A high-sensitivity circular dichroism precision measurement device and method

Abstract

The invention discloses a high-sensitivity circular dichroism precision measurement device and method, a light source module; a double-arm balanced optical path module, a polarization modulation module, a micro-area positioning module, a balanced detection module and a control processing module. The double-arm balanced optical path module is adopted so that a measuring light arm and a reference light arm have light source fluctuation noises that are simultaneous and have the same intensity, and the real-time difference of the left-right circular polarization state time-varying noise of the measuring light arm at different times relative to the reference light time-varying noise is achieved, which greatly suppresses the system noise and exceeds the sensitivity of the prior art in the current measurement band; in the set micro-area positioning module, the lens group can freely adjust the size of the measuring light spot, which solves the problem of insufficient flexibility in positioning the measuring area in the prior art.

Description

Technical Field

[0001] The invention relates to the technical field of optical and spectroscopy precision measurement, and in particular to a high-sensitivity circular dichroism precision measurement device and method. Background Art

[0002] Precise measurement of circular dichroism is a key technology for quantitatively determining the chiral characteristics of substances. Chirality is ubiquitous in common molecules in nature and often determines their physical and chemical properties. The effective distinction of chiral enantiomers, especially chiral molecules, is crucial to the development of biology, chemistry, and pharmaceuticals. Since chiral substances have different absorbances for left-handed and right-handed circularly polarized light, i.e., A L ≠A R , Circular dichroism is defined as the difference in absorption of left-handed and right-handed circularly polarized light of the same intensity by a chiral substance. The wavelength in the measured spectral region is taken as the horizontal axis, and the absorbance difference of the measured chiral substance (ΔA=A L -A R ) is the ordinate, which can represent the circular dichroism spectrum of a chiral substance. The actual measurement of circular dichroism is to obtain the transmitted light intensity I after the left-right circularly polarized light passes through the measured object. L and I R The difference in transmitted light intensity and the average value of transmitted light intensity are mathematically calculated and converted into the absorbance difference expressed in the form of the ellipticity of the synthetic ellipse. Therefore, the key to the circular dichroism measurement device and method is how to accurately measure the transmitted light intensity of left-right circularly polarized light after passing through a chiral substance.

[0003] In most circular dichroism measurements, since the difference in absorbance of left-handed and right-handed circularly polarized light by chiral substances is extremely small, simple gain amplification of the light intensity difference is often accompanied by a simultaneous amplification of noise, making it difficult to extract the left-handed and right-handed circularly polarized transmission light intensity difference from the system noise; in existing publicly reported results, high-frequency modulation methods are often used to periodically modulate single-arm measurement light into left-handed and right-handed circularly polarized light. The light passing through the sample is collected by a photodetector and enters an A / D converter via an amplifier, and then the circular dichroism value is obtained by a digital processing device, such as the circular dichroism measurement device and circular dichroism measurement method (CN 113574362 A) of JASCO Corporation; this type of method uses a polarization modulation unit such as a photoelastic modulator (PEM) to modulate a single beam of measurement light into a left-handed and right-handed circular polarization state at a high frequency (typically 50kHz), and then the required signal is demodulated from the amplified detection signal by a digital processing unit.

[0004] Although this type of method suppresses the noise fluctuations before and after polarization modulation to a certain extent, the modulation process has high requirements on the time synchronization of the instrument and the stability of the light source. The time-varying noise of the left-handed circular polarization state cannot be completely eliminated, which limits the improvement of the sensitivity of circular dichroism value measurement. In addition, the measurement device based on this method often measures the sample with a high light flux and a large spot. For micro-area chiral samples such as artificial metasurface structures, additional light-clearance aperture devices are required to limit the measurement area, and the positioning flexibility of the measurement area is insufficient. Only by improving the above two defects in a targeted manner can the sensitivity of circular dichroism measurement be further improved and flexibly applied to a variety of measurement scenarios. Summary of the invention

[0005] The purpose of the present invention is to solve the above-mentioned defects of existing circular dichroism spectroscopy measurement devices and methods, such as limited measurement sensitivity improvement and insufficient flexibility of micro-area measurement. The present invention proposes a high-sensitivity circular dichroism spectroscopy precision measurement device and method.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solution: a high-sensitivity circular dichroism precision measurement device, comprising:

[0007] Light source module;

[0008] A double-arm balanced optical path module is used to divide the light source emitted by the light source module into two parallel optical paths, one of which is a measurement optical path and the other is a reference optical path, and the power of the measurement optical path and the reference optical path is equal;

[0009] A polarization modulation module is used to periodically modulate the light in the measurement optical path to form alternating left-handed and right-handed circularly polarized light;

[0010] The micro-area positioning module is used to adjust the spot size of the circularly polarized light formed by the polarization modulation module, and the adjusted circularly polarized light is projected onto the chiral object to be tested;

[0011] A balanced detection module is used to receive light from the reference light path and light passing through the chiral object to be measured, and convert the received light into a voltage signal for output;

[0012] The control processing module is used to control the wavelength of the light emitted by the light source module, provide the polarization modulation module with a half-wave voltage signal and a circular polarization modulation frequency signal corresponding to the wavelength during the periodic modulation process, and receive the voltage signal output by the balance detection module to obtain the circular dichroism spectrum of the chiral object to be tested.

