CN104007480A - Horizontal gravity gradient measuring sensor based on cold atomic beam interferometer - Google Patents
Horizontal gravity gradient measuring sensor based on cold atomic beam interferometer Download PDFInfo
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Abstract
The invention discloses a horizontal gravity gradient measuring sensor based on a cold atomic beam interferometer, and belongs to the technical field of gravity survey. The sensor is composed of a first gravity sensitive cold atom interference unit and a second gravity sensitive cold atom interference unit, wherein the first gravity sensitive cold atom interference unit and the second gravity sensitive cold atom interference unit are the same in structure and are arranged in parallel in the horizontal direction; or the sensor is formed by communicating the first gravity sensitive cold atom interference unit and the second gravity sensitive cold atom interference unit through a vacuum pipeline, and the first gravity sensitive cold atom interference unit and the second gravity sensitive cold atom interference unit are the same in structure ; the first gravity sensitive cold atom interference unit is composed of a first cold atomic beam generating part, a first cold atomic beam deflection part and a first atom interference and detection part, wherein the first cold atomic beam generating part, the first cold atomic beam deflection part and the first atom interference and detection part are sequentially connected from bottom to top. The sensor solves the problem that emergent atoms in the cold atom beam generating device are irradiated by pushing and loading lasers, the measuring bandwidth of an atom interference gravity gradiometer is greatly improved, and system errors and noise caused by air clearances and window piece structure deflection can be avoided through the communication structure of the vacuum pipeline on a Raman laser beam propagation path.
Description
Technical field
The invention belongs to gravity survey technical field, particularly a kind of horizontal gravity gradient survey sensor based on cold atomic beam interferometer.
Background technology
In geologic structure, the inhomogeneous meeting of quality and Density Distribution causes the abnormal of earth's surface gravity and gravity gradient field.And as the more higher derivative higher order derivative of gravity position, gravity gradient field has the higher spatial resolution in the proportion field of force and sensitivity.Therefore, gradiometry has application and significance very widely in fields such as resources survey, environmental monitoring and national defense construction.
At present more ripe gravity gradiometer scheme mainly comprises: " rotary accelerometer scheme " (J. B. Lee that Bell Aerospace company of the U.S. and Australian BHP Billiton company adopt, FALCON gravity gradiometer technology, BHP Billiton Discovery Technologies, 1～4, 1992), " superconduction scheme " (M. V. Moody that ARKeX company of Britain adopts, H. J. Paik, and E. R. Canavanc, Three-axis superconducting gravity gradiometer for sensitive gravity Experiments, Rev.Sci.Instrum.73, 3957, 2002), " electrostatic support accelerometer scheme " (P Touboul that Air France Group space center (ONERA) adopts, B Foulon, M Rodrigues, J.P Marque, In orbit nano-g measurements, lessons for future space missions, Aerospace Science and Technology, 8, 431, 2004), and " atomic interferometer scheme " (M. J. Snadden involved in the present invention, J. M. McGuirk, P. Bouyer, et al, Measurement of the earth ' s gravity gradient with an atom interferometer-based gravity gradiometer, Phys. Rev. Lett. 81, 971, 1998).
Compare with electrostatic support accelerometer scheme with rotary accelerometer, atomic interferometer scheme has higher theoretical precision and (has realized 10 at present
-12 gsingle gravity meter (S. M. Dickerson, J. M. Hogan, A. Sugarbaker, et al, Multiaxis inertial sensing with long-time point source atom interferometry, Phys. Rev. Lett.111,083001,2013)), compared with the superconduction scheme suitable with precision, owing to not needing extreme superconduction condition, therefore have more the through engineering approaches advantage of the schemes such as volume, power consumption and cost.In addition, other each schemes are all taking relative acceleration (gravity meter) as Component units, cannot provide absolute gravity value, and the difference of systematic error between different acceleration also can be introduced the result of gradiometry, and intervening atom gravity gradiometer is made up of two absolute gravity gradometers, not only can carry out absolute gradiometry, also can provide in the lump absolute gravity value.
