阅读说明：本技术 一种用于真空光镊系统的微粒多次起支实验装置及方法 (Particle repeated supporting experimental device and method for vacuum optical tweezers system ) 是由 李楠 祝训敏 舒晓武 胡慧珠 刘承 于 2020-03-11 设计创作，主要内容包括：本发明公开了一种用于真空光镊系统的微粒多次起支实验装置及方法。电动平移台上面安装有超声波换能器,超声波换能器上固定有基板；电动平移台侧方设有金属箱,金属箱内安装有可移动底板,可移动底板底面和金属箱内底面之间连接有弹簧,可移动底板顶面之上的金属箱上部腔内充满有微粒；聚焦光束在真空腔内,聚焦光束的焦点在超声波换能器侧方和金属箱之间且位于基板和金属箱之间的正下方；基板靠近金属箱的一端作为吸附端,吸附端加工成削尖的尖头形态,金属箱在靠近正对基板吸附端的侧壁开设有槽口。本发明将真空光镊系统中的微粒起支次数从数十次提高至数千次,进一步保证了整体实验系统的稳定性,具有实际应用价值。(The invention discloses a device and a method for a particle multi-support experiment of a vacuum optical tweezers system. An ultrasonic transducer is arranged on the electric translation table, and a substrate is fixed on the ultrasonic transducer; a metal box is arranged at the side of the electric translation table, a movable bottom plate is arranged in the metal box, a spring is connected between the bottom surface of the movable bottom plate and the inner bottom surface of the metal box, and a cavity at the upper part of the metal box above the top surface of the movable bottom plate is filled with particles; the focused light beam is in the vacuum cavity, and the focus of the focused light beam is between the side of the ultrasonic transducer and the metal box and is positioned right below the space between the substrate and the metal box; one end of the base plate close to the metal box is used as an adsorption end, the adsorption end is processed into a pointed tip shape, and a notch is formed in the side wall of the metal box close to the adsorption end opposite to the base plate. The invention improves the supporting times of the particles in the vacuum optical tweezers system from dozens of times to thousands of times, further ensures the stability of the whole experiment system and has practical application value.)

1. A microparticle plays a set of experimental apparatus many times for vacuum optical tweezers system which characterized in that: comprises a vacuum cavity (9), a focusing beam (1) positioned in the vacuum cavity (9), a substrate (2), an ultrasonic transducer (3), an electric translation table (4), a metal box (6), a movable bottom plate (7) and a spring (8); an ultrasonic transducer (3) is arranged on the electric translation table (4), and a substrate (2) is fixed on the ultrasonic transducer (3); a metal box (6) is arranged on the side of the electric translation table (4), a movable bottom plate (7) is arranged in the metal box (6), a spring (8) is connected between the bottom surface of the movable bottom plate (7) and the inner bottom surface of the metal box (6), and a cavity at the upper part of the metal box (6) above the top surface of the movable bottom plate (7) is filled with particles (5); the focused light beam (1) is in the vacuum cavity (9), and the focus of the focused light beam (1) is positioned between the side of the ultrasonic transducer (3) and the metal box (6) and is positioned right below the space between the substrate (2) and the metal box (6); one end of the base plate (2) close to the metal box (6) is used as an adsorption end, the adsorption end is processed into a pointed tip shape, and the metal box (6) is provided with a notch close to the side wall opposite to the adsorption end of the base plate (2).

2. The apparatus according to claim 1, wherein the apparatus comprises: the shape of the particles (5) includes but is not limited to sphere, rod and dumbbell.

3. The apparatus according to claim 1, wherein the apparatus comprises: the radial dimensions of the particles (5) in three spatial dimensions are between a few nanometers and several hundred micrometers.

4. The apparatus according to claim 1, wherein the apparatus comprises: the size of a notch formed in the side wall, close to the side wall opposite to the adsorption end of the substrate (2), of the metal box (6) enables the adsorption end of the substrate (2) to be just inserted.

5. The apparatus according to claim 1, wherein the apparatus comprises: the focused light beam (1) is laser which is generated by a light source outside the vacuum cavity (9) and is incident into the vacuum cavity.

6. The apparatus according to claim 1, wherein the apparatus comprises: the ultrasonic transducer is characterized by further comprising an ultrasonic driver (10) and a translation stage driver (11), wherein the ultrasonic driver (10) and the translation stage driver (11) are located outside the vacuum cavity (9), the ultrasonic transducer (3) is connected with the ultrasonic driver (10) through a lead, the electric translation stage (4) is connected with the translation stage driver (11) through a lead, and the ultrasonic transducer (3) and the electric translation stage (4) are controlled to work by the ultrasonic driver (10) and the translation stage driver (11) respectively.

