Optical levitation system-based electric field tilt detection and correction device and method

Abstract

The application discloses an electric field tilt detection and correction device and method based on an optical suspension system and belongs to the technical field of optical tweezers. The device reflects and converges a single laser propagating horizontally to form an optical trap capturing a microsphere vertically upward, and enables the suspended microsphere to be stably suspended under high vacuum through a feedback cooling technology; one electrode plate is placed on the upper and lower parts of the suspended microsphere respectively; an alternating voltage is applied to the two parallel electrode plates, the multi-axis displacement table is adjusted according to the power spectrum density signal of the XYZ three-axis movement of the microsphere and the electric field intensity amplitude, so that the posture of the parallel electrode plates is controlled, and the electric field formed by the parallel electrode plates is vertical. The application realizes high-precision electric field tilt detection and correction, is simple and convenient to operate, provides guarantee for higher-precision electric field measurement and weak force value measurement, and has a wide range of application scenarios.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical tweezers, and particularly relates to an electric field tilt detection and correction device and method based on an optical suspension system. BACKGROUND

[0002] With the progress of modern science and technology, the accurate measurement of the absolute value of nN-level and pN-level force has become a focus of attention. The measurement and traceability of micro-weak force play an extremely important role in the quality assurance of industrial production and academic research. In particular, the research on piconewton-level micro-force value measurement technology has been listed as a development priority.

[0003] In recent years, due to the characteristics of super-high sensitivity and miniaturization potential of the optical suspension system, it has unique advantages in high-precision extremely weak force sensing. It has been reported that the force sensitivity of the suspended microsphere reaches 10 -21 N / Hz 1 / 2 orders of magnitude, which is one of the means that can achieve the highest precision measurement of fundamental physical quantities such as mass, force, and magnetic field.

[0004] There are also many practical applications of optical suspension systems for measuring micro-weak force in the prior art. For example, patent CN117310832A discloses a wavelength division multiplexing capture and extremely weak force measurement device and method of single-beam vacuum optical trap, which uses a suspended optical force system and an electric field to measure the gravity of a microsphere. Patent CN117331134A discloses an optical fiber capture and measurement device and method of single-beam vacuum optical trap, which uses optical fiber to miniaturize the suspended optical force system and measures and traces the gravity of the microsphere. In addition, it has been reported that a microsphere can be suspended in a high vacuum environment, and the mass of the microsphere can be measured with high precision by using electrostatic force-optical force co-suspension technology (Blakemore, Charles P., et al. "Precision mass and density measurement of individual optically levitated microspheres." Physical Review Applied 12.2 (2019): 024037.). The uncertainty can reach 1.8%. It can be seen that the method and device for measuring weak force value based on electric field and optical suspension system have been widely applied in the field of sensing.

[0005] However, the gravity of μm-scale microspheres is generally in the pN range. To calibrate their gravity by electric field force, it is necessary to ensure that the direction of the electric field force is consistent with the direction of gravity of the microspheres. The existing electric field force calibration method usually applies a voltage of known frequency and known amplitude to a set of parallel electrode plates to generate an electric field force on the microspheres. However, in reality, due to the installation error of the parallel electrode plates, there is an angle between the direction of the electric field and the direction of the captured laser beam, resulting in the direction of the electric field force applied to the microspheres and the direction of gravity of the microspheres not being strictly consistent. There are electric field components in other directions, which leads to errors in the final gravity calibration of the microspheres. Summary of the Invention

[0006] In order to overcome the shortcomings of the existing technology, the present invention proposes an electric field tilt detection and correction device and method based on an optical suspension system. A vertically upward single-beam optical suspension system that can operate in a high vacuum is adopted. The optical suspension system is used to capture micron-scale silica spheres, and a group of parallel electrode plates are placed above and below the capture area. The electric field tilt detection and correction are achieved by analyzing the movement state of the spheres in the electric field generated by the parallel electrode plate group.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention provides an electric field tilt detection and correction device based on an optical suspension system, comprising:

[0009] a laser for emitting a laser beam;

[0010] An optical power stabilization module is installed in the laser optical path and is used to stabilize the optical power intensity of the laser emitted by the laser;

[0011] A first beam splitting module is used to split the stabilized laser into two perpendicular beams, one for capturing and suspending the microspheres, and the other for capturing a reference beam B for comparison. The captured beam A passes through the electric field tilt detection control module and then enters the signal detection and processing module, while the captured reference beam B directly enters the signal detection and processing module.

[0012] An electric field tilt detection and control module, designed based on an optical suspension system, includes a signal generator, a vacuum chamber, a lens assembly within the vacuum chamber, a reflector, and an attitude-adjustable parallel electrode plate assembly based on a multi-axis translation stage. The signal generator is connected to a pair of parallel electrode plates in the parallel electrode plate assembly and is used to apply an AC voltage to the parallel electrode plates. Light emitted from the electric field tilt detection and control module is divided into a vertical beam coaxial with the output optical axis and a horizontal beam perpendicular to the output optical axis, which respectively enter a laser vertical correction module and a signal detection and processing module.

