Optical force accelerometer based on spin cooling and method of use

Abstract

The application relates to the technical field of acceleration detection by using optical force, and discloses an optical force accelerometer based on spin cooling and a use method, which realizes acceleration detection by using laser-suspended microspheres, and improves detection precision by using the spin cooling effect of the microspheres in an optical field to inhibit thermal motion of the microspheres. Laser is processed into circularly polarized light suitable for capture and rotation driving by a laser modulation unit, and is input into a capture cooling unit; the capture cooling unit utilizes a potential well formed by an optical field to realize capture and rotation cooling of microparticles, simultaneously outputs laser carrying state information of the microparticles, and a displacement detection unit realizes acceleration response output by analyzing and monitoring the displacement state of the microparticles in real time through analysis of outgoing laser; a test unit provides auxiliary illumination and completes visual observation of behaviors of the microparticles, and together forms an optical capture and measurement system. The spin cooling method is adopted to realize cooling of a sensitive mass of the optical force accelerometer, the structure of a cooling system is simplified, performance requirements are reduced, practical potential is high, and cost is low.

Description

Technical Field

[0001] This invention relates to the field of optical acceleration detection technology, and in particular, to a spin-cooled optical accelerometer and its usage method. Background Technology

[0002] An optical accelerometer is a high-precision inertial sensor based on optical levitation technology and the principle of optical force measurement, used to measure the acceleration of moving objects. It utilizes the optical momentum (optical force) of lasers to achieve non-contact levitation and control of sensitive masses at the micro-nano scale, and uses optical means to detect the displacement changes of the sensitive mass to infer the acceleration value.

[0003] Optical levitation technology utilizes the optical momentum of laser light to capture and levitate micro- and nano-scale particles. By focusing the laser beam through optical devices, an optical potential well can be formed at the focal point, allowing the particle to levitate stably at the center of the potential well. When the particle is subjected to external acceleration, its displacement from its equilibrium position is linearly related to the restoring force. Based on this principle, high-precision measurement of acceleration can be achieved. Because this technology avoids mechanical contact, it can achieve extremely low damping in a vacuum environment, thus possessing extremely high measurement sensitivity and accuracy.

[0004] However, the thermal motion of the particles themselves leads to instability in their capture in a vacuum environment and introduces displacement oscillation noise, thus limiting the range and accuracy of the optical accelerometer. To suppress the effects of thermal motion, existing technologies have proposed various cooling schemes, mainly including active feedback cooling and passive feedback cooling. Active feedback cooling methods (such as photomomentum feedback cooling and electrostatic force feedback cooling) require real-time monitoring of the particle motion state and the application of feedback through an external control loop, resulting in a complex system structure and cooling performance limited by the circuit response speed. Passive feedback cooling methods (such as optical cavity cooling and self-feedback cooling) rely on high-quality optical cavities or scattered light modulation, and their cooling effect is limited by the quality factors of external devices.

[0005] Existing cooling technologies generally suffer from complex system structures, large size, and high cost, making it difficult to meet the demands of high-speed cooling. For example, patent CN211697862U discloses a scheme using six laser beams for active feedback cooling, which not only has a complex optical path structure but also requires the construction of additional control loops, and the cooling effect is limited by circuit performance. Furthermore, while achieving efficient cooling, existing cooling methods often struggle to balance system compactness and practicality. Summary of the Invention

[0006] This invention provides a spin-cooled optical accelerometer and its application method. It utilizes a laser to suspend a high-speed spinning microsphere for acceleration detection, and leverages the spin-cooling effect of the microsphere in the optical field to suppress its thermal motion, thereby improving detection accuracy. This invention fundamentally changes the cooling method by employing a rotational cooling approach to cool the sensitive mass of the optical accelerometer. It simplifies the cooling system structure and reduces performance requirements, resulting in a simple structure, high practical potential, and low cost. This addresses the technical problems of existing cooling methods that require external control loops or high-quality devices, leading to complex structures, large sizes, high costs, and limited practicality. This invention provides effective technical support for the practical application of optical accelerometers.

