CN108181663A - Quasi-pyramid structure type atomic interference gravity acceleration measuring device based on two-dimensional cross grating - Google Patents

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

Gravitational Acceleration Measurement Based on Two-Dimensional Cross Grating measuring device

technical field

The invention mainly relates to the field of atomic interferometers, in particular to a pyramid-like structure atomic interference gravitational acceleration measurement device based on a two-dimensional cross grating.

Background technique

Since the invention of the Michelson interferometer, interferometric instruments constructed based on the diffraction and interference characteristics of light waves have been widely used in basic scientific research, production practice, aerospace, geological prospecting, and national defense industries due to their extremely high measurement accuracy and sensitivity. field. In practice, people gradually realized that the use of shorter wavelength waves for interference can improve measurement accuracy, so an electronic interferometer was built in 1952, and a neutron interferometer was built in 1962. It was not until the 1970s that people began to conceive Atom interferometer. An atomic interferometer is an interferometer composed of atomic matter waves instead of classical light waves as the interference medium, and atomic optical devices instead of classical optical devices to achieve beam splitting, reflection, and beam combining processes.

Compared with other interference media, atomic interferometer has the following advantages: ① Since the mass of atoms is much larger than that of photons, neutrons and electrons, the corresponding matter wave wavelength is shorter, so higher measurement accuracy and sensitivity can be obtained. Theoretical analysis shows that the sensitivity of the atomic interference gyroscope is 10 ¹¹ times higher than that of the He-Ne laser gyroscope with the same loop area, and the sensitivity of the atomic accelerometer is 10 ¹⁷ times higher than that of the existing accelerometers. ②Because atoms have rich internal energy levels and can be precisely manipulated by electromagnetic fields, atomic interferometers can provide a wider range of basic research and applications. ③ Atoms are electrically neutral, less disturbed by stray electric fields, and there is no Coulomb interaction between atoms, so the measurement accuracy can be better than that of electronic interferometers. ④In addition, the development of laser cooling atom technology makes it easier to obtain high-throughput cold or ultracold atomic beams, so the construction of atomic interferometers is simpler and cheaper than neutron interferometers.

The atomic interferometer is a matter-wave interference system composed of atomic matter waves instead of classical light waves as the interference medium, and atomic optical devices instead of classical optical devices to realize beam splitting, reflection, and beam combining processes. It can realize angular velocity, acceleration, and time-frequency reference. , High sensitivity measurement of gravity/gravity gradient. Theoretical analysis shows that the atomic interference absolute gravimeter can increase the sensitivity of the existing absolute gravimeter by at least 3 orders of magnitude. Therefore, the cold atom interference gravimeter is a research hotspot in the field of absolute gravimeter and gravity gradient The detection of the Earth's gravity field and the establishment of the gravity field model have brought revolutionary impact. The basic process of the cold atom interference gravimeter is as follows: first, a large number of alkali metal (such as rubidium Rb or cesium Cs) atoms are imprisoned and cooled to the μK level by using the 3-dimensional magneto-optical trap technology of six beams of light, so that The speed of the atoms moving at the speed of sound is reduced to below 1mm/s; secondly, the cooled atomic clusters are placed in the gravitational field for free fall, and interact with phase-coherent laser pulses to split, reflect, and combine the atomic wave packets. Beam and other coherent manipulation, and achieve atomic interference; finally, detect the final state of atomic groups, use fluorescence collection or absorption imaging to obtain atomic interference fringes, and fit the phase shift caused by gravitational acceleration to achieve accurate measurement of absolute gravitational acceleration. The basic process of the cold atom interference gravimeter is similar to that of the gravimeter. The gravity measurement result is obtained by making difference between the measurement results of the upper and lower atomic interference gravimeters with a certain distance difference.

At present, the main scheme of atomic interference gravimeter is to form magneto-optic traps (Magnetic-optic traps, abbreviated as MOT) through six beams of light in three dimensions, trap and cool atomic groups, and then perform speed selection and state selection on atomic groups, and finally Perform Raman interferometry. The six laser beams of the magneto-optical trap need to install six beam expanders on the vacuum cavity, and a large number of optical devices are required in the optical path, which inevitably increases the volume of the system.