[0013] A laser vertical correction module, which is used to correct the vertical light beam emitted by the electric field tilt detection control module;

[0014] The signal detection and processing module is used to analyze the collected capture light beam A and capture reference beam B, demodulate the time domain signal of the simple harmonic motion of the microsphere in the three directions of X, Y, and Z and output the power spectrum density curve of the motion in the three directions of X, Y, and Z, calculate the electric field intensity amplitude in the three directions of X, Y, and Z, and adjust the posture-adjustable parallel electrode plate assembly according to the power spectrum density curve and the electric field intensity amplitude until the power spectrum density curve of the motion in the three directions of X, Y, and Z does not have a peak at the frequency of the AC voltage and the electric field intensity amplitude in the three directions of X, Y, and Z is zero.

[0015] Preferably, the optical power stabilization module includes a first acousto-optic modulator, a first beam splitter, a first detector and a light intensity modulator, wherein the first acousto-optic modulator is connected to the light output end of the laser, and the laser emitted by the laser is modulated by the acousto-optic modulator and then passes through the first beam splitter, wherein the light reflected by the first beam splitter is incident on the first detector, the first detector, the light intensity modulator and the first acousto-optic modulator are connected in sequence through a signal line, and the light transmitted through the first beam splitter is transmitted to the first beam splitting module.

[0016] Preferably, the laser light after power stabilization passes through the second acousto-optic modulator and the second beam splitter in sequence, and the second acousto-optic modulator is used to modulate the light intensity of the stabilized laser light; the light transmitted through the second beam splitter is used as the captured reference beam B, and the light reflected by the second beam splitter is used as the captured beam A. The captured beam A passes through the galvanometer 8 and enters the electric field tilt detection control module, and the pitch angle and deflection angle of the galvanometer are adjustable.

[0017] Preferably, the signal detection and processing module includes a second detector and a controller connected thereto, and the controller is also connected to the second acousto-optic modulator and the galvanometer in the first beam splitting module; the second detector is a four-quadrant detector.

[0018] Preferably, the lens group includes a focusing lens and a collecting lens. The focusing lens is located on the front optical path in the vacuum chamber, and focuses the capture light beam A entering the electric field tilt detection control module. The focused capture light beam A then passes through the reflector and enters the parallel electrode plate assembly; the collecting lens is located on the rear optical path in the vacuum chamber, and collects the light emitted from the parallel electrode plate assembly before emitting it from the vacuum chamber.

[0019] Preferably, the posture-adjustable parallel electrode plate assembly includes an electrode plate fixing frame, a pair of parallel electrode plates fixed on the electrode plate fixing frame, a microsphere located between the pair of parallel electrode plates, and a multi-axis displacement platform for adjusting the posture of the electrode plate fixing frame; the pair of parallel electrode plates are designed to be perpendicular to the optical path.

[0020] Preferably, the distance between the pair of parallel electrode plates is 4-25 mm, and a small hole for the capture light beam to pass through is provided at the center of the upper electrode plate and the lower electrode plate, and the diameter of the small hole is 2-5 mm.

[0021] Preferably, the laser vertical correction module includes a first corner cube prism, a second corner cube prism, a liquid level mirror, a second beam splitter, a plano-convex lens and a CMOS; the captured light beam A emitted from the electric field tilt detection control module is split into two by the first beam splitter, and the vertical light beam transmitted through the second beam splitter is then transmitted through the second beam splitter to form a liquid level beam C and reflected to form a liquid level reference beam D; the liquid level beam C is reflected by the first corner cube prism to the liquid level mirror surface parallel to the horizontal plane, and then reflected from the liquid level mirror surface and returned through the first corner cube prism and the second beam splitter in sequence, and the returned liquid level beam C is then reflected by the second beam splitter to the plano-convex lens and focused to the CMOS by the plano-convex lens; the liquid level reference beam D is reflected by the second corner cube prism, and then transmitted through the second beam splitter and focused to the CMOS by the plano-convex lens; the plano-convex lens is at an angle of 90° to the horizontal plane, and the CMOS is placed at the focal position of the plano-convex lens.

[0022] Preferably, the microspheres are charged, made of a material transparent to laser light, and have a diameter of 1-25 μm.