[0013] Preferably, the double-arm balanced optical path module includes a first polarizer, a first non-polarizing beam splitter prism, a second non-polarizing beam splitter prism and a third non-polarizing beam splitter prism; the detection light emitted by the light source module is polarized by the first polarizer and then split through the first non-polarizing beam splitter prism to form a measurement optical path and a reference optical path, and the light in the measurement optical path after passing through the second non-polarizing beam splitter prism is parallel to the light in the reference optical path after passing through the third non-polarizing beam splitter prism.

[0014] Preferably, the double-arm balanced optical path module further includes a third polarizer and a third lens, and the reference optical path passing through the third non-polarizing beam splitter prism passes through the third polarizer and the third lens in sequence and is received by the balanced detection module.

[0015] Preferably, the polarization modulation module includes a second polarizer, a Pockels cell and a broadband achromatic quarter-wave plate, the Pockels cell is driven by a Pockels cell high-voltage driver, the control processing module is connected to the Pockels cell high-voltage driver, the control processing module sends a half-wave voltage signal and a circular polarization modulation frequency signal corresponding to the wavelength to the Pockels cell high-voltage driver, the Pockels cell high-voltage driver controls the phase of the Pockels cell according to the received circular polarization modulation frequency signal, and the light in the measuring optical path passes through the second polarizer, the Pockels cell and the broadband achromatic quarter-wave plate in sequence to form left-right circularly polarized light.

[0016] Preferably, the micro-area positioning module includes a lens group formed by a first lens and a second lens, and the left-right circularly polarized light after passing through the polarization modulation module is adjusted to a light spot size through the lens group, and the adjusted light is absorbed by the chiral object to be measured.

[0017] Preferably, the balanced detection module includes a balanced detector, a first response collection probe and a second response collection probe arranged on the balanced detector, the first response collection probe is used to collect light passing through the chiral object to be measured, and the second response collection probe is used to collect light in the reference light path, and the balanced detector includes an M1 output terminal and an RF output terminal, and the M1 output terminal and the RF output terminal are respectively connected to the control processing module.

[0018] Preferably, the light source module includes a supercontinuum laser, a monochromator and a long-wave pass filter, the control processing module is connected to the monochromator, and the control processing module is used to control the monochromator to separate monochromatic light; the laser emitted by the supercontinuum laser forms monochromatic light after passing through the monochromator, and the formed monochromatic light is filtered through the long-wave pass filter and then enters the double-arm balanced optical path module for branching.

[0019] Preferably, the control processing module includes a control processor, a phase-locked amplifier, an oscilloscope and an arbitrary waveform generator; the signal output by the RF output terminal of the balanced detector is received by the control processor after being phase-locked by the phase-locked amplifier, and the signal output by the M1 output terminal of the balanced detector is received by the control processor after passing through the oscilloscope, and the control processor processes the signals received from the oscilloscope and the phase-locked amplifier to obtain the circular dichroism spectrum of the chiral object to be tested; the control processor sends a circular polarization modulation frequency signal to the arbitrary waveform generator, and the arbitrary waveform generator uses the received circular polarization modulation frequency signal to control the Pockels cell high-voltage driver.

[0020] A high-sensitivity circular dichroism precision measurement method, which is implemented based on the device, comprises:

[0021] Putting the chiral test object onto the detection table of the micro-area positioning module;

[0022] The control processing module sends instructions to the light source module, and the light source module emits monochromatic light. At the same time, the control processing module sends a half-wave voltage signal and a circular polarization modulation frequency signal corresponding to the wavelength to the polarization modulation module. The polarization modulation module periodically modulates the light passing through the polarization modulation module according to the received signal to form left-right circularly polarized light.

[0023] The monochromatic light emitted by the light source module forms the measuring light and the reference light after passing through the double-arm balanced optical path module. The measuring light forms the left-handed circularly polarized light after passing through the polarization modulation module. The left-handed circularly polarized light adjusts the light spot through the micro-area positioning module and is absorbed by the chiral object to be tested placed on the test table.

[0024] The balance detection module processes the transmitted light and the reference light after passing through the chiral object to be tested to obtain a voltage signal, and sends the obtained voltage signal to the control processing module;

[0025] The control processing module uses the received voltage signal to process and obtain voltage intensity information and phase information, and calculates the circular dichroism value of the chiral object to be tested at the current wavelength; switches the wavelength within the measurement range and performs wavelength-by-wavelength measurement in steps to obtain the circular dichroism spectrum of the chiral object to be tested.