7. A vacuum optical tweezers particle multiple supporting experiment method applied to the device of any one of claims 1 to 6, characterized by comprising the following steps:

step 1): loading particles: the electric translation table (4) moves towards the direction close to the metal box (6) to enable the adsorption end of the substrate (2) to be inserted into the notch of the metal box (6), so that particles (5) are attached to the lower surface of the adsorption end of the substrate (2);

step 2): and (3) capturing particles: the electric translation table (4) moves towards the direction far away from the metal box (6) to enable the adsorption end of the substrate (2) to be positioned right above the focus of the focused light beam (1), the ultrasonic transducer (3) works and vibrates to drive the substrate (2) to vibrate and fall particles (5), and one of the particles (5) is captured by light radiation pressure when the gravity falls to pass through the focus of the focused light beam (1);

step 3): the electric translation table (4) moves towards the direction far away from the metal box (6) so that the front end of the substrate (2) moves out of the position right above the focus of the light beam, the position right above the focus of the focused light beam (1) is in an unblocked state, and the position right above the captured particles (5) is in an unblocked state;

step 4): performing an optical tweezers experiment on the trapped particles (5);

step 5): in the experimental process, if the particles (5) at the focus of the focused light beam (1) are lost and the particles (5) are still attached to the lower surface of the adsorption end of the substrate (2), repeating the steps 2) -4) to support the particles (5) again and continuing the experiment;

if the particles (5) at the focus of the focused light beam (1) are lost, and the particles (5) are not attached to the lower surface of the adsorption end of the substrate (2) but still exist in the metal box (6), repeating the steps 1-4) to support the particles (5) again, and continuing the experiment;

otherwise, opening the vacuum cavity (9), supplementing the particles (5) into the metal box (6), repeating the steps 1) -4), starting the particles (5) again, and continuing the experiment.

8. The vacuum optical tweezers particle multiple supporting experiment method according to claim 7, wherein:

the number of the particles attached to the lower surface of the substrate (2) in the step 2) is at least two orders of magnitude lower than that of the particles in the metal box (6), and the particles (5) attached to the lower surface of the substrate (2) are repeatedly lifted and supported for multiple times.

Technical Field

The invention relates to a device and a method for supporting particles in optical tweezers, in particular to a device and a method for supporting particles for a vacuum optical tweezers system for multiple times.

Background

In 1971, the american physicist Ashkin et al first stabilized optically suspended glass particles of 20um diameter by weakly focusing a beam of vertically upward propagating laser light with a lens. In 1986, he discovered that particles could be stably trapped without relying on gravity after focusing the single-beam laser intensity, and this technique was named optical tweezers. In 2018, Ashkin awards the Nobel prize for the optical tweezers technology of the invention. The principle of the optical tweezers is that a strong focusing laser beam generates a force which is always directed to a focal point on a medium particle, the magnitude of the force is in direct proportion to the gradient of an electric field, so that the force is called as gradient force, and the medium particle is three-dimensionally trapped near the focal point. The optical tweezers provide an excellent means for controlling and measuring the characteristics of a micrometer-to-submicron-scale object, such as non-contact, nondestructive and high spatial time resolution, and have wide application and attractive prospects in the aspects of biology, high-sensitivity sensing, quantum physics and the like.

Ashkin predicts that when first achieving particle suspension in vacuum: if the (air) viscous damping is further reduced, it will be possible to use (vacuum optical tweezers) for implementing inertial sensors like gyroscopes and accelerometers. "in recent years, it has been found that subjecting trapped media particles to a vacuum environment, i.e., to isolate the effects of external thermodynamic noise, results in measurement accuracy that far exceeds current conventional approaches. For example, the David Moore group at yale university has achieved an acceleration measurement sensitivity in the ng class in 2017, which is 3 orders of magnitude higher than the detection sensitivity achievable by mechano-mechanical sensors at room temperature. The vacuum optical tweezers have shown important application value in the aspects of precision mechanical quantity measurement, high-performance inertial sensors and the like.