[0023] In a second aspect, the present invention further proposes a method for detecting and correcting electric field tilt applied to the above-mentioned device. The method adjusts a multi-axis translation stage based on the power spectrum density signal of the microsphere's XYZ three-axis motion and the electric field intensity amplitude, thereby controlling the posture of the parallel electrode plates so that the electric field formed by the parallel electrode plates is vertical. The method comprises:

[0024] 1) Turn on the laser, adjust the galvanometer and the reflector in the electric field tilt detection control module until the liquid surface beam C and the liquid surface reference beam D focused on the CMOS in the laser vertical correction module coincide at the center of the image; place a light baffle between the first beam splitter and the second beam splitter, and then use a piezoelectric ceramic support method to capture and suspend the microsphere between the upper and lower electrode plates of the parallel electrode plate group by the capture beam A;

[0025] 2) The second detector in the signal detection and processing module collects the optical signals of the capture beam A and the capture reference beam B in real time, converts them into electrical signals, and transmits them to the controller in real time;

[0026] 3) Pumping down the vacuum chamber in the electric field tilt detection control module until a set vacuum threshold is reached. During the pumping process, the controller continuously fine-tunes the second acousto-optic modulator and the galvanometer mirror to ensure that the microsphere is stably suspended in the center of the parallel electrode plate assembly.

[0027] 4) Apply a frequency of ω to the parallel electrode platesdr , amplitude is 200-400V pp An AC voltage is applied to the parallel electrode plates, thereby forming an AC electric field between the parallel electrode plates, causing the microsphere 13 to perform simple harmonic motion under the action of the AC electric field; the controller demodulates the time domain signal of the simple harmonic motion of the microsphere in the XYZ directions and outputs the power spectrum density curve of the motion in the XYZ directions, and calculates the electric field intensity amplitude in the XYZ directions;

[0028] If the power spectrum density curve in the XY direction is dr If there is no peak at the frequency and the electric field strength amplitude in the XY direction is zero, it means that the electric field is vertical; otherwise, it means that the electric field is tilted. According to the calculation results, perform step 5) to adjust the posture of the parallel electrode plate assembly:

[0029] 5) The power spectrum density curve in the X direction only is dr When there is a peak at the frequency, adjust the X-direction deflection angle of the multi-axis translation stage until the power spectrum density curve in the X direction is at ω dr The peak at the frequency disappears, and the electric field intensity amplitude in the X direction is zero;

[0030] Only the power spectrum density curve in the Y direction is dr When there is a peak at the frequency, adjust the Y-direction deflection angle of the multi-axis translation stage until the power spectrum density curve in the Y direction is at ω dr The peak at the frequency disappears, and the electric field intensity amplitude in the Y direction is zero;

[0031] The power spectrum density curve in the XY direction is dr When there are peaks at all frequencies, first adjust the X-direction deflection angle of the multi-axis translation stage until the power spectrum density curve in the X direction is at ω dr The peak amplitude at the frequency cannot be further reduced; then adjust the Y-direction deflection angle of the multi-axis translation stage until the power spectrum density curve in the Y direction is at ω dr The peak amplitude at the frequency cannot be further reduced; alternately adjust the X-direction deflection angle and the Y-direction deflection angle of the multi-axis translation stage until the power spectrum density curve in the XY direction is at ω dr There is no peak at any frequency, and the electric field strength amplitude in the XY direction is zero.

[0032] The beneficial effects of the present invention are:

[0033] (1) The present invention reflects and converges a horizontally propagating single laser beam to form a vertically upward light trap to capture microspheres, and uses feedback cooling technology to enable the suspended microspheres to be stably suspended under high vacuum; a set of parallel electrode plates are placed above and below the suspended microspheres, and by analyzing the movement state of the microspheres in the electric field generated by the parallel electrode plate group, very high-precision electric field tilt detection and correction can be achieved, and the operation is simple and convenient.

[0034] (2) The present invention can be applied to existing mass, density, and weak force measurement systems based on electric fields and optical levitation. In devices that utilize electric fields and optical levitation systems to measure tiny signals such as mass, density, extremely weak forces, and acceleration, the tilt detection and correction of the electric field can ensure that the direction of the electric field vector is consistent with the direction of the detected signal vector, resulting in more accurate measurement results and lower uncertainty. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of the electric field tilt detection and correction device based on the optical suspension system used in the present invention;

[0036] Wherein: laser 1, first acousto-optic modulator 2, first beam splitter 3, first detector 4, light intensity modulator 5, second acousto-optic modulator 6, second beam splitter 7, galvanometer 8, focusing lens 9, reflecting mirror 10, parallel electrode plate group 11, electrode plate fixing frame 12, microsphere 13, multi-axis translation stage 14, collecting lens 15, vacuum chamber 16, signal generator 17, first corner cube prism 18, second corner cube prism 19, liquid level mirror 20, second beam splitter 21, plano-convex lens 22, CMOS 23, second detector 24, controller 25, first beam splitter 26;

[0037] Figure 2 The power spectrum density curves of the electric field in the X direction obtained by the electric field tilt detection and correction device based on the optical suspension system of the present invention are obtained when the electric field is tilted and when the electric field is not tilted in the X direction;

[0038] Figure 3 The present invention uses an electric field tilt detection and correction device based on an optical suspension system to obtain a power spectrum density curve when the electric field is in a vertical state; DETAILED DESCRIPTION

[0039] The present invention will be further described and illustrated below in conjunction with specific embodiments. The embodiments are merely illustrative of the present disclosure and do not limit its scope. The technical features of the various embodiments of the present invention may be combined accordingly, provided that there is no conflict between them.