[0007] According to one aspect of the present invention, a spin-cooled optical accelerometer is provided, comprising: a laser modulation unit for expanding a parallel laser beam and converting it into circularly polarized light, thereby providing master control optical field conditions for optical field requirements; a capture and cooling unit for first completing the oscillation and loading of particles, and then capturing and driving the particles to rotate using an optical potential well to achieve thermal motion cooling; a displacement detection unit for real-time monitoring of particle displacement changes through the emitted laser signal; and a testing unit for providing visible light auxiliary illumination, and realizing real-time observation and imaging analysis of particles through visible light illumination and optical filtering; the laser is processed into circularly polarized light suitable for capture by the laser modulation unit and input into the capture and cooling unit, the capture and cooling unit uses the optical field to form a potential well to achieve particle capture and rotational cooling, and simultaneously outputs laser carrying particle state information; the displacement detection unit monitors the particle displacement dynamics in real time by analyzing the emitted laser; and the testing unit provides auxiliary illumination and completes the visual observation of particle behavior, together constituting an optical capture and measurement system.

[0008] Furthermore, the laser modulation unit includes a beam expander group, a first dichroic mirror, and a quarter-wave plate. The beam expander group is composed of a concave lens and an aspherical convex lens. The parallel laser first passes through the concave lens, is reflected by the first dichroic mirror, and is then collimated by the aspherical convex lens to form a vertically upward propagating light field structure. After being modulated into circularly polarized light by the quarter-wave plate, it shines into the capture and cooling unit. The first dichroic mirror is also used to transmit visible light incident from the test unit.

[0009] Furthermore, the beam expander group consists of a concave lens and an aspherical convex lens, with the concave surface of the concave lens and the convex surface of the aspherical convex lens placed opposite each other in the optical path.

[0010] Furthermore, the capture and cooling unit includes a vacuum chamber, a focusing objective, a oscillator, and an imaging objective. The focusing objective, oscillator, and imaging objective are located inside the vacuum chamber and arranged sequentially from the input end to the output end. After the circularly polarized light output from the laser modulation unit enters the vacuum chamber, it is focused by the focusing objective inside the vacuum chamber to form an optical potential well. The optical potential well captures the particles, causing the particles to form a dynamic behavior similar to a "spring-oscillator" in the potential well to respond to the input acceleration. At the same time, it drives the particles to rotate at high speed to suppress translational thermal motion. Afterward, the particles leave the vacuum chamber through the imaging objective.

[0011] Furthermore, driving the high-speed rotation of the particles to suppress translational thermal motion is achieved as follows: the birefringent particles exhibit a coupling effect between translational and rotational degrees of freedom in the polarized light potential trap. The translational oscillation of the particles in the light field promotes torsional oscillation, and the torsional oscillation further promotes translational oscillation, thus exhibiting extremely strong coherence characteristics. Based on this coupling effect, the particles are driven to rotate by the transfer of the spin angular momentum of circularly polarized light. The directional stabilization effect of the angular momentum generated by the high-speed spin of the particles can effectively suppress the translational oscillation, thereby achieving translational thermal motion cooling.

[0012] Furthermore, the particles are made of birefringent materials such as aragonite, quartz, and calcite, and are spherical or ellipsoidal in shape.

[0013] Furthermore, in the capture and cooling unit, the circularly polarized light interacts directly with the particles after being focused by the focusing objective lens, and simultaneously undergoes polarization phase modulation and light intensity distribution modulation. Polarization phase modulation drives the particles to rotate, while light intensity distribution modulation enables the outgoing light to carry particle displacement information.

[0014] Furthermore, the oscillator includes a glass plate and a piezoelectric plate; the glass plate and the piezoelectric plate are located in the area between the focusing objective and the imaging objective and are used for the support and oscillation of the particles, with the glass plate fixed above the piezoelectric plate.

[0015] Furthermore, the displacement detection unit adopts a QPD four-quadrant detection device composed of a second dichroic mirror and a photodetector; the laser carrying the particle state information emitted from the capture cooling unit is reflected by the second dichroic mirror and enters the QPD four-quadrant detection device to realize displacement detection. The QPD four-quadrant detection device uses a spot position detection algorithm to calculate the centroid position of the spot of the four light intensity output signals to obtain the particle displacement information.

[0016] Furthermore, the test unit includes a visible light source, a filter, and an imaging device. The visible light output from the visible light source is transmitted through the first dichroic mirror and enters the capture and cooling unit to provide illumination and form microsphere imaging light. The microsphere imaging light passes through the imaging objective lens, the second dichroic mirror, and the filter in sequence before entering the imaging device.