As far back as 1991, the Kasevich of Stanford Univ USA has just realized in the world first atomic interferometer and for gravimetry (M. Kasevich and S. Chu under the leading of its tutor's Steven Chu, Atomic interferometry using stimulated Raman transitions, Phys. Rev. Lett. 67,181,1991); Subsequently Kasevich Yale University set up research group and in 1998 by vertical two atomic interference gravimeters stacked and carry out common mode difference measurement and realized first for measuring the vertical gravity gradiometer of intervening atom (the M. J. Snadden of vertical gravity gradient, J. M. McGuirk, P. Bouyer, et al, Measurement of the Earth ' s gravity gradient with an atom interferometer-based gravity gradiometer, Phys.Rev.Lett. 81,971,1998); 2006, Kasevich returned to Stanford University and has successfully developed one in 2009 for measuring the vehicle-mounted horizontal gravity gradient instrument of horizontal gravity gradient, and after the integral time of 180 seconds, its measuring accuracy can reach 7
e(X. A. Wu, Gravity gradient survey with a mobile atom interferometer, PhD thesis, Stanford University, 2009)) (1
e≈ 10
-10 g/m).The Tino group of Florence, Italy university has adopted the single gravity meter two fountain schemes different from Stanford University two gravity meter schemes, has passed through the integral time of 8000 seconds, and having realized precision is 0.5
evertical gradiometry (F. Sorrentino, Q. Bodart, L. Cacciapuoti, et al, Sensitivity limits of a Raman atom interferometer as a gravity gradiometer, Phys. Rev. is A.89,023607,2014).
The restriction of the geographical conditions such as mountain region, ocean taken Aeronautics and Astronautics aircraft and can break through by gravity gradiometer, significantly improve the efficiency of exploration, spaceborne gravity gradiometer even can be measured global gravity gradient, therefore the measurement of high resolving power Aeronautics and Astronautics is the important development direction of gravity gradiometer, this has just made very high requirement to its Measurement bandwidth, and this short slab place of intervening atom gravity gradiometer exactly.At present all intervening atom gravity and all cold atom groups based on impulse ejection of gradiometry scheme in the world, atom of every transmitting can only obtain a data point, sample and just can launch next time afterwards, wherein single data acquisition comprises the preparation of cold atom group, upthrow, state preparation, the operation of raman laser pulse coherence and final states are surveyed several steps, the preparation that wherein single cold atom is rolled into a ball is wanted 0.3～1 second consuming time conventionally, make single-point sampling rate only can reach 0.5～2.5 Hz, and the measured value that will obtain a gravity gradient often needs the data point of multiple outs of phase to carry out process of fitting treatment, this just makes actual gradiometry bandwidth generally below 1 Hz, obtaining high-precision measured value needs the integral mean of thousands of seconds especially.At present, the Measurement bandwidth of the airborne gradiometer based on GT-1A accelerometer that U.S. Bell Aerospace and Canadian McPHAR company produce can reach 100 Hz, takes Piper Navajo type aircraft (140 nautical miles/hour) and can realize 1
mexploration linear resolution.And intervening atom gravity gradiometer will meet the demand that high resolving power Aeronautics and Astronautics is measured, its Measurement bandwidth is a problem in the urgent need to address.
Utilize atomic beam to replace atomic group can significantly improve the sampling rate of atomic interferometer.The Kasevich group of the U.S. was once used continuous hot atomic beam interferometer to carry out rotation measuring, obtain the measurement data points of Time Continuous, but due to the atom flying speed in hot atomic beam too fast (at km/second-time), obtain the relevant running time of the required raman laser of high accuracy data, just must build very large-sized measurement mechanism, cannot meet the demand of through engineering approaches.The people such as the Lu Zhengtian of NBS had once demonstrated in 1996 and a kind ofly can produce the method for cold atomic beam and obtain line 5 × 10
9/
s, average velocity 14
m/s, distribute 2.7
m/srubidium cold atomic beam.But the atomic beam that the method obtains under the irradiation of propelling cooling light, cannot carry out phase dry run to state in it all the time.Thereby the Feng Yan of Tsing-Hua University grain husk group once utilized gravity to fall to avoiding the irradiation of cooling light by atom in horizontal cold atomic beam generation device.But in gradiometry process, need to vertically launch atom, the method for utilizing gravity to change atom flight path needs very large-sized experimental provision, therefore also inapplicable.