[0026] Preferably, the method for calculating the circular dichroism spectrum of a chiral analyte comprises:

[0027] Where: represents the circular dichroism value of the chiral analyte in millidegrees; Represents the readout value of the differential amplified output voltage of the balanced detection module through the phase-locked amplifier; Represents the average value of the voltage in response to light absorbed by the chiral analyte, read out by an oscilloscope; Represents the phase information value.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] In the present invention, the monochromatic light emitted by the light source module passes through the double-arm balanced optical path module, so that the received monochromatic light is divided into measurement light and reference light through the double-arm balanced optical path module, and a light source with consistent intensity is formed. The real-time difference of the variable noise of the left-right circular polarization state formed by the measurement light through the polarization modulation module relative to the variable noise of the reference light greatly suppresses the system noise and exceeds the sensitivity of the prior art in the current measurement band; the set micro-area positioning module and the lens group can freely adjust the size of the measurement spot, which solves the problem of insufficient flexibility in the positioning of the measurement area in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 It is a structural block diagram of the high-sensitivity circular dichroism precision measurement device in the present invention;

[0032] Figure 2 It is a schematic diagram of the structure of the high-sensitivity circular dichroism precision measurement device in the present invention;

[0033] Figure 3 is a schematic diagram of horizontal polarization through a polarization modulation module in an embodiment of the present invention;

[0034] Figure 4 Schematic diagram of converting horizontal polarization to vertical polarization through a polarization modulation module in an embodiment of the present invention;

[0035] Figure 5 Schematic diagram of left-hand circular polarization through a polarization modulation module in an embodiment of the present invention;

[0036] Figure 6 Schematic diagram of right-hand circular polarization through a polarization modulation module in an embodiment of the present invention;

[0037] Figure 7 A schematic diagram of signal modulation and response in an embodiment of the present invention;

[0038] Figure 8 Schematic diagram of the measurement method in the embodiment of the present invention.

[0039] In the figure: 1. supercontinuum laser; 2. monochromator; 3. long wave pass filter; 4. first polarizer; 5. first non-polarizing beam splitter prism; 6. second non-polarizing beam splitter prism; 7. second polarizer; 8. Pockels cell; 9. broadband achromatic quarter wave plate; 10. first lens; 11. second lens; 12. detection table; 13. balanced detector; 14. third non-polarizing beam splitter prism; 15. third polarizer; 16. third lens; 17. first right angle prism; 18. fourth lens; 19. phase-locked amplifier; 20. oscilloscope; 21. control processor; 22. arbitrary function generator; 23. Pockels cell high voltage driver. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] This embodiment provides Figure 1 and Figure 2 A high-sensitivity circular dichroism precision measurement device is shown, comprising:

[0042] Light source module; the light source can provide a wide-spectrum measurement laser light source for the entire device and be split into monochromatic light by a monochromator; the light source module can provide the required light source according to demand. In this embodiment, the light source module can be a wavelength-adjustable monochromatic laser or the light source module includes a supercontinuum laser 1, a monochromator 2 and a long-wave pass filter 3. The control processing module is connected to the monochromator 2, and the control processing module is used to control the monochromator 2 to separate the monochromatic light; the laser emitted by the supercontinuum laser 1 forms monochromatic light after passing through the monochromator 2, and the formed monochromatic light is filtered by the long-wave pass filter 3 and then enters the double-arm balanced optical path module for branching. When working, the supercontinuum laser 1, the monochromator 2 and the long-wave pass filter 3 are arranged in sequence to form a light source part, the supercontinuum laser 1 outputs a wide-spectrum continuous laser, and the spectral range covers the wavelength range to be measured. The laser is split into monochromatic light by the monochromator 2, and the monochromatic light is filtered by the long-wave pass filter 3 to filter out the target wavelength doubled frequency light generated by the grating diffraction of the monochromator 2.

[0043] A double-arm balanced optical path module is used to divide the light source emitted by the light source module into two parallel optical paths, one of which is a measurement optical path and the other is a reference optical path, and the power of the measurement optical path and the reference optical path is equal;

[0044] In one embodiment, the double-arm balanced optical path module includes a first polarizer 4, a first non-polarizing beam splitter prism 5, a second non-polarizing beam splitter prism 6 and a third non-polarizing beam splitter prism 14; the detection light (monochromatic light) emitted by the light source module is incident on the first polarizer 4 and enters the first non-polarizing beam splitter prism 5 after being polarized, the laser passing through the first non-polarizing beam splitter prism 5 is used as the measurement optical path, and the laser reflected by the first non-polarizing beam splitter prism 5 is used as the reference optical path; the measurement optical path of the laser passing through the first non-polarizing beam splitter prism 5 and reflected by the second non-polarizing beam splitter prism 6 forms a parallel optical path with the reference optical path;

[0045] A third polarizer 15 and a third lens 16 are installed on the reference light path. The laser reflected by the first non-polarizing beam splitter prism 5 passes through the third non-polarizing beam splitter prism 14, and the reference light passing through the third non-polarizing beam splitter prism 14 passes through the third polarizer 15 and the third lens 16 in sequence.