Both theory and experiment show that for silica particles with a diameter of more than 1um in air, the laser light, at a power of 100mW and a focusing numerical aperture of 0.5, has a resultant force on the particles acting near the focal point and is not directed to the focal point but along the light transmission direction. The numerical aperture needs to be increased to create a force directed to the focal point. However, the high numerical aperture requires a combination of multiple lenses to suppress the aberration increased with the increase of the aperture angle of the object space or (and) the environment of the oil immersion medium, which significantly increases the volume and cost of the optical tweezers system, and the oil immersion is not suitable for the application of air or vacuum optical tweezers. The increase of the focus numerical aperture is limited. In summary, particles with diameters above 1um cannot be stably captured in air and vacuum environments using only a single strongly focused beam without relying on gravity or other factors. On the other hand, in a high vacuum environment, the minimum measurable acceleration value of particles is inversely proportional to √ m (m is the mass of the particles), and more mass of particles is required for higher sensitivity acceleration measurements.

Two strongly focused beams of light aimed at trapping particles over 1um in diameter are a viable alternative to optical paths. In the scheme, two light beams are required to be focused and focused to coincide, the optical axes of the two light beams coincide, and the coincidence degree directly influences the capture stability of the particles. Since it is difficult for devices such as lasers to be compatible with vacuum, a part of the optical elements is generally placed outside the vacuum chamber. The method of transferring particles from outside the vacuum chamber into the chamber for lifting is called "out-of-chamber lifting". The disadvantage of the support outside the cavity is that the vacuum cavity needs to be sealed after the support is lifted, and the relative displacement of the internal and external optical elements of the vacuum cavity can be caused in the process of sealing the vacuum cavity, so that the coincidence degree of the focusing focuses of two reflected light beams is damaged, and the capture stability of particles is influenced.

The intracavity supporting method of supporting particles in a vacuum chamber is an alternative solution to avoid the above-mentioned optical path destruction. But the number of starts in the chamber is limited by the number of particles that can be loaded on the substrate. The number of particles remaining on a single substrate generally decreases exponentially with the number of counted particles, and each time the particles on the substrate are depleted by shock, the vacuum chamber must be opened to replenish the particles and the alignment path is broken. The total number of the existing intracavitary supporters is generally in the order of ten. In practical engineering application, once the particles are separated from the focal point of the optical tweezers, the optical tweezers apparatus stops working, and the particles must be supported as soon as possible. Therefore, the optical tweezers instrument can be used for multiple supporting in the cavity, the maintainability of the optical tweezers instrument can be improved, and the single continuous measurement life of the optical tweezers instrument can be prolonged.

On the other hand, in the conventional method for directly supporting particles in a vacuum chamber, since an upward propagating light beam which is difficult to adjust by gravity and the use of an optical path is avoided, the substrate is inevitably on the optical path of a focused light beam which vertically propagates downward. The existing method for selecting transparent materials for the substrate can influence the measurement precision of an optical tweezers system because the substrate and particles attached to the substrate generate aberration in a vertical focusing beam; the substrate hole digging method reduces the surface density of particles near the focus of the light beam when the particles are supported, and reduces the success rate of capturing the particles by the light beam.

Therefore, the research on the device and the method for supporting particles in the vacuum cavity for multiple times with high success rate without influencing the measurement precision of the optical tweezers system has important significance for improving the operation stability, the measurement continuity, the measurement precision and the like of the whole optical tweezers system.

Disclosure of Invention

Aiming at the current situation that the total number of times of starting and supporting of the existing direct starting and supporting method in a cavity is generally in the order of ten times, the starting and supporting times are few, and the performances of particle capture stability, measurement continuity, measurement accuracy and the like of an optical tweezers system are insufficient in the current optical tweezers research, the invention provides the device and the method for the multiple starting and supporting experiment of the particles for the vacuum optical tweezers system, which can improve the starting and supporting times of the particles in the vacuum optical tweezers system from tens of times to thousands of times, further ensure the stability of the whole experiment system and have practical application value.

The invention adopts the following specific technical scheme:

a microparticle multi-support experimental device for a vacuum optical tweezers system comprises:

the device comprises a vacuum cavity, a focusing light beam, a substrate, an ultrasonic transducer, an electric translation table, a metal box, a movable bottom plate and a spring, wherein the focusing light beam, the substrate, the ultrasonic transducer, the electric translation table, the metal box, the movable bottom plate and the spring are positioned in the vacuum cavity; an ultrasonic transducer is arranged on the electric translation table, and a substrate is fixed on the ultrasonic transducer; a metal box is arranged at the side of the electric translation table, a movable bottom plate is arranged in the metal box, a spring is connected between the bottom surface of the movable bottom plate and the inner bottom surface of the metal box, and a cavity at the upper part of the metal box above the top surface of the movable bottom plate is filled with particles; the focused light beam is in the vacuum cavity, and the focus of the focused light beam is between the side of the ultrasonic transducer and the metal box and is positioned right below the space between the substrate and the metal box; one end of the base plate close to the metal box is used as an adsorption end, the adsorption end is processed into a pointed tip shape, and a notch is formed in the side wall of the metal box close to the adsorption end opposite to the base plate.