[0017] According to another aspect of the present invention, a method for using a spin-cooled optical accelerometer is also provided. The method includes the following steps: S100, turning on the visible light source and imaging device, and adjusting the position of the imaging objective lens to make the particle image clear; S200, turning on the laser source, activating the oscillator, separating the particle from the glass plate to achieve capture and drive rotation; S300, activating the vacuum pumping device, slowly evacuating to increase the microsphere rotation frequency, and adjusting the microsphere rotation frequency according to the equivalent cooling temperature reflected by the displacement detection unit to achieve the best cooling effect and minimize thermal noise; S400, adjusting the displacement detection output to zero; S500, inputting a known acceleration, and performing detection signal output and acceleration calibration.

[0018] Further, in step S300, the microsphere rotation frequency is adjusted based on the equivalent cooling temperature reflected by the displacement detection unit. While maintaining a constant laser beam, the rotation frequency is controlled by changing the vacuum level within the vacuum chamber using an external vacuum pumping device. Specifically: the microsphere material has birefringence properties. The microsphere modulates the polarization state of the laser beam within the potential well, externally manifested as the transfer of optical spin angular momentum generating a driving torque, thus driving the microsphere to spin. When the microsphere spins within the vacuum chamber, it is simultaneously subjected to both driving and damping torques. Upon reaching a stable rotational speed, the driving and damping torques balance each other, as expressed as:

[0019] ;

[0020] Among them, damping torque It can be represented as:

[0021] ;

[0022] in, The damping coefficient is related to the vacuum level inside vacuum chamber 7. For the rotational inertia of the particle, The rotational frequency of the particles;

[0023] With the laser and the particles remaining constant, and the driving torque remaining constant, the rotation frequency of the particles can be controlled by changing the vacuum level within the vacuum chamber.

[0024] The present invention has the following beneficial effects:

[0025] 1. Improved Accuracy Through Simplified Structure: Traditional active feedback cooling requires an additional control loop to monitor and adjust the microsphere's state in real time, while passive cooling (such as optical cavity cooling) relies on high-precision optical components. This invention drives the birefringent microsphere to spin at high speed using circularly polarized light, utilizing the coupling effect between rotational and translational degrees of freedom to directly suppress translational thermal noise, thereby improving the accelerometer's detection accuracy. Since rotational cooling requires no external feedback loop or auxiliary optical cavity, a single beam is sufficient for levitation, rotational drive, and detection, significantly simplifying the system structure.

[0026] 2. High compatibility and application expansion potential: The cooling mechanism of this invention is based on the rotational drive principle of optical levitation technology, which can be adapted to various optical tweezers architectures (such as single beam and dual beam). In addition, the physical mechanism of rotational cooling (translational-rotational coupling to suppress noise) can be extended to other fields of high-precision micro-force measurement such as force and torque.

[0027] 3. Ease of Operation and Flexible Parameter Control: This invention achieves feedback-free rotational speed control by adjusting the gas pressure in the vacuum chamber to control gas damping. Compared to driving methods that rely on laser power or polarization state adjustments, gas pressure control avoids the risk of capture instability caused by changes in optical trap stiffness. Furthermore, it is simple to operate and highly robust, making it suitable for mass production of industrial-grade sensors.

[0028] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0029] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0030] Figure 1 This is a schematic diagram of the structure of a spin-cooled optical accelerometer according to a preferred embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of the external acceleration response principle;

[0032] Figure 3 This is a schematic diagram illustrating how rotating cooling particles improve the accuracy of acceleration measurement through translational thermal motion.

[0033] Legend:

[0034] 1. Concave lens; 2. Aspherical convex lens; 3. Visible light source; 4. First dichroic mirror; 5. Quarter wave plate; 6. Focusing objective; 7. Vacuum chamber; 8. Imaging objective; 9. Displacement detection unit; 10. Second dichroic mirror; 11. Filter; 12. Imaging device; 13. Microparticle; 14. Glass slide; 15. Piezoelectric element. Detailed Implementation

[0035] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below.

[0036] Figure 1 This is a schematic diagram of the structure of a spin-cooled optical accelerometer according to a preferred embodiment of the present invention; Figure 2 This is a schematic diagram of the external acceleration response principle; Figure 3 This is a schematic diagram illustrating how rotating cooling particles improve the accuracy of acceleration measurement through translational thermal motion.

