Three-dimensional vacuum single-beam suspension system active cooling device

Abstract

The application discloses a three-dimensional vacuum single-beam suspension system active cooling device, and belongs to the technical field of optical tweezers, which comprises a laser trapping module, an electric control system and a three-axis cooling module; in the laser trapping module, a trapping objective lens and a condensing objective lens are arranged in a vacuum cavity, trapping laser, a first plano-convex lens, a second plano-convex lens and a first dichroic mirror are sequentially arranged and coaxial along an x-axis direction; the first dichroic mirror, the trapping objective lens, the condensing objective lens and a second dichroic mirror are sequentially arranged and coaxial along a z-axis direction; the first dichroic mirror reflects the trapping laser to the trapping objective lens; light floating particles are loaded to an optical trap, and backscattered light enters the electric control system; the third plano-convex lens of the three-axis cooling module is coaxially arranged with a first AOM along the x-axis, and after axial cooling laser is diffracted by a second AOM, first-order diffracted light is reflected by a third dichroic mirror and enters the vacuum cavity; the first and second AOMs are connected with the electric control system. The application can realize stable trapping of mesoscopic particles in a high-vacuum environment.

Description

Technical Field

[0001] This invention belongs to the field of optical tweezers technology, specifically relating to an active cooling device for a three-dimensional vacuum single-beam suspension system. Background Technology

[0002] Optical tweezers is a non-contact, non-invasive method for manipulating micro- and nano-particles. This technology utilizes a highly focused laser beam to form a three-dimensional optical potential trap, stably suspending particles near the focal point. Vacuum optical tweezers, by isolating particles from environmental molecular collisions and external interference in a vacuum environment, can serve as ultra-high-sensitivity sensing units, providing an ideal experimental platform for fields such as macroscopic quantum physics, precision measurement, non-equilibrium thermodynamics, and fundamental physics testing. In an atmospheric environment, the presence of air molecules dampens the particles suspended in the optical trap, allowing for stable capture. However, as the vacuum level increases (typically below 10 Pa), gas damping decreases sharply. The captured particles become heated due to laser shot noise and residual air molecule collisions, exhibiting violent Brownian motion or harmonic oscillator thermal excitation in all degrees of freedom, with an equivalent temperature far exceeding the ambient temperature. As the vacuum level further decreases, the particle's center-of-mass motion intensifies, eventually causing it to escape from the optical trap, severely limiting its performance as a high-sensitivity force sensor or a high-quality harmonic oscillator.

[0003] To suppress the random thermal motion of particles in ultra-high vacuum environments, momentum feedback cooling technology can be employed. This involves using photoelectric detection to monitor the instantaneous position of particles in real time. By differentiating the position signal, the real-time velocity of the particles is extracted. A feedback control system then generates a braking signal proportional to the particle's velocity, in the opposite direction, and converts this signal into a controllable external optical force. This simulates a strong damping effect, cooling the particle's center of mass. Existing systems for achieving three-dimensional cooling typically consist of multiple discrete optoelectronic modules, resulting in large size, cumbersome adjustment procedures, and extreme sensitivity to environmental vibrations and drift. This hinders the development of standardized and practical instruments.

[0004] Therefore, there is an urgent need for a new type of active cooling device that can solve the above problems, while maintaining the core simplicity advantage of single-beam suspension, and achieve efficient and highly integrated three-dimensional momentum feedback cooling. With a compact optical path and circuit design, it can effectively cool the center of mass motion of the suspended particles to the millikelvin (mK) level or even the quantum ground state temperature range. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] An active cooling device for a three-dimensional vacuum single-beam levitation system includes: a laser capture module, an electronic control system, and a triaxial cooling module;