Contents of the invention

The technical problem to be solved by the present invention is that: aiming at the technical problems existing in the prior art, the present invention provides a pyramid-like structure type based on two-dimensional intersecting grating with small overall volume, strong robustness, low cost and high measurement accuracy. Atom interference gravitational acceleration measurement device.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

A kind of pyramidal structure-like atom interference gravitational acceleration measurement device based on two-dimensional cross grating, including vacuum chamber, beam expander, two-dimensional cross grating and reflector assembly for producing separated pyramid structure; the beam expander is used To introduce a single optical fiber into the vacuum system, the two-dimensional cross grating is located between the beam expander and the mirror assembly; the mirror assembly is divided into: MOT area, interference area and detection area from top to bottom; The MOT area includes four first reflection mirrors, and the second reflection mirror is arranged under the detection area.

As a further improvement of the device of the present invention: a beam of cooling light is introduced by the beam expander, and is divided into five beams after passing through a two-dimensional cross grating.

As a further improvement of the device of the present invention: the characteristics of the five beams of light are the same.

As a further improvement of the device of the present invention: in the MOT area, the four first mirrors are located on four sides of the vacuum chamber and are in a horizontal direction.

As a further improvement of the device of the present invention: after the four first reflectors and one second reflector, three pairs of mutually orthogonal trapping light and pump light are formed to form a magneto-optical trap to realize the cooling and trapping of atomic groups .

As a further improvement of the device of the present invention: the vacuum chamber adopts a three-stage vacuum pump of frequency conversion dry scroll pump, turbo molecular pump and compound pump to realize the ultra-high vacuum environment required by the system.

As a further improvement of the device of the present invention: the beam introduced by the beam expander includes expanded beams of cooling light, back pumping light, probe light and Raman light.

As a further improvement of the device of the present invention: the frequency difference between the two beams of Raman light in the light beam is 6.8 GHz, a group of atomic groups after cooling is in a magnetically insensitive state after state preparation, and then the atomic groups are applied π/2, The three light pulses of π and π/2 realize the beam splitting and combining of atomic groups, and construct an atomic interferometer.

As a further improvement of the device of the present invention: through the combination of the detection light and the pump light, the population numbers of atoms in the two ground state hyperfine energy levels are respectively measured, and finally the transition probability and the acceleration of gravity are obtained.

Compared with the prior art, the present invention has the advantages of:

1. The pyramid-like structure atomic interference gravitational acceleration measurement device based on the two-dimensional cross grating of the present invention has a small overall system volume, and since only one beam of light is required to enter the vacuum cavity, the laser module saves a large number of optical devices, and the vacuum module omits A beam expander tube with four beams in the horizontal direction is provided, thereby reducing the volume of the vacuum module and the laser module.

2. The pyramid-like atomic interference gravitational acceleration measurement device based on the two-dimensional cross grating of the present invention has strong robustness, and only needs to ensure the stability of the optical fiber power introduced into the vacuum cavity during system debugging, which is easy to implement. Due to the simple structure of the system and few adjustment variables, the error probability is low when working for a long time.

3. The pyramid-like atomic interference gravitational acceleration measurement device based on the two-dimensional cross grating of the present invention has low cost. Compared with the classic six-beam solution, this solution saves a large number of optical devices, thereby reducing the overall cost.

Description of drawings

Fig. 1 is a schematic diagram of the front view structure of the device of the present invention.

Fig. 2 is a schematic diagram of the side view structure of the device of the present invention.

Fig. 3 is a schematic diagram of the three-dimensional structure principle of the device of the present invention.

