CN111983708B

CN111983708B - Gravity measurement device and method based on optical trap

Info

Publication number: CN111983708B
Application number: CN202010790955.7A
Authority: CN
Inventors: 胡慧珠; 李文强; 李楠; 陈杏藩; 舒晓武; 刘承
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2020-08-07
Filing date: 2020-08-07
Publication date: 2021-11-23
Anticipated expiration: 2040-08-07
Also published as: CN111983708A

Abstract

The invention discloses a gravity measurement device and method based on an optical trap. The device includes an optical trap capturing module, a vacuum module, a feedback module and a position detection module. The vacuum module is used to realize that the microspheres are in a high vacuum environment during gravity testing; the optical trap capturing module is used to capture the microspheres in a vacuum environment and cool their center of mass. Movement, the laser light intensity is adjusted to zero by the acousto-optic modulator (AOM) to close the optical trap, at this time the microspheres will fall freely under the action of gravity, after a short time, the AOM is controlled to reopen the optical trap, and the microspheres are re-captured , and the free fall process of the microspheres is measured by the position detection module, and the absolute gravity measurement can be performed according to the falling process of the microspheres. Repeating the above process can achieve continuous measurement of absolute gravity. The invention utilizes the optical trap to realize the free fall of the suspended microspheres under high vacuum conditions, thereby calibrating the absolute gravity of the environment, and has the advantages of short test time, small size of the device and continuous measurement of absolute gravity.

Description

Gravity measurement device and method based on optical trap

Technical Field

The invention relates to the technical field of optical trap based measurement, in particular to a gravity measurement device and method based on an optical trap.

Background

According to the quantum theory, a light beam is a group of photons which move at the speed of light and have mass and momentum, when the photons are incident on the surface of a medium, refraction and reflection are generated, the speed and the direction of the photons are changed, so that the momentum vector of the photons is changed, the change can be deduced by the law of momentum conservation, when the light beam irradiates on particles, the momentum change of the photons is equal to the momentum change of the particles, so that the light beam has mechanical action on the particles, namely optical radiation pressure, the optical radiation pressure comprises scattering force along the propagation direction of the light beam and gradient force always pointing to the position with larger light intensity, and under the action of the two forces, the light beam can capture the particles in a certain area, so that the particles are stabilized at a certain position, and the area is called an optical trap.

The existing gravity measurement mode mainly utilizes a mode of mechanically releasing a mass block, and realizes measurement of the absolute gravity of the mass block through the free falling motion of the mechanical block, but the measurement mode has the defects of complex reset, large volume, multiple error factors and the like.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a gravity measurement device and method based on an optical trap.

An optical trap-based gravity measurement device, comprising four modules: the device comprises an optical trap capturing module, a vacuum module, a position detection module and a feedback module;

the optical trap capturing module is used for stabilizing the suspended microspheres, and simultaneously, the opening and closing of the optical trap can be controlled through an acousto-optic modulator (AOM), so that the microspheres can freely fall;

the vacuum module is used for ensuring that the suspension capture of the microspheres is realized under a high vacuum condition and the gravity measurement is carried out, so that the influence of air molecule flow and collision on the detection precision is reduced;

the position detection module is used for realizing the detection of the movement information of the microspheres so as to obtain the landing distance of the microspheres when the microspheres freely land;

the feedback module is used for transmitting the movement information of the microspheres to an upper computer, and simultaneously outputting feedback signals for completing the mass center movement cooling of the microspheres according to the acquired movement information of the microspheres.

The optical trap capturing module comprises a laser, an acousto-optic modulator (AOM), a reflector and a focusing lens, wherein the laser outputs high-intensity laser to suspend the microspheres, the AOM completes the movement and cooling of the mass center of the microspheres by adjusting the light intensity of the laser, controls the optical trap to be closed to enable the microspheres to freely fall, and the focusing lens is used for focusing the laser to construct an optical trap for capturing the microspheres at a focus.

The vacuum module comprises a vacuum cavity and a vacuum pump, the vacuum cavity is used for ensuring that the microspheres are in a high vacuum condition during capture, the vacuum pump is used for adjusting the pressure in the vacuum cavity, and optical windows are arranged on two sides of the vacuum cavity to ensure that captured laser passes through.

The position detection module comprises a light spot displacement detector and a converging lens, the converging lens is used for collecting scattered light of the microspheres, then the scattered light is converged on the light spot position detector, and position information of the microspheres is obtained by analyzing light field distribution on the light spot position detector.