[0007] The laser capture module includes a capture laser, a first plano-convex lens, a second plano-convex lens, a first dichroic mirror, a vacuum cavity, a capture objective lens, a condenser objective lens, a second dichroic mirror, and a bandpass filter. The capture objective lens and the condenser objective lens are disposed in the vacuum cavity. The capture laser, the first plano-convex lens, the second plano-convex lens, and the first dichroic mirror are arranged sequentially and coaxially along the x-axis. The first dichroic mirror, the capture objective lens, the condenser objective lens, and the second dichroic mirror are arranged sequentially and coaxially along the z-axis. The first dichroic mirror reflects the capture laser to the capture objective lens located in the vacuum cavity. Optical particles are loaded into an optical trap generated by the capture objective lens. The backscattered light from the optical particles is collected by the condenser objective lens located in the vacuum cavity and emitted in parallel. After being reflected by the second dichroic mirror to capture the laser, it is filtered by the bandpass filter and enters the electronic control system.

[0008] The third plano-convex lens of the triaxial cooling module is arranged coaxially with the first AOM along the x-axis. The height of the third plano-convex lens and the first AOM is flush with the optical floating particles in the optical trap. The cooling laser after weak focusing is incident on the vacuum cavity from the side. The axial cooling laser of the triaxial cooling module is diffracted by the second AOM. The first-order diffracted light is reflected by the third dichroic mirror and coaxial with the z-axis, and then incident on the vacuum cavity. The first AOM and the second AOM are respectively connected to the electronic control system.

[0009] The present invention has the following beneficial effects:

[0010] (1) The present invention suspends and cools micron-sized particles by single beam non-contact suspension. Compared with the traditional dual-beam momentum feedback vacuum optical tweezers system, it has a simple structure, does not require precise dual-beam alignment, and has the potential for miniaturization.

[0011] (2) The present invention uses a laser diode integrated small laser as a space light-cooled laser, which has low cost, small space occupation, convenient adjustment, and the optical path alignment can be assisted by camera imaging, resulting in high light efficiency.

[0012] (3) The present invention processes the optical levitation particle displacement signal through an integrated circuit board that integrates power supply and signal processing. The circuit board can be powered by PD and directly process the input optical levitation particle displacement signal into a momentum feedback output signal. The system has high integration and good real-time performance. Attached Figure Description

[0013] Figure 1This is a schematic diagram of the active cooling device of the three-dimensional vacuum single-beam suspension system of the present invention, wherein: 1-imaging camera, 2-capturing laser, 3-first plano-convex lens, 4-second plano-convex lens, 5-first dichroic mirror, 6-vacuum cavity, 7-capturing objective lens, 8-condensing objective lens, 9-second dichroic mirror, 10-bandpass filter, 11-third plano-convex lens, 12-first AOM, 13-radial cooling laser, 14-third dichroic mirror, 15-second AOM, 16-axial cooling laser, 17-four-quadrant detector, 18-first AOM driver, 19-second AOM driver, 20-analog signal processing PCB, 21-coaxial light source, xx axis, yy axis, zz axis;

[0014] Figure 2 This is a schematic diagram of the functional modules of the electronic control system of the present invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0016] This invention provides an active cooling device for a three-dimensional vacuum single-beam levitation system. This invention enables centroid cooling of the single-beam levitation system, achieving stable vacuum capture of optically levitated particles. Optically levitated particles within a vacuum cavity 6 are stably suspended by a single beam. When the vacuum level in the vacuum cavity 6 decreases to 100 Pa, radial cooling laser 13 and axial cooling laser 16 are simultaneously activated. While suspended in the single optical trap, the optically levitated particles are simultaneously subjected to triaxial orthogonal external optical force input. The electrical control system detects the centroid motion of the optically levitated particles in real time and transmits the voltage signal output from the four-quadrant detector 17 to the electrical control system for analysis, thereby obtaining the optical force driving signal. This optical force driving signal serves as the input signal for an acousto-optic modulator, altering the diffraction efficiency of the radial cooling laser 13 and the axial cooling laser 16, thus making the triaxial cooling input optical force opposite to the centroid motion velocity of the optically levitated particles, achieving centroid motion cooling of the optically levitated particles.

