (22) of the sample (8) in the sample arrangement section; a second curved mirror (12) for focusing on the light-reflecting side of the mirror (11), and a slit or aperture (13) for receiving the light reflected by the second curved mirror (12).

9. A spectrometer system for determining all optical parameters of a material comprising a turbid medium according to claim 1, characterized in that the signal measuring part comprises: a linear array photodetector (7) that receives a diffusely reflected light beam (21) of a sample (8); a separate photodetector (6) located on one side of the beam splitter (5) for receiving the specularly reflected light beam (20) for indirectly measuring the incident light intensity signal; a discrete photodetector (10) for receiving a diffusely transmitted light beam (23) from the sample (8) for measuring a diffuse transmitted light intensity signal; a discrete photodetector (14) positioned on the exit side of the slit (13) for measuring a signal of collimated transmitted light intensity; and a signal processing circuit (15) for receiving the optical signals of the photodetectors (6, 7, 10, 14), processing the optical signals and sending the processed optical signals to a computer part (16).

10. A method for a spectrometer system for determining all optical parameters of a material comprising a turbid medium, characterized in that it comprises the following stages:

the first stage is as follows: acquiring input and calculating actual measurement optical signals and measurement error values on all wavelengths in a set waveband, and acquiring and inputting sample system parameters;

and a second stage: entering a refractive index calculation subprogram in the calculation program, and calculating and determining the refractive indexes of the sample on all wavelengths in the set waveband to obtain a refractive index spectrum of the sample;

and a third stage: inputting an initial value of an optical parameter of a sample and adjusting the optical parameter value of the sample in a set waveband to enter a light transmission theory calculation subprogram in a calculation program to obtain a calculation optical signal;

a fourth stage: comparing the difference between the actually measured optical signal and the calculated optical signal at the set wavelength;

the fifth stage: in the comparison of the fourth stage, when the difference is smaller than the measurement error value, the entire optical parameter spectrum of the sample is output, otherwise, the third stage is returned.

11. A method according to claim 10 for a spectrometer system for determining all optical parameters including turbid medium materials, characterized in that said taking input and calculating the measured optical signals at all wavelengths within a set wavelength band is: the ratio of the reflected light to the incident light intensity is the specular reflectance, the ratio of the diffuse reflected light intensity to the incident light intensity is the diffuse reflectance, the ratio of the collimated transmitted light to the incident light intensity is the collimated transmittance, and the ratio of the diffuse transmitted light intensity to the incident light intensity is the diffuse transmittance.

12. A method according to claim 10 for a spectrometer system for determining all optical parameters of a material comprising a turbid medium, characterized in that the sample system parameters comprise: incident light parameters, sample and sample box shape parameters, and orientation parameters of the photodetector relative to the sample box.

13. A method according to claim 10 for a spectrometer system for determining all optical parameters including the material of a turbid medium, characterized in that the refractive index calculation sub-routine in the calculation routine comprises the following steps:

the first step is as follows: setting the initial value of the sample refractive index on the incident light wavelength according to the sample system parameters, the sample box material refractive index on the set incident light wavelength and the actually measured function curve of the specular reflectivity and the incident angle;

the second step is that: obtaining a function curve of the calculated specular reflectivity and the incident angle according to a Fresnel equation;

the third step: comparing the calculated difference between the measured specular reflectivity and the incident angle curve, and repeating the second step by repeatedly adjusting the refractive index of the sample until the difference is smaller than the measurement error value;

the fourth step: and judging whether the refractive index spectrum is calculated on all wavelengths in the set wave band, returning to the first step if the refractive index spectrum is not calculated, outputting the sample refractive index spectrum if the refractive index spectrum is calculated, and returning to the main procedure.

14. A method as claimed in claim 13 for a spectrometer system for determining all optical parameters including the material of the turbid medium, characterized in that the sample system parameters comprise: the area, direction and power distribution of the incident beam cross section, the shape parameters of the sample and sample box, and the orientation parameters of the photodetector relative to the sample box.

15. A method of a spectrometer system for determining all optical parameters including turbid medium materials according to claim 10, characterized in that the optical transmission theory calculation subroutine in the calculation procedure comprises the following steps:

the first step is as follows: inputting system parameters of a sample, actually measuring absorption coefficients, scattering coefficients and initial set values of various anisotropic parameters in optical signals and optical parameters of the sample; inputting the total number N0 of the tracked incident beam photons; randomly determining the total path of the photons according to the set absorption coefficient of the sample;

the second step is that: determine if the number of accumulated photons N tracked is greater than 1? Determining the photon scattering angle, namely the traveling direction, and randomly determining the traveling free path of the photons; tracking the photons to a next scattering point;

the third step: is it determined whether the photon cumulative travel distance is greater than the total distance? Is a photon touching a sample boundary or sample box boundary? Is a photon spill out of the sample box? And whether the photon was accepted by the detector;

the fourth step: calculating an optical signal; and judging whether the accumulated photon number N is greater than the total photon number N₀ ；

The fifth step: and outputting a calculation optical signal and returning to the main program.

16. A method according to claim 15 for a spectrometer system for determining all optical parameters including turbid medium materials, characterized in that the sample system parameters comprise: incident light parameters, sample and sample box shape parameters, and orientation parameters of the photodetector relative to the sample box.

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