[0040] like Figure 1 The electric field tilt detection and correction device based on the optical suspension system shown includes the following parts:

[0041] Laser 1, first acousto-optic modulator 2, first beam splitter 3, first detector 4, light intensity modulator 5, second acousto-optic modulator 6, second beam splitter 7, galvanometer 8, focusing lens 9, reflecting mirror 10, parallel electrode plate group 11, electrode plate fixing frame 12, microsphere 13, multi-axis translation stage 14, collecting lens 15, vacuum chamber 16, signal generator 17, first corner cube prism 18, second corner cube prism 19, liquid level mirror 20, second beam splitter 21, plano-convex lens 22, CMOS 23, second detector 24, controller 25, first beam splitter 26; the second detector 24 is a four-quadrant detector.

[0042] In the above device, the laser 1 is used as a light source, the wavelength of the emitted laser is 1064nm, and the optical power is 0-5W. An optical power stabilization module consisting of a first acousto-optic modulator 2, a first beam splitter 3, a first detector 4, and an optical intensity modulator 5 is placed in front of the laser outlet, which is used to stabilize the optical power intensity of the laser emitted by the laser 1; the first acousto-optic modulator 2 is connected to the optical output end of the laser 1, and the laser emitted by the laser 1 is modulated by the acousto-optic modulator 2 and then passes through the first beam splitter 3. The first detector 4 demodulates the light reflected by the first beam splitter 3 into a voltage signal and transmits it to the optical intensity modulator 5 through a signal line. The optical intensity modulator 5 analyzes and modulates the signal transmitted by the first detector 4 and reflects it. The laser beam is fed to the acousto-optic modulator 2, so that the peak-to-peak value of the power fluctuation of the laser light emitted from the laser 1 is reduced after passing through the acousto-optic modulator 2; then the laser light after power stabilization passes through the second acousto-optic modulator 6 and the second beam splitter 7 in sequence, and the second acousto-optic modulator 6 is used to modulate the light intensity of the laser light after power stabilization by the optical power stabilization module; the second beam splitter 7 reflects the laser light after power stabilization to form a capture beam A for capturing and suspending the microsphere 13, and transmits it to form a capture reference beam B for comparison; the reference beam B is directly transmitted to the second limit detector 24; the capture beam A is reflected by the galvanometer 8 with an angular resolution of 0.004 to 0.1urad and a scanning range of ±2° and then enters the vacuum chamber 16.

[0043] A focusing lens with a focal length of 20-100 mm and a reflector 10 with a 45° angle to the horizontal plane are placed in sequence along the optical path in the vacuum chamber 16. A parallel electrode plate group 11 is placed directly above the reflector 10 at a distance of 4-20 mm. A small hole with a diameter of 2-5 mm is opened in the center of the parallel electrode plate group to capture the transmission of the light beam A. The parallel electrode plate group 11 is fixed to an electrode plate fixing frame 12. The electrode plate fixing frame 12 ensures that the upper and lower electrode plates of the parallel electrode plate group 11 are parallel. The upper and lower electrode plates are connected to a signal generator 17. The electrode plate fixing frame 12 is mounted on a multi-axis translation stage 14, which is used to control the horizontal and vertical position movement of the parallel electrode plate group 11 in the vacuum chamber 16 with high precision, as well as the rotational movement of the parallel electrode plate group 11 in the horizontal and vertical planes with high precision. In this embodiment, the multi-axis translation stage 14 has a repeatability of 0.1 to 0.5 μm in horizontal and vertical movement and a repeatability of 1 to 5 urad in angular deflection. A collecting lens 15 with a focal length of 20 to 100 mm is placed above the electrode plate fixing frame 12.

