In-situ circular dichroism spectroscopy measurement system and method under strong magnetic field

Abstract

The application discloses a kind of in-situ circular dichroism spectrum measurement system and method under strong magnetic field, double light source remote module is coupled with monochromator in the system, the center coaxial arrangement of monochromator, collimating lens L1, polarizer LX, non-magnetic polarization switching module and mirror M1, the center coaxial arrangement of mirror M1, diaphragm S1 and mirror M2, the center coaxial arrangement of mirror M2, focusing lens L2, sample, collimating lens L3 and mirror M3, the center coaxial arrangement of mirror M3, diaphragm S2 and mirror M4, the center coaxial arrangement of mirror M4, diaphragm S3, converging lens L4 and photomultiplier, photomultiplier converts optical signal into electrical signal, with the synchronous reference signal of non-magnetic polarization switching module together input lock-in amplifier;The application has the advantages that: meet the requirements such as light source magnetic avoidance, polarization state stable switching and multi-device synchronous acquisition, realize in-situ circular dichroism spectrum measurement under strong magnetic field.

Description

Technical Field

[0001] This invention relates to the field of spectral measurement, specifically to an in-situ circular dichroism spectral measurement system and method under a strong magnetic field. Background Technology

[0002] Circular dichroism refers to the difference in absorption of left-handed and right-handed circularly polarized light by a sample. According to absorbance A = -log... 10 (I / I0) is defined as follows: I0 represents the initial light intensity, and I represents the light intensity detected in real time. If A... L Indicates the absorbance of left-handed circularly polarized light, expressed in A R Let A represent the absorbance of right-handed circularly polarized light. Then, the circular dichroism absorption difference can be expressed as ΔA = A. L -A R Ordinary circular dichroism spectrometers are typically used in conventional experimental environments, with their light sources, polarization modulators, sample cells, detectors, and control software designed for ambient temperature, atmospheric pressure, and non-strong magnetic field environments. When the sample to be measured needs to be placed in an in-situ magnetic field of 10 T generated by a superconducting magnet for in-situ measurement, ordinary circular dichroism spectrometers cannot directly meet the requirements of magnetically shielded light sources, confined space sample placement, stable polarization state switching, leakage magnetic field detection, and simultaneous acquisition by multiple devices.

[0003] Regarding the light source input, when xenon lamps and deuterium lamps are near strong magnetic fields or areas with strong leakage magnetic fields, their discharge state, power supply, and metal components may be affected by the magnetic field. If the light source is placed away from the magnet, it will lead to fiber optic transmission loss and insufficient light intensity in the ultraviolet band. Especially in ultraviolet circular dichroism measurements, relying solely on xenon lamps for long-distance transmission may make it difficult to obtain sufficient incident light intensity in the 190-350 nm wavelength range.

[0004] Regarding polarization state generation, traditional photoelastic modulators or modulation components containing magnetic, metallic, piezoelectric, and driving circuitry face compatibility risks in strong magnetic fields or leakage magnetic fields. If mechanical polarization switching is used, it is also necessary to clarify the angular relationship between the quarter-wave plate and the polarization direction of the incident beam and ensure that it matches the subsequent synchronous demodulation method.

[0005] In terms of sample processing, if liquid samples are measured offline, sampling, transfer, and repacking may alter the reaction equilibrium, concentration, temperature, conformational state, or magnetic field-induced state. Traditional magnetic stir bar may become unstable in orientation, adsorption, displacement, or rotation under strong magnetic fields, making it difficult to meet the requirements for in-situ mixing and continuous measurement of liquid samples under strong magnetic field conditions.

[0006] In signal detection, the trajectories of photoelectrons and secondary electrons inside a photomultiplier tube (PMT) are easily affected by magnetic leakage, leading to gain drift, decreased collection efficiency, and nonlinear response. A single high-permeability material shielding layer may experience local magnetic saturation under strong magnetic leakage conditions; therefore, a graded shielding approach considering strong magnetic leakage shunting and residual weak magnetic field attenuation is necessary.

[0007] In terms of wideband scanning and synchronous acquisition, there may be significant differences in light source output, fiber transmittance, monochromator efficiency, sample absorption, and PMT response at different wavelengths. At the same time, wavelength scanning, polarization switching, magnetic field changes, and PMT signal acquisition are performed by different devices. If there is a lack of unified timing correlation, it is easy to cause errors in the correspondence between wavelength, polarization state, magnetic field strength, and circular dichroism signals.

[0008] In summary, existing technologies still require an in-situ circular dichroism spectroscopy measurement system that can integrate dual-source input, wavelength selection, circular polarization switching, in-situ sample mixing, magnetic shielding detection, and synchronous signal processing in a 10 T-level strong magnetic field and leakage magnetic environment. Summary of the Invention

[0009] The technical problem to be solved by this invention is that ordinary circular dichroism spectrometers cannot directly meet the requirements of light source magnetic avoidance, stable switching of polarization state, and synchronous acquisition by multiple devices.