[0017] like Figure 1 As shown, the active cooling device for a three-dimensional vacuum single-beam suspension system of the present invention includes a laser capture module, an electrical control system, and a triaxial cooling module.

[0018] The laser capturing module consists of a capturing laser 2, a first plano-convex lens 3, a second plano-convex lens 4, a first dichroic mirror 5, a vacuum cavity 6, a capturing objective lens 7, a condenser objective lens 8, a second dichroic mirror 9, and a bandpass filter 10. The capturing objective lens 7 and the condenser objective lens 8 are disposed in the vacuum cavity 6. The capturing laser 2, the first plano-convex lens 3, the second plano-convex lens 4, and the first dichroic mirror 5 are arranged sequentially and coaxially along the x-axis. The first dichroic mirror 5, the capturing objective lens 7, the condenser objective lens 8, and the second dichroic mirror 9 are arranged sequentially and coaxially along the z-axis. The first dichroic mirror 5 reflects the captured laser to the capturing objective lens 7 located in the vacuum cavity 6. The optically levitated particles are loaded into the optical trap generated by the capturing objective lens 7 by piezoelectric ceramic support or atomization. The backscattered light of the optically levitated particles is collected by the condenser objective lens 8 located in the vacuum cavity 6 and emitted in parallel. After being reflected and captured by the second dichroic mirror 9, the laser light is filtered by the bandpass filter 10 and enters the electronic control system.

[0019] like Figure 1 As shown, in the laser capturing module, the captured laser 2 is a single-mode Gaussian beam. After being expanded by a beam expander group consisting of a first plano-convex lens 3 and a second plano-convex lens 4, it is reflected by a first dichroic mirror 5 and enters the vacuum cavity 6, where it is captured by the capturing objective lens 7 to form a three-dimensional suspended optical trap. After the captured light-floating particles are loaded into the three-dimensional suspended optical trap, the vacuum cavity 6 is evacuated until the vacuum level is below 500 Pa. The reflection wavelengths of the first dichroic mirror 5 and the second dichroic mirror 9 are matched with the wavelength of the captured laser 2. The beam expansion factor of the beam expander group consisting of the first plano-convex lens 3 and the second plano-convex lens 4 is usually selected as 3 to 5 times. The numerical aperture of the capturing objective lens 7 is 0.8 to 0.95, and the numerical aperture of the condenser objective lens 8 is 0.2.

[0020] like Figure 1As shown, the triaxial cooling module consists of a third plano-convex lens 11, a first AOM (Acousto-Optic Modulator) 12, a radial cooling laser 13, a third dichroic mirror 14, a second AOM 15, and an axial cooling laser 16. The first AOM 12 and the third plano-convex lens 11 are coaxial along the x-axis. The third plano-convex lens 11 is positioned on the side of the first AOM 12 closest to the vacuum cavity 6. The height of the first AOM 12 and the third plano-convex lens 11 along the z-axis is the same as the height of the optically levitated particles stably suspended in the optical trap. The radial cooling laser 13 is positioned on the other side of the first AOM 12. The height of the emitted laser is the same as the height of the incident aperture of the first AOM 12. Its direction of incidence on the first AOM 12 in the xy-plane has a slight tilt angle with the positive x-axis to ensure that the first AOM 12 has sufficiently high diffraction efficiency. The first-order diffracted light of the first AOM 12 is coaxial with the x-axis. After being weakly focused by the third plano-convex lens 11, it provides feedback force to the optical levitation particles in the x-axis direction (radial cooling requires y-axis cooling in addition to x-axis cooling; the optical path structure for y-axis cooling is the same as that for x-axis cooling (including the third plano-convex lens 11, the first AOM 12, and the radial cooling laser 13 connected in sequence), so it is not shown in the figure). The third dichroic mirror 14 is coaxial with the capturing objective 7 and the condensing objective 8 and is located in the positive z-axis direction of the second dichroic mirror 9; the second AOM 15 and the axial cooling laser 16 are sequentially located on one side of the third dichroic mirror 14, at the same z-axis height as the third dichroic mirror 14, and the first-order diffracted light diffracted by the second AOM 15 is coaxial with the third dichroic mirror 14 in the x-axis direction. After the axially cooled laser 16 is diffracted by the second AOM 15, the first-order diffracted light is reflected by the third dichroic mirror 14 and becomes coaxial with the z-axis, and is incident into the vacuum cavity 6. After being weakly focused by the condenser objective 8, it provides feedback force in the z-axis direction of the optical levitation particles.