[0046] Specifically, during operation, the monochromatic light emitted by the light source module is set as horizontal linear polarized light through the first polarizer 4, and then is divided into two paths, namely, transmission and reflection, through the first non-polarizing beam splitter prism 5; the transmitted light is reflected by the second non-polarizing beam splitter prism 6 to form measurement light, and the reflected light is transmitted through the third non-polarizing beam splitter prism 14 to form reference light; the measurement light and the reference light are respectively transmitted once (T) and reflected once (R) to form parallel light paths, wherein the first non-polarizing beam splitter prism, the second non-polarizing beam splitter prism, The third non-polarizing beam splitter prism is a product with the same parameters manufactured in the same batch, that is, T1(λ)=T2(λ)=T3(λ), and has the same transmittance-reflection splitting ratio, that is, T1(λ):R1(λ)=T2(λ):R2(λ)=T3(λ):R3(λ). Therefore, the power of the measuring light and the reference light are equal, that is, P0×T1(λ)×R2(λ)=P0×R1(λ)×T3(λ), ensuring that the measuring light and the reference light have simultaneous and consistent light source fluctuation noise.

[0047] A polarization modulation module is used to periodically modulate the light in the measuring optical path to form left-handed circularly polarized light; the polarization modulation module includes a second polarizer 7, a Pockels cell 8 and a broadband achromatic quarter-wave plate 9, the Pockels cell 8 is driven by a Pockels cell high-voltage driver 23, the control processing module is connected to the Pockels cell high-voltage driver 23, the control processing module sends a half-wave voltage signal and a circular polarization modulation frequency signal corresponding to the wavelength to the Pockels cell high-voltage driver 23, the Pockels cell high-voltage driver 23 controls the phase of the Pockels cell 8 according to the received signal, and the light in the measuring optical path passes through the second polarizer 7, the Pockels cell 8 and the broadband achromatic quarter-wave plate 9 in sequence to form left-handed circularly polarized light;

[0048] In this embodiment, the Pockels cell high voltage driver 23 is modulated by the half-wave voltage signal output by the arbitrary function generator and the circular polarization modulation frequency signal to drive the Pockels cell to generate periodic 0 and π phase delays.

[0049] The control processing module sends a signal to the arbitrary waveform generator 22, and then drives the Pockels cell 8 to work by controlling the Pockels cell high voltage driver 23. Specifically, when working, the arbitrary waveform generator 22 is controlled to output a half-wave voltage signal V π (λ) and circular polarization modulated frequency signal f to the Pockels cell high voltage driver 23, the Pockels cell high voltage driver 23 outputs an amplified periodic high voltage signal of the same frequency to control the phase delay synchronization of the Pockels cell 8 to periodically alternate between 0 and π, such as Figure 3 , Figure 4 , Figure 5 and Figure 6 The horizontal linear polarized light passing through the Pockels cell 8 is periodically modulated into horizontal linear polarized light and vertical linear polarized light; the broadband achromatic quarter wave plate 9 after the Pockels cell 8 has its fast axis set to be at an angle of 45° to the horizontal polarization direction, so the aforementioned linear polarized light is modulated into periodically alternating left-right circular polarized light, and the modulation frequency can be set to 1kHz. The above parts together constitute a polarization modulation module, which is used Figure 3 , Figure 4 , Figure 5 and Figure 6 To illustrate the above polarization modulation principle.

[0050] The measurement light modulated by the polarization modulation module enters the micro-area positioning module, which is used to adjust the spot size of the polarized light formed by the polarization modulation module, and the adjusted polarized light is projected onto the chiral object to be measured; the micro-area positioning module includes a lens group formed by a first lens 10 and a second lens 11, and the left-right circularly polarized light after passing through the polarization modulation module is adjusted to the spot size by the lens group, and the adjusted light is absorbed by the chiral object to be measured; the relative position of the first lens 10 and the second lens 11 can be moved, and the distance between the first lens 10 and the second lens 11 can change the measurement light spot size. The size of the spot can be ensured by adjusting the distance between the first lens 10 and the second lens 11. At the same time, a detection platform 12 is provided at the rear end of the second lens 11. The detection platform 12 is used to place the chiral object to be tested. Specifically, when working, the periodically alternating left-right circularly polarized light emitted by the polarization modulation module passes through the beam reduction lens group formed by the first lens 10 and the second lens 11, and the polarization remains unchanged. The size of the measurement light spot can be adjusted by adjusting the distance between the lens groups. Combined with the detection platform 12 with displacement, the size and position of the measurement spot passing through the chiral object to be tested area can be flexibly adjusted.