[0010] This invention solves the above-mentioned technical problems through the following technical means: an in-situ circular dichroism spectroscopy measurement system under a strong magnetic field, comprising a dual-source remote module, a monochromator, a collimating lens L1, a polarizer LX, a non-magnetic polarization switching module, a reflector M1, an aperture S1, and a reflector M2. The common end of the dual-source remote module is coupled to the incident end of the monochromator. The monochromator, collimating lens L1, polarizer LX, non-magnetic polarization switching module, and reflector M1 are coaxially arranged as the first optical path. The reflector M1, aperture S1, and reflector M2 are coaxially arranged as the second optical path. The first and second optical paths are perpendicular. The reflector M2 and the focusing lens... The centers of mirror L2, sample, collimating lens L3, and reflecting mirror M3 are arranged coaxially to form the third optical path, which is perpendicular to the second optical path and parallel to the first optical path. The centers of reflecting mirror M3, aperture S2, and reflecting mirror M4 are arranged coaxially to form the fourth optical path, which is perpendicular to the third optical path and parallel to the second optical path. The centers of reflecting mirror M4, aperture S3, converging lens L4, and photomultiplier tube are arranged coaxially to form the fifth optical path, which is perpendicular to the fourth optical path. The photomultiplier tube converts the optical signal into an electrical signal, which, together with the synchronization reference signal from the non-magnetic polarization switching module, is input into the lock-in amplifier. The host computer demodulates and calculates the final spectrum.

[0011] Furthermore, the reflecting surface of the reflector M1 is tilted at a 45° angle relative to the outlet of the non-magnetic polarization switching module.

[0012] Furthermore, the reflecting surface of the mirror M2 is tilted at a 45° angle relative to the exit port of the aperture S1, and the reflecting surface of the mirror M2 is tilted at a 45° angle relative to the entrance port of the focusing lens L2.

[0013] Furthermore, the reflecting surface of the reflector M3 is tilted at a 45° angle relative to the exit port of the collimating lens L3, and the reflecting surface of the reflector M3 is tilted at a 45° angle relative to the entrance port of the aperture S2.

[0014] Furthermore, the reflecting surface of the reflector M4 is tilted at a 45° angle relative to the exit port of the aperture S2 and at a 45° angle relative to the incident angle of the aperture S3.

[0015] Furthermore, the dual-source remote module includes a xenon lamp, a deuterium lamp, and a Y-type fiber optic coupling transmission unit. The xenon lamp and the deuterium lamp are located in an area at a preset distance away from the center of the superconducting magnet and are lit simultaneously. The xenon lamp and the deuterium lamp are respectively coupled to the two branches of the Y-type fiber optic coupling transmission unit, and the common end of the Y-type fiber optic coupling transmission unit is coupled to the monochromator incident end.

[0016] Furthermore, the non-magnetic polarization switching module includes polarizers and superachromatic quarter-wave plates arranged coaxially along the main optical axis of the system, as well as a non-magnetic rotary drive mechanism for driving the superachromatic quarter-wave plates to oscillate. The non-magnetic rotary drive mechanism includes a stator and a rotor rotatable on the stator. The superachromatic quarter-wave plate is fixed inside the rotor of the non-magnetic rotary drive mechanism. A non-magnetic photoelectric encoder disk is integrated on the outer edge of the rotor, and a photoelectric sensor is correspondingly installed on the stator. A high-frequency piezoelectric ceramic ring is attached to the surface of the stator. The host computer reads the position signal of the photoelectric encoder disk and controls the driving voltage of the high-frequency piezoelectric ceramic ring in real time in a closed loop, driving the rotor to oscillate back and forth between two mechanical limits of +45° and -45°.

[0017] Furthermore, the sample is placed inside a reaction vessel, which is equipped with two stirring blades that are driven to rotate by a motor.

[0018] Furthermore, the photomultiplier tube is installed at a position 1m away from the center of the superconducting magnet. The photomultiplier tube is provided with a multi-layer magnetic shielding structure. The multi-layer magnetic shielding structure includes, from the inside out, an aluminum alloy layer, eight layers of permalloy, and an electrical pure iron layer. The layers are bonded together with plastic and adhesive.

[0019] This invention also provides a method for applying the above-mentioned in-situ circular dichroism spectroscopy measurement system under a strong magnetic field, the method comprising: The electrical signal output by the photomultiplier tube is a mixture of AC signal and DC baseline signal. The mixed signal is output to the lock-in amplifier to separate the DC baseline signal and AC signal. At the same time, the host computer synchronously sends a sinusoidal reference signal that is completely consistent with the switching frequency of the non-magnetic polarization switching module to the lock-in amplifier. The automatic gain control circuit acquires the DC baseline signal in real time, performs high-frequency differential comparison between the DC baseline signal and the constant absolute reference voltage set by the system, calculates the error in real time using the PI control algorithm, and dynamically adjusts the negative high voltage applied to the photomultiplier tube through the PI loop. The host computer collects and records wavelength data in real time. Real-time magnetic field strength data The AC signal output from the lock-in amplifier and the negative high voltage dynamically output from the automatic gain control circuit are used to calculate the absolutely quantitative in-situ circular dichroism spectrum. The calculation formula is:

[0020] In the formula, Wavelength data of the lock-in amplifier at the current moment and real-time magnetic field strength data The demodulated AC signal under the condition; A constant absolute reference voltage set for the automatic gain control circuit; For the system at different magnetic field strengths and different negative high pressure Under these conditions, the gain and response nonlinearity correction coefficient matrices are obtained by pre-calibrating with standard chiral samples.