[0037] like Figure 1 As shown, the spin-cooled optical accelerometer of this embodiment includes: a laser modulation unit for expanding a parallel laser beam and converting it into circularly polarized light, thereby providing the master control optical field conditions for the optical field requirements; a capture and cooling unit for first completing the oscillation and loading of the particle 13, and then using an optical potential well to capture and drive the particle 13 to rotate to achieve thermal motion cooling; a displacement detection unit 9 for monitoring the displacement change of the particle 13 in real time through the emitted laser signal; and a testing unit for providing visible light auxiliary illumination, and realizing real-time observation and imaging analysis of the particle 13 through visible light illumination and optical filtering; the laser is processed into circularly polarized light suitable for capture by the laser modulation unit and input into the capture and cooling unit, the capture and cooling unit uses the optical field to form a potential well to realize the capture and rotational cooling of the particle 13, and at the same time outputs laser carrying the state information of the particle 13; the displacement detection unit 9 monitors the displacement dynamics of the particle 13 in real time by analyzing the reflected laser; and the testing unit provides auxiliary illumination and completes the visual observation of the behavior of the particle 13, together constituting an optical capture and measurement system. This invention is based on a spin-cooled optical accelerometer, which integrates the core functions of the optical accelerometer through modular design. In terms of system structure optimization, the laser modulation unit achieves unified control of the optical field conditions by converting laser light into circularly polarized light, replacing the separate trapping and cooling optical paths in traditional schemes. This allows the formation of the optical potential well and the thermal cooling of the particle 13 to be completed through a single optical path. This integrated design directly reduces the number of optical components, lowers the difficulty of optical path calibration, and avoids system instability caused by multi-beam interference. Regarding functional synergy, the trapping and cooling unit integrates optical trapping and spin cooling functions into the same physical process, using circularly polarized light to simultaneously achieve the suspension stabilization and rotational drive of the particle 13, such as... Figure 3As shown, this coupling effect allows the thermal noise of the translational degree of freedom of particle 13 to be suppressed by introducing the rotational degree of freedom, thereby improving the capture efficiency and acceleration measurement accuracy. This eliminates the need for additional feedback control circuits or auxiliary cooling optical paths, significantly simplifying the system architecture. Regarding measurement reliability, the displacement detection unit 9 and the testing unit employ a beam splitting design to achieve parallel acquisition of measurement and observation signals. The reflected laser signal is used for high-precision displacement analysis, while visible light-assisted illumination provides intuitive verification of particle 13 behavior. The two mutually corroborate each other, ensuring the accuracy of the measurement data. This dual-channel monitoring mechanism effectively solves the signal reliability problem in nanoscale displacement measurement without increasing system complexity.

[0038] like Figure 1 As shown, in this embodiment, the laser modulation unit includes a beam expander group, a first dichroic mirror 4, and a quarter-wave plate 5. The beam expander group is composed of a concave lens 1 and an aspherical convex lens 2. The parallel laser first passes through the concave lens 1, is reflected by the first dichroic mirror 4, and is then collimated by the aspherical convex lens 2 to form a vertically upward propagating light field structure. After being modulated into circularly polarized light by the quarter-wave plate 5, it shines into the capture and cooling unit. The first dichroic mirror 4 is also used to transmit visible light incident from the test unit. By combining the beam expander group with the first dichroic mirror 4, the functions of laser beam expansion and optical path steering are integrated. The use of a combination of positive and negative lenses can effectively correct aberrations, improve wavefront quality, and avoid the formation of focal points within the system while shortening the optical path length. The axial positioning design of the quarter-wave plate 5 ensures efficient conversion of linearly polarized light to circularly polarized light. Its position at the end of the reflected optical path avoids the polarization state degradation problem caused by excessively long optical path transmission distance in traditional schemes, resulting in a small or even negligible ellipticity error in the output optical field, providing the necessary conditions for the stable rotation drive of the particle 13. The wavelength-selective reflection characteristics of the first dichroic mirror 4, while completing the main laser reflection function, reserve a transmission channel for the detection optical path of the subsequent displacement detection unit 9, realizing the parallel transmission of measurement signals while ensuring the function of the main optical path.