[0021] Both radially cooled laser 13 and axially cooled laser 16 are generated by semiconductor laser diodes and output as parallel lasers after shaping. Their wavelengths are different from those of the capturing laser 2 and the coaxial light source 21. The reflection wavelength of the third dichroic mirror 14 is matched with that of the axially cooled laser 16. The central diffraction wavelengths of the first AOM 12 and the second AOM 15 are matched with the wavelengths of the radially cooled laser 13 and the axially cooled laser 16, respectively.

[0022] like Figure 1As shown, the active cooling device of the three-dimensional vacuum single-beam levitation system of the present invention also includes an imaging camera 1 and a coaxial light source 21, which are respectively set in the negative z-axis direction of the first dichroic mirror 5 and the positive z-axis direction of the third dichroic mirror 14; the coaxial light source 21 is used to provide field illumination for the imaging camera 1, and the imaging camera 1 is used to provide the operator with real-time captured images of the light-levitation particles, and to assist in adjusting the laser incident direction of the radial cooling laser 13 and the axial cooling laser 16 of the three-axis cooling module.

[0023] Imaging camera 1, capturing objective lens 7 and coaxial light source 21 are coaxial along the z-axis. The lens of imaging camera 1 is equipped with a filter, and the transmission wavelength of the filter is matched with that of coaxial light source 21.

[0024] like Figure 1 As shown, the electronic control system consists of a quadrant detector 17, a first AOM driver 18, a second AOM driver 19, and an analog signal processing PCB (printed circuit board) 20. The quadrant detector 17 receives the backscattered light from the optically levitated particles in real time to detect the position of the light spot and converts it into a voltage signal, which is then output to the analog signal processing PCB 20. The optically levitated particle centroid displacement feedback signal generated by the analog signal processing PCB 20 is input to the first AOM driver 18 and the second AOM driver 19. The first AOM driver 18 and the second AOM driver 19 control the diffraction efficiency of the first AOM 12 and the second AOM 15, respectively, thereby realizing the optical power modulation of the radially cooled laser 13 and the axially cooled laser 16 and the centroid displacement feedback control of the optically levitated particles.

[0025] Figure 2 The diagram shows the functional modules of the electronic control system. The analog signal processing PCB20 mainly includes the power supply section and the signal processing section.

[0026] The power supply section consists of a Type-C (USB interface standard) power supply interface, a DC-DC Buck (DC-DC step-down converter) circuit, and a bipolar LDO (linear regulator) module connected in sequence. The input of the DC-DC Buck circuit can be induced to 20V through the Type-C power supply interface PD (USB power transfer protocol, used for voltage / current negotiation between the device and the charger). The 20V power supply induced by PD is output as ±12V and input to the bipolar LDO for voltage regulation and filtering, providing a stable power supply for the operational amplifiers used in the differentiating circuit, biasing circuit, and limiting circuit of the signal processing section.

