CN108181663B - Atomic interference gravity acceleration measuring device based on pyramid-like structure - Google Patents
Atomic interference gravity acceleration measuring device based on pyramid-like structure Download PDFInfo
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Abstract
The invention discloses an atomic interference gravity acceleration measuring device with a pyramid-like structure based on a two-dimensional crossed grating, which comprises a vacuum cavity, a beam expanding cylinder, the two-dimensional crossed grating and a reflector assembly for generating a separated pyramid structure; the beam expanding cylinder is used for introducing a single optical fiber of a vacuum system, and the two-dimensional crossed grating is positioned between the beam expanding cylinder and the reflector component; the reflector component is divided into from top to bottom in sequence: an MOT region, an interference region and a detection region; the MOT area comprises four first reflecting mirrors, and a second reflecting mirror is arranged below the detection area. The invention has the advantages of small integral volume, strong robustness, low cost, high measurement precision and the like.
Description
Technical Field
The invention mainly relates to the field of atom interferometers, in particular to a pyramid-like structure type atom interference gravity acceleration measuring device based on two-dimensional crossed gratings.
Background
Since the invention of the michelson interferometer, the interference measuring instrument constructed according to the diffraction and interference characteristics of the optical wave is widely applied to a plurality of fields such as basic scientific research, production practice, aerospace, geological prospecting, national defense industry and the like due to extremely high measurement precision and sensitivity. In practice, it is gradually recognized that interference with shorter wavelength waves can improve the measurement accuracy, so that electronic interferometers were constructed in 1952 and neutron interferometers were constructed in 1962, and atomic interferometers were not conceived until the 70 s of the 20 th century. The atomic interferometer is formed by using atomic substance waves to replace classical light waves as interference media and using an atomic optical device to replace a classical optical device to realize beam splitting, reflecting and combining processes.
Compared with other interference media, the atomic interferometer has the following advantages: the atomic mass is far greater than that of photons, neutrons and electrons, and the wavelength of corresponding matter waves is shorter, so that higher measurement accuracy and sensitivity can be obtained. Theoretical analysis shows that the sensitivity of the atomic interference gyroscope is 10 times higher than that of the He-Ne laser gyroscope with the same loop area11The sensitivity of the atomic accelerometer is 10 times higher than that of the existing accelerometer17And (4) doubling. Secondly, because the atoms have rich internal energy levels, the atoms can be precisely controlled by using an electromagnetic field, so that the atom interferometer can provide wider basic research and application. Atoms show electric neutrality, are slightly interfered by stray electric fields, and have no coulomb interaction among atoms, so that the measurement precision superior to that of an electronic interferometer can be obtained. Furthermore, the development of laser cooled atomic technology makes high flux cold or supercooled atomic beams easier to obtain, so that the construction of the atomic interferometer is simpler and cheaper than that of a neutron interferometer.
The atomic interferometer uses atomic substance waves to replace classical light waves as interference media, uses an atomic optical device to replace a classical optical device to realize a substance wave interference system formed by beam splitting, reflecting and combining processes, and can realize high-sensitivity measurement of angular velocity, acceleration, time-frequency reference and gravity/gravity gradient. Theoretical analysis shows that the sensitivity of the existing absolute gravimeter can be improved by at least 3 orders of magnitude by the atomic interference absolute gravimeter, so that the cold atomic interference absolute gravimeter is a research hotspot in the field of the existing absolute gravimeter and gravity gradiometer and is expected to bring revolutionary influence on detection of a high-precision earth gravitational field and establishment of a gravitational field model in the future. The basic flow of the cold atom interference gravimeter is as follows: firstly, a 3-dimensional magneto-optical trap technology of six beams of light is utilized to trap a large number of alkali metal (such as rubidium Rb or cesium Cs) atoms and cool the atoms to a mu K magnitude, so that the atom speed of supersonic motion at normal temperature is reduced to be below 1 mm/s; secondly, placing the cooled atomic group in a gravity field to do free-fall motion, interacting with phase coherent laser pulses, performing coherent control on the atomic wave packet such as beam splitting, reflection and beam combination, and realizing atomic interference; and finally, detecting the atomic group terminal state, obtaining atomic interference fringes by utilizing a fluorescence collection or absorption imaging method, fitting out the phase shift caused by the gravitational acceleration, and realizing the accurate measurement of the absolute gravitational acceleration. The basic flow of the cold atom interference gravimeter is similar to that of a gravimeter, and a gravity measurement result is obtained by subtracting the measurement results of an upper atom interference gravimeter and a lower atom interference gravimeter with a certain distance difference.