[0051] A balanced detection module, used to receive light from a reference optical path and light passing through a chiral object to be detected, and convert the received light into a voltage signal for output; the balanced detection module includes a balanced detector 13, a first response collection probe and a second response collection probe provided on the balanced detector 13, the first response collection probe is used to collect light passing through the chiral object to be detected, the second response collection probe is used to collect light from the reference optical path, the balanced detector 13 includes an M1 output terminal and an RF output terminal, the M1 output terminal and the RF output terminal are respectively connected to the control processing module;

[0052] The measured light passes through the chiral object to be measured with different absorbance for left-handed circularly polarized light and is collected by the first response probe of the balanced detector 13, and is output from the output terminal M1, and its response output voltage V M1 The intensity of the transmitted left-right circularly polarized light is I L ,I R are square wave AC signals with high and low values, that is, they contain AC components I with the same frequency as the modulation frequency f. AC And the average value of left and right rotation transmission power I DC The DC component of this modulation response process is as follows Figure 7 The reference light passes through the beam reduction lens group formed by the third lens 16 and the fourth lens 18 and is totally reflected by the right-angle prism 17 and enters the second response probe of the balanced detector 13 for collection. The response output voltage V M2 is a DC signal. Using the common mode rejection principle of the balanced detector 13, the voltage difference signal V between the two response probes RF =G×(V M1 -V M2 ), which is a differential voltage signal containing left-right handed transmitted light intensity information, is amplified and output from the RF output terminal, wherein the gain is adjustable and set to G in this embodiment.

[0053] The signal processed by the balanced detection module enters the control processing module, and the circular dichroism spectrum of the chiral object to be tested is obtained through the control processing module. The control processing module at least includes a control processor 21, a phase-locked amplifier 19, an oscilloscope 20 and an arbitrary waveform generator 22; the signal output by the RF output terminal of the balanced detector 13 is received by the control processor 21 after phase-locked processing by the phase-locked amplifier 19, and the signal output by the M1 output terminal of the balanced detector 13 is received by the control processor 21 after passing through the oscilloscope 20. The control processor 21 processes the signals received from the oscilloscope 20 and the phase-locked amplifier 19 to obtain the circular dichroism spectrum of the chiral object to be tested;

[0054] In operation, the signal from the RF output terminal of the balanced detector 13 is input to the signal input terminal of the phase-locked amplifier 19, the reference signal comes from the circular polarization modulation frequency signal f output by the arbitrary waveform generator 22, and the intensity readout value V is read by the computer. AC and phase information The intensity readout value of the lock-in amplifier 19 only indicates the magnitude, and its positive or negative value is determined by the phase information The signal from the output terminal of the balanced detector 13 M1 is input to the signal input terminal of the oscilloscope 20, and the waveform average value V is read by the computer. DC .

[0055] When working, the measurement wavelength range, measurement step and integration time of the chiral object to be measured are first determined. At the initial target wavelength, the control processor 21 controls the monochromator 2 to split the light to the target wavelength, and then calls the calibrated half-wave voltage data set to collect the current wavelength half-wave voltage, and controls the arbitrary waveform generator 22 to output the half-wave voltage signal V π (λ) and the circular polarization modulation frequency signal f are transmitted to the Pockels cell high-voltage driver 23, so that the polarization modulation module where the Pockels cell 8 is located generates periodically alternating left-handed and right-handed circularly polarized light. Then, the readout data of the phase-locked amplifier 19 and the oscilloscope 20 are read, and the circular dichroism value of the current wavelength is obtained based on the above-mentioned read data. This process is repeated according to the measured wavelength to obtain the circular dichroism spectrum of the measured wavelength range.

[0056] A high-sensitivity circular dichroism precision measurement method, which is implemented based on the device, comprises:

[0057] like Figure 8 As shown, the chiral test object is placed on the detection platform 12 of the micro-area positioning module;

[0058] The control processing module sends instructions to the light source module, and the light source module emits monochromatic light. At the same time, the control processing module sends a half-wave voltage signal and a circular polarization modulation frequency signal corresponding to the wavelength to the polarization modulation module. The polarization modulation module periodically modulates the light passing through the polarization modulation module according to the received frequency signal to form left-handed and right-handed circularly polarized light. Specifically, the processing controller controls the arbitrary waveform generator to load the corresponding wavelength half-wave voltage DC signal and the modulation frequency signal f to the Pockels cell high-voltage driver when the monochromator splits the light to the required wavelength. The Pockels cell is combined with a broadband achromatic quarter-wave plate to form periodically alternating left-handed and right-handed circularly polarized light.

[0059] The monochromatic light emitted by the light source module passes through the double-arm balanced optical path module to form measurement light and reference light. The measurement light passes through the polarization modulation module to form left-handed circularly polarized light. The left-handed circularly polarized light is adjusted by the micro-area positioning module to be absorbed by the chiral object to be tested placed on the detection table 12.