[0021] The advantages of this invention are: (1) The present invention uses a dual-source remote module to move the light source away from the center of the magnetic field to achieve magnetic avoidance of the light source. At the same time, it uses a non-magnetic polarization switching module to achieve stable switching of polarization state. The host computer performs multi-channel timing synchronization of the wavelength scanning, lock-in amplifier demodulation signal and real-time magnetic field strength, etc., to achieve synchronous acquisition of multiple devices. The overall solution can realize in-situ circular dichroism spectroscopy measurement in a strong magnetic field environment.

[0022] (2) The present invention includes a first optical path containing sensitive devices (monochromator, non-magnetic polarization switching module) and a fifth optical path containing a photomultiplier tube, both of which are set horizontally and located outside the magnet. By guiding the light source, which is extremely sensitive to magnetism, the polarization modulator and the photomultiplier tube are placed in a safe area with a weak magnetic field or even no magnetic field far away from the center of the magnet. This completely solves the technical problem of strong magnetic field interference with the working state of the core optical device from a physical distance perspective, and meets the requirement of magnetic avoidance of the light source. The reflector M1 converts the horizontal light into a second optical path that is vertically downward, and the reflector M3 converts the light passing through the sample into a fourth optical path that is vertically upward. These are two vertical channels that enter and exit. By utilizing the narrow vertical aperture of the superconducting magnet, the beam carrying the polarization state is accurately delivered to the high field strength region buried deep in the core without damaging any physical structure of the magnet, and the beam carrying the sample signal is extracted without loss. At the deepest part of the magnet, the third optical path composed of reflectors M2 and M3 is turned horizontal again and penetrates the sample laterally, so that the light passes through the reaction vessel in a horizontal direction at the center of the magnet. This means that the reaction vessel can remain in a normal vertical position. If it were a vertical optical path, the sample cell would have to lie flat, making stirring and liquid sealing completely impossible.

[0023] The 10 T superconducting magnet upon which this system relies has its internal cold aperture operating space, which is strictly limited to a deep-well cylinder with a diameter of 200 mm, allowing for optical path movement. After deducting the 52 mm outer diameter in-situ reaction vessel and its anti-displacement fixing mechanism in the central region, the available space for beam introduction and exit is extremely small. The Π-shaped spatial folding optical path defined in this invention, 'horizontal-vertical-horizontal-vertical-horizontal', is precisely to maximize the use of this 200 mm cylindrical spatial boundary condition. The second and fourth optical paths are vertically submerged into the inner wall of the 200 mm cylindrical aperture, and then deflected by the bottom mirrors M2 and M3 at a 90° angle within the extremely small space, forming a third optical path that traverses the sample. This spatial topology ensures that the core optical components are kept away from strong magnetic fields while perfectly avoiding mechanical and optical path interference conflicts within the limited cylindrical aperture.

[0024] (3) To address the shortcomings of strong magnetic field interference and deep ultraviolet light intensity attenuation in the light source input, this invention uses a dual-light source remote module to place the light source in a weak magnetic field region far from the magnet, fundamentally eliminating the interference of strong magnetic field on the bulb discharge state and power supply. More importantly, to address the problem of insufficient photon flux in the deep ultraviolet region (200 nm - 400 nm) caused by long-distance fiber optic transmission of a single xenon lamp, this invention innovatively introduces a Y-type fiber-coupled transmission unit. This structure utilizes the beam-combining effect of fiber waveguides to physically complement the energy of the xenon lamp responsible for the visible region and the deuterium lamp responsible for the deep ultraviolet region, effectively filling the ultraviolet energy trough without the need for complex dichroic mirrors, greatly improving the incident light intensity and system signal-to-noise ratio in the 190-350 nm band.

[0025] (4) Addressing the incompatibility of conventional modulator (PEM) magnetic fields in polarization state generation, traditional photoelastic modulators containing metals and piezoelectric resonant circuits are prone to failure under 10 T conditions. This invention employs a design combining a pure free-space optical path with physical mechanical polarization in the non-magnetic polarization switching module. In particular, the independently designed non-magnetic rotary drive mechanism abandons the traditional electromagnetic motor, using a piezoelectric ultrasonic stator completely unaffected by magnetic fields to drive the non-magnetic rotor. Combined with the closed-loop limiting of a high-precision photoelectric encoder disk, it precisely drives the fast axis of the supercomplex achromatic quarter-wave plate to perform high-frequency (1-10 Hz) reciprocating switching between +45° and -45°. This structure achieves high-fidelity modulation of the pure physical non-magnetic polarization state under strong magnetic field conditions.

