Absolute gravimeter and measurement method based on vacuum optical tweezers

Patent metadata

Field	Value
Publication number	US-12174335-B2
Application number	US-202017927748-A
Country	US
Kind code	B2
Filing date	Aug 28, 2020
Priority date	Jun 12, 2020
Publication date	Dec 24, 2024
Grant date	Dec 24, 2024

Abstract

An absolute gravimeter and a measurement method based on vacuum optical tweezers. The micro-nano particle releasing device is equipped with micro-nano particles, and is located above laser optical tweezers, and the laser optical tweezers have two capturing beams which pass through the respective convergent lenses and then converge at an intersection. An area where the intersection is located serves as an optical trap capturing region, and the micro-nano particles are stably captured by the two capturing beams in the optical trap capturing region. The optical interferometer is electrically connected to the signal processing device, the optical interferometer measures a displacement of the micro-nano particles in real time at the beginning of a free fall process from the optical trap capturing region and sends the displacement signal to the signal processing device. The signal processing device obtains a measured value of an absolute gravitational acceleration.

First claim

What is claimed is:

1. An absolute gravimeter based on vacuum optical tweezers, comprising a vacuum system, micro-nano particles, a micro-nano particle releasing device, laser optical tweezers, an optical interferometer, and a signal processing device; wherein the micro-nano particle releasing device and the laser optical tweezers are all placed in the vacuum system; the optical interferometer and the signal processing device are all located outside the vacuum system; the micro-nano particle releasing device is equipped with the micro-nano particles, the micro-nano particle releasing device is located above the laser optical tweezers, and the laser optical tweezers comprising two capturing beams which are horizontally coaxial and two convergent lenses, the two capturing beams pass through the respective convergent lenses and then converge at an intersection, an area where the intersection is located serves as an optical trap capturing region, and the micro-nano particles are stably captured by the two capturing beams in the optical trap capturing region; the optical interferometer is electrically connected to the signal processing device, the optical interferometer measures a displacement of the micro-nano particles in real time at the beginning of a free fall process from the optical trap capturing region and sends a displacement signal to the signal processing device, the signal processing device obtains a measured value of an absolute gravitational acceleration through method processing according to a real-time displacement of the micro-nano particles,
wherein the optical interferometer comprises a laser, an upper emitting mirror, a lower emitting mirror, an upper polarizing beam splitting prism, a lower polarizing beam splitting prism, a receiving polarizing beam splitting prism, an upper glass plate, a lower glass plate, and a polarizer, the upper polarizing beam splitting prism and the upper glass plate are provided right above gravity drop of the micro-nano particles, the upper emitting mirror is arranged on a lateral side of the upper polarizing beam splitting prism, and the lower polarizing beam splitting prism and the lower glass plate are arranged directly under gravity drop of the micro-nano particles, the lower emitting mirror is set directly under the lower polarizing beam splitter prism, and the receiving polarizing beam splitter prism and the polarizer are arranged on a lateral side of the lower emitting mirror; the laser emits first and second linearly polarized beams with different frequencies, the first linearly polarized beam is transmitted through the upper polarizing beam splitter prism and the upper glass plate in turn from right above the micro-nano particles along a positive direction of a gravity direction, and then irradiated on the micro-nano particles, after being scattered by a surface of the micro-nano particles, an upper scattered light is generated, and the upper scattered light returns upward along an optical path, is transmitted by the upper glass plate, reflected by the upper polarizing beam splitter prism, and then incident on the upper emitting mirror, and incident on the receiving polarizing beam splitter prism after being reflected by the upper emitting mirror, and is reflected again, thus forming a first probe optical path, the second linearly polarized beam is reflected by the lower polarizing beam splitter prism in turn from a bottom of the micro-nano particles in an opposite direction of the gravity direction, and transmitted through the lower glass plate, and then irradiated to the micro-nano particles, after being scattered by the surface of the micro-nano particles, a lower scattered light is generated, and the lower scattered light is returned downward along the optical path, transmitted by the lower glass plate, reflected by the lower polarizing beam splitter prism, and then incident on the lower emitting mirror, and then incident on a receiving polarizing beam splitter prism after being reflected by the lower emitting mirror, and is transmitted again, thus forming a second probe optical path; the upper scattered light reflected by the receiving polarizing beam splitter and the lower scattered light reflected by the receiving polarizing beam splitter are converged and interfered, and then incident on a photoelectric conversion circuit through the polarizer to be collected and probed to obtain an interference signal.

2. The absolute gravimeter based on the vacuum optical tweezers according to claim 1 , wherein a material of the micro-nano particles is silicon dioxide, of which a diameter is 1 micron to 30 microns in diameter.

3. An absolute gravity measuring method that is applied to the absolute gravimeter according to claim 1 , wherein the method comprising the following steps:
a) a laser of the vacuum optical tweezers is turned on to output the two horizontally capturing beams, and the optical trap capturing region is formed in a vacuum chamber through the respective converging lenses;
b) the micro-nano particles are released through a micro-nano ball releasing device, and then the micro-nano particles move downward under the action of gravity to free fall to the optical trap capturing region, and are stably captured in the center of the optical trap capturing region;
c) the optical interferometer is turned on, and an interferometric measurement of a displacement of the micro-nano particles begins;
the capturing beams of the laser of the vacuum optical tweezers are turned off, and the micro-nano particles are released from the center of the optical trap capturing region under the action of gravity and free fall downward along the direction of gravity;
when the capturing beams are turned off, a real-time change process of the displacement of the micro-nano particles is measured by the optical interferometer, and a measurement time series s of the displacement over time is obtained;
d) fitting is performed according to the measurement time series s to obtain a measurement value of the absolute gravity;
e) the optical interferometer is turned off and the measurement is ended;
f) the above a)˜e) steps are repeated to achieve continuous measurement of the absolute gravity.

4. The absolute gravity measuring method according to claim 3 , wherein the method for measuring a displacement signal s(n) of the micro-nano particles during free fall is specifically as follows: an interference signal is collected and detected by the optical interferometer, according to an analysis of the interference signal, a current phase do is measured in real time and output at regular intervals, a measurement value of an optical phase change is obtained for each acquisition, and a sampling interval is T, sampling is performed continuously to obtain n real-time measurement value series dφ(n) of the optical phase change, according to the following equation, the displacement signal s(n) of the n-th measurement of the micro-nano particles is obtained, and then the measurement time series s of the displacement over time is obtained:
s ( n )= d φ( n )×λ/8π

wherein λ is a light wavelength adopted by the optical interferometer, n is a serial number of the measurement sampling, which is taken as a natural number, and an atomic clock provides a unified timing signal and a time reference.

5. The absolute gravity measuring method according to claim 3 , wherein the fitting according to the measurement time series s is performed by adopting a least squares method, and a measurement value g of the absolute gravity is obtained by fitting the input measurement time series s according to the following equation:
s ( n )= s (0)+ g ×( nT ) 2 /2

wherein s(n) represents the displacement signal of the n-th measurement of micro-nano particles, s(0) is a constant coefficient, n represents a total number of the measurem

Assignees

• Univ Zhejiang
• Zhejiang Lab

Inventors

• Chen Xingfan
• Liu Yishi
• Gao Xiaowen
• Li Nan
• Hu Huizhu
• Liu Cheng

Classifications

• G01J9/02

  by interferometric methods (using interferometers for measuring optically the linear dimensions of objects G01B9/02) · CPC title

• G01V7/04 Primary

  Electric, photoelectric, or magnetic indicating or recording means · CPC title

• G01V7/14 Primary

  using free-fall time · CPC title