Summary of the invention
Object of the present invention is just to overcome the shortcoming and defect that prior art exists, and especially overcomes cold atom and interferes the too low problem of gravity gradiometer Measurement bandwidth, and a kind of horizontal gravity gradient survey sensor based on cold atomic beam interferometer is provided.
The problem of required solution is:
1, as introduced in background technology, at present all intervening atom gradiometry scheme all adopts the cold atom groups based on impulse ejection in the world, atom of every transmitting can only obtain a data point, often need the data point of multiple outs of phase to carry out process of fitting treatment and obtain a Grad, this just makes gradiometry bandwidth generally below 1Hz, cannot meet the demand that high resolving power Aeronautics and Astronautics is measured.
2, in order to improve the sampling rate of intervening atom gravity gradiometer, can adopt in theory cold atomic beam to substitute the experimental program of cold atom group, but the atomic beam that existing cold atomic beam generation technology obtains is for a long time in propelling under the irradiation of cooling light, cannot carry out phase dry run to state in it, also just cannot realize intervening atom.Thereby if utilize gravity to avoid the irradiation of cooling light by atom free-falling, need large-sized experimental provision, can greatly increase undoubtedly cost, complicacy and the space hold of experimental provision system, be more unfavorable for through engineering approaches and traverse measurement.
The object of the present invention is achieved like this:
The first, in existing cold atomic beam technical foundation, solve by two-dimensional transversal mobile optical viscose but light and the overlapping problem of atom track of refrigerating that push away;
Second, utilize the discrete continuous Raman laser solution in space to replace discrete pulse raman laser scheme of traditional time, cold atomic beam is carried out to continual phase dry run and continuous sampling, thereby realize the quasi-continuous measurement to horizontal gravity gradient, meet the Demand of Nation of high spatial resolution, the measurement of high precision Aeronautics and Astronautics.
Specifically, this sensor by two structures identical and the 1st gravity sensitive type cold atom interference unit and the 2nd gravity sensitive type cold atom interference unit of parallel arranged form in the horizontal direction;
Or be communicated with and form by vacuum pipe by two identical the 1st gravity sensitive type cold atom interference unit and the 2nd gravity sensitive type cold atom interference unit of structure;
The 1st gravity sensitive type cold atom interference unit is made up of the 1st cold atomic beam generating portion connecting successively from bottom to top, the 1st cold atomic beam deflector and the 1st intervening atom and probe portion.
The present invention has following advantages and good effect:
1. solved outgoing atom in cold atomic beam generation device and pushed away the problem of carrying Ear Mucosa Treated by He Ne Laser Irradiation, the interior state of the atom in cold atomic beam can freely be operated and develop;
2. significantly improve the Measurement bandwidth of intervening atom gravity gradiometer, realized the quasi-continuous measurement to horizontal gravity gradient, met the demand that high resolving power Aeronautics and Astronautics is measured;
3. the 1st gravity sensitive type cold atom interference unit and the 2nd gravity sensitive type cold atom interference unit can be avoided systematic error and the noise introduced by clearance and window structural deviation in the coconnected structure of raman laser propagation path by vacuum pipe.
Brief description of the drawings
Fig. 1 is the structural representation of this sensor;
Fig. 2 is the energy level schematic diagram of two photon transition;
Fig. 3 is intervening atom schematic diagram.