At present, the main scheme of the atomic interference gravimeter is to form a magneto-optical trap (abbreviated as MOT) by six beams of light with three dimensions, trap and cool the atomic groups, perform speed selection and state selection on the atomic groups, and finally perform a raman interference process. Six laser beams of the magneto-optical trap need to be provided with six beam expanding cylinders on a vacuum cavity, and a large number of optical devices are needed in an optical path part, so that the system volume is inevitably increased.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the technical problems in the prior art, the invention provides the pyramid-like structure type atomic interference gravity acceleration measuring device based on the two-dimensional cross grating, which has the advantages of small overall size, strong robustness, low cost and high measuring precision.
In order to solve the technical problems, the invention adopts the following technical scheme:
an atomic interference gravity acceleration measuring device with a pyramid-like structure based on a two-dimensional crossed grating comprises a vacuum cavity, a beam expanding cylinder, the two-dimensional crossed grating and a reflector assembly for generating a separated pyramid structure; the beam expanding cylinder is used for introducing a single optical fiber of a vacuum system, and the two-dimensional crossed grating is positioned between the beam expanding cylinder and the reflector component; the reflector component is divided into from top to bottom in sequence: an MOT region, an interference region and a detection region; the MOT area comprises four first reflecting mirrors, and a second reflecting mirror is arranged below the detection area.
As a further improvement of the device of the invention: and a beam of cooling light is introduced by the beam expanding cylinder, passes through the two-dimensional crossed grating and is divided into five beams of light.
As a further improvement of the device of the invention: the characteristics of the five beams of light are the same.
As a further improvement of the device of the invention: in the MOT area, the four first reflecting mirrors are positioned on four sides of the cavity of the vacuum cavity and are in the horizontal direction.
As a further improvement of the device of the invention: after passing through the four first reflectors and the second reflector, three pairs of mutually orthogonal trapping light and pumping light are formed to form a magneto-optical trap, so that the cooling and trapping of atomic groups are realized.
As a further improvement of the device of the invention: the vacuum cavity adopts a variable-frequency dry type scroll pump, a turbine type molecular pump and a compound pump three-level vacuum pump to realize an ultrahigh vacuum environment required by the system.
As a further improvement of the device of the invention: the light beam introduced by the beam expanding cylinder comprises the beam expansion of cooling light, back pump light, detection light and Raman light.
As a further improvement of the device of the invention: the frequency difference of two Raman lights in the light beam is 6.8GHz, the cooled atomic group is in a magnetic insensitive state after state preparation, and then three light pulses of pi/2, pi and pi/2 are applied to the atomic group, so that the beam splitting and beam combining of the atomic group are realized, and the atomic interferometer is constructed.
As a further improvement of the device of the invention: and respectively measuring the atomic population numbers on the hyperfine energy levels of the two ground states by the action of the probe light and the return pump light, and finally obtaining the transition probability and the gravitational acceleration value.
Compared with the prior art, the invention has the advantages that:
1. the atomic interference gravity acceleration measuring device based on the two-dimensional cross grating pyramid-like structure has the advantages that the overall size of the system is small, only one beam of light is needed to enter the vacuum cavity, a large number of optical devices are omitted from the laser module, and the beam expanding cylinder for four beams of light in the horizontal direction is omitted from the vacuum module, so that the sizes of the vacuum module and the laser module are reduced.
2. The atomic interference gravity acceleration measuring device based on the two-dimensional cross grating pyramid-like structure has strong robustness, and the system debugging only needs to ensure that the power of the optical fiber introduced into the vacuum cavity is stable, so that the atomic interference gravity acceleration measuring device is easy to realize. Because the system has simple structure and few adjusting variables, the error probability is low when the system works for a long time.
3. The atomic interference gravity acceleration measuring device based on the two-dimensional crossed grating pyramid-like structure is low in cost, and compared with a classical six-beam optical scheme, the scheme saves a large number of optical devices, so that the overall cost is reduced.
Drawings
Fig. 1 is a schematic diagram of the principle of the front view structure of the device of the invention.
FIG. 2 is a schematic diagram of the side view of the device of the present invention.
Fig. 3 is a schematic perspective view of the device of the present invention.
FIG. 4 is a detailed flow chart of the present invention in a specific application example.
Illustration of the drawings:
1. a vacuum chamber; 2. a beam expanding cylinder; 3. two-dimensional cross grating; 4. an MOT region; 5. a first interference region; 6. a second reflector; 7. a detection region; 8. a first reflector; 9. a compound pump.
Detailed Description
The invention will be described in further detail below with reference to the drawings and specific examples.
