CN100464208C - A single-beam magneto-optical trap system - Google Patents

Abstract

The invention discloses a single-beam magneto-optical trap system, which includes four identical total reflection prisms, a pair of anti-Helmholtz coils, a semiconductor laser, a quarter-wave plate of a single-sided coated reflection mirror, and a vacuum conduit , Confined laser beam splitting, the vacuum pump is connected to a vacuum conduit, the ion pump is connected to another vacuum conduit, the above-mentioned vacuum conduits are connected to the metal gas chamber, the total reflection prism is placed in the center of the metal gas chamber, and the semiconductor laser outputs the trapped laser beam , the confinement laser beam is split into confinement laser beams by a total reflection prism, the anti-Helmholtz coil is connected with the metal air chamber, and placed in the propagation direction of the confinement laser beam, and the quarter-wave plate of the single-sided plated reflector is placed on The lower part of the metal gas chamber is located in the center of the metal gas chamber in the horizontal direction, allowing the trapped laser split beam to enter from the center of the quarter-wave plate of the single-sided coated mirror. The invention has the advantages of simple structure, small volume, easy adjustment of light, strong practicability, convenient operation, stability and reliability.

Description

A single-beam magneto-optical trap system

technical field

The present invention relates to a magneto-optical trap system, in particular to a single-beam magneto-optic trap system, which is applicable to many scientific fields that use the basic characteristics of cold atoms to realize measurement and calibration, and have demands for cold atom sources. At the same time, it is also applicable to products that can be commercialized and industrialized by utilizing the characteristics of cold atoms, such as practical atomic clocks.

Background technique

Magneto-optical traps are also called Zeeman-shifted optical traps. It is a potential well formed by the combination of magnetic field and laser scattering force. In 1987, Bell Laboratories cooperated with MIT to realize the first magneto-optical trap for trapping sodium atoms. The basic principle is: three pairs of laser beams facing each other and perpendicular to each other meet at the center of the vacuum chamber containing the sample to be imprisoned. Each pair of laser beams is composed of circularly polarized light with opposite polarization directions. There is a pair of anti-Helmholtz coils outside the gas chamber, which generate a non-uniform magnetic field whose size is related to the coordinate position. At the coordinate center, the magnetic field is zero. Under the action of the magnetic field, the energy level of the atoms to be trapped in the vacuum chamber will undergo Zeeman splitting phenomenon, and the degree of energy level splitting is related to the coordinate position. The laser frequency is tuned to be just below the transition frequency of the atoms. According to the selection rule and the Doppler effect, the trapping laser can produce a linear restoring force on the atoms to be trapped in the vacuum chamber in the three-dimensional direction, so that the atoms can be perfectly trapped. In 1996, the Department of Physics of Seoul National University successfully realized the use of a pyramid funnel-shaped mirror to trap atoms. Soon they cooperated with Japan's Interdisciplinary Graduate School to realize the use of a conical funnel-shaped mirror to trap atoms. Both of these methods are single-beam methods. Compared with the single-beam light-trapping atom, the traditional six-beam light-trapping atom has disadvantages such as complex structure, large device volume, and difficult adjustment of the optical path.

Contents of the invention

The purpose of the present invention is to provide a single-beam magneto-optical trap system, which has a simple structure, small volume, easy adjustment of optical Louis, strong practicability, convenient operation, stable and reliable.

The present invention has the following technical solutions: a single-beam magneto-optical trap system, which includes four identical total reflection prisms, a pair of anti-Helmholtz coils, semiconductor lasers, and a quarter-wave reflective film coated on one side sheet, vacuum conduit, and captive laser beam splitting, characterized in that: the vacuum pump is connected with a vacuum conduit, the ion pump is connected with another vacuum conduit, the above-mentioned vacuum conduits are all connected with a metal gas chamber, and four identical total reflection prisms are placed in a metal chamber. In the central position of the gas chamber, the semiconductor laser outputs the trapped laser beam, which is divided into the trapped laser beam by four identical total reflection prisms, a pair of anti-Helmholtz coils are connected with the metal gas chamber, and a pair of anti-Helmholtz coils are connected to the metal gas chamber. The magnetic coil is placed in the propagation direction of the trapped laser beam, and the quarter-wave plate of the single-sided plated mirror is placed below the vertical direction of the metal gas chamber, and in the center of the metal gas chamber in the horizontal direction, so that the trapped laser beam The split beam is incident vertically from the center of the quarter-wave plate of the single-sided mirror. At the beginning, when people realized the first magneto-optical trap, they used six laser beams, so it was very inconvenient to adjust the optical path and magnetic field, and the entire magneto-optical trap device was relatively large, so the magneto-optical trap was used to develop products And it is very inconvenient to carry out related scientific experiments. Later, people considered using some axisymmetric reflectors (such as: pyramid type, conical surface type), and only one beam of laser light can be used to realize the magneto-optical trap. This method only needs one beam of laser light, so the optical path adjustment is simple. Very simple, the center of the magnetic field is also easy to adjust to coincide with the center of the optical field, and the device of the entire magneto-optical trap is greatly simplified. However, the previous axisymmetric mirrors are usually realized by coating the glass surface or metal surface. The entire reflector is to be placed in the entire vacuum chamber, which is filled with steam of atoms to be imprisoned. Over time, this vapor will corrode the reflective film, making the reflective film irregular, thus Affect the stability and quality of magneto-optical trap.