[0027] The signal processing section consists of a differentiating circuit, a bias circuit, and a limiting circuit connected in sequence. The differentiating circuit uses an integrated operational amplifier to differentiate the input optical levitation particle displacement signal, calculating the particle displacement in real time and converting it into a velocity signal, simultaneously generating a velocity feedback signal. The scaling factor of the differentiating circuit can be adjusted by an adjustable resistor to ensure the output velocity feedback signal varies within 1V. Simultaneously, the differentiating circuit includes a high-pass filter capacitor to prevent high-frequency signals from gaining too much and interfering with the velocity feedback signal after passing through the differentiating circuit. The bias circuit is an adder composed of an integrated operational amplifier, superimposing a 500mV DC bias voltage onto the velocity feedback signal to meet the analog input range of the first AOM driver 18 and the second AOM driver 19. To prevent oversaturation of the differentiated signal, a limiting circuit is designed using a Zener diode and an operational amplifier to clamp the feedback signal amplitude to 0-1V. The feedback signal is input to the first AOM driver 18 and the second AOM driver 19 to control the real-time cooling laser output power, providing cooling light force for the optical levitation particles.

[0028] The above description is merely an embodiment of the present invention and does not limit the scope of the invention. Any equivalent structural or procedural transformations made based on the description and drawings of this invention, or direct or indirect applications in other related system fields, are similarly included within the protection scope of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. An active cooling device for a three-dimensional vacuum single-beam levitation system, characterized in that, include: Laser capture module, electronic control system, and triaxial cooling module; The laser capturing module includes a capturing laser, a first plano-convex lens, a second plano-convex lens, a first dichroic mirror, a vacuum cavity, a capturing objective lens, a condenser objective lens, a second dichroic mirror, and a bandpass filter. The capturing objective lens and the condenser objective lens are disposed in the vacuum cavity. The capturing laser, the first plano-convex lens, the second plano-convex lens, and the first dichroic mirror are arranged sequentially and coaxially along the x-axis. The first dichroic mirror, the capturing objective lens, the condenser objective lens, and the second dichroic mirror are arranged sequentially and coaxially along the z-axis. The first dichroic mirror reflects the captured laser laser to the capturing objective lens located in the vacuum cavity. The optically levitated particles are loaded into the optical trap generated by the capturing objective. The backscattered light of the optically levitated particles is collected by the condenser objective located in the vacuum cavity and emitted in parallel. After being captured by the second dichroic mirror, the laser light is filtered by the bandpass filter and enters the electronic control system. The third plano-convex lens of the triaxial cooling module is arranged coaxially with the first AOM along the x-axis. The height of the third plano-convex lens and the first AOM is flush with the optical floating particles in the optical trap. The cooling laser after weak focusing is incident on the vacuum cavity from the side. The axial cooling laser of the triaxial cooling module is diffracted by the second AOM. The first-order diffracted light is reflected by the third dichroic mirror and coaxial with the z-axis, and then incident on the vacuum cavity. The first AOM and the second AOM are respectively connected to the electronic control system.

2. The active cooling device for the three-dimensional vacuum single-beam levitation system according to claim 1, characterized in that, Optical particles are loaded into an optical trap generated by a trapping objective lens using a piezoelectric ceramic support method or an atomization method.

3. The active cooling device for the three-dimensional vacuum single-beam levitation system according to claim 1, characterized in that, In the laser capture module, the captured laser is a single-mode Gaussian beam, which is expanded by a beam expander group consisting of a first plano-convex lens and a second plano-convex lens, and then reflected by a first dichroic mirror before entering the vacuum cavity. A three-dimensional suspended light trap is generated by the capture objective lens. After the captured optical particles are loaded into the three-dimensional suspended optical trap, the vacuum chamber is evacuated.

4. The active cooling device for the three-dimensional vacuum single-beam levitation system according to claim 1, characterized in that, The reflection wavelengths of the first and second dichroic mirrors are matched with the wavelength of the captured laser.

