阅读说明：本技术 一种实时测量原子绝对重力仪波前畸变的装置和测量方法 (Device and method for measuring wavefront distortion of atomic absolute gravimeter in real time ) 是由 朱皓冉 汤彪 黄攀威 陈曦 王谨 詹明生 于 2019-10-17 设计创作，主要内容包括：本发明公开了一种实时测量原子绝对重力仪波前畸变的装置,包括激光光源,还包括激光耦合头、分光平片、反射镜、WFS波前分析仪、和设置在真空腔上的真空腔底部窗片,本发明还公开了一种实时测量原子绝对重力仪波前畸变的测量方法,本发明在真空腔抽真空之后,在真空腔外部就可以实时进行测量,就可以得到激光经过真空腔底部窗片之后的波前畸变,克服了在真空腔安装后测量真空腔底部窗片面型的困难。(The invention discloses a device for measuring wavefront distortion of an atomic absolute gravimeter in real time, which comprises a laser source, a laser coupling head, a light splitting flat sheet, a reflector, a WFS wavefront analyzer, and a vacuum cavity bottom window sheet arranged on a vacuum cavity.)

1. A device for measuring wave front distortion of an atomic absolute gravimeter in real time comprises a laser source (6), and is characterized by further comprising a laser coupling head (1), a light splitting flat sheet (2), a reflector (3), a WFS wave front analyzer (4) and a vacuum cavity bottom window sheet (5) arranged on a vacuum cavity,

the laser light source (6) emits laser light through the laser coupling head (1), the laser light emitted by the laser coupling head (1) forms transmitted light and reflected light through the light splitting flat sheet (2), the transmitted light emits to the reflecting mirror (3), the reflecting mirror (3) reflects the transmitted light, the transmitted light reflected by the reflecting mirror (3) returns to the light splitting flat sheet (2) along an original light path, and the light splitting flat sheet (2) reflects the transmitted light reflected by the reflecting mirror (3) to the WFS wavefront analyzer (4); the reflected light enters the vacuum cavity bottom window sheet (5), the vacuum cavity bottom window sheet (5) reflects the reflected light, the original light path of the reflected light reflected by the vacuum cavity bottom window sheet (5) returns to the light splitting flat sheet (2) and transmits the light splitting flat sheet (2) to enter the WFS wavefront analyzer (4).

2. The device for measuring the wave front distortion of the atomic absolute gravimeter in real time according to claim 1, wherein the laser source (6) emits laser light as first laser light or second laser light through the laser coupling head (1), a first reflective film is plated on one outer side of the vacuum chamber bottom window (5), the wavelength of the first laser light is the same as the reflection wavelength of the first reflective film, a second reflective film is plated on one inner side of the vacuum chamber bottom window (5), and the wavelength of the second laser light is the same as the reflection wavelength of the second reflective film.

3. The device for measuring the wave front distortion of the atomic absolute gravimeter in real time according to claim 1, wherein the laser coupling head (1) is coated with a transparent film, and the wavelength range of the first laser to the second laser is contained in the transmission wavelength range of the transparent film.

4. A method for measuring wavefront distortion of an atomic absolute gravimeter in real time, which is characterized in that the device for measuring wavefront distortion of an atomic absolute gravimeter in real time according to claim 3 comprises the following steps:

step 1, emitting first laser by a laser source (6) through a laser coupling head (1), shielding a window sheet (5) at the bottom of a vacuum cavity, enabling the first laser to partially transmit a light splitting flat sheet (2) to emit to a reflector (3), reflecting the first laser by the reflector (3), reflecting the first laser to the light splitting flat sheet (2) through a first laser original optical path reflected by the reflector (3) and reflecting the first laser to a WFS wavefront analyzer (4) through the light splitting flat sheet (2), recording a first surface type measurement result measured by the WFS wavefront analyzer (4),

step 2, shielding a reflector (3), reflecting a first laser part by a light splitting flat sheet (2) and then irradiating the first laser part to a vacuum cavity bottom window sheet (5), reflecting a first laser by a first reflection film plated on one side of the outer side of the vacuum cavity bottom window sheet (5), reflecting the first laser by a first laser original light path reflected by the first reflection film back to the light splitting flat sheet (2) and transmitting the light splitting flat sheet (2) to irradiate the WFS wavefront analyzer (4), recording a second surface type measurement result measured by the WFS wavefront analyzer (4), and subtracting the first surface type measurement result from the second surface type measurement result to obtain a first surface type difference value;