The feedback module comprises a Field Programmable Gate Array (FPGA) and an upper computer PC, wherein the FPGA can acquire microsphere position information and output the microsphere position information to the upper computer to realize communication, and meanwhile, a feedback control algorithm in the FPGA outputs a feedback signal according to a microsphere motion signal to control the AOM to adjust the light intensity, so that the centroid cooling of the microsphere motion is realized.

The microsphere is an optically uniform transparent microsphere with the size of nanometer to millimeter magnitude.

The testing method of the device comprises the following steps:

1) after the optical trap captures the microspheres, the movement information of the microspheres is detected in real time through a position detection module, displacement signals obtained by the detection of the position detection module are input into an FPGA (field programmable gate array), the FPGA transmits the position information to an upper computer, and simultaneously outputs feedback signals by using an internal algorithm, and the feedback signals adjust an AOM (automatic optical module) so as to control the laser intensity to inhibit the mass center movement of the microspheres;

2) when the microspheres need to freely fall, the AOM is controlled through the FPGA to enable the output light intensity to be 0, the optical trap is in a non-working state at the moment, the microspheres freely fall under the action of gravity, after milliseconds, the optical trap is opened again through the AOM, the positions of the initial and final states of the falling of the microspheres are recorded, and the gravity is calculated according to the falling time and the falling distance of the microspheres;

3) after the optical trap is opened again, the microspheres overcome the gravity under the action of the optical trap force and are lifted to the initial capturing position again, at the moment, the movement state of the microspheres is cooled again by the AOM, and then the environmental gravity calibration can be repeatedly carried out in the system.

The invention has the beneficial effects that:

according to the characteristic that the optical trap can suspend microspheres, after the optical trap suspends the microspheres in a high-vacuum environment, the laser intensity is modulated through the AOM, so that the optical trap is closed temporarily, the microspheres can fall freely under the action of gravity during the period, then the optical trap is opened again through the AOM to measure the positions of the microspheres, the falling time and the distance of the microspheres are calculated, and the measurement and calibration of the environment gravity are completed;

the optical trap is opened and closed by using the AOM, so that the gravity measurement can be completed in a very short time, and in addition, after the optical trap is opened to stably capture the microspheres again, the gravity measurement of the microspheres can be realized again by using the process, so that the scheme has the advantage of multiple gravity measurements;

the optical trap is used for measuring gravity under the high vacuum condition, the interference of air molecules of the environment on the microspheres is small, the AOM inhibits the movement speed of the microspheres in the vertical direction before the microspheres land, so that the initial landing speed of the microspheres approaches to zero, and higher gravity measurement precision can be obtained.

The invention has the advantages that the general gravity measuring device does not have: compared with the traditional gravimeter, the working range of the gravity measuring device is only a plurality of millimeters, and the gravity measuring device has the advantage of miniaturization; in addition, the photo-induced suspension microspheres are utilized, the gravity of the microspheres can be measured in a high vacuum environment, and the collision of air molecules in the high vacuum environment is less, so that the method has high sensitivity; after each detection, the optical trap can be used for capturing the microspheres again, so that the repeated measurement of the gravity can be realized.

Drawings

FIG. 1 is a schematic diagram of a gravity measurement device module based on an optical trap.

Fig. 2 is a block diagram of an embodiment of the apparatus of the present invention.

Detailed Description

The invention is further elucidated below with reference to the accompanying drawing.

Referring to fig. 1, the optical trap-based gravity measurement device includes four modules, namely, an optical trap capturing module, a position detecting module, a feedback module, and a vacuum module.

Referring to fig. 2, the optical trap capturing module includes a laser 1, an AOM2, a reflector 3, and a focusing lens 4, the laser can emit high-power laser, and after being modulated by the AOM light intensity and focused by the focusing lens, the laser can be configured into a high-focusing light spot, and a microsphere can be stably captured at the focusing light spot.

Referring to fig. 2, the vacuum module includes a vacuum chamber 10 and a vacuum pump 11, wherein the vacuum chamber is a closed chamber for ensuring that the gravity testing environment is in a vacuum state, and the vacuum pump includes an air pump and a molecular pump for reducing the pressure in the vacuum chamber to a high vacuum condition.

Referring to fig. 2, the position detection module includes a converging lens 6 and a light spot position detector 7, where the converging lens is used to collect a scattered light field after interaction between the microsphere and the light field, and when the position of the microsphere moves, the shape of the light spot projected onto the light spot position detector through the converging lens also changes correspondingly, so as to complete analysis of the position of the microsphere.

Referring to fig. 2, the feedback device comprises an upper computer PC8 and an FPGA9, wherein a position signal in the position detection module is input into the FPGA, the FPGA inputs position information of the microspheres into the upper computer for real-time display, and outputs a control signal for inhibiting the movement speed of the microspheres through a PID algorithm, and the feedback signal regulates the AOM to control the laser intensity, thereby realizing the cooling of the centroid of the movement of the particles.