[0060] The balanced detection module processes the transmitted light and reference light after the chiral object to be tested to obtain a voltage signal, and sends the obtained voltage signal to the control processing module; specifically, the output signal of the balanced detector RF terminal and the circular polarization modulation frequency signal f are input to the phase-locked amplifier, and the phase-locked amplifier reads the signal V AC And phase information The output signal of the balanced detector M1 terminal is input to the oscilloscope, and the oscilloscope reads the signal V DC ;

[0061] The control processing module calculates the circular dichroism spectrum of the chiral object to be measured using the received voltage information and phase information. During implementation, the control processor calculates the circular dichroism spectrum of the chiral object to be measured based on the readout signal V of the lock-in amplifier. AC , phase information And the readout signal of the oscilloscope is V DC Compute circular dichroism values.

[0062] In one embodiment, a method for obtaining a circular dichroism spectrum of a chiral analyte includes:

[0063] The circular dichroism value measures the difference in absorption of left-handed circularly polarized light by the chiral test object, and is expressed as the amplitude E of the left-handed circularly polarized light after passing through the chiral test object. L 、E R Ellipticity θ of the composite ellipse rad Indicated by absorbance difference ΔA.

[0064] The circular dichroic value is expressed as the ellipticity θ of the synthetic ellipse. rad It can be expressed as the difference Δa between the left-hand and right-hand absorbance coefficients under Euler absorbance. CD In the form of L ,I R They are respectively the left and right circularly polarized transmitted light intensity and the absorption coefficient difference Δa CD The following formula can be used to express the ratio of the left-right transmitted light intensity difference to the average left-right transmitted light intensity.

[0065] The conversion coefficient from radians to degrees when the circular dichroism value is expressed in conventional units [mdeg] is given in the formula, and the difference in absorption coefficient Δa CD It can be expressed by measurement, and the typical conversion coefficient is C1=180000 / 4π=14324. Among them, it can be converted into the circular dichroism value represented by the tenth power absorbance difference ΔA, and its coefficient C2=180000×ln10 / 4π is also consistent with the literature in the field.

[0066] That is to say, combined with the above formula, the measurement of circular dichroism value only needs to obtain the actual measured left-right hand transmission intensity difference I ACand the average value of the left-right transmitted light intensity I DC , the circular dichroic value can be obtained correctly.

[0067] In this embodiment, the left-right transmitted light intensity difference I AC The RF output terminal of the balanced detector 13 is measured by the phase-locked amplifier 19. From the above signal acquisition process, it can be seen that the measured light response voltage output terminal M1 outputs an AC voltage signal V M1 The high and low values ​​of the AC square wave component are respectively the left-right transmitted light intensity I L ,I R Its amplitude is VAC=I L -I R After being amplified G times by the RF output terminal of the balanced detector 13, the AC component amplitude is phase-locked and read out in the form of effective value, which is the voltage value V AC , where the AC component is a square wave; hence:

[0068] Phase information To determine I AC The positive and negative properties of , the method is: Average value of left-right transmitted light intensity I DC The AC voltage signal V output by the balanced detector M1 is read by the oscilloscope 20 M1 The average value is obtained; According to the above expression, the measurement expression of circular dichroism value can be obtained: Where: represents the circular dichroism value of the chiral analyte in millidegrees; Represents the readout value of the differential amplified output voltage of the balanced detection module through the phase-locked amplifier; Represents the average value of the voltage in response to light absorbed by the chiral analyte, read out by an oscilloscope; Represents the phase information value.

[0069] The supercontinuum laser is split by a monochromator and filtered by a long-wave filter to form monochromatic light. After polarization, horizontal linear polarized light is formed. The horizontal linear polarized light is split twice by a non-polarizing beam splitter prism to form parallel measuring light and reference light with equal power. The measuring light is generated by a polarization modulation module to generate periodically alternating left-right circularly polarized light. After passing through the sample area, the alternating left-right transmitted light intensity is converted by the first light response probe of the balanced detector into an AC voltage signal V consistent with the alternating frequency of the circularly polarized light. M1 The reference light is converted into a DC voltage signal V by the second light response probe of the balanced detector M2 , the voltage signals of the two arms have the same noise at the same time, and the voltage difference signal V RF It is an AC voltage signal. After amplification, it enters the phase-locked amplifier and uses the circular polarization modulation frequency as the reference frequency to perform phase locking to obtain the read value VAC , that is, the difference in the intensity of the amplified left-right transmitted light; the oscilloscope measures the optical AC voltage signal V M1 The average value V DC , that is, the average value of the left- and right-handed transmitted light intensity, based on which the circular dichroism value is obtained.