Fig. 4 is a detailed flow diagram of the present invention in a specific application example.

illustration:

1. Vacuum chamber; 2. Beam expander; 3. Two-dimensional cross grating; 4. First MOT area; 5. First interference area; 6. Second mirror; 7. Detection area; 8. First mirror ; 9, compound pump.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

As shown in Fig. 1, Fig. 2 and Fig. 3, the quasi-pyramid structure type atomic interference gravity measurement device based on two-dimensional cross grating of the present invention adopts two-dimensional cross grating 3 to carry out beam splitting, the design scheme of the quasi-pyramid magneto-optical trap formed . Specifically, the entire vacuum system only needs one beam of light from top to bottom, which is divided into five beams of light with the same characteristics through the two-dimensional cross grating 3, and is formed by four mirrors in the horizontal direction and the bottom mirror. Three pairs of orthogonal confinement light and pump light form a magneto-optical trap to realize the cooling and confinement of atomic groups, replacing the traditional six-beam light scheme.

The device of the present invention specifically includes a vacuum chamber 1, a beam expander cylinder 2, a two-dimensional cross grating 3 and a mirror assembly for producing a split pyramid structure. All devices are installed in the vacuum chamber 1, the beam expander 2 is used to introduce a single optical fiber of the vacuum system, and the two-dimensional cross grating 3 is located between the beam expander 2 and the mirror assembly. The mirror assembly is divided into: MOT area 4 , first interference area 5 and detection area 7 from top to bottom. The MOT area 4 includes four first reflection mirrors 8 , and the second reflection mirror 6 is arranged under the detection area 7 . A beam of cooling light is introduced by the beam expander tube 2 and divided into five beams of light with the same characteristics after passing through the two-dimensional cross grating 3 . Four first reflectors 8 and one second reflector 6 form three pairs of mutually orthogonal trapping light and pumping light to form a magneto-optical trap to realize cooling and confinement of atomic groups.

In a specific application example, a first reflector 8 in a horizontal direction is placed on each of the four sides of the vacuum chamber 1 .

The atomic interference gravimeter of the present invention uses cold atoms as the test medium, and its thermal diffusion rate is small, which is beneficial to increase the measurement time, but the atoms are easy to randomly collide with the background stray gas during the cooling and trapping process, thus causing cold atoms The lifetime and coherence time are reduced, so cold atom interference experiments need to be carried out in an ultra-high vacuum environment. In a specific application example, the vacuum chamber 1 adopts 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 present invention adopts a frequency conversion dry scroll pump, a turbomolecular pump and a compound pump 9 (combined by an ion pump and a getter) three-stage vacuum pump to achieve the ultra-high vacuum required by the system. Vacuum environment (better than 10 ^-8 Pa).

In a specific application example, the light introduced by the optical fiber includes: cooling light, back-pumping light, probe light and beam expansion of Raman light. The frequency difference between the two Raman beams is 6.8GHz. A group of cooled atomic groups (temperature about 1μk) is in a magnetically insensitive state |F=1, m _F ＝0> after state preparation, and then three beams of π/2, π and π/2 are applied to the atomic group pulse to realize the beam splitting and combining of atomic groups, and construct an atomic interferometer. Finally, through the combination of probe light and back-pump light, the population numbers of atoms in the two ground state hyperfine energy levels are measured respectively, and the transition probability and the acceleration of gravity are finally obtained.

As shown in Figure 4, the detailed process of the present invention in the specific application example is:

S1: Preparation of cold atomic groups.

Firstly, pre-cooling is performed by magneto-optical trap and Polarization Gradient Cooling (abbreviated as PGC) to obtain cold atomic groups with a temperature of about 15 μk.

S2: Speed selection and state preparation.

By Raman velocity selection, the cluster temperature is further reduced to about 1 μk. The state is prepared on the magnetically insensitive state |F=1,m _F ＝0>.

S3: Atom interference.

Three beams of π/2, π and π/2 light pulses are applied to the atomic cluster by two beams of Raman light to realize beam splitting and beam combining of the atomic cluster, and an atomic interferometer is constructed.

S4: internal state detection.

After the interference is completed, the atomic clusters fall freely for a period of time, and then through the action of the probe light combined with the pump light and the blown light, the population numbers of atoms in the two ground state hyperfine energy levels are respectively measured, and finally the transition probability and gravity are obtained. Acceleration value.