[0044] In the above-mentioned vacuum chamber 16, the captured light beam A passes through the focusing lens 9 and is reflected by the reflector 10, passes through the center of the small holes of the lower electrode plate and the upper electrode plate of the parallel electrode plate group 11, is collected by the collecting lens 15, and then emitted from the vacuum chamber 16. The captured light beam A emitted from the vacuum chamber 16 passes through a first beam splitter 26 at an angle of 45° to the horizontal plane. The light transmitted through the first beam splitter 26 is then transmitted through a second beam splitter 21 at an angle of 45° to the horizontal plane to form a liquid surface light beam C and reflected to form a liquid surface reference light beam D. The liquid surface light beam C is reflected by the first corner cube prism 18 to the surface of the liquid surface mirror 20 parallel to the horizontal plane, and then reflected from the surface of the liquid surface mirror 20 and returned through the first corner cube prism 18 and the second beam splitter 21 in sequence. The returned liquid surface light beam C is then reflected by the second beam splitter 21 to a plano-convex lens 22 with a focal length of 50-100 mm, and is focused by the plano-convex lens 22 to a CMOS 23 with 2 million to 5 million pixels. At this time, it is transmitted through the second beam splitter 21 The returned liquid surface light beam does not need to be processed; the liquid surface reference light beam D is reflected by the second corner cone prism 19, then transmitted through the second beam splitter 21 and focused to CMOS23 by the plano-convex lens 22. At this time, the reference light beam reflected and returned by the second beam splitter 21 does not need to be processed; the plano-convex lens 22 is at an angle of 90° to the horizontal plane, and CMOS23 is placed at the focal position of the plano-convex lens 22; the pitch angle and deflection angle of the galvanometer 8 and the reflector 10 are adjusted according to the imaging position of the liquid surface light beam C and the reference light beam D on CMOS23 until the center positions of the imaging of the liquid surface light beam C and the liquid surface reference light beam D on CMOS23 coincide, which ensures that the captured light beam A propagates in the vertical direction after being reflected by the reflector 10. A light baffle is then placed between the first beam splitter 26 and the second beam splitter 21 to block the liquid surface light beam transmitted through the second beam splitter 21 and the liquid surface reference light beam reflected back by the second beam splitter. A piezoelectric ceramic support method is then used to allow the microsphere 13 to be captured and suspended by the capture light beam A between the upper and lower electrode plates of the parallel electrode plate set.

[0045] At the same time, the captured light beam A emitted from the vacuum chamber 16 and reflected by the second spectrometer 26 is directly transmitted to the second detector 24. The second detector 24 and the controller 25 are connected through a signal line, and the controller 25 is respectively connected to the second acousto-optic modulator 6 and the galvanometer 8 through a signal line.

[0046] The second detector 24 is a four-quadrant detector, which is used to receive the optical signal of the capture light beam A and the optical signal of the capture reference beam B, convert them into corresponding electrical signals, and then transmit them to the controller 25; the controller 25 is used to analyze and compare the electrical signals transmitted by the second detector 24, and modulate the bias voltage of the acousto-optic modulator 6 according to the comparison results to modulate the optical power of the capture light beam A, so that the position of the microsphere 13 in the optical axis direction in the light trap area does not shift; and control the pitch angle and deflection angle of the galvanometer 8 according to the analysis and comparison results, thereby changing the XY direction position of the capture light beam A incident on the vacuum chamber 16, so that the XY direction position of the microsphere 13 in the light trap area does not shift.

[0047] Based on the above electric field tilt detection and correction device, a method for realizing electric field tilt detection and correction is provided. Figure 2 The power spectrum density curves of the electric field detected by the electric field tilt detection and correction device based on the optical suspension system are shown in FIG. 1 , when the electric field is tilted in the X direction and when it is not tilted. In this embodiment, the driving voltage frequency ω applied to the parallel electrode plate group 11 is dr is 71Hz, Figure 2 The power spectrum density curve in (a) is at the driving voltage frequency ω dr There is a peak at , indicating that the electric field is tilted in the X direction; Figure 2 The curve in (b) is dr There is no peak at the X direction and the electric field intensity is zero, indicating that the electric field does not have an inclination in the X direction. The method of the present invention mainly includes the following steps:

[0048] Step S1, first follow Figure 1 Build an electric field tilt detection and correction device based on the optical suspension system to ensure that the captured light beam A propagates in the vertical direction after being reflected by the reflector 10, and use a light shield placed between the first beam splitter 26 and the second beam splitter 21;

[0049] Step S2, the microsphere 13 is vibrated and dropped by means of a piezoelectric ceramic support, so that it is captured by the light trap formed by the capture light beam A between the parallel electrode plate group 11 and stably suspended;

[0050] In step S3, after the microsphere 13 is captured by the light trap, the vacuum chamber 16 starts operating until the vacuum level reaches a set threshold value. In this embodiment, the vacuum level threshold value is 1e-6 mbar. While the vacuum chamber is operating, the second limit detector 24 collects the three-dimensional motion signal formed by the capture beam A and the microsphere 13, and the reference signal formed by the capture reference beam B, in real time, and transmits them to the controller 25 for analysis. The controller 25 fine-tunes the bias voltage of the acousto-optic modulator 6 and controls the pitch and deflection angles of the galvanometer 8 by analyzing the electrical signal transmitted by the second limit detector 24, thereby performing motion cooling on the microsphere 13 in the vertical and horizontal directions, thereby achieving stable suspension of the microsphere 13 in the central area of ​​the parallel electrode plate group 11. Since the microsphere moves only at the nm level in the xy direction, the adjustment of the galvanometer in this step is very small, and the effect on the verticality of the optical path is negligible.