[0039] like Figure 1As shown, in this embodiment, the capture and cooling unit includes a vacuum chamber 7, a focusing objective lens 6, a oscillator plate, and an imaging objective lens 8. The focusing objective lens 6, the oscillator plate, and the imaging objective lens 8 are disposed in the vacuum chamber 7 and arranged sequentially from the input end to the output end. After the circularly polarized light output by the laser modulation unit enters the vacuum chamber 7, it is focused by the focusing objective lens 6 in the vacuum chamber 7 to form an optical potential well. The optical potential well captures the microparticles 13, causing the microparticles 13 to form a dynamic behavior similar to a "spring-oscillator" in the potential well to respond to the input acceleration. At the same time, it drives the microparticles 13 to rotate at high speed to achieve translational thermal motion suppression. Then, it leaves the vacuum chamber 7 through the imaging objective lens 8. By integrating the focusing objective 6, the oscillator, and the imaging objective 8 into the vacuum chamber 7, a closed optical path channel is formed, realizing the integration of optical potential well formation, particle rotation drive, and signal output functions. This eliminates the optical path offset problem caused by cross-medium interfaces (such as the vacuum-atmosphere boundary) in traditional solutions, thereby improving beam positioning accuracy. The vacuum level of the vacuum chamber is adjusted to increase the rotation speed of the particle 13. The high-speed rotation of the particle 13 suppresses the translational thermal noise of the particle 13 through the translational-rotational coupling effect. The conjugate position design of the imaging objective 8 ensures efficient extraction of scattered light carrying particle displacement information. Its numerical aperture is matched with that of the focusing objective 6, which improves the signal light transmittance. Compared with the external objective solution, this structure reduces the signal attenuation rate and improves the displacement detection signal-to-noise ratio.

[0040] In this embodiment, the microparticle 13 is made of birefringent materials such as aragonite, quartz, and calcite, and is spherical or ellipsoidal in shape.

[0041] In this embodiment, as Figure 2 As shown, in the capture and cooling unit, under a certain acceleration input, circularly polarized light is focused by the focusing objective lens 6 and directly interacts with the microparticle 13. The high-speed spinning microsphere deviates from the center of the potential well and stabilizes under the action of gradient force and inertial force. The polarized light simultaneously undergoes polarization phase modulation and light intensity distribution modulation. Polarization phase modulation drives the microparticle 13 to rotate, and light intensity distribution modulation enables the outgoing light to carry the displacement information of the microparticle 13, thereby realizing the response to acceleration.

[0042] In this embodiment, in the capture and cooling unit, the vacuum chamber 7 is connected to an external vacuum pumping device, and the vacuum level is adjustable, thereby changing the rotation frequency of the particles 13.

[0043] like Figure 1As shown, in this embodiment, the vibration plate includes a glass plate 14 and a piezoelectric plate 15. The glass plate 14 and the piezoelectric plate 15 are located in the area between the focusing objective lens 6 and the imaging objective lens 8 and are used to support and initiate the vibration of the microparticles 13. The glass plate 14 is fixedly connected above the piezoelectric plate 15. The glass plate 14 provides a flat contact surface as a support platform for the microparticles 13, and the piezoelectric plate 15 generates mechanical vibration through the inverse piezoelectric effect. The two are rigidly connected to form a composite vibration module, which enables the vibration energy to be efficiently transferred and acted on the captured microparticles 13.

[0044] like Figure 1 As shown, in this embodiment, the displacement detection unit 9 includes a second dichroic mirror 10 and a QPD four-quadrant detection device. The laser carrying the state information of the particles 13 emitted from the cooling unit is reflected by the second dichroic mirror 10 and enters the QPD four-quadrant detection device to achieve displacement detection. The second dichroic mirror 10 uses wavelength selective reflection characteristics to physically separate the detection laser carrying the particle displacement information from other optical path signals in the system, ensuring the spectral purity of the displacement detection channel and avoiding signal crosstalk caused by multi-wavelength interference. The QPD four-quadrant detection device has high detection resolution, short response time, and only requires a single scattered beam to complete the particle position information calculation. The displacement detection unit 9 achieves optical path reversal through the dichroic mirror (second dichroic mirror 10), completing the lateral detection function while maintaining the axial layout of the main optical path, which not only meets the compact packaging requirements but also reserves optical interfaces for possible future functional expansion. Considering both performance and complexity, the detection method in this embodiment preferably adopts QPD.

[0045] In this embodiment, the second dichroic mirror 10 transmits visible light after it has passed through the capture and cooling unit and enters the imaging device 12, which uses a CCD camera for imaging.