step 3, a laser source (6) emits second laser through a laser coupling head (1), a window sheet (5) at the bottom of the vacuum cavity is shielded firstly, the second laser partially transmits a light splitting flat sheet (2) to a reflector (3), the reflector (3) reflects the second laser, a second laser original light path reflected by the reflector (3) is reflected back to the light splitting flat sheet (2) and reflected to a WFS wavefront analyzer (4) by the light splitting flat sheet (2), and a third surface type measurement result measured by the WFS wavefront analyzer (4) is recorded,

step 4, shielding a reflector (3), reflecting a second laser part by a beam splitter flat sheet (2) and then irradiating the second laser part to a vacuum cavity bottom window sheet (5), reflecting the second laser by a second reflecting film plated on one surface of the inner side of the vacuum cavity bottom window sheet (5), reflecting the second laser by a second laser original light path reflected by the second reflecting film back to the beam splitter flat sheet (2) and transmitting the beam splitter flat sheet (2) to irradiate the WFS wave front analyzer (4), recording a fourth surface type measurement result measured by the WFS wave front analyzer (4), and subtracting the third surface type measurement result from the fourth surface type measurement result to obtain a second surface type difference value;

the surface type function H of the side, plated with the first reflecting film, of the vacuum cavity bottom window sheet (5) is obtained through the following equation system₂And the surface type function H of the surface of the vacuum cavity bottom window sheet (5) with the second reflecting film plated on the inner side₁，

Wherein k is₁、k₂Wave vectors, n, of the first laser light and the second laser light, respectively₁，n₂The refractive indices of the first laser light and the second laser light respectively in a bottom window (5) of the vacuum chamber,

the wave front distortion delta added by the laser with the wavelength between the first laser wavelength and the second laser wavelength through the window (5) at the bottom of the vacuum cavity is obtained through the following formula₃：

δ₃＝k₃(n₃-1){H₁-H₂}

k₃The wave vector of the third laser, the wavelength of the third laser is between the first laser wavelength and the second laser wavelength, n₃Is the refractive index of the third laser in the vacuum chamber bottom pane (5).

Technical Field

The invention belongs to the field of wavefront distortion measurement of an atomic absolute gravimeter, and particularly relates to a device for measuring wavefront distortion of the atomic absolute gravimeter in real time and a measuring method for measuring wavefront distortion of the atomic absolute gravimeter in real time.

Background

The atomic absolute gravimeter is a novel gravimeter based on an atomic interferometer, and the basic principle of the atomic absolute gravimeter is that a group of atoms is thrown up or freely falls down in vacuum, the beam splitting, reflection and interference of the group of atoms are realized by utilizing the control of a pair of Raman lights (with the wavelength of 780nm), and interference fringes containing gravity information are obtained, so that the value of absolute gravity acceleration is deduced. Since the interferometer measurement relies on the phase difference between its two paths, each atom acts like a separate gravity detector and is not subject to drift, aging or wear. The development of atomic absolute gravimeters has been over decades, and has become one of the main instruments for high-precision absolute gravity measurement.

One important factor affecting the measurement accuracy of the atomic absolute gravimeter is the influence caused by wavefront distortion. FIG. 1 shows

Is a drawing of an experimental apparatus and process for implementing atomic interference in a vacuum chamber by using a raman pulse (pulse laser with a wavelength of 780nm) sequence. The atomic average transition probability obtained finally is:

wherein, Δ φ ═ Δ φ₀+ delta phi, the part containing gravity information being delta phi₀＝k_effgT²And delta phi is the phase shift caused by the systematic error of wavefront distortion. The measurement error δ g of gravity can therefore be expressed as:

k_effis the effective wave vector, which can be written as k_eff＝k_a+k_bAnd T is the atom free evolution time.