1. The present invention uses a total reflection prism instead of a coated mirror to reflect the laser beam, so that the vacuum of the entire system can be kept high, thereby improving the stability of the cold atomic group. The principle of the total reflection prism is to realize the reflection of light by using the phenomenon of total reflection when the light goes from light dense to light sparse medium, so the total reflection prism does not need coating. Therefore, it is avoided that the atoms to be trapped corrode the reflective film and affect the stability of the magneto-optical trap.

2. The unique design of one side of the quarter-wave plate coated with reflective film reduces the optical interface on the optical path and simplifies the system. In the past, people usually let the light pass through the quarter-wave plate of a single-sided mirror, and then reflect it by a mirror, and coat the bottom of the quarter-wave plate of the single-sided mirror with a reflective film. The method saves a reflector, simplifies the system, and reduces the optical interface on the optical path, making the adjustment of the optical path simple, and also increases the stability of the optical path itself.

3. The vacuum chamber adopts metal air chamber. Compared with the glass air chamber, the anti-interference ability of the whole magneto-optical trap system will be increased. And when vacuuming, the air chamber is not easy to be damaged. This will greatly increase the practicability of the magneto-optical trap.

Compared with the prior art, the present invention has the following advantages and effects: simple structure, small volume, less lasers and optical elements required, easy adjustment of light, easy vacuum maintenance, strong practicability, convenient operation, stable and reliable.

Description of drawings

Fig. 1 is a schematic diagram of the structure of a single-beam magneto-optical trap system.

Among them: 1a, 1b—total reflection prism, 2—trapped laser beam, 3a, 3b—anti-Helmholtz coil, 4—metal gas chamber, 5—one-quarter glass slide of single-sided mirror, 6— Semiconductor laser, 7—ion pump, 8—vacuum pump, 9—sample bubble, 10a, 10b—vacuum tube, 11a, 11b, 12—trapped laser beam splitter, 13a, 13b—current direction in coil

Detailed ways

Below in conjunction with accompanying drawing, the present invention is described in further detail:

1. The vacuum pump (8) is connected with a vacuum conduit (10a). The vacuum pump (8) includes a molecular pump and a mechanical pump, as well as bellows used for connecting the vacuum system. The ion pump (7) is connected with another vacuum conduit (10b). The ion pump (7) is a small sputtering ion pump. Both the vacuum conduit (10a) and the vacuum conduit (10b) are connected to the metal air chamber (4), and the connected windows are windows facing each other. The vacuum pump (8), that is, the molecular pump and the mechanical pump are used to pre-pump the entire device system. After the pre-pumping, the molecular pump and the mechanical pump can be turned off, and the ion pump (7) can be turned on to make the entire device system vacuum is maintained.

2. The vacuum conduit (10a) is connected to the sample bubble (9), and the vacuum conduit (10a) is connected to the metal gas chamber (4). The sample bubble (9) is a glass vesicle, and the vesicle is equipped with a sample to be imprisoned. As a sample source, the sample in the sample bubble will slowly enter the metal gas chamber (4) in the form of steam.

3, the metal air chamber (4) is realized with a standard cubic cavity of six windows. As shown in accompanying drawing 1, the metal air chamber (4) has four windows in the horizontal direction, wherein a horizontal window is connected with a vacuum conduit (10a), and a vacuum conduit (10a) is connected with the vacuum pump (8) and the sample bubble ( 9) is connected, and the window on the other horizontal direction opposite to this horizontal window is connected with another vacuum conduit (10b), and the vacuum conduit (10b) is connected with the ion pump (7). The metal air chamber (4) has two windows in the vertical direction, one on the top and one on the bottom, which are respectively connected to the anti-Helmholtz coils (3a, 3b), wherein the upper window is connected to the anti-Helmholtz coil ( 3a) and the lower window is connected to the anti-Helmholtz coil (3b). The upper window is also connected to the prison laser (2). The metal gas chamber (4) has four windows in the horizontal direction, one of which is connected to a vacuum conduit (10a), and the window on the other horizontal direction opposite to this horizontal window is connected to another vacuum conduit (10b) connected, the remaining pair of windows in the horizontal direction are used as detection windows for detecting cold atomic groups, and can also be used for adding detection beams to perform correlation detection on the properties of cold atomic groups. Four identical total reflection prisms (1a, 1b) require that the two right-angled sides of each total reflection prism be in the horizontal and vertical directions respectively, and the right-angled surfaces of the horizontal direction of these four total reflection prisms are in the same plane , and is uniformly distributed on this horizontal plane. Four identical total reflection prisms (1a, 1b) are placed in the central position of the metal air chamber (4). When the trapped laser beam (2) enters from the window of the metal air chamber (4), The reflective prisms (1a, 1b) are divided into the trapping laser beams (11a, 11b, 12), which provide the necessary laser beams for the realization of the magneto-optical trap.