[0046] like Figure 1 As shown, in this embodiment, the test unit includes a visible light source 3, a filter 11, and an imaging device 12. The visible light output from the visible light source 3 is transmitted through the first dichroic mirror 4 and enters the capture and cooling unit to provide illumination and form microsphere imaging light. The microsphere imaging light passes sequentially through the imaging objective lens 8, the second dichroic mirror 10, and the filter 11 before entering the imaging device 12. The visible light source 3 enters the device through the transmission channel of the first dichroic mirror 4 to provide illumination. The filter 11 isolates the capture laser and protects the imaging device 12. The imaging optical path reuses the imaging objective lens 8 in the capture and cooling unit, so that particle observation and optical capture share the same optical window, allowing direct observation of the rotation state and capture stability of the particles 13 without introducing additional lens groups. The particle motion image recorded by the imaging device 12 enables direct observation of the particle state and is supplemented by zero-point calibration.

[0047] The method of using the spin-cooled optical accelerometer in this embodiment includes the following steps: S100, turn on the visible light source 3 and the imaging device 12, and adjust the position of the imaging objective lens 8 to make the microparticle 13 clearly imaged; S200, turn on the laser source, start the oscillator, and separate the microparticle 13 from the glass plate 14 to achieve capture and drive rotation; S300, start the vacuum pumping device, slowly pump vacuum to increase the microsphere rotation frequency, and adjust the microsphere rotation frequency according to the equivalent cooling temperature reflected by the displacement detection unit 9 to achieve the best cooling effect and achieve minimum thermal noise; S400, adjust the displacement detection output to zero; S500, input the known acceleration, and perform detection signal output and acceleration calibration. In step S100, through the coordinated work of visible light source 3 and imaging device 12, an optical observation benchmark is established in the initial stage of calibration to ensure that the spatial position of particle 13 is accurately mapped to the electrical signal of displacement detection unit 9, thereby improving the zero-point calibration accuracy of the system. In step S200, the active start of the oscillator and the synchronous control of laser capture enable the particle 13 to detach from the glass surface attachment constraint through vibration, thereby improving the capture efficiency. The "electrical signal-acceleration" calibration curve established in steps S400-S500 is verified by a two-stage process of first zeroing and then inputting a known acceleration, thereby eliminating the system's accumulated error.

[0048] In this embodiment, step S300 adjusts the microsphere rotation frequency based on the equivalent cooling temperature reflected by the displacement detection unit 9. Specifically, the material of the microparticle 13 has birefringence properties. The microparticle 13 modulates the polarization state of the laser in the potential well, which manifests externally as the transfer of optical spin angular momentum generating a driving torque, thereby driving the microparticle to spin. When the microparticle 13 spins in the vacuum chamber 7, it is simultaneously subjected to driving torque and damping torque. When a stable rotational speed is reached, the driving torque and damping torque are balanced, as shown in the following expression:

[0049] ;

[0050] Among them, damping torque It can be represented as:

[0051] ;

[0052] in, The damping coefficient is related to the vacuum level inside vacuum chamber 7. For the rotational inertia of the particle, The rotational frequency of the particles;

[0053] With the laser and particle 13 remaining constant, the driving torque remains constant, and the rotation frequency of particle 13 is thus controlled by changing the vacuum level within the vacuum chamber 7. Step S300 controls the particle rotation frequency by adjusting the vacuum level, directly changing the gas damping coefficient γ by adjusting the vacuum level of the vacuum chamber 7, utilizing the balance between the driving torque and the damping torque (…). The rotational frequency control of particle 13 reduces the equivalent translational temperature of the particles, eliminating the need for active modulation of laser parameters and avoiding the introduction of other thermal effects that could affect the displacement detection signal. The modulation of the laser polarization state by the birefringent particles 13 converts the optical spin angular momentum into a driving torque, which, along with the gas damping torque (…),… A dynamic equilibrium is formed, and this coupling mechanism makes the rotation frequency a single-valued function of the vacuum degree, resulting in high frequency control sensitivity.

[0054] In practice, a spin-cooled optical accelerometer is provided, which uses a rotational cooling method to cool the sensitive mass of the optical accelerometer.

[0055] Rotational cooling principle: Rotational cooling refers to cooling the equivalent temperature of the center of mass motion directly by driving the microparticles to rotate. This technology is based on the principle of the torque generated by the transfer of optical spin angular momentum driving the rotation of birefringent microspheres, and the constructive coupling effect of the translational and rotational degrees of freedom of the birefringent microspheres in the polarized optical potential trap. By driving the high-speed spin of the microparticles, directional stability is achieved, suppressing the torsional oscillations of the rotational degrees of freedom and thus suppressing the translational oscillations of the translational degrees of freedom, thereby achieving relative cooling of the equivalent temperature of the center of mass motion.