In figure:
The 100-the 1 gravity sensitive type cold atom interference unit;
The 110-the 1 cold atomic beam generating portion;
The 111-the 1 imprison laser beam transmitter; The 112-the 1 imprison laser beam;
The 113-the 2 imprison laser beam transmitter; The 114-the 2 imprison laser beam;
The reverse helmholtz coil of the 115-the 1 Three-Dimensional Magnetic ligh trap;
The 116-the 1 alkali metal source;
The 117-the 1 catoptron group that comprises quarter wave plate;
The 118-the 1 three-dimensional cold atomic beam;
The 120-the 1 cold atomic beam deflector;
121-the 1 moves two-dimension optical viscose laser beam transmitter;
122-the 1 moves two-dimension optical viscose laser beam;
The 123-the 1 two-dimentional cold atomic beam;
The 130-the 1 intervening atom and probe portion;
The 131-the 1 raman laser light-beam transmitter; The 132-the 1 raman laser light beam;
The 133-the 2 raman laser light-beam transmitter; The 134-the 2 raman laser light beam;
The 135-the 3 raman laser light-beam transmitter; The 136-the 3 raman laser light beam;
The 137-the 1 photodetector; The 138-the 1 bias magnetic field coil;
The 200-the 2 gravity sensitive type cold atom interference unit;
The 210-the 2 cold atomic beam generating portion;
The 211-the 3 imprison laser beam transmitter; The 212-the 3 imprison laser beam;
The 213-the 4 imprison laser beam transmitter; The 214-the 4 imprison laser beam;
The reverse helmholtz coil of the 215-the 2 Three-Dimensional Magnetic ligh trap;
The 216-the 2 alkali metal source;
The 217-the 2 catoptron group that comprises quarter wave plate;
The 218-the 2 three-dimensional cold atomic beam;
The 220-the 2 cold atomic beam deflector;
221-the 2 moves two-dimension optical viscose laser beam transmitter;
222-the 2 moves two-dimension optical viscose laser beam;
The 222-the 2 two-dimentional cold atomic beam;
The 230-the 2 intervening atom and probe portion;
The 231-the 4 raman laser light-beam transmitter; The 232-the 4 raman laser light beam;
The 233-the 5 raman laser light-beam transmitter; The 234-the 5 raman laser light beam;
The 235-the 6 raman laser light-beam transmitter; The 236-the 6 raman laser light beam;
The 237-the 2 photodetector; The 238-the 2 bias magnetic field coil;
300-vacuum pipe;
| energy level under 1>-atomic ground state;
| energy level in 2>-atomic ground state;
| 3>-virtual level;
| 4>-excited of atoms energy level;
Δ-energy level off resonance amount.
embodiment:
Below in conjunction with accompanying drawing and example in detail:
One, overall
As Fig. 1, this sensor by two structures identical and in the horizontal direction the 1st gravity sensitive type cold atom interference unit the 100 and the 2nd gravity sensitive type cold atom interference unit 200 of parallel arranged form;
Or be communicated with and form by vacuum pipe 300 by two the 1st identical gravity sensitive type cold atom interference unit the 100 and the 2nd gravity sensitive type cold atom interference unit 200 of structure;
The 1st gravity sensitive type cold atom interference unit 100 is made up of the 1st cold atomic beam generating portion the 110, the 1st cold atomic beam deflector 120 connecting successively from bottom to top and the 1st intervening atom and probe portion 130.
Two, functional part
1, the 1st cold atomic beam generating portion 110
The 1st intervening atom and probe portion 110 comprise the 1st imprison laser beam transmitter the 111, the 2nd imprison laser beam transmitter reverse helmholtz coil the 115, the 1st alkali metal source 116 of the 113, the 1st Three-Dimensional Magnetic ligh trap and the 1st catoptron group 117 that comprises quarter wave plate;
Centered by the 1st three-dimensional cold atomic beam 118 is prepared district, vertical direction is provided with 1 transmit direction and points to the 1st imprison laser beam transmitter 111 at this center, be provided with the 2nd imprison laser beam transmitter 113 that 2 pairs of transmit directions point to this center horizontal direction space symmetr, separately have the 1st catoptron group 117 that comprises quarter wave plate be placed in this center directly over, taking the 1st direction of propagation of imprisoning laser beam 112 as axle, be provided with the reverse helmholtz coil 115 of a pair of the 1st Three-Dimensional Magnetic ligh trap simultaneously space symmetr.
2, the 1st cold atomic beam deflector 120
The 1st cold atomic beam deflector 120 comprises that the 1st moves two-dimension optical viscose laser beam transmitter 121;
Centered by the 1st two-dimentional cold atomic beam 123, be provided with 2 pairs of transmit directions horizontal direction space symmetr and point to the 1st of this center and move two-dimension optical viscose laser beam transmitter 121.
3, the 1st intervening atom and probe portion 130
The 1st intervening atom and probe portion 130 comprise the 1st raman laser light-beam transmitter the 131, the 2nd raman laser light-beam transmitter the 133, the 3rd raman laser light-beam transmitter the 135, the 1st photodetector 137 and the 1st bias magnetic field coil 138;
In sensor outside, be disposed with the 1st raman laser light-beam transmitter the 131, the 2nd raman laser light-beam transmitter the 133, the 3rd raman laser light-beam transmitter 135 from bottom to top along the direction vertical with vacuum pipe 300; Be provided with symmetrically a pair of the 1st bias magnetic field coil 138 along the director space of vacuum pipe 300, separately have the 1st photodetector 137 to be arranged at the end of atomic beam motion path.