[0026] (5) To address the shortcomings of "magnetic stirring failure and space constraints" in sample processing, and the problem of severe magnetization and swaying of traditional magnetic stir bar in strong magnetic fields, this invention designs a quartz transparent reaction chamber (outer diameter 52 mm) with a height adapted to the magnet aperture, and constructs a precise detection window with an optical path of only 2 mm at the center of the chamber. Simultaneously, an inert gas-driven pneumatic motor, introduced from the top, distributes the single rotational power to two insulated stirring shafts via a non-magnetic plastic gearbox. The two stirring blades rotate synchronously in opposite directions within the narrow two-sided chamber separated by the detection window, forming an "∞"-shaped convection mixing. This structure not only completely eliminates the risks of magnetic disturbance and sealing leakage, but also ensures the uniformity of the mobile phase solution concentration within the extremely short 2 mm optical path, guaranteeing the accuracy of spectral detection.

[0027] (6) To address the defect of "magnetic leakage causing PMT gain drift and nonlinearity" in signal detection, a strong magnetic leakage field can severely deflect the trajectory of secondary electrons inside the PMT. This invention addresses this by spatially positioning the PMT detection unit 1 m away from the center of the magnet (with a magnetic leakage of approximately 200 mT), and by constructing a high-specification multi-layered, hierarchical magnetic shielding structure outside the detector. This structure comprises eight layers of permalloy, one layer of electrical pure iron, and multi-layered POM structural components that provide process support. The outer layer of pure iron is responsible for shunting the high-flux, strong magnetic leakage, while the inner layer of multi-layered permalloy is responsible for the deep absorption of the residual weak magnetic field, ultimately attenuating the residual magnetic field in the core region of the PMT to below 0.3 mT, thus completely ensuring the linearity of the weak optical signal amplification process.

[0028] (7) To address the shortcomings of "detector saturation failure due to drastic changes in light intensity and lack of timing synchronization" in wideband scanning, this invention establishes a closed-loop architecture that combines hardware and software through a synchronization signal processing module. At the hardware level, the independently developed automatic gain control circuit (AGC) extracts the DC baseline signal output by the PMT in real time and calculates the error by introducing a PI (proportional-integral) algorithm to dynamically adjust the negative high voltage of the PMT in real time. This closed-loop mechanism forcibly locks the DC gain denominator, completely avoiding signal saturation failure and signal annihilation during the wideband scanning process, and expanding the dynamic measurement range of the instrument. At the software level, the host computer (PC) acts as the central hub, performing multi-channel timing synchronization of wavelength scanning, AC chiral signals demodulated by the lock-in amplifier, dynamic high voltage data, and real-time magnetic field strength. In conjunction with the gain distortion calibration curve pre-built by the system, real-time numerical compensation is performed on the demodulated signal, ultimately achieving in-situ absolute quantitative measurement of weak chiral AC signals under a 10 T extreme disturbance environment. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of an in-situ circular dichroism spectroscopy measurement system under a strong magnetic field, as disclosed in an embodiment of the present invention. Figure 2 This is a schematic diagram of a dual-light source remote module in an in-situ circular dichroism spectroscopy measurement system under a strong magnetic field, as disclosed in an embodiment of the present invention. Figure 3 This is a schematic diagram of a non-magnetic polarization switching module in an in-situ circular dichroism spectroscopy measurement system under a strong magnetic field, as disclosed in an embodiment of the present invention. Figure 4 This is a schematic diagram of a magnetic shielding detection module in an in-situ circular dichroism spectroscopy measurement system under a strong magnetic field, as disclosed in an embodiment of the present invention. Figure 5 This is a schematic diagram of an in-situ circular dichroism spectroscopy measurement method under a strong magnetic field, as disclosed in an embodiment of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] like Figure 1 As shown, Embodiment 1 of the present invention provides an in-situ circular dichroism spectroscopy measurement system under a strong magnetic field, including a dual-source remote module, a monochromator, a collimating lens L1, a polarizer LX, a non-magnetic polarization switching module, a reflector M1, an aperture S1, a reflector M2, a reaction container, a focusing lens L2, a sample, a collimating lens L3, a reflector M3, an aperture S2, a reflector M4, an aperture S3, a converging lens L4, a photomultiplier tube, a lock-in amplifier, and a host computer.