[0056] Optical spin angular momentum transfer: Optical spin angular momentum is only related to the polarization of light. Birefringent particles change the phase of transmitted light, resulting in a difference in the polarization properties of incident and outgoing light. This difference manifests as the transfer of photon spin angular momentum.

[0057] Explanation of the working principle of a spin-cooled optical accelerometer:

[0058] (1) External acceleration input response principle:

[0059] The particle in the potential well is subjected to laser scattering force and gradient force, and is subjected to external acceleration input. The restoring force F generated by the particle deviating from the center of the potential well is proportional to the displacement x, which can be expressed as:

[0060] ;

[0061] In a steady state, we have:

[0062] ;

[0063] Where m is the mass of the particle, and k is the potential trap stiffness, which depends on the microsphere and the optical potential trap. In fact, if the microsphere and the light are constant, then m and k are constant. The output acceleration a is proportional to the displacement x, and this proportionality coefficient can be determined by calibration.

[0064] (2) Explanation of particle oscillation:

[0065] Before being captured by a laser, the particles are supported by a glass plate. Since the force of the optical potential trap is insufficient to overcome the attraction between the particles and the glass plate, vibration excitation is required to first separate the particles from the glass surface before subsequent capture operations can proceed. In this invention, the high-frequency vibration generated by energizing a piezoelectric element drives the glass plate to vibrate, thereby achieving separation.

[0066] (3) Technical principles of driving rotation and controlling rotation frequency:

[0067] The microparticles used in this invention are made of birefringent materials (materials with birefringence, such as quartz, aragonite, and calcite). Within the potential well, the microparticles modulate the polarization state of the laser, manifesting externally as a driving torque generated by the transfer of optical spin angular momentum, thus driving the microparticles to spin. While spinning within the vacuum chamber, the microparticles are simultaneously subjected to this driving torque. and damping torque When a stable rotational speed is reached, the driving torque and damping torque are balanced, which can be expressed as:

[0068] ;

[0069] Among them, damping torque It can be represented as:

[0070] ;

[0071] in This is the damping coefficient, which is related to the vacuum level inside the vacuum chamber. For the rotational inertia of the particle, Let be the particle rotation frequency. With the laser and the particle remaining constant, the driving torque can be considered constant; therefore, the particle rotation frequency can be controlled by changing the vacuum level within the vacuum chamber.

[0072] Matters not covered in this invention are common knowledge.

[0073] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0074] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A spin-cooled optical accelerometer, characterized in that, include: The laser modulation unit is used to expand the parallel laser beam and convert it into circularly polarized light, thereby providing the master optical field conditions for optical field requirements; The capture and cooling unit is used to first complete the oscillation and loading of the particles (13), and then use the optical potential trap to capture and drive the particles (13) to rotate to achieve thermal motion cooling; The displacement detection unit (9) is used to monitor the displacement change of the particles (13) in real time by emitting laser signals; The test unit is used to provide visible light auxiliary illumination, and to realize real-time observation and imaging analysis of particles (13) through visible light illumination and optical filtering; The laser is processed into circularly polarized light suitable for capture by the laser modulation unit and input into the capture and cooling unit. The capture and cooling unit uses the light field to form a potential trap to capture and rotate the particle (13) and output laser carrying the state information of the particle (13). The displacement detection unit (9) monitors the displacement dynamics of the particle (13) in real time by analyzing the reflected laser. The test unit provides auxiliary illumination and completes the visualization observation of the behavior of the particle (13), and together they constitute the optical capture and measurement system.

2. The spin-cooled optical accelerometer according to claim 1, characterized in that, The laser modulation unit includes a beam expander group, a first dichroic mirror (4) and a quarter wave plate (5). The beam expander group is composed of a concave lens (1) and an aspherical convex lens (2). The parallel laser first passes through a concave lens (1), then is reflected by a first dichroic mirror (4), and then collimated by an aspherical convex lens (2) to form a vertically upward propagating light field structure. After being modulated into circularly polarized light by a quarter-wave plate (5), it shines into the capture and cooling unit. The first dichroic mirror (4) is also used to transmit visible light incident from the test unit.

3. The spin-cooled optical accelerometer according to claim 1, characterized in that, The particles (13) are made of birefringent materials and are spherical or ellipsoidal in shape.