* the 1,2 imprison laser beam transmitters 111,113, the 1st to move two-dimension optical viscose laser beam transmitter 121 and the 1st, 2,3 raman laser light-beam transmitters 131,133,135 are all launch terminals that a kind of general propagation device such as adjustment System and such as optical fiber being made up of universal optical elements such as the NC laser of such as semiconductor laser and such as lens, prism, acousto-optic, electrooptic modulators is connected to form, and end can be fiber collimating lenses or mirror system.
* the reverse helmholtz coil 115 of the 1 Three-Dimensional Magnetic ligh trap is a kind of general coils, formed by plain conductor coiling.
* the 1 bias magnetic field coil 138 is a kind of general coils, formed by plain conductor coiling.
* the 1 alkali metal source 116 can be one or more of the alkali metals such as lithium, sodium, potassium, rubidium, caesium.
The * the 1 also parallel composition of shelving of narrow meshed catoptron of the catoptron group that comprises quarter wave plate 117 narrow meshed quarter wave plate He Yige centers, You Yige center.
* the 1 gravity sensitive type cold atom interference unit the 100 and the 2nd gravity sensitive type cold atom interference unit 200 shares the the the 1st, 2,3,4,5,6 raman laser light beams 132,134,136,232,234,236.
Can be found out by above explanation, this sensor has following feature:
The 1st gravity sensitive type cold atom interference unit 100 is made up of the 1st cold atomic beam generating portion the 110, the 1st cold atomic beam deflector 120 connecting successively from bottom to top and the 1st intervening atom and probe portion 130; Wherein the 1st cold atomic beam deflector 120 moves two-dimension optical viscose laser beam 122 by two pairs the 1st and forms; The 1st gravity sensitive type cold atom interference unit the 100 and the 2nd gravity sensitive type cold atom interference unit 200 can be communicated with vacuum pipe 300 in raman laser propagation path; The 1st gravity sensitive type cold atom interference unit the 100 and the 2nd gravity sensitive type cold atom interference unit 200 shares the the the 1st, 2,3,4,5,6 raman laser light beams 132,134,136,232,234,236.
Three, principle of work
Principle of work of the present invention can be decomposed into following process and sketch: deflection, state preparation, intervening atom and the data handling procedure of the imprison of cold atomic beam, transmitting, cold atomic beam.
1) imprison of cold atomic beam, emission process
As shown in Figure 1, by vertically a pair of the 1st imprison laser beam 112, level two form a Three-Dimensional Magnetic ligh trap to the 2nd imprison laser beam 114 and the reverse helmholtz coil 115 of the 1st Three-Dimensional Magnetic ligh trap, can complete the imprison to alkali metal atom, realize transmitting simultaneously.Its specific works principle is as follows
Imprison process:
Suppose that frequency is
ωlaser (wave vector of laser is
k) with a speed be
vatom interact, the in the situation that of red off resonance (swash light frequency be less than the resonant transition frequency of atom between ground state and excited level
ω 0,
ω<
ω 0), due to Doppler effect, in the time that the direction of motion of atom is identical with the direction of propagation of laser, the laser frequency that atom is experienced can be expressed as (
ω-
kv), in the time that the direction of motion of atom and the propagation of laser are oppositely contrary, the laser frequency that atom is experienced be just expressed as (
ω+
kv).Generally, the frequency that atom is experienced more approaches resonant frequency, and the absorption probability of atom pair photon is just larger.Therefore, in red off resonance
ω<
ω 0situation under, one has certain initial velocity
vatom and a pair of frequency, intensity identical, when the direction of propagation contrary laser action, atom can more absorb the laser of the direction of propagation and atomic velocity opposite direction, thereby the acting force of one of acquisition and atom initial velocity opposite direction reaches the object that atom is slowed down.If when atom is subject to three pairs of correlation and imprison laser perpendicular to each other, just can realizes the three-dimensional of atom is slowed down.The intersection point of the center of the reverse helmholtz coil of Three-Dimensional Magnetic ligh trap and six bundle imprison laser beams overlaps, its effect be exactly can generation Yi Ge center be 0, along the gradient magnetic of three-dimensional strength increase.Under the environment that has magnetic field, can there is Zeeman splitting in the energy level of atom, the energy level of atom can change along with the variation of magnetic field intensity, thereby the photon that therefore can select suitable transition magnetic sublevel to make off-centered atom absorb sensing center with larger probability obtains the restoring force with imprison effect, like this, under the acting in conjunction of magnetic field and light, just can the cooling and highdensity cold atom of imprison group.