[0032] The common end of the dual-source remote module is coupled to the incident end of the monochromator. The monochromator, collimating lens L1, polarizer LX, non-magnetic polarization switching module, and reflector M1 are coaxially arranged as the first optical path. The reflecting surface of reflector M1 is tilted at a 45° angle relative to the exit port of the non-magnetic polarization switching module. The centers of reflector M1, aperture S1, and reflector M2 are coaxially arranged as the second optical path. The first and second optical paths are perpendicular, and the reflecting surface of reflector M2 is tilted at a 45° angle relative to the exit port of aperture S1. The composite broadband light is emitted by the dual-source remote module, and after wavelength selection by the monochromator, a monochromatic beam is output. This monochromatic beam passes sequentially through collimating lens L1 and polarizer LX, enters the non-magnetic polarization switching module, and is modulated into alternating left- and right-hand circularly polarized light, defined as the modulated beam. Subsequently, the modulated beam enters the Π-shaped spatial optical path constructed by four reflecting mirrors (M1, M2, M3, M4): the modulated beam first shines horizontally towards the reflecting mirror M1, is reflected vertically downwards, passes through the aperture S1, and then turns 90° again via the bottom reflecting mirror M2.

[0033] The reflector M2, focusing lens L2, sample, collimating lens L3, and reflector M3 are coaxially arranged as a third optical path. This third optical path is perpendicular to the second optical path and parallel to the first optical path. The reflecting surface of reflector M2 is tilted at a 45° angle relative to the entrance of focusing lens L2, and the reflecting surface of reflector M3 is tilted at a 45° angle relative to the exit of collimating lens L3. The light beam reflected from reflector M2 is focused by focusing lens L2 into the interior of the superconducting magnet, and then horizontally passes through the reaction vessel and the sample inside, located at the center of the magnetic field. The superconducting magnet is a deep-well cylinder with a diameter of 200 mm, and its central region is a reaction vessel with an outer diameter of 52 mm, inside which the sample is placed. The light beam carrying the circular dichroism absorption difference information of the sample is collimated by collimating lens L3 after passing through the sample, and then reflected vertically upwards by reflector M3. In terms of structural arrangement, it is strictly ensured that the right branch of the Π-shaped optical path (i.e., the optical path from the reflector M3 vertically upward through the aperture S2 to the reflector M4) is completely within the effective aperture limit range inside the magnet.

[0034] The centers of mirror M3, aperture S2, and mirror M4 are coaxially arranged to form a fourth optical path, which is perpendicular to the third optical path and parallel to the second optical path. The centers of mirror M4, aperture S3, converging lens L4, and photomultiplier tube are coaxially arranged to form a fifth optical path, which is perpendicular to the fourth optical path. The reflecting surface of mirror M3 is tilted at a 45° angle relative to the entrance of aperture S2, and the reflecting surface of mirror M4 is tilted at a 45° angle relative to the exit of aperture S2 and the entrance angle of aperture S3. The beam reflected from mirror M3 reaches the top mirror M4 after passing through aperture S2, undergoes horizontal deflection again, and finally passes through aperture S3 to filter out stray light, and is then converged by converging lens L4 to the center of the photocathode of the photomultiplier tube (PMT). The photomultiplier tube converts the optical signal into an electrical signal, which, together with the synchronization reference signal from the non-magnetic polarization switching module, is input into a lock-in amplifier. The host computer (PC) then demodulates and calculates the final spectrum.

[0035] like Figure 2As shown, the dual-source remote module includes a xenon lamp, a deuterium lamp, and a Y-type fiber-coupled transmission unit. The xenon and deuterium lamps are positioned in a weak magnetic field region far from the center of the superconducting magnet and are lit simultaneously. The xenon and deuterium lamps are coupled to two branches of the Y-type fiber-coupled transmission unit, and the common end of the Y-type fiber-coupled transmission unit is coupled to the monochromator's incident end. Thus, the broadband continuous light from the xenon lamp and the 190-350 nm ultraviolet-enhanced light from the deuterium lamp are guided into the same wavelength-selective optical path. To overcome the sharp drop in signal-to-noise ratio caused by the limited photon flux of a single xenon lamp in the deep ultraviolet region (200 nm-400 nm), the beam-combining effect of the Y-type fiber waveguide is utilized to physically complement and spatially overlap the energy of the deuterium lamp responsible for the deep ultraviolet region and the xenon lamp responsible for the visible region, ultimately outputting from the trunk end of the Y-type fiber. This design effectively fills the ultraviolet energy trough of the system and improves the incident light intensity in the ultraviolet band without adding a complex dichroic mirror.

[0036] like Figure 3 As shown, the non-magnetic polarization switching module includes polarizers and superachromatic quarter-wave plates (hereinafter referred to as quarter-wave plates) arranged coaxially along the main optical axis of the system, as well as a non-magnetic rotary drive mechanism that drives the fast axis of the quarter-wave plate to switch at high frequency between two angles of +45° and -45° relative to the polarization direction of the incident ray.

[0037] In the optical path arrangement, the polarizer and quarter-wave plate are arranged coaxially and sequentially along the principal optical axis of the system. The monochromatic beam is first incident perpendicularly on the polarizer and modulated into linearly polarized light; then the linearly polarized light is incident perpendicularly on the quarter-wave plate. The quarter-wave plate is fixed inside the rotor of a non-magnetic rotary drive mechanism.