[0051] Step S4: After the microspheres 13 are stably suspended at the set vacuum threshold, a voltage with a frequency of ωd is applied to the parallel electrode plate group 11. r , amplitude is 200-400V pp The AC voltage will form a simple harmonic oscillation electric field E(t)=E0cos(ω dr t), where E0 is the amplitude constant of the electric field, so the microsphere will be subjected to a simple harmonic oscillation electric field force F el (t); then the motion equation of the microsphere in this electric field can be obtained by the following formula (taking the motion equation in the X direction as an example):

[0052]

[0053] Where m is the mass of the microsphere, x is the displacement of the microsphere in the X direction, Γ is the damping rate of the microsphere, k is the stiffness of the light trap, and F th (t) is the random force of residual gas molecules collision on the microsphere, F th (t) = ση(t), where η(t) has a Gaussian probability distribution and satisfies <η(t)η(t+t′)> = δ(t′). σ is related to the damping through the fluctuation-dissipation theorem: Where kB is the Boltzmann constant, T is the thermal margin temperature; F el (t) is the electric field force on the microsphere, F el (t) = F0cos(ω dr t), F0=Nq e E0, N is the number of elementary charges carried by the microsphere, q e is the elementary charge;

[0054] Performing Fourier transform on the above formula, we can get:

[0055]

[0056] S x (ω) is the unilateral power spectrum density, is the unilateral power spectral density caused by thermal noise, is the unilateral power spectrum density corresponding to the electric field force, τ represents the sampling time, ωω x represents the resonant frequency of the microsphere's motion in the X direction in the optical trap;

[0057] Then the electric field amplitude E of the microsphere in the X direction is x It can be expressed as:

[0058]

[0059] The signal detection and processing module will convert the above S i (ω), and E i , demodulated and output to the front-end computer interface for display, where i = x, y, z represents any direction in the three directions of XYZ;

[0060] Step S5, according to the demodulation result analysis of the signal detection processing module in step S4, if only S z (ω) in ω dr The peak value appears at the frequency, and S x (ω) and S y (ω) spectrum line on ω dr When there is no peak at the frequency, and E x and E y The electric field strength amplitude is zero, indicating that the electric field is vertical, such as Figure 3 As shown, Figure 3 (a) to (c) represent the vertical electric field and the driving electric field frequency ω. dr When , the power spectrum density curve of the microsphere 13 moving in the X, Y, and Z directions; on the contrary, it means that the electric field is tilted;

[0061] Step S6, when only S x (ω) and S z (ω) spectrum line on ωd r When a peak appears at the frequency, it means that the electric field is tilted toward the X direction. Adjust the X-direction deflection angle of the multi-axis translation stage 14 until S x (ω) spectrum line on ω dr The peak at the frequency disappears, and E x The electric field strength amplitude is zero;

[0062] Step S7, when only S y (ω) and S z (ω) spectrum line on ω drWhen a peak appears at the frequency, it means that the electric field is tilted toward the Y direction. Adjust the Y-direction deflection angle of the multi-axis translation stage 14 until S y (ω) spectrum line on ω dr The peak at the frequency disappears, and E y The electric field strength amplitude is zero;

[0063] Step S8, when S x (ω), S y (ω) and S z (ω) spectrum line on ω dr When peaks appear at all frequencies, it means that the electric field is tilted in both X and Y directions. First, adjust the X-direction deflection angle of the multi-axis translation stage 14 until S x (ω) spectrum line on ω dr The peak amplitude at the frequency cannot be further reduced; then adjust the Y-direction deflection angle of the multi-axis translation stage 14 until S y (ω) spectrum line on ω dr The peak amplitude at the frequency cannot be further reduced;

[0064] Step S9, repeat the operation in step S8 until S x (ω), S y (ω) in ω dr There is no peak at any frequency, and E x and E y The electric field strength amplitude is zero;

[0065] The present invention determines whether the electric field is tilted and corrects it according to the power spectrum density response curve of the suspended microspheres in the simple harmonic electric field and the detected electric field amplitude, and the operation is simple and convenient.

[0066] This invention can be applied to existing electric field and optical levitation-based measurement systems for mass, density, and weak forces. In devices that utilize electric field and optical levitation systems to measure tiny signals such as mass, density, extremely weak forces, and acceleration, electric field tilt detection and correction ensures that the direction of the electric field vector aligns with the direction of the detected signal vector, resulting in more accurate measurements and lower uncertainty.

[0067] The above-described embodiments merely illustrate several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. Persons skilled in the art will readily appreciate that variations and modifications may be made without departing from the scope of the present invention, all of which fall within the scope of protection of the present invention.