Emission process:
As mentioned above, the intensity of three pairs of cooling lasers of general Magneto-Optical Trap is all the same, can only and imprison in central area atom cooling like this, but the special feature in this invention is: one the 1st catoptron group 117 that comprises quarter wave plate is installed in the inside center top of the first cold atomic beam generating portion 100, and the imprison laser beam of top is to reflect generation by the imprison laser beam from below through the 1st catoptron group 117 that comprises quarter wave plate, it is hollow-core construction that the existence of aperture makes the imprison laser beam of top, the cold atom group imprisoning in above-mentioned like this imprison process will be subject to the radiation pressure of below imprison cooling laser light beam and upwards go out via small hole injection under its effect, thereby formation cold atomic beam.
2) deflection of cold atomic beam
Cold atomic beam is after aperture ejection, above aperture, there are two pairs the 1st to move two-dimension optical viscose laser beam 122, by regulating this two pairs of light frequencies, thereby the horizontal velocity that can obtain atom departs from irradiation area from the below imprison laser beam of aperture in the lump outgoing, (constant horizontal velocity can not exert an influence to the result of gradiometry, velocity magnitude can be by regulating two pairs the 1st frequencies that move two-dimension optical viscose laser beam 122 to control), this process realizes laterally cooling to atomic beam in the lump, improves its collimation.
3) state preparation process
By laser or the combination of laser-microwave, atom is prepared into energy level under atomic ground state | energy level in 1> or atomic ground state | on the magnetic sublevel that the magnetic quantum number of 2> is 0, then the atom in other energy level and magnetic sublevel is removed.
4) intervening atom process
Raman laser and alkali metal atom effect can be described with the Three-level Atom shown in Fig. 2 and light field interaction model.Wherein | 1> be energy level under atomic ground state, | 2> is energy level in atomic ground state, | 3> is atom virtual level, | 4> is excited of atoms energy level,
Δfor energy level off resonance amount.Being respectively by a pair of frequency of raman laser
ω 1,
ω 2two bundle correlation laser form, in the time of raman laser and atomic interaction, suitable by selecting
ω 1,
ω 2, make
ω 1,
ω 2with respect to the off resonance amount of jump frequency between atomic energy level
Δ>>
Γ(wherein
Γbe expressed as the natural width of excited of atoms energy level), when
Δ>>
Γtime, can effectively suppress the spontaneous radiation process of atom, atom now can only change interior state by excited absorption or stimulated radiation, thereby forms the excited Raman transition of two-photon.Atom is in the process of absorption and release photon, and the momentum of atom also can change.?
Δ>>
Γand
Δ>> Ω
1, Ω
2(Ω
1, Ω
2be respectively form raman laser right two bundle laser effective Rabi frequency) large off resonance condition under, this Three-level Atom is equivalent to energy level under the ground state of only having atom | energy level in the ground state of 1> and atom | and the two level atom systems of 2>, energy level under the ground state of initial state in atom | after the atom of 1> and the transition of raman laser light beam generation two-photon excited Raman
Energy level under atomic ground state | the probability on 1> can be expressed as
p 1=(1+cos (Ω
eff t))/2
Energy level under atomic ground state | the probability on 2> can be expressed as
p 2=(1-cos (Ω
eff t))/2
Wherein
tfor the time of raman laser bundle and atom effect, Ω
effeffective Rabi frequency (Ω of raman laser light beam
effwith Ω
1, Ω
2relevant).