5. The active cooling device for a three-dimensional vacuum single-beam levitation system according to claim 1, characterized in that, The triaxial cooling module includes: a third plano-convex lens, a first AOM, a radial cooling laser, a third dichroic mirror, a second AOM, and an axial cooling laser; The first AOM and the third plano-convex lens are coaxial along the x-axis. The third plano-convex lens is positioned on the side of the first AOM closer to the vacuum cavity. The height of the first AOM and the third plano-convex lens along the z-axis is the same as the height of the optically levitated particles stably suspended in the optical trap. The radially cooling laser is positioned on the other side of the first AOM. The height of the emitted laser is the same as the height of the incident aperture of the first AOM. The direction of the laser incident on the first AOM in the xy plane has a slight tilt angle with the positive x-axis. The first-order diffracted light of the first AOM is coaxial with the x-axis and provides feedback force to the optically levitated particles along the x-axis after being weakly focused by the third plano-convex lens. The third dichroic mirror is coaxial with the capturing objective and the condenser objective and is positioned in the positive z-axis direction of the second dichroic mirror. The second AOM and the axially cooled laser are sequentially positioned on one side of the third dichroic mirror, with the same z-axis height as the third dichroic mirror. The first-order diffracted light diffracted by the second AOM is coaxial with the third dichroic mirror along the x-axis. After being diffracted by the second AOM, the first-order diffracted light of the axially cooled laser is reflected by the third dichroic mirror and becomes coaxial with the z-axis, and is incident into the vacuum cavity. After being weakly focused by the condenser objective, it provides feedback force in the z-axis direction for the optically levitated particles.

6. The active cooling device for a three-dimensional vacuum single-beam levitation system according to claim 5, characterized in that, Both radially cooled laser and axially cooled laser sources are generated by semiconductor laser diodes and output as parallel lasers after shaping. Their wavelengths are different from the wavelengths of the captured laser and the coaxial source. The reflection wavelength of the third dichroic mirror is matched with that of the axially cooled laser. The central diffraction wavelengths of the first AOM and the second AOM are matched with the wavelengths of the radially cooled laser and the axially cooled laser, respectively.

7. The active cooling device for a three-dimensional vacuum single-beam levitation system according to claim 5, characterized in that, Also includes: The imaging camera and coaxial light source are respectively positioned in the negative z-axis direction of the first dichroic mirror and the positive z-axis direction of the third dichroic mirror; the imaging camera, the capturing objective lens, and the coaxial light source are coaxial along the z-axis direction.

8. The active cooling device for the three-dimensional vacuum single-beam levitation system according to claim 7, characterized in that, The lens of the imaging camera is equipped with a filter whose transmission wavelength is matched to that of the coaxial light source.

9. The active cooling device for the three-dimensional vacuum single-beam levitation system according to claim 1, characterized in that, The electronic control system includes: a four-quadrant detector, a first AOM driver, a second AOM driver, and an analog signal processing PCB; the four-quadrant detector receives the backscattered light from the optically levitated particles in real time to detect the position of the light spot and converts it into a voltage signal, which is then output to the analog signal processing PCB; the optically levitated particle centroid displacement feedback signal generated by the analog signal processing PCB is input to the first AOM driver and the second AOM driver, and the first AOM driver and the second AOM driver control the diffraction efficiency of the first AOM and the second AOM, respectively.

10. The active cooling device for a three-dimensional vacuum single-beam levitation system according to claim 9, characterized in that, Analog signal processing PCBs include power supply sections and signal processing sections; The power supply section includes a Type-C power interface, a DC-DC Buck circuit, and a bipolar LDO module connected in sequence. The signal processing section includes a differentiating circuit, a bias circuit, and a limiting circuit connected in sequence. The differentiating circuit performs differential operations on the input optical levitation particle displacement signal through an integrated operational amplifier, calculates the optical levitation particle displacement in real time, converts it into a velocity signal, and synchronously generates a velocity feedback signal. The scaling factor of the differentiating circuit is adjusted by an adjustable resistor. The bias circuit is an adder composed of an integrated operational amplifier.

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