The particle shapes include, but are not limited to, spheres, rods, and dumbbells.

The radial size of the particles in three dimensions of space is between a few nanometers and hundreds of micrometers.

The metal box is close to the side wall opposite to the substrate adsorption end and is provided with a notch, so that the substrate adsorption end can be just inserted.

The focused light beam is laser light generated by a light source outside the vacuum cavity and is incident into the vacuum cavity, but is not limited to laser light

The vacuum cavity is provided with an ultrasonic driver and a translation stage driver, the ultrasonic driver and the translation stage driver are positioned outside the vacuum cavity, the ultrasonic transducer is connected with the ultrasonic driver through a lead, the electric translation stage is connected with the translation stage driver through a lead, and the ultrasonic transducer and the electric translation stage are controlled to work by the ultrasonic driver and the translation stage driver respectively.

The optical axis direction of the focused light beam includes, but is not limited to, a direction parallel or perpendicular to a connecting line between the motorized translation stage and the metal box, and also includes, but is not limited to, a horizontal direction and a vertical direction.

The substrate material includes, but is not limited to, ceramic, glass, and metal.

The ultrasonic transducer refers to an element for converting electric energy into vibrational kinetic energy, and includes but is not limited to piezoelectric ceramics and a rotating permanent magnet motor.

The electric translation stage is an element for converting electric energy into translation kinetic energy, and includes but is not limited to a piezoelectric actuator and a linear permanent magnet motor.

The three-dimensional size of the substrate adsorption end is in millimeter order of magnitude.

Secondly, a vacuum optical tweezers particle multi-time supporting experiment method:

step 1): loading particles: the electric translation table moves towards the direction close to the metal box to enable the substrate adsorption end to be inserted into the notch of the metal box, so that a batch of particles are adsorbed and attached to the lower surface of the substrate adsorption end;

step 2): and (3) capturing particles: the electric translation table moves towards the direction far away from the metal box so that the adsorption end of the substrate is positioned right above the focus of the focused light beam, the ultrasonic transducer works and vibrates to drive the substrate to vibrate and fall a plurality of particles, and one of the particles is captured by light radiation pressure when the gravity of the particles falls through the focus of the focused light beam;

step 3): the electric translation table moves towards the direction far away from the metal box so that the front end of the substrate moves out of the position right above the focus of the light beam, and the position right above the focus of the focused light beam is in an unblocked state, namely the position right above the captured particles is in an unblocked state;

step 4): performing an optical tweezers experiment on the captured particles;

step 5): in the experimental process, if the particles at the focus of the focused light beam are lost and the particles are still attached to the lower surface of the adsorption end of the substrate, repeating the steps 2) -4) to support the particles again and continuing the experiment;

if the particles at the focus of the focused light beam are lost, and the particles are not attached to the lower surface of the adsorption end of the substrate but still exist in the metal box, repeating the steps 1) -4) to support the particles again, and continuing the experiment;

otherwise, opening the vacuum cavity, replenishing the particles into the metal box, repeating the steps 1) -4) again to support the particles, and continuing the experiment.

When the adsorption end of the substrate is drawn out of the notch of the metal box in the step 2), particles are attached to the lower surface of the adsorption end of the substrate, the number of the particles in the metal box is reduced, the volume of the inner cavity is also reduced, the spring in a compressed state pushes the movable bottom plate upwards to compress the space of the inner cavity, so that the particles are always in a full-filling and pressing state, and when the step 1) is repeated next time, the adsorption end of the substrate can be fully contacted with the particles, and the density of an attachment surface is increased.

The number of the particles attached to the lower surface of the substrate in the step 2) is at least two orders of magnitude lower than that of the particles in the metal box, and the particles attached to the lower surface of the substrate are repeatedly supported for multiple times.

The device and the support method can ensure the support times of thousands of orders of magnitude, and the performance can be improved by two orders of magnitude compared with the traditional support method for loading particles on the lower surface of the substrate outside the vacuum cavity.

The size of the focus beam waist of the focused light beam in the steps 1), 2) and 3) is between one tenth of micrometers and tens of micrometers, the stroke range of the electric translation stage is ensured, and the substrate can move out of the position right above the focus of the focused light beam by backward movement, so that the position right above the captured particles near the focus is in a non-shielding state, and a space is reserved for subsequent observation.