In traditional cold atom interference scheme, raman laser is all pulsed operation, supposes that atom starts all energy levels under atomic ground state most | 1>, and when the action time of atom and raman laser pulse
tmeet
t=
π/ (2 Ω
eff) time,
p 1=1/2,
p 2=1/2, meet such raman laser pulse and be called
π/ 2 pulses; Work as action time
tmeet
t=
π/ (Ω
eff) time,
p 1=0,
p 2=1, meet such raman laser pulse and be called
πpulse.
Feature of the present invention is: (the 1st raman laser light beam 132 and the 4th raman laser light beam 232 form the 1st pair of raman laser in experimental technique scheme, to keep three pairs of raman lasers; The 2nd raman laser light beam 134 and the 5th raman laser light beam 234 form the 2nd pair of raman laser; The 3rd raman laser light beam 136 and the 6th raman laser light beam 236 form the 3rd pair of raman laser) often open continuously, because of the time of atom and the effect of raman laser light beam
tjointly determined by the spot diameter of raman laser light beam and the movement velocity of atom, therefore can not be by observing action effect sweep time as traditional experimental program, can utilize separately respectively in advance the Lapie that three pairs of raman laser light beams and atomic beam scan light intensity to shake experiment, determine light intensity magnitude separately by observing the layout number reversion effect of atom between two energy levels.Suppose the initial phase of the 1st pair of raman laser, the 2nd pair of raman laser, the 3rd pair of raman laser
φ effbe respectively
φ 1,
φ 2,
φ 3, and suppose that atom starts all energy levels under atomic ground state most | on 1>.
Do not considering under the effect of earth gravity field impact, atom is after being finished with three pairs of raman laser light beams, and atom is energy level under atomic ground state | energy level in 1> and atomic ground state | and the probability on 2> can represent respectively:
P 1=(1+cos(
φ 1-2
φ 2+
φ 3))/2
P 2=(1-cos(
φ 1-2
φ 2+
φ 3))/2
Wherein
φ=
φ 1-2
φ 2+
φ 3for the phase place of interference fringe.
If consider the impact of earth gravity field, suppose that the time interval between the 1st pair of raman laser, the 2nd pair of raman laser, the 3rd pair of raman laser is
t, the change amount of interference fringe final states phase place can be expressed as
Δ φ=
k eff gT 2, wherein
k effexpression raman laser light beam is made effective wave vector of used time to atom.If by the phase change δ of raman laser light beam
φ, finally energy level under atomic ground state of atom | energy level in 1> and atomic ground state | the probability on 2> is expressed as:
P 1=(1+cos(
φ+δ
φ+
k eff ·gT 2))/2
P 2=(1-cos(
φ+δ
φ+
k eff ·gT 2))/2
5) data handling procedure
For the gravity gradiometer being formed by two atomic interferometers, suppose the interference fringe that the first gravity sensitive type cold atom interference unit 100 and the second gravity sensitive type cold atom interference unit 200 obtain (be respectively for expression formula corresponding to same interior state (energy level under the ground state of atom | energy level in the ground state of 1> or atom | 2>):
P A=
?A 1?sin(
φ 1+δ
φ)+
?B 1
P B=
?C 1?sin(
φ 2+δ
φ)+
?D 1
Wherein
a 1,
b 1,
c 1,
d 1for unknown constant, corresponding amplitude and the skew of interference fringe,
Δ φ=
φ 1-
φ 2it is the phase differential of two interferometers.
Utilizing the variance of the gravity gradient value that trigonometric function the Fitting Calculation obtains is the variance sum of two independent interferometers, cannot reach the noise of common mode inhibition fringe phase.In order better to suppress the common-mode noise of two interferometers, can adopt the method deal with data of ellipse fitting, concrete grammar is as follows:
By the cancellation δ that joins together of two equations above
φ, can obtain
C 1 2(
P A)
2+
A 1 2(
P B)
2-2
A 1 C 1 P A P Bcos
Δ φ-2
C 1 P A(
B 1 C 1-
A 1 D 1cos
Δ φ)-
2
A 1 P B(
A 1 D 1-
B 1 C 1cos
Δ φ)+
?A 1 2 D 1 2+
B 1 2 C 1 2-2
A 1 B 1 C 1 D 1cos
Δ φ
-
A 1 2 C 1 2(1-cos
2 Δ φ)=0
For typical gradiometry experimental data, what above formula was corresponding is an elliptic equation.If with objective function
ax 2+
bxy+
cy 2+
dx+
ey+
f=0 pair of data is carried out matching, and phase differential meets:
cos
Δ φ=-
B/2
Then obtain
Δ φ=arcos (
b/2)
Use least square fitting method to obtain parameter
a, B, C, D, Evalue, thereby obtain
Δ φvalue.?