The phase error of wavefront distortion means that the measurement of g is shifted due to non-parallelism of the wavefront of raman light (780nm wavelength laser). Its wavefront aberration can be expressed as:

Δφ_wavefront＝Δφ₁-2Δφ₂+Δφ₃，

Δφ₁、Δφ₂、Δφ₃are respectively shown inPulse-pi pulse

As shown in fig. 2, because the atoms have a transverse diffusion velocity and the phase of the atoms is related to the position of the atomic group, the phase error caused by the wavefront distortion after the interference process is:

n_i(r) represents

Pulse, pi pulse,

The distribution of the radicals in the pulse is different from stage to stage because the atoms have a transverse diffusion speed. Delta phi_wfReferring to the phase difference of the raman wave front, the collimated raman light can be regarded as a plane wave, so the wave front aberration is caused by the fact that a window at the bottom of a vacuum cavity in the device, a quarter wave plate and a raman light reflector at the bottom of the device are not strictly planes as shown in fig. 1. Under the condition that the mirror distortion of the optical element cannot be eliminated, the optimal method is to measure the surface shapes of the cavity bottom window, the quarter-wave plate and the bottom reflector and calculate the wavefront distortion and the brought deviation of the Raman light.

In fact, we can measure the profile of the measured element using a Shack Hartmann wavefront analyzer. As shown in fig. 4, the surface shape of the transmission element is measured, and the wavefront distortion introduced by the transmission of the laser light through the element can be known only by measuring the collimated laser light (the laser light with 780nm wavelength is selected as the raman wavelength in the atomic interferometer) with the same area as or larger than the surface shape to be measured as the reference surface shape, putting the element to be measured into the optical path and measuring the result by the wavefront analyzer, and subtracting the two results to obtain the surface shape of the element. The wavefront distortion caused by the quarter-wave plate and the reflecting mirror can be easily measured by the method, but because the vacuum cavity is closed, the laser emitted from the interior of the vacuum cavity can not be used as reference light to be measured in real time in the technical aspect, and therefore the uncertainty of the measurement of g caused by the wavefront distortion cannot be analyzed by the ideal method for system errors. Solving the wavefront distortion added by the vacuum chamber bottom louver is the key to solving our proposed problem.

At present, the most common method is to use the deviation value of g obtained each time to fit and reshape the wave surface shape by changing the conditions of Raman light spot size or temperature. Because the signal-to-noise ratio of interference signals is extremely low after the diameter of the light spot is small to a certain degree, the wave surface cannot be perfectly fitted, and the extrapolation through the known data is predicted according to the trend of the known data, so that the uncertainty is still high. The existing technical method cannot be accurately obtained.

Disclosure of Invention

The invention aims to overcome the defects of the existing method, provide a device for measuring the wavefront distortion of the atomic absolute gravimeter in real time, and also provide a measuring method for measuring the wavefront distortion of the atomic absolute gravimeter in real time.

The purpose of the invention is realized by the following technical scheme:

a device for measuring wave front distortion of an atomic absolute gravimeter in real time comprises a laser source, a laser coupling head, a beam splitter flat sheet, a reflector, a WFS wave front analyzer, and a vacuum cavity bottom window sheet arranged on a vacuum cavity,

the laser light source emits laser through the laser coupling head, the laser emitted by the laser coupling head forms transmission light and reflection light through the light splitting flat sheet, the transmission light emits to the reflecting mirror, the reflecting mirror reflects the transmission light, the transmission light reflected by the reflecting mirror returns to the light splitting flat sheet along an original light path, and the light splitting flat sheet reflects the transmission light reflected by the reflecting mirror to the WFS wavefront analyzer; the reflected light enters the vacuum cavity bottom window sheet, the vacuum cavity bottom window sheet reflects the reflected light, the original light path of the reflected light reflected by the vacuum cavity bottom window sheet returns to the light splitting flat sheet and transmits the light splitting flat sheet to enter the WFS wavefront analyzer.

The laser source emits laser as first laser or second laser through the laser coupling head, a first reflecting film is plated on one surface of the outer side of the window sheet at the bottom of the vacuum cavity, the wavelength of the first laser is the same as the reflecting wavelength of the first reflecting film, a second reflecting film is plated on one surface of the inner side of the window sheet at the bottom of the vacuum cavity, and the wavelength of the second laser is the same as the reflecting wavelength of the second reflecting film.

The laser coupling head is plated with a full-transmission film, and the wavelength range of the first laser to the second laser is included in the transmission wavelength range of the full-transmission film.