The present invention proposes a separate inverted pyramid scheme design, which only needs one optical fiber to be introduced into the vacuum cavity 1 . The advantages of the present invention are:

(1) The overall volume of the system is small. Compared with the classic six-beam MOT, the present invention only needs one beam of light to enter the vacuum cavity 1, the laser module saves a large number of optical devices, and the vacuum module omits the beam expander 2 of the MOT light in the horizontal direction, thus reducing the vacuum space. The volume of the module and the laser module.

(2) Strong robustness. During system debugging, it is only necessary to ensure that the power of the optical fiber introduced into the vacuum chamber 1 is stable, which is easy to implement. Due to the simple structure of the system and few adjustment variables, the error probability is low when working for a long time.

(3) Flexible adjustment. Compared with the traditional pyramid scheme, the present invention combines the four faces of the pyramid with discrete components, and each face can be adjusted flexibly and independently, reducing the accuracy requirements of processing and installation, and improving the stability of the measurement results .

(4) Low cost. Compared with the classical scheme of six beams of light, the present invention saves a lot of optical devices, thereby reducing the overall cost.

The above are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions under the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims (9)

1. a kind of pyramid-like structure type intervening atom acceleration of gravity measuring device based on two-dimentional crossed grating, feature exist In including vacuum chamber, expanding cylinder, two-dimentional crossed grating and mirror assembly for generating separate type pyramid structure；Institute State and expand cylinder and be used for introducing the simple optical fiber of vacuum system, the two dimension crossed grating be located at expand cylinder and mirror assembly it Between；The mirror assembly is from top to bottom divided into：MOT areas, interference region and detecting area；Include four the in the MOT areas One speculum is provided with the second reflective mirror below detecting area.

2. the pyramid-like structure type intervening atom acceleration of gravity according to claim 1 based on two-dimentional crossed grating is surveyed Measure device, which is characterized in that a branch of cooling light is introduced by the cylinder that expands, and five beam light are divided into after two-dimentional crossed grating.

3. the pyramid-like structure type intervening atom acceleration of gravity according to claim 2 based on two-dimentional crossed grating is surveyed Measure device, which is characterized in that the characteristic of the five beams light is identical.

4. the pyramid-like structure type intervening atom gravity based on two-dimentional crossed grating according to claims 1 or 2 or 3 adds Velocity measuring device, which is characterized in that in the MOT areas, four first speculums are located at the cavity four of the vacuum chamber Face, and be horizontally oriented.

5. the pyramid-like structure type intervening atom gravity based on two-dimentional crossed grating according to claims 1 or 2 or 3 adds Velocity measuring device, which is characterized in that after four first speculums and second speculum, form three pairs mutually just The imprison light and pump light of friendship form Magneto-Optical Trap, realize the cooling and imprison of atomic group.

6. the pyramid-like structure type intervening atom gravity based on two-dimentional crossed grating according to claims 1 or 2 or 3 adds Velocity measuring device, which is characterized in that the vacuum chamber uses frequency conversion dry scroll pumps, turbomolecular pump and combination pump three-level Vacuum pump realizes the ultra-high vacuum environment needed for system.

7. the pyramid-like structure type intervening atom gravity based on two-dimentional crossed grating according to claims 1 or 2 or 3 adds Velocity measuring device, which is characterized in that the light beam for expanding cylinder introducing includes cooling light, returns pump light, detection light and Raman light Expand.

8. the pyramid-like structure type intervening atom acceleration of gravity according to claim 7 based on two-dimentional crossed grating is surveyed Measure device, which is characterized in that in the light beam difference on the frequency of two beam Raman lights be 6.8GHz, a process atom after cooling Group then applies pi/2, π and pi/2 three beams light pulse in the insensitive state of magnetic after prepared by state to atomic group, realizes former The beam splitting of son group constructs an atomic interferometer with closing beam.

9. the pyramid-like structure type intervening atom gravity based on two-dimentional crossed grating according to claims 1 or 2 or 3 adds Velocity measuring device, which is characterized in that coordinate back the effect of pump light by detecting light, measured respectively in the hyperfine energy of two ground state Atomic population in grade, and finally obtain transition probability and gravity acceleration value.