[0070] A balanced optical path is adopted to construct a double-arm balanced optical path module, so that the measuring light and the reference light have simultaneous and consistent light source fluctuation noise, and the real-time differentiation of the left-right circular polarization state time-varying noise of the measuring light relative to the reference light time-varying noise is realized, which greatly suppresses the system noise and exceeds the sensitivity of the existing technology in the current measurement band. The lens group can freely adjust the size of the measuring spot and expand the measuring scene from conventional cuvettes to micro areas, which solves the problem of insufficient flexibility in positioning the measuring area in the existing technology.

[0071] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A high-sensitivity circular dichroism precision measurement device, characterized in that: include: Light source module; A double-arm balanced optical path module is used to divide the light emitted by the light source module into two parallel optical paths, one of which is a measurement optical path and the other is a reference optical path, and the power of the measurement optical path and the reference optical path is equal; A polarization modulation module is used to periodically modulate the light in the measurement optical path to form alternating left-handed and right-handed circularly polarized light; The micro-area positioning module is used to adjust the spot size of the circularly polarized light formed by the polarization modulation module, and the adjusted circularly polarized light is projected onto the chiral object to be tested; A balanced detection module is used to receive light from the reference light path and light passing through the chiral object to be measured, and convert the received light into a voltage signal for output; A control processing module is used to control the wavelength of the light emitted by the light source module, provide a half-wave voltage signal and a circular polarization modulation frequency signal corresponding to the wavelength during the periodic modulation process of the polarization modulation module, and receive the voltage signal output by the balance detection module to obtain the circular dichroism spectrum of the chiral object to be tested; The double-arm balanced optical path module comprises a first polarizing plate (4), a first non-polarizing beam splitting prism (5), a second non-polarizing beam splitting prism (6) and a third non-polarizing beam splitting prism (14); the detection light emitted by the light source module is polarized by the first polarizing plate (4) and then split by the first non-polarizing beam splitting prism (5) to form a measurement light path and a reference light path; the light of the measurement light path after passing through the second non-polarizing beam splitting prism (6) and the light of the reference light path after passing through the third non-polarizing beam splitting prism (14) are parallel to each other; The monochromatic light emitted by the light source module is set as horizontal linear polarized light after passing through a first polarizing plate (4), and then is divided into two paths, namely, transmission light and reflection light, after passing through a first non-polarizing beam splitter prism (5); the transmitted light is reflected by a second non-polarizing beam splitter prism (6) to form measurement light, and the reflected light is transmitted by a third non-polarizing beam splitter prism (14) to form reference light; the measurement light and the reference light are respectively transmitted once (T) and reflected once (R) to form parallel light paths, wherein the first non-polarizing beam splitter prism (5), the second non-polarizing beam splitter prism (6), and the third non-polarizing beam splitter prism (14) are products with the same parameters manufactured in the same batch, namely, T1(λ)=T2(λ)=T3(λ), and have the same transmission and reflection splitting ratio, namely, T1(λ):R1(λ)=T2(λ):R2(λ)=T3(λ):R3(λ); The polarization modulation module comprises a second polarizer (7), a Pockels cell (8) and a broadband achromatic quarter-wave plate (9), the Pockels cell (8) is driven by a Pockels cell high-voltage driver (23), the control processing module is connected to the Pockels cell high-voltage driver (23), the control processing module sends a half-wave voltage signal and a circular polarization modulation frequency signal corresponding to the wavelength to the Pockels cell high-voltage driver (23), the Pockels cell high-voltage driver (23) controls the phase of the Pockels cell (8) according to the received signal, and the light of the measuring light path passes through the second polarizer (7), the Pockels cell (8) and the broadband achromatic quarter-wave plate (9) in sequence to form left-right circularly polarized light; The balanced detection module comprises a balanced detector (13), a first response collection probe and a second response collection probe provided on the balanced detector (13), the first response collection probe being used to collect light passing through the chiral object to be detected, the second response collection probe being used to collect light in a reference light path, the balanced detector (13) comprising an M1 output terminal and an RF output terminal, the M1 output terminal and the RF output terminal being respectively connected to the control processing module; The measurement light is collected by the first response collection probe of the balanced detector (13) through the chiral test object with different absorbance for left-handed circularly polarized light, and output from the output terminal M1, and its response output voltage V M1 The intensity of the transmitted left-right circularly polarized light is I L ,I R are square wave AC signals with high and low values, i.e., they contain an AC component I with the same frequency as the modulation frequency f. AC And the average value of left-right rotation transmission power I DC The DC component of the two response probes; the voltage difference signal between the two response probes is amplified and output from the RF output terminal, wherein the adjustable amplification factor is set to G; The control processing module comprises a control processor (21), a phase-locked amplifier (19), an oscilloscope (20) and an arbitrary waveform generator (22); the signal outputted from the RF output terminal of the balanced detector (13) is received by the control processor (21) after being phase-locked by the phase-locked amplifier (19); the signal outputted from the M1 output terminal of the balanced detector (13) is received by the control processor (21) after being phase-locked by the phase-locked amplifier (19); the control processor (21) processes the signals received from the oscilloscope (20) and the phase-locked amplifier (19) to obtain a circular dichroism spectrum of the chiral object to be measured; the control processor (21) sends a circular polarization modulation frequency signal to the arbitrary waveform generator (22); and the arbitrary waveform generator (22) uses the received circular polarization modulation frequency signal to control a Pockels cell high-voltage driver (23).