As shown in fig. 1, fig. 2 and fig. 3, the atomic interference gravity measuring device based on the two-dimensional cross grating and with the pyramid-like structure of the present invention adopts a design scheme of the pyramid-like magneto-optical trap formed by splitting beams by the two-dimensional cross grating 3. Specifically, the whole vacuum system only needs one beam of light from top to bottom, the five beams of light with the same characteristics are split through the two-dimensional crossed grating 3, three pairs of orthogonal trapping light and pumping light are formed through the four reflectors and the lowermost reflector in the horizontal direction, a magneto-optical trap is formed, cooling and trapping of atomic groups are achieved, and the traditional six-beam light scheme is replaced.
The device specifically comprises a vacuum cavity 1, a beam expanding cylinder 2, a two-dimensional crossed grating 3 and a reflector component for generating a separated pyramid structure. All the devices are arranged in a vacuum cavity 1, a beam expanding cylinder 2 is used for introducing a single optical fiber of a vacuum system, and a two-dimensional cross grating 3 is positioned between the beam expanding cylinder 2 and a reflector component. The reflector component is divided into from top to bottom in sequence: MOT region 4, first interference region 5, and detection region 7. Four first reflecting mirrors 8 are included in the MOT region 4, and a second reflecting mirror 6 is disposed below the detection region 7. A beam of cooling light is introduced by the beam expanding cylinder 2 and is divided into five beams of light with the same characteristics after passing through the two-dimensional crossed grating 3. Three pairs of mutually orthogonal trapping light and pumping light are formed by the four first reflectors 8 and the second reflector 6 to form a magneto-optical trap, so that the cooling and trapping of atomic groups are realized.
In the specific application example, a first reflecting mirror 8 is disposed on each of four sides of the vacuum chamber 1.
The atom interference gravimeter provided by the invention adopts cold atoms as an inspection medium, the thermal diffusion rate is low, the measurement time is favorably increased, but the atoms are easy to randomly collide with background stray gas in the cooling and trapping processes, so that the service life and coherence time of the cold atoms are reduced, and therefore, a cold atom interference experiment needs to be carried out in an ultrahigh vacuum environment. In a specific application example, the vacuum chamber 1 is a glass vacuum chamber 1 which is a cuboid with a side length of 20 mm. As a preferred embodiment, the vacuum system of the invention adopts a three-stage vacuum pump of a variable-frequency dry type scroll pump, a turbo type molecular pump and a compound pump 9 (formed by combining an ion pump and a getter) to realize the ultrahigh vacuum environment (better than 10) required by the system-8Pa)。
In a specific application example, the light introduced by the optical fiber comprises: cooling light, pump back light, probe light and Raman light. The frequency difference between the two Raman lights is 6.8 GHz. A cooled radical (temperature about 1 μ k) in a magnetically insensitive state F-1, m after state preparationFAnd then applying three light pulses of pi/2, pi and pi/2 to the atomic group to realize the beam splitting and beam combining of the atomic group and construct an original atom groupA sub-interferometer. And finally, respectively measuring the atomic population numbers on the hyperfine energy levels of the two ground states by the action of the probe light and the return pump light, and finally obtaining the transition probability and the gravitational acceleration value.
As shown in fig. 4, the detailed process of the present invention in the specific application example is as follows:
s1: and (4) preparing cold atomic groups.
First, pre-Cooling by a magneto-optical trap and Polarization Gradient Cooling (PGC) to obtain a cold radical with a temperature of about 15 μ k.
S2: speed selection and state preparation.
The radical temperature is further reduced to about 1 μ k by raman velocity selection. State preparation in magnetically insensitive state F ═ 1, mFEqual to 0.
S3: atomic interference.
And (3) applying three light pulses of pi/2, pi and pi/2 to the atomic group through the two Raman light beams to realize beam splitting and beam combining of the atomic group and construct an atomic interferometer.
S4: and (5) detecting an internal state.
After the interference is finished, the atomic groups fall freely for a period of time, then atomic population numbers on the hyperfine energy levels of the two ground states are respectively measured through the cooperation of the probe light and the action of the pump light and the blown light, and finally transition probability and a gravitational acceleration value are obtained.
The invention provides a scheme design of a separated inverted pyramid, and only one optical fiber is required to be introduced into the vacuum cavity 1. The invention has the advantages that:
(1) the whole system is small in volume. Compared with the classic six-beam MOT, the invention only needs one beam of light to enter the vacuum cavity 1, the laser module omits a large amount of optical devices, and the vacuum module omits the beam expanding cylinder 2 of the MOT light in the horizontal direction, thereby reducing the volume of the vacuum module and the laser module.
(2) And the robustness is strong. The system debugging only needs to ensure that the power of the optical fiber introduced into the vacuum cavity 1 is stable, and the system debugging is easy to realize. Because the system has simple structure and few adjusting variables, the error probability is low when the system works for a long time.