The substrate insertion depth may be one to two orders of magnitude higher than the focal beam waist size of the focused beam. Therefore, the stroke range of the electric translation stage does not exceed several millimeters, and the design is favorable for reducing the volume of the whole device.

In the step 3), the position right above the captured particles near the focal point is in an unobstructed state, space is reserved for subsequent observation, and a transparent material is selected relative to the substrate. Compared with the method of digging holes at the position of the substrate right above the focus of the focused light beam, the method improves the surface density of the particles near the focus of the light beam when the particles are supported, and greatly increases the success rate of capturing the microspheres by the light beam.

The invention has the beneficial effects that:

the invention avoids the damage to the light path caused by closing the vacuum cavity after the support in the cavity, and influences the particle capture stability and the measurement precision of the optical tweezers system; the micro-sphere capturing device has the advantages that the micro-sphere is loaded to the translation table, the metal box and other elements on the substrate in the cavity, the number of times of starting and supporting in the existing cavity is increased from typical tens of orders to thousands of orders, and compared with the existing substrate, the transparent material is selected, and the substrate hole digging method avoids optical path aberration of a vertically focused light beam and increases the success rate of capturing the micro-sphere by the light beam.

Therefore, the invention has practical application value and can improve the capture stability, the measurement continuity and the measurement precision of the whole optical tweezers system.

Drawings

FIG. 1 is a schematic diagram showing the construction of the device;

FIG. 2 is a schematic structural diagram of the elements in step 1) in the first embodiment;

FIG. 3 is a schematic view of the device structure in step 2) according to the first embodiment;

FIG. 4 is a graph showing the distance that the microspheres have fallen when their velocity reaches the equilibrium velocity at different initial velocities;

fig. 5 is a schematic structural diagram of the elements in step 3) in the first embodiment.

In the figure, 1, focused beam, 2, substrate, 3, ultrasonic transducer, 4, motorized translation stage, 5, particle, 6, metal box, 7, movable bottom plate, 8, spring, 9, vacuum chamber, 10, ultrasonic driver, 11, translation stage driver. The dimensions of the various elements in the figures are not intended to represent actual dimensions of the elements.

Detailed Description

The invention is further illustrated by the following figures and examples.

As shown in fig. 1, the embodiment of the present invention comprises a vacuum chamber 9, and a focused light beam 1, a substrate 2, an ultrasonic transducer 3, an electric translation stage 4, a metal box 6, a movable bottom plate 7 and springs 8 which are positioned in the vacuum chamber 9; an ultrasonic transducer 3 is arranged on the electric translation table 4, and a substrate 2 is fixed on the ultrasonic transducer 3; the metal box 6 is arranged on the side of the electric translation table 4, the particles 5, the movable bottom plate 7 and the spring 8 are all arranged in the metal box 6, the movable bottom plate 7 is arranged in the metal box 6, the spring 8 is connected between the bottom surface of the movable bottom plate 7 and the inner bottom surface of the metal box 6, and the cavity on the upper part of the metal box 6 above the top surface of the movable bottom plate 7 is filled with the particles 5. The movable base 7 is in the sub-particle position, the spring 8 is always in compression, and the elements 3 to 8 are all vacuum compatible elements.

Within the vacuum chamber 9 is a focused beam of light 1. the focused beam of light 1 is a laser light, but is not limited to a laser light, emitted by a light source within the vacuum chamber 9. The focus of the focused beam 1 is between the side of the ultrasonic transducer 3 and the metal box 6 and is positioned right below the space between the substrate 2 and the metal box 6; one end of the base plate 2 close to the metal box 6 serves as an adsorption end, the adsorption end is processed into a pointed tip shape, and the metal box 6 is close to the side wall opposite to the adsorption end of the base plate 2 and is provided with a notch.

The electric translation table 4 drives the ultrasonic transducer 3 to move horizontally so as to drive the substrate 2 to move horizontally, so that the adsorption end of the substrate 2 is horizontally inserted into the notch of the metal box 6. The size of the notch formed on the side wall of the metal box 6, which is close to the adsorption end of the substrate 2, enables the adsorption end of the substrate 2 to be just inserted. In the stroke range of the electric translation table 4, the electric translation table moves towards the direction far away from the metal box 6 to enable the substrate 2 to move out of the position right above the focus of the focused light beam 1, so that the position right above the captured particles near the focus is in a non-shielding state, and the electric translation table moves towards the direction close to the metal box 6 to enable the adsorption end of the substrate 2 to be inserted into the notch of the metal box 6.