2. A high-sensitivity circular dichroism precision measurement device as claimed in claim 1, characterized in that: The double-arm balanced optical path module further comprises a third polarizer (15) and a third lens (16), and the reference optical path passing through the third non-polarizing beam splitter prism (14) passes through the third polarizer (15) and the third lens (16) in sequence and is received by the balanced detection module.

3. A high-sensitivity circular dichroism precision measurement device as claimed in claim 1, characterized in that: The micro-area positioning module comprises a lens group formed by a first lens (10) and a second lens (11); the left-right circularly polarized light after passing through the polarization modulation module is adjusted through the lens group to adjust the light spot size; the adjusted light is absorbed by the chiral object to be measured.

4. A high-sensitivity circular dichroism precision measurement device as claimed in claim 1, characterized in that: The light source module comprises a supercontinuum laser (1), a monochromator (2) and a long-wave pass filter (3); the control processing module is connected to the monochromator (2); the control processing module is used to control the monochromator (2) to separate monochromatic light; laser light emitted by the supercontinuum laser (1) passes through the monochromator (2) to form monochromatic light, and the formed monochromatic light is filtered by the long-wave pass filter (3) and then enters the double-arm balanced optical path module for branching.

5. A high-sensitivity circular dichroism precision measurement method, applied to a high-sensitivity circular dichroism precision measurement device according to any one of claims 1 to 4, characterized in that: include: Placing the chiral test object on the detection platform (12) of the micro-area positioning module; The control processing module sends instructions to the light source module, and the light source module emits monochromatic light. At the same time, the control processing module sends a half-wave voltage signal and a circular polarization modulation frequency signal corresponding to the wavelength to the polarization modulation module. The polarization modulation module periodically modulates the light passing through the polarization modulation module according to the received signal to form left-right circularly polarized light. The monochromatic light emitted by the light source module passes through the double-arm balanced optical path module to form measurement light and reference light. The measurement light passes through the polarization modulation module to form left-handed circularly polarized light. The left-handed circularly polarized light passes through the micro-area positioning module to adjust the light spot and then passes through the chiral object to be tested placed on the detection table (12); The balance detection module processes the transmitted light and the reference light after passing through the chiral object to be tested to obtain a voltage signal, and sends the obtained voltage signal to the control processing module; The control processing module uses the received voltage signal to process and obtain voltage intensity information and phase information, and calculates the circular dichroism value of the chiral object to be measured at the current wavelength; switches the wavelength within the measurement range and performs wavelength-by-wavelength measurement in steps to obtain the circular dichroism spectrum of the chiral object to be measured; The double-arm balanced optical path module comprises a first polarizing plate (4), a first non-polarizing beam splitting prism (5), a second non-polarizing beam splitting prism (6) and a third non-polarizing beam splitting prism (14); the detection light emitted by the light source module is polarized by the first polarizing plate (4) and then split by the first non-polarizing beam splitting prism (5) to form a measurement light path and a reference light path; the light of the measurement light path after passing through the second non-polarizing beam splitting prism (6) and the light of the reference light path after passing through the third non-polarizing beam splitting prism (14) are parallel to each other; The monochromatic light emitted by the light source module is set as horizontal linear polarized light after passing through a first polarizing plate (4), and then passes through a first non-polarizing beam splitter prism (5) to be divided into two paths, namely, transmission light and reflection light; the transmitted light is reflected by a second non-polarizing beam splitter prism (6) to form measurement light, and the reflected light is transmitted by a third non-polarizing beam splitter prism (14) to form reference light; the measurement light and the reference light are respectively transmitted once (T) and reflected once (R) to form parallel light paths, wherein the first non-polarizing beam splitter prism (5), the second non-polarizing beam splitter prism (6), and the third non-polarizing beam splitter prism (14) are products with the same parameters manufactured in the same batch, namely, T1(λ)=T2(λ)=T3(λ), and have the same transmission and reflection splitting ratio, namely, T1(λ):R1(λ)=T2(λ):R2(λ)=T3(λ):R3(λ).

6. A high-sensitivity circular dichroism precision measurement method as claimed in claim 5, characterized in that: Methods for calculating the circular dichroism spectrum of chiral analytes include: ； Where: represents the circular dichroism value of the chiral analyte in millidegrees; Represents the readout value of the differential amplified output voltage of the balanced detection module through the phase-locked amplifier; Represents the average value of the voltage in response to light absorbed by the chiral analyte, read out by an oscilloscope; Represents confirmation AC The positive and negative phase information value.

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