4. A pair of anti-Helmholtz coils (3a, 3b) are connected to the metal air chamber (4), and a pair of anti-Helmholtz coils (3a, 3b) are placed in a window in the propagation direction of the trapped laser beam (2) superior. It is wound with an enameled wire, installed on a pair of light-transmitting window surfaces of the metal air chamber (4), and passed with electric currents of equal magnitude and opposite directions. A proper ampere-turn ratio is selected so that the coil pair generates a magnetic field gradient of about 15 Gauss/cm along the coil axis near the center of the metal air chamber (4).

5. The semiconductor laser (6) outputs the trapped laser beam (2). The semiconductor laser (6) represents two lasers: one has a higher power, generally chooses the DL100 laser of TOPTICA Company or other lasers with comparable performance, the output laser power is above 60mW, the wavelength is tuned at 780.24nm, and linear polarization is used to provide The trapped light that cools the atoms and forms the magneto-optical trap; one with low power, generally chooses the DL100 laser of TOPTICA Company or other lasers with comparable performance, the output power is above 10mw, the wavelength is tuned at 780.24nm, and linear polarization is used to provide Repump the light source.

6. After the imprisoned laser beam (2) is produced from the semiconductor laser (6), the imprisoned laser beam (2) from the conductor laser (6) is a kind of linearly polarized light, which is transformed by a quarter-wave plate of a single-sided coated reflector. for circularly polarized light. Then through the beam expansion and collimation of the lens group, the diameter of the light beam reaches about 35mm, and then vertically injects into the metal gas chamber (4) along the center of the upper window in the vertical direction of the metal gas chamber (4).

7. The wavelength of the light applied to the quarter-wave plate (5) of the single-sided coated reflector is 780nm, and the backlight surface is coated with a reflective film. The propagation direction of the trapped laser split beam (12) is perpendicular to the quarter-wave plate (5) of the single-sided coated reflector, and is incident from the center of the quarter-wave plate (5) of the single-sided coated reflector. The function of the quarter-wave plate (5) of the single-sided coated reflector is to make the trapped laser beam split (12) reach the required circular polarization direction, and reflect the trapped laser split beam (12). The quarter-wave plate (5) of the single-sided plated reflector is placed below the vertical direction of the metal gas chamber (4), and is in the central position of the metal gas chamber (4) in the horizontal direction. The light-receiving surface is in the horizontal direction and faces upward. The backlit side of the wave plate is horizontal and facing downwards.

8. After the components of the whole system are assembled, after the vacuum pump (8) pre-pumps the metal air chamber (4), turn off the vacuum pump (8) and turn on the ion pump (7). In (3a, 3b), a suitable current is passed to turn on the semiconductor laser (6), and the relative position between the optical path and the magnetic field is adjusted to form a relatively stable magneto-optical trap. Wherein the arrows (13a, 13b) respectively represent the directions of the currents in the two coils;

The above technical scheme can realize a magneto-optical trap with simple structure, high stability and miniaturization, and has broad application prospects.

Claims (2)

1. single beam magneto-optic well system, it comprises four identical total reflection prism (1a, 1b), a pair of anti-Helmholtz coils (3a, 3b), semiconductor laser (6), the quarter-wave plate (5) of single face plating reflectance coating, vacuum pipeline (10a, 10b), imprison laser beam splitter (11a, 11b, 12), it is characterized in that: vacuum pump (8) links to each other with a vacuum pipeline (10a), ionic pump (7) links to each other with another vacuum pipeline (10b), above-mentioned vacuum pipeline (10a, 10b) all link to each other with metal air chamber (4), four identical total reflection prism (1a, 1b) place the middle position of metal air chamber (4), semiconductor laser (6) output imprison laser beam (2), imprison laser beam (2) is through four identical total reflection prism (1a, 1b) be divided into imprison laser beam splitter (11a, 11b, 12), a pair of anti-Helmholtz coils (3a, 3b) link to each other with metal air chamber (4), a pair of anti-Helmholtz coils (3a, 3b) be placed on imprison laser beam (2) direction of propagation, the quarter-wave plate (5) of single face plating catoptron is placed on the below of the vertical direction of metal air chamber (4), be in the middle position of metal air chamber (4) in the horizontal direction, allow imprison laser beam splitter (12) inject from the central vertical of the quarter-wave plate (5) of single face plating catoptron.

2. a kind of single beam magneto-optic well system according to claim 1 is characterized in that: a described vacuum pipeline (10a), vacuum pump (8) and sample bubble (9) link to each other.

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