4. The spin-cooled optical accelerometer according to claim 1, characterized in that, The capture and cooling unit includes a vacuum chamber (7), a focusing objective (6), a oscillator, and an imaging objective (8). The focusing objective (6), the oscillator, and the imaging objective (8) are located in the vacuum chamber (7) and arranged sequentially from the input end to the output end. After the circularly polarized light output by the laser modulation unit enters the vacuum chamber (7), it is focused by the focusing objective (6) in the vacuum chamber (7) to form an optical potential well. The optical potential well captures the particles (13), causing the particles (13) to form a dynamic behavior similar to a "spring-oscillator" in the potential well to respond to the input acceleration. At the same time, it drives the particles (13) to rotate at high speed to suppress translational thermal motion. Then, it leaves the vacuum chamber (7) through the imaging objective (8).

5. The spin-cooled optical accelerometer according to claim 4, characterized in that, The high-speed rotation of the driving particles (13) achieves the suppression of translational thermal motion, specifically as follows: The birefringent particle (13) exhibits a coupling effect of translational and rotational degrees of freedom in the polarized light potential trap. The translational oscillation of the particle (13) in the light field promotes the torsional oscillation, and the torsional oscillation further promotes the translational oscillation, thus exhibiting a very strong coherent characteristic. Based on this coupling effect, the particle (13) is driven to rotate by the transfer of the spin angular momentum of the circularly polarized light. The angular momentum orientation stabilization effect generated by the high-speed spin of the particle (13) can effectively suppress the translational oscillation, thereby realizing translational thermal motion cooling.

6. The spin-cooled optical accelerometer according to claim 4, characterized in that, The oscillator includes a glass plate (14) and a piezoelectric plate (15). The glass plate (14) and the piezoelectric plate (15) are located in the area between the focusing objective (6) and the imaging objective (8) and are used to support and oscillate the particles (13). The glass plate (14) is fixed above the piezoelectric plate (15).

7. The spin-cooled optical accelerometer according to claim 1, characterized in that, The displacement detection unit (9) adopts a QPD four-quadrant detection device composed of a second dichroic mirror (10) and a photodetector; The laser carrying the state information of the particles (13) emitted from the cooling unit is reflected by the second dichroic mirror (10) and enters the QPD four-quadrant detection device to realize displacement detection. The QPD four-quadrant detection device uses the spot position detection algorithm to calculate the centroid position of the spot of the four light intensity output signals to obtain the particle displacement information.

8. The spin-cooled optical accelerometer according to claim 1, characterized in that, The test unit includes a visible light source (3), a filter (11) and an imaging device (12). The visible light output from the visible light source (3) is transmitted through the first dichroic mirror (4) and enters the capture and cooling unit to provide illumination and form microsphere imaging light. The microsphere imaging light passes through the imaging objective (8), the second dichroic mirror (10) and the filter (11) in sequence and then enters the imaging device (12).

9. A method of using a spin-cooled optical accelerometer, employing any one of claims 1 to 8, characterized in that, Includes the following steps: S100. Turn on the visible light source (3) and imaging device (12), and adjust the position of the imaging objective (8) to make the particle (13) image clear; S200. Turn on the laser source and start the oscillator to separate the particles (13) and the glass plate (14) to achieve capture and drive rotation; S300, Start the vacuum pumping device, slowly pump vacuum to increase the microsphere rotation frequency, and adjust the microsphere rotation frequency according to the equivalent cooling temperature reflected by the displacement detection unit (9) to achieve the best cooling effect and achieve the minimum thermal noise. S400, Adjust the displacement detection output to zero; S500: Input a known acceleration, and output the detection signal and calibrate the acceleration.

10. The method of using the spin-cooled optical accelerometer according to claim 9, characterized in that, In step S300, the rotation frequency of the microspheres is adjusted according to the equivalent cooling temperature reflected by the displacement detection unit (9), specifically as follows: The material of the microparticle (13) has birefringence properties. The microparticle (13) modulates the polarization state of the laser in the potential well. Externally, it is manifested as the transmission of the optical spin angular momentum, which generates a driving torque, thereby driving the spin. When the microparticle (13) spins in the vacuum chamber (7), it is simultaneously subjected to the driving torque and the damping torque. When the stable rotation speed is reached, the driving torque and the damping torque are balanced, which can be expressed as: ； Among them, damping torque It can be represented as: ； in, The damping coefficient is related to the vacuum level inside the vacuum chamber (7). For the rotational inertia of the particle, The rotational frequency of the particles; With the laser and the particle (13) remaining constant, the driving torque remains constant, and the rotation frequency of the particle (13) is controlled by changing the vacuum level in the vacuum chamber (7).

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