[0038] Because traditional electromagnetic motors (such as stepper motors and voice coil motors) fail or undergo severe magnetization under a 10 T strong magnetic field due to Lorentz force, the non-magnetic rotary drive mechanism designed in this invention completely abandons electromagnetic transmission. Its core utilizes a piezoelectric ultrasonic drive structure and a photoelectric closed-loop control structure. The specific structure is as follows: Piezoelectric ultrasonic stator and rotor: The drive mechanism consists of a fixed base (stator) and a rotatable frame (rotor), both made of non-magnetic materials (such as pure titanium alloy, PEEK, or phosphor bronze). High-frequency piezoelectric ceramic rings (PZT) are mounted on the stator surface. Because the inverse piezoelectric effect of the high-frequency piezoelectric ceramic depends solely on electric field deformation, it is completely unaffected by external strong magnetic fields.

[0039] Friction drive principle: When a specific frequency AC driving voltage is applied to a high-frequency piezoelectric ceramic ring, micron-level traveling wave vibrations are excited on the stator surface. This high-frequency micro-vibration acts on the rotor bottom surface through friction, thereby driving the rotor, which contains quarter-wave plates, to rotate smoothly.

[0040] Photoelectric closed-loop limiting: In order to ensure that the fast axis of the quarter-wave plate can switch precisely at high frequency between two angles of +45° and -45° relative to the polarization direction of the incident line, the outer edge of the rotor of the drive mechanism is integrated with a non-magnetic high-precision photoelectric encoder disk, and a photoelectric sensor is installed on the base (or optical fiber is used to lead the light signal to the outside of the magnetic field for reading).

[0041] When the system is working, the photoelectric sensor reads the scale pulse signal of the photoelectric encoder disk in real time and converts it into a feedback signal indicating the actual angular position of the rotor. The host computer will set the target polarization angle. (Right now or Feedback signal between actual angular position and actual position Perform differential calculations to determine the current angular position deviation in real time. The host computer has a built-in PID algorithm that calculates the angular position deviation value. The amplitude of the driving voltage and the AC driving frequency applied to the piezoelectric ceramic ring are adjusted in real time to drive the rotor to reciprocate (or continuously step) between two mechanical limits of +45° and -45°, with the oscillation frequency controlled between 1-10 Hz. When the quarter-wave plate is at +45°, left-handed circularly polarized light is output; when the quarter-wave plate is at -45°, right-handed circularly polarized light is output, thus realizing pure physical non-magnetic polarization modulation under a strong magnetic field.

[0042] The reaction vessel is equipped with two stirring blades, which are driven by a motor. Specifically, the drive structure includes a pneumatic motor driven by an inert gas and a driving gear and a driven gear that convert the single rotational power into dual-axis counter-rotation. The driving gear and driven gear are driven by the pneumatic motor. The driving gear and driven gear are connected to the stirring blades through insulated transmission shafts. The two stirring blades rotate synchronously in opposite directions, forming an "∞"-shaped convection mixing within the cavity. This convection not only accelerates the flow of the reaction solutions on both sides but also ensures the concentration uniformity of the solution within the 2 mm optical path detection window. The entire gear transmission mechanism is positioned above the sample chamber, strictly avoiding occupying valuable experimental space inside the magnet. To prevent micro-displacement of the reaction cell caused by pneumatic stirring or fluid disturbance, which could lead to optical path offset errors, the device is mechanically rigidly fixed to the outside using non-magnetic, corrosion-resistant nylon screws.

[0043] like Figure 4The diagram shows a schematic of the magnetic shielding detection module, which is mainly used to house the photomultiplier tube (PMT) and shield it from magnetic field interference. The PMT is installed 1 meter from the center of the superconducting magnet, where the measured leakage magnetic field strength before shielding is approximately 200 mT. The PMT is externally shielded by a multi-layered magnetic shielding structure, which, from the inside out, consists of an aluminum alloy layer 1, eight layers of permalloy 2, and an electrical pure iron layer 3. The layers are bonded together with plastic and adhesive. A plastic outer shell is also installed outside the electrical pure iron layer 3. Measurements show that this reduces the residual magnetic field in the core region of the PMT to below 0.3 mT.

[0044] like Figure 5 As shown, the synchronization signal processing module specifically corresponds to Figure 1 The lock-in amplifier and host computer (PC) section are shown. To achieve precise synchronization and absolute quantification of wavelength, polarization, magnetic field, and weak chiral signals under a 10 T strong magnetic field, the internal collaborative operation of this module is described in detail below: The raw, weak electrical signal output by the photomultiplier tube (PMT) is a mixture of alternating current (AC) and a direct current (DC) baseline signal. This mixture is output to a lock-in amplifier (which employs mature commercial high-frequency lock-in demodulation technology) to separate the DC baseline and AC signals. Simultaneously, the host computer synchronously sends a sinusoidal reference signal to the lock-in amplifier, which is exactly the same as the switching frequency of the non-magnetic polarization switching module.