The method comprises the following specific implementation steps:

1) after the optical trap captures the microspheres, detecting the movement information of the microspheres in real time through a position detection module, inputting displacement signals obtained by the detection of the position detection module into an FPGA (field programmable gate array), outputting signals for inhibiting the movement of the microspheres by using a related algorithm in the FPGA, outputting the signals to an AOM (automatic optical network), and controlling the laser intensity through the AOM so as to inhibit the movement of the mass center of the microspheres;

2) when the microspheres need to freely fall, the AOM is controlled through the FPGA to enable the output light intensity to be 0, the optical trap is in a non-working state at the moment, the microspheres freely fall under the action of gravity, after a short time (several milliseconds), the optical trap is opened again through the AOM, the falling distance of the microspheres is calculated at the moment, and the gravity can be calculated according to the falling time of the microspheres;

3) and after the optical trap is opened again, the microspheres overcome the gravity under the action of the optical trap force, rise to the initial capturing position again, re-cool the motion state of the microspheres by using the AOM, and repeat the process to calibrate the environmental gravity again.

Finally, the above embodiments are merely illustrative and not restrictive, and it should be understood by those skilled in the art that modifications and equivalents may be made to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention, and all such modifications and equivalents are intended to be included in the scope of the claims of the present invention.

Claims

1. a gravity measuring device based on optical trap, is characterized in that, described device comprises four modules: optical trap capture module, vacuum module, position detection module and feedback module;

The optical trap trapping module is used to stably suspend the microspheres, and at the same time, the optical trap can be controlled to open and close through the acousto-optic modulator (AOM), so as to realize the free fall of the microspheres;

The vacuum module is used to ensure the suspension capture of microspheres and gravity measurement under high vacuum conditions, thereby reducing the influence of air molecular flow and collision on detection accuracy;

The position detection module is used to detect the motion information of the microsphere, so as to obtain the landing distance of the microsphere when it falls freely;

The feedback module is used to transmit the motion information of the microspheres to the host computer, and at the same time, according to the collected motion information of the microspheres, a feedback signal is output to complete the cooling of the centroid motion of the microspheres;

The optical trap capturing module includes a laser, an acousto-optic modulator AOM, a mirror and a focusing lens. The laser outputs high-intensity laser light to suspend the microsphere, and the AOM completes the cooling of the center of mass of the microsphere by adjusting the laser light intensity. The optical trap is controlled to be closed to make the microspheres fall freely, and the focusing lens is used to focus the laser to construct an optical trap that captures the microspheres at the focal point;

The vacuum module includes a vacuum chamber and a vacuum pump, the vacuum chamber is used to ensure that the microspheres are captured in a high vacuum condition, the vacuum pump is used to adjust the pressure in the vacuum chamber, and the two sides of the vacuum chamber are optical windows to ensure the passage of the captured laser light;

The position detection module includes a spot displacement detector and a converging lens. The converging lens is used to collect the scattered light of the microspheres, and then the scattered light is collected on the spot position detector. ball position information;

The feedback module includes a field programmable gate array (FPGA) and a host computer PC, wherein the FPGA can collect the position information of the microspheres and output it to the host computer for communication, and the feedback control algorithm inside the FPGA is based on the movement of the microspheres. The signal output feedback signal controls the AOM to adjust the light intensity, so as to realize the cooling of the center of mass of the microsphere movement;

The microspheres are optically uniform and transparent microspheres with sizes ranging from nanometers to millimeters.

2. the testing method of device according to claim 1 is characterized in that, comprises the steps:

1) After the optical trap captures the microspheres, the motion information of the microspheres is detected in real time by the position detection module, and the displacement signal detected by the position detection module is input to the FPGA. After the FPGA transmits the position information to the host computer, it uses the internal The algorithm outputs a feedback signal that adjusts the AOM to control the laser intensity to suppress the centroid movement of the microspheres;

2) When the microspheres need to fall freely, the AOM is controlled by FPGA to make the output light intensity 0. At this time, the optical trap is in a non-working state, and the microspheres will fall freely under the action of gravity. After a few milliseconds, the optical trap is turned on again through the AOM. , record the position of the initial and final state of the drop of the microsphere, and then calculate the gravity according to the drop time and distance of the microsphere;

3) After reopening the optical trap, the microspheres will overcome the gravity under the action of the optical trapping force and rise again to the initial capture position. At this time, the AOM is used to re-cool the motion state of the microspheres, and the environmental gravity can be repeated in the system. Calibration.