A method for measuring wavefront distortion of an atomic absolute gravimeter in real time comprises the following steps:

step 1, emitting first laser by a laser source through a laser coupling head, shielding a window sheet at the bottom of a vacuum cavity, enabling the first laser to partially transmit a beam splitter to emit to a reflector, reflecting the first laser by the reflector, reflecting the beam splitter back by a first laser original optical path reflected by the reflector and reflecting the beam splitter to a WFS wavefront analyzer by the beam splitter, recording a first surface type measurement result measured by the WFS wavefront analyzer,

step 2, shielding a reflector, reflecting a first laser part to a vacuum cavity bottom window sheet after the first laser part is reflected by a light splitting flat sheet, reflecting the first laser by a first reflection film plated on one side of the outer side of the vacuum cavity bottom window sheet, reflecting the first laser back to the light splitting flat sheet through a first laser original light path reflected by the first reflection film and transmitting the light splitting flat sheet to a WFS (wavefront analyzer), recording a second surface type measurement result measured by the WFS wavefront analyzer, and subtracting the first surface type measurement result from the second surface type measurement result to obtain a first surface type difference value;

step 3, emitting a second laser by the laser source through the laser coupling head, shielding the window sheet at the bottom of the vacuum cavity, enabling the second laser to partially transmit the beam splitter to emit to the reflector, reflecting the second laser by the reflector, reflecting the second laser back to the beam splitter through a second laser original optical path reflected by the reflector and reflecting the second laser back to the WFS wavefront analyzer through the beam splitter, recording a third surface type measurement result measured by the WFS wavefront analyzer,

step 4, shielding a reflector, reflecting a second laser part to a vacuum cavity bottom window sheet after the second laser part is reflected by a light splitting flat sheet, reflecting the second laser by a second reflecting film plated on one side of the inner side of the vacuum cavity bottom window sheet, reflecting the second laser back to the light splitting flat sheet through a second laser original light path reflected by the second reflecting film, transmitting the light splitting flat sheet to a WFS (window grating surface) wavefront analyzer, recording a fourth surface type measurement result measured by the WFS wavefront analyzer, and subtracting the third surface type measurement result from the fourth surface type measurement result to obtain a second surface type difference value;

obtaining a surface type function H of one surface of the window sheet at the bottom of the vacuum cavity, which is plated with the first reflecting film, through the following equation system₂And the surface type function H of the surface of the vacuum cavity bottom window sheet with the second reflecting film plated on the inner side₁，

Wherein k is₁、k₂Wave vectors, n, of the first laser light and the second laser light, respectively₁，n₂The refractive indices of the first laser light and the second laser light respectively in the bottom pane of the vacuum chamber,

the wave front distortion delta of the laser with the wavelength between the first laser wavelength and the second laser wavelength, which is added by the laser passing through the window at the bottom of the vacuum cavity, is obtained through the following formula₃：

δ₃＝k₃(n₃-1){H₁-H₂}

k₃The wave vector of the third laser, the wavelength of the third laser is between the first laser wavelength and the second laser wavelength, n₃Is the refractive index of the third laser in the bottom pane of the vacuum chamber.

Compared with the prior art, the invention has the following beneficial effects:

after the vacuum cavity is vacuumized, the real-time measurement can be carried out outside the vacuum cavity, the wavefront distortion of laser passing through the window at the bottom of the vacuum cavity can be obtained, the difficulty of measuring the surface type of the window at the bottom of the vacuum cavity after the vacuum cavity is installed is overcome, the surface type of the window 5 at the bottom of the vacuum cavity can be measured in real time, and the method is more accurate compared with the method mainly used at home and abroad for evaluating the system error of the wavefront distortion by an extrapolation method.

Drawings

FIG. 1 is an atomic absolute gravimeter experimental apparatus and schematic diagram;

FIG. 2 is a schematic diagram of wavefront distortion; k is a radical of_a，k_bIs Raman light with a wavelength of 780 nm;

FIG. 3 is a schematic view of a measuring device according to the present invention;

FIG. 4 is a schematic diagram of a WFS wavefront analyzer (Shack Hartmann wavefront analyzer) in use;

FIG. 5 is a schematic view of the vacuum chamber bottom window coating.

Detailed Description

The present invention will be described in further detail with reference to examples for the purpose of facilitating understanding and practice of the invention by those of ordinary skill in the art, and it is to be understood that the present invention has been described in the illustrative embodiments and is not to be construed as limited thereto.