[0045] The Automatic Gain Control (AGC) circuit is a core, self-developed architecture specifically designed to overcome gain suppression under a strong 10 T leakage magnetic field and the drastic intensity variations during wide-spectrum full-scan (200 nm - 800 nm) light. Simple constant high-voltage drive is highly susceptible to detector saturation failure or signal annihilation under alternating extreme magnetic fields and strong light. The AGC circuit is composed of an externally programmable variable resistor connected in series at the photomultiplier tube control terminal and a PI control algorithm running internally in the host computer, forming a hardware-software integrated gain closed-loop adjustment architecture. The host computer reads the DC baseline signal separated by the lock-in amplifier in real time through the data acquisition interface. The host computer compares this DC baseline signal with a set constant absolute reference voltage. A comparison is performed, and the built-in PI control algorithm is used to calculate the error adjustment amount. The host computer is connected to the control terminal of the external programmable variable resistor via a digital communication interface. Based on the error adjustment amount calculated by the PI algorithm, it sends a resistance adjustment command to the programmable variable resistor, changing the resistance value of the programmable variable resistor in real time. This programmable variable resistor is connected in series in the control voltage input circuit of the photomultiplier tube. The dynamic change of the resistance value directly adjusts the control voltage input to the inside of the photomultiplier tube, thereby generating a dynamically changing negative high voltage inside the photomultiplier tube, realizing physical-level real-time control of the electron multiplication gain inside the photomultiplier tube. This closed-loop mechanism forcibly locks the DC signal output of the photomultiplier tube (i.e., locks the denominator of the circular dichroism calculation formula), avoiding signal saturation failure from the physical level and greatly expanding the dynamic measurement range of the instrument.

[0046] The host computer acts as the central hub, coordinating the overall hardware timing. It synchronously sends control commands to the monochromator's wavelength scanning unit and polarization modulation control unit, driving the stepper motor or grating inside the monochromator to perform precise step angle deflections. This allows for the adjustment of the start wavelength, cutoff wavelength, step wavelength, and step duration of the monochromatic light wavelength scan, and drives the non-magnetic rotary drive mechanism. and The system performs high-frequency switching (1-10 Hz) between positions, simultaneously triggering the generation of a sinusoidal reference signal that is completely in phase and frequency with the polarization switching sequence, and synchronously transmitting it to the lock-in amplifier; at the same time, the host computer acquires and records the wavelength data of the current moment in real time through multiple channels. Real-time magnetic field strength data The system uses the AC signal output from the lock-in amplifier and the dynamic high-voltage control data output from the automatic gain control circuit. Finally, the host computer calculates the absolutely quantitative in-situ circular dichroism spectrum. The calculation formula is:

[0047] In the formula, Wavelength data of the lock-in amplifier at the current moment and real-time magnetic field strength data The demodulated AC signal under the condition; A constant absolute reference voltage set for the automatic gain control circuit; For the system at different magnetic field strengths and different PMT negative high voltage Under these conditions, the gain and response nonlinearity correction coefficient matrix is ​​obtained by pre-calibration using a standard chiral sample (such as D-(+)-camphorsulfonic acid). Using the above formula, the host computer, during the full-spectrum scan, utilizes the real-time acquired data... and The dynamic correction coefficient is calculated by looking up the table and interpolating. ,right Millisecond-level real-time numerical correction was performed, enabling absolute quantitative measurement of weak circular dichroism signals under conditions of a 10 T strong magnetic field and rapid changes in broadband light intensity. This included the gain and response nonlinear correction coefficient matrices. The calculation process is as follows: Place a standard chiral substance with a known and highly stable circular dichroic spectrum (such as standard concentration of D-(+)-camphorsulfonic acid, i.e., D-CSA) into the reaction vessel. Set the magnetic field to a fixed value. (like Under each magnetic field, the negative high voltage of the automatic gain control circuit is manually or forcibly changed via software. (like Record the AC signal read from the lock-in amplifier at this time. ; The theoretical circular dichroism spectrum value of the known standard sample By comparing the original value with the measured value, the correction factor on this grid node is calculated:

[0048] All the calculated The data is stored in the database of the host computer software to form a matrix of gain and response nonlinearity correction coefficients. A two-dimensional calibration lookup table.

[0049] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A system for in-situ circular dichroism spectroscopy measurement under a strong magnetic field, characterized in that, The system includes a dual-source remote module, a monochromator, a collimating lens L1, a polarizer LX, a non-magnetic polarization switching module, a reflector M1, an aperture S1, and a reflector M2. The common end of the dual-source remote module is coupled to the incident end of the monochromator. The monochromator, collimating lens L1, polarizer LX, non-magnetic polarization switching module, and reflector M1 are arranged coaxially as the first optical path. The reflector M1, aperture S1, and reflector M2 are arranged coaxially as the second optical path. The first and second optical paths are perpendicular. The reflector M2 and focusing lens L1 are also included.