(3) The adjustment is flexible. Compared with the traditional pyramid scheme, the pyramid measuring device has the advantages that the four surfaces of the pyramid are formed by combining discrete components, each surface can be flexibly and independently adjusted, the precision requirements of processing and installation are reduced, and meanwhile, the stability of a measuring result is improved.
(4) The cost is low. Compared with the classical six-beam light scheme, the invention saves a large number of optical devices, thereby reducing the overall cost.
The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention.
Claims (9)
1. An atomic interference gravity acceleration measuring device with a pyramid-like structure based on a two-dimensional crossed grating is characterized by comprising a vacuum cavity, a beam expanding cylinder, the two-dimensional crossed grating and a reflector assembly for generating a separated pyramid structure; the beam expanding cylinder is used for introducing a single optical fiber of a vacuum system, and the two-dimensional crossed grating is positioned between the beam expanding cylinder and the reflector component; the reflector component is divided into from top to bottom in sequence: an MOT region, an interference region and a detection region; the MOT area comprises four first reflecting mirrors, and a second reflecting mirror is arranged below the detection area.
2. The atomic interference gravitational acceleration measuring device of pyramid-like structure type based on two-dimensional cross grating as claimed in claim 1, wherein a beam of cooling light is introduced by said beam expanding cylinder, and is divided into five beams of light after passing through two-dimensional cross grating.
3. The two-dimensional crossed grating-based atomic interference gravitational acceleration measuring device of pyramid-like structure type according to claim 2, wherein the characteristics of the five beams of light are the same.
4. The atomic interference gravity acceleration measurement device of the pyramid-like structure type based on the two-dimensional cross grating as claimed in claim 1, 2 or 3, wherein the four first reflection mirrors are located on four sides of the vacuum chamber in the MOT region and are in horizontal direction.
5. The atomic interference gravitational acceleration measuring device of the pyramid-like structure type based on the two-dimensional crossed grating as claimed in claim 2 or 3, wherein the five beams of light form three pairs of mutually orthogonal trapping light and pumping light after passing through the four first reflectors and the one second reflector, thereby forming a magneto-optical trap and realizing the cooling and trapping of atomic groups.
6. The atomic interference gravitational acceleration measurement device of the two-dimensional cross grating-based pyramid-like structure type according to claim 1, 2 or 3, wherein the vacuum chamber adopts a variable frequency dry scroll pump, a turbo molecular pump and a compound pump three-stage vacuum pump to realize the ultra-high vacuum environment required by the system.
7. The atomic interference gravitational acceleration measuring device of pyramid-like structure type based on two-dimensional cross grating as claimed in claim 1, 2 or 3, wherein the light beam introduced by the beam expanding cylinder comprises a beam expansion of cooling light, back pump light, probe light and Raman light.
8. The two-dimensional cross grating-based pyramid-like structure type atomic interference gravitational acceleration measuring device as claimed in claim 7, wherein a frequency difference between two raman light beams in the light beam is 6.8GHz, a cooled atomic group is in a magnetically insensitive state after state preparation, and then three light pulses of pi/2, pi and pi/2 are applied to the atomic group, so that splitting and combining of the atomic group are realized, and an atomic interferometer is constructed.
9. The atomic interference gravitational acceleration measurement device of the two-dimensional cross grating-based pyramid-like structure type according to claim 1, 2 or 3, wherein atomic population numbers at two ground state hyperfine energy levels are respectively measured by the action of probe light and pump-back light, and finally transition probability and gravitational acceleration values are obtained.
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| CN112421373A (en) * | 2020-08-13 | 2021-02-26 | 中国人民解放军国防科技大学 | Cold atom interference phase modulation type single-sideband Raman light generation method and system |
| CN112421371B (en) * | 2020-08-13 | 2022-06-14 | 中国人民解放军国防科技大学 | Cold atom interferometer single laser light source system |
| CN112764114B (en) * | 2020-12-29 | 2022-06-24 | 杭州微伽量子科技有限公司 | Quantum absolute gravimeter and light path structure thereof |
| CN116466273B (en) * | 2023-06-20 | 2023-08-29 | 广东威纳格科技有限公司 | Atomic interferometer for synchronously measuring gravitational acceleration and magnetic field and method thereof |
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| US9134450B2 (en) * | 2013-01-07 | 2015-09-15 | Muquans | Cold atom gravity gradiometer |
| CN103837904B (en) * | 2014-03-20 | 2016-04-20 | 中国科学院武汉物理与数学研究所 | Based on combination inertial sensor and the measuring method thereof of many constituent atoms interferometer |
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