k eff,
tknown and accurately know in the situation of two base length between interference unit, according to
Δ φvalue just can obtain the value of horizontal gravity gradient.By the phase place of the 2nd pair of raman laser of continuous modulation, thus upper quasi-continuous horizontal gravity gradient value of acquisition time.The phase noise of two interference be can effectively suppress by the method for ellipse fitting, precision and the sensitivity of measuring improved.
Claims (5)
1. the horizontal gravity gradient survey sensor based on cold atomic beam interferometer, is characterized in that:
By two structures identical and the 1st gravity sensitive type cold atom interference unit (100) and the 2nd gravity sensitive type cold atom interference unit (200) of parallel arranged form in the horizontal direction;
Or be communicated with and form by vacuum pipe (300) by two identical the 1st gravity sensitive type cold atom interference unit (100) and the 2nd gravity sensitive type cold atom interference unit (200) of structure;
The 1st gravity sensitive type cold atom interference unit (100) is made up of the 1st cold atomic beam generating portion (110) connecting successively from bottom to top, the 1st cold atomic beam deflector (120) and the 1st intervening atom and probe portion (130).
2. by a kind of horizontal gravity gradient survey sensor based on cold atomic beam interferometer claimed in claim 1, it is characterized in that:
The 1st described cold atomic beam generating portion (110) comprises the catoptron group (117) that the 1st imprison laser beam transmitter (111), the 2nd imprison laser beam transmitter (113), the reverse helmholtz coil of the 1st Three-Dimensional Magnetic ligh trap (115), the 1st alkali metal source (116) and the 1st comprise quarter wave plate;
Centered by the 1st three-dimensional cold atomic beam (118) is prepared district, vertical direction be provided with 1 transmit direction point to this center the 1st imprison laser beam transmitter (111), be provided with the 2nd imprison laser beam transmitter (113) that 2 pairs of transmit directions point to this center horizontal direction space symmetr, separately have the 1st catoptron group (117) that comprises quarter wave plate be placed in this center directly over, taking the 1st direction of propagation of imprisoning laser beam (112) as axle, be provided with the reverse helmholtz coil of a pair of the 1st Three-Dimensional Magnetic ligh trap (115) simultaneously space symmetr.
3. by a kind of horizontal gravity gradient survey sensor based on cold atomic beam interferometer claimed in claim 1, it is characterized in that:
The 1st described cold atomic beam deflector (120) comprises that the 1st moves two-dimension optical viscose laser beam transmitter (121);
Centered by the 1st two-dimentional cold atomic beam (123), be provided with 2 pairs of transmit directions horizontal direction space symmetr and point to the 1st of this center and move two-dimension optical viscose laser beam transmitter (121).
4. by a kind of horizontal gravity gradient survey sensor based on cold atomic beam interferometer claimed in claim 1, it is characterized in that:
The 1st described intervening atom and probe portion (130) comprise the 1st raman laser light-beam transmitter (131), the 2nd raman laser light-beam transmitter (133), the 3rd raman laser light-beam transmitter (135), the 1st photodetector (137) and the 1st bias magnetic field coil (138);
In sensor outside, be disposed with the 1st raman laser light-beam transmitter (131), the 2nd raman laser light-beam transmitter (133), the 3rd raman laser light-beam transmitter (135) from bottom to top along the direction vertical with vacuum pipe (300); Be provided with symmetrically a pair of the 1st bias magnetic field coil (138) along the director space of vacuum pipe (300), separately have the 1st photodetector (137) to be arranged at the end of atomic beam motion path.
5. the claimed in claim 1 a kind of horizontal gravity gradient survey sensor based on cold atomic beam interferometer described in, is characterized in that:
The 1st gravity sensitive type cold atom interference unit (100) and the 2nd gravity sensitive type cold atom interference unit (200) share the the the 1st, 2,3,4,5,6 raman laser light beams (132,134,136,232,234,236).
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