Claims

1. An electric field tilt detection and correction device based on an optical suspension system, characterized in that: include: a laser (1) for emitting a laser beam; An optical power stabilization module is installed in the laser optical path and is used to stabilize the optical power intensity of the laser emitted by the laser (1); A first beam splitting module is used to split the stabilized laser into two perpendicular beams, one for capturing and suspending the microsphere (13) and the other for capturing a reference beam B for comparison. The captured beam A enters the signal detection and processing module after passing through the electric field tilt detection control module, and the captured reference beam B directly enters the signal detection and processing module. An electric field tilt detection control module is designed based on an optical suspension system and includes a signal generator (17), a vacuum chamber (16), a lens group located in the vacuum chamber, a reflector (10), and a parallel electrode plate assembly with adjustable posture based on a multi-axis displacement stage (14); the signal generator (17) is connected to a pair of parallel electrode plates in the parallel electrode plate assembly and is used to apply an AC voltage to the parallel electrode plates; light emitted from the electric field tilt detection control module is divided into a vertical beam coaxial with the output optical axis and a horizontal beam perpendicular to the output optical axis, and enters a laser vertical correction module and a signal detection processing module respectively; A laser vertical correction module, which is used to correct the vertical light beam emitted by the electric field tilt detection control module; A signal detection and processing module is used to analyze the captured capture light beam A and the captured reference light beam B, demodulate the time domain signal of the simple harmonic motion of the microsphere (13) in the X, Y, and Z directions and output the power spectrum density curve of the motion in the X, Y, and Z directions, calculate the electric field intensity amplitude in the X, Y, and Z directions, and adjust the attitude-adjustable parallel electrode plate assembly according to the power spectrum density curve and the electric field intensity amplitude until the power spectrum density curve of the motion in the X, Y, and Z directions does not have a peak at the frequency of the AC voltage and the electric field intensity amplitude in the X, Y, and Z directions is zero.

2. The electric field tilt detection and correction device based on the optical suspension system according to claim 1, characterized in that: The optical power stabilization module comprises a first acousto-optic modulator (2), a first beam splitter (3), a first detector (4) and an optical intensity modulator (5); the first acousto-optic modulator (2) is connected to the optical output end of the laser (1); the laser light emitted by the laser (1) is modulated by the acousto-optic modulator (2) and then passes through the first beam splitter (3); the light reflected by the first beam splitter (3) is incident on the first detector (4); the first detector (4), the optical intensity modulator (5) and the first acousto-optic modulator (2) are connected in sequence through a signal line; the light transmitted through the first beam splitter (3) is transmitted to the first beam splitter module.

3. The electric field tilt detection and correction device based on the optical suspension system according to claim 1, characterized in that: The first beam splitting module comprises a second acousto-optic modulator (6), a second beam splitter (7) and a galvanometer (8); the stabilized laser light passes through the second acousto-optic modulator (6) and the second beam splitter (7) in sequence; the second acousto-optic modulator (6) is used to perform light intensity modulation on the stabilized laser light; the light transmitted through the second beam splitter (7) is used as a captured reference beam B, and the light reflected by the second beam splitter (7) is used as a captured beam A; the captured beam A enters the electric field tilt detection control module after passing through the galvanometer (8); the pitch angle and deflection angle of the galvanometer (8) are adjustable.

4. The electric field tilt detection and correction device based on the optical suspension system according to claim 3, characterized in that: The signal detection and processing module includes a second detector (24) and a controller (25) connected thereto. The controller (25) is also connected to a second acousto-optic modulator (6) and a galvanometer (8) in the first beam splitting module. The second detector (24) is a four-quadrant detector.

5. The electric field tilt detection and correction device based on the optical suspension system according to claim 1, characterized in that: The lens group comprises a focusing lens (9) and a collecting lens (15). The focusing lens (9) is located on a front optical path in a vacuum chamber (16) and focuses a captured light beam A entering an electric field tilt detection control module. The focused captured light beam A then passes through a reflector (10) and enters a parallel electrode plate assembly. The collecting lens (15) is located on a rear optical path in the vacuum chamber (16) and collects light emitted from the parallel electrode plate assembly before emitting the light from the vacuum chamber (16).

6. The electric field tilt detection and correction device based on the optical suspension system according to claim 1, characterized in that: The posture-adjustable parallel electrode plate assembly comprises an electrode plate fixing frame (12), a pair of parallel electrode plates fixed on the electrode plate fixing frame (12), a microsphere (13) located between the pair of parallel electrode plates, and a multi-axis displacement stage (14) for adjusting the posture of the electrode plate fixing frame (12); the pair of parallel electrode plates are designed to be perpendicular to the optical path.

7. The electric field tilt detection and correction device based on the optical suspension system according to claim 6, characterized in that: The distance between the pair of parallel electrode plates is 4-25 mm. A small hole for the capture light beam to pass through is opened at the center of the upper electrode plate and the lower electrode plate. The diameter of the small hole is 2-5 mm.