2. The sample, collimating lens L3, and reflecting mirror M3 are coaxially arranged to form the third optical path, which is perpendicular to the second optical path and parallel to the first optical path. The reflecting mirror M3, aperture S2, and reflecting mirror M4 are coaxially arranged to form the fourth optical path, which is perpendicular to the third optical path and parallel to the second optical path. The reflecting mirror M4, aperture S3, converging lens L4, and photomultiplier tube are coaxially arranged to form the fifth optical path, which is perpendicular to the fourth optical path. The photomultiplier tube converts the optical signal into an electrical signal, which is then switched with non-magnetic polarization. The module's synchronization reference signal is input to the lock-in amplifier, demodulated by the host computer, and the final spectrum is calculated. The dual-source remote module includes a Y-type fiber-coupled transmission unit and xenon and deuterium lamps coupled to its two branches respectively. The xenon and deuterium lamps are positioned at a preset distance away from the center of the superconducting magnet and are lit simultaneously. The common end of the Y-type fiber-coupled transmission unit is coupled to the monochromator's incident end. The non-magnetic polarization switching module includes polarizers and supercomplex achromatic quarter-wave plates arranged coaxially along the system's principal optical axis, and a driving supercomplex achromatic quarter-wave plate. A non-magnetic rotary drive mechanism for oscillating a quarter-wave plate; the non-magnetic rotary drive mechanism includes a stator and a rotor, with a supercomplex achromatic quarter-wave plate fixed inside the rotor of the non-magnetic rotary drive mechanism; a non-magnetic photoelectric encoder disk is integrated on the outer edge of the rotor, and a photoelectric sensor is correspondingly installed on the stator, with a high-frequency piezoelectric ceramic ring attached to the surface of the stator; the host computer reads the position signal of the photoelectric encoder disk and controls the driving voltage of the high-frequency piezoelectric ceramic ring in real time in a closed loop, driving the rotor to oscillate back and forth between two mechanical limits of +45° and -45°.

2. The in-situ circular dichroism spectroscopy measurement system under a strong magnetic field according to claim 1, characterized in that, The reflective surface of the reflector M1 is tilted at a 45° angle relative to the outlet of the non-magnetic polarization switching module.

3. The in-situ circular dichroism spectroscopy measurement system under a strong magnetic field according to claim 1, characterized in that, The reflecting surface of the mirror M2 is tilted at a 45° angle relative to the exit port of the aperture S1, and the reflecting surface of the mirror M2 is tilted at a 45° angle relative to the entrance port of the focusing lens L2.

4. The in-situ circular dichroism spectroscopy measurement system under a strong magnetic field according to claim 1, characterized in that, The reflecting surface of the mirror M3 is tilted at a 45° angle relative to the exit port of the collimating lens L3, and the reflecting surface of the mirror M3 is tilted at a 45° angle relative to the entrance port of the aperture S2.

5. The in-situ circular dichroism spectroscopy measurement system under a strong magnetic field according to claim 1, characterized in that, The reflecting surface of the reflector M4 is tilted at a 45° angle relative to the exit port of the aperture S2 and at a 45° angle relative to the incident angle of the aperture S3.

6. The in-situ circular dichroism spectroscopy measurement system under a strong magnetic field according to claim 1, characterized in that, The sample is placed inside a reaction vessel, which is equipped with two stirring blades that are driven to rotate by a motor.

7. The in-situ circular dichroism spectroscopy measurement system under a strong magnetic field according to claim 1, characterized in that, The photomultiplier tube is installed 1m away from the center of the superconducting magnet. The photomultiplier tube is equipped with a multi-layer magnetic shielding structure. The multi-layer magnetic shielding structure includes an aluminum alloy layer, eight layers of permalloy, and an electrical pure iron layer from the inside out. The layers are bonded together with plastic and adhesive.

8. A method applied to an in-situ circular dichroism spectroscopy measurement system under a strong magnetic field as described in any one of claims 1-7, characterized in that, The method includes: The electrical signal output by the photomultiplier tube is a mixture of AC signal and DC baseline signal. The mixed signal is output to the lock-in amplifier to separate the DC baseline signal and AC signal. At the same time, the host computer synchronously sends a sinusoidal reference signal that is completely consistent with the switching frequency of the non-magnetic polarization switching module to the lock-in amplifier. The automatic gain control circuit acquires the DC baseline signal in real time, performs high-frequency differential comparison between the DC baseline signal and the constant absolute reference voltage set by the system, calculates the error in real time using the PI control algorithm, and dynamically adjusts the negative high voltage applied to the photomultiplier tube through the PI loop. The host computer collects and records wavelength data in real time. Real-time magnetic field strength data The AC signal output from the lock-in amplifier and the negative high voltage dynamically output from the automatic gain control circuit are used to calculate the absolutely quantitative in-situ circular dichroism spectrum. The calculation formula is: In the formula, Wavelength data of the lock-in amplifier at the current moment and real-time magnetic field strength data The demodulated AC signal under the condition; A constant absolute reference voltage set for the automatic gain control circuit; For the system at different magnetic field strengths and different negative high pressure Under these conditions, the gain and response nonlinearity correction coefficient matrices are obtained by pre-calibrating with standard chiral samples.

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