8. The electric field tilt detection and correction device based on the optical suspension system according to claim 4, characterized in that: The laser vertical correction module comprises a first corner cube prism (18), a second corner cube prism (19), a liquid level mirror (20), a second beam splitter (21), a plano-convex lens (22) and a CMOS (23); a captured light beam A emitted from the electric field tilt detection control module is split into two by the first beam splitter (26); a vertical light beam transmitted through the second beam splitter (26) is transmitted through the second beam splitter (21) to form a liquid level light beam C and is reflected to form a liquid level reference light beam D; the liquid level light beam C is reflected by the first corner cube prism (18) to the surface of the liquid level mirror (20) parallel to the horizontal plane, and then is reflected from the first beam splitter (21) to form a liquid level reference light beam D. The liquid surface mirror (20) reflects and returns through the first corner cube prism (18) and the second beam splitter (21) in sequence. The returned liquid surface light beam C is then reflected by the second beam splitter (21) to the plano-convex lens (22) and focused by the plano-convex lens (22) to the CMOS (23). The liquid surface reference light beam D is reflected by the second corner cube prism (19), then transmitted through the second beam splitter (21) and focused by the plano-convex lens (22) to the CMOS (23). The plano-convex lens (22) forms an angle of 90° with the horizontal plane, and the CMOS (23) is placed at the focal position of the plano-convex lens (22).

9. The electric field tilt detection and correction device based on the optical suspension system according to claim 1, characterized in that: The microspheres (13) are charged, made of a material transparent to laser light, and have a diameter of 1-25 μm.

10. A method for detecting and correcting electric field tilt applied to the device according to claim 8, characterized in that: include: 1) Turn on the laser (1), adjust the galvanometer (8) and the reflector (10) in the electric field tilt detection control module until the liquid surface beam C and the liquid surface reference beam D focused on the CMOS (23) in the laser vertical correction module coincide at the center of the imaging; then place a light shield between the first beam splitter (26) and the second beam splitter (21), and use a piezoelectric ceramic support method to allow the microsphere (13) to be captured and suspended by the capture beam A between the upper electrode plate and the lower electrode plate of the parallel electrode plate group (11); 2) The second detector (24) in the signal detection and processing module collects the optical signals of the capture beam A and the capture reference beam B in real time, converts them into electrical signals, and transmits them to the controller (25) in real time; 3) performing an evacuation process on the vacuum chamber (16) in the electric field tilt detection control module until a set vacuum threshold is reached; during the evacuation process, the controller (25) continuously fine-tunes the second acousto-optic modulator (6) and the galvanometer (8) so that the microsphere (13) is stably suspended in the central area of ​​the parallel electrode plate assembly; 4) Apply a frequency of ω to the parallel electrode plates dr , amplitude is 200-400V pp An AC voltage is applied to the microspheres (13), thereby forming an AC electric field between the parallel electrode plates, so that the microspheres (13) perform simple harmonic motion under the action of the AC electric field; the controller (25) demodulates the time domain signal of the simple harmonic motion of the microspheres (13) in the X, Y, and Z directions and outputs the power spectrum density curve of the motion in the X, Y, and Z directions, and calculates the electric field intensity amplitude in the X, Y, and Z directions; If the power spectrum density curve in the XY direction is dr If there is no peak at the frequency and the electric field strength amplitude in the XY direction is zero, it means that the electric field is vertical; otherwise, it means that the electric field is tilted. According to the calculation results, perform step 5) to adjust the posture of the parallel electrode plate assembly: 5) The power spectrum density curve in the X direction only is dr When there is a peak at the frequency, adjust the X-direction deflection angle of the multi-axis translation stage (14) until the power spectrum density curve in the X direction is at ω dr The peak at the frequency disappears, and the electric field intensity amplitude in the X direction is zero; Only the power spectrum density curve in the Y direction is dr When there is a peak at the frequency, adjust the Y-direction deflection angle of the multi-axis translation stage (14) until the power spectrum density curve in the Y direction is at ω dr The peak at the frequency disappears, and the electric field intensity amplitude in the Y direction is zero; The power spectrum density curve in the XY direction is dr When there are peaks at all frequencies, first adjust the X-direction deflection angle of the multi-axis translation stage (14) until the power spectrum density curve in the X direction is at ω dr The peak amplitude at the frequency cannot be further reduced; then adjust the Y-direction deflection angle of the multi-axis translation stage (14) until the power spectrum density curve in the Y direction is at ω dr The peak amplitude at the frequency cannot be further reduced; the X-direction deflection angle and the Y-direction deflection angle of the multi-axis translation stage (14) are alternately adjusted until the power spectrum density curve in the XY direction is at ω dr There is no peak at any frequency, and the electric field strength amplitude in the XY direction is zero.

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