JP2009140984A - Atomic oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an atomic oscillator which can strongly produce a coherent population trapping (CPT) phenomena and ensure a high ratio of signal to noise. <P>SOLUTION: The atomic oscillator 10 is provided with a coherent light source 14 (light emitting element), a gas cell 20 for transmitting a resonated light output from the coherent light source 14, and an optical detector 16 (light receiving element) for detecting a light transmitting the gas cell 20. The gas cell 20 has a partition part 22 in a direction crossing the transmitting direction of the resonated light, of which inside is divided into a plurality of chambers 24. The partition part 22 can be plurally provided inside the gas cell 20. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an atomic oscillator.

  An atomic oscillator using a quantum interference effect (CPT: Coherent Population Trapping) includes a semiconductor laser, a gas cell, a photodetector, and the like. The physical cell structure of an atomic oscillator using CPT described in Patent Document 1 is a structure in which a semiconductor laser, a gas cell, and a photodetector are integrated vertically. The semiconductor laser generates two types of light (coupling light and probe light) having different wavelengths and outputs them to the gas cell. In this gas cell, alkali metal atoms (quantum absorbers) such as rubidium atoms and cesium atoms are enclosed. And the quantum absorber in a gas cell absorbs the said light, and an absorption characteristic will change according to the frequency difference of two types of light. In addition, when the frequency difference between the coupling light and the probe light is a specific value, a phenomenon is known in which neither of the two types of light is transmitted without being absorbed (electromagnetically induced transmission (EIT) phenomenon). .

  Further, it has been proposed to make a gas cell used in an atomic oscillator thin with respect to the optical axis direction of excitation light. The atomic oscillation acquisition device described in Patent Document 2 uses a gas cell that is thinner than usual. Specifically, the gas cell is preferably cylindrical, particularly cylindrical, and the length of the cylinder side surface is preferably 0.1 mm to 5 mm, more preferably 1 mm to 2 mm. .

  In the rubidium atomic oscillator described in Patent Document 3, a metal case is disposed between the optical pumping light source and the photodetector, and a plurality of gas cells and dielectric resonators are disposed in combination in the metal case. ing.

Moreover, in the rubidium atomic oscillator described in Patent Document 4, a rubidium gas cell having a shape (eyebrows) in which two spheres are communicated is disposed inside the cavity. A light receiving element is disposed between the cavity and the rubidium gas cell, and a protruding protrusion for tuning is disposed so as to avoid the rubidium gas cell while penetrating the wall surface of the cavity.
US Pat. No. 6,806,784 Japanese Patent No. 3755001 (page 5) JP-A-6-244722 (page 3, FIG. 4 (A)) Japanese Patent Laid-Open No. 5-190934 (right column on page 2, FIG. 1)

  By reducing the thickness of the gas cell as described above, the Doppler effect of the thermal motion of atoms in the cell with respect to the excitation light can be suppressed, so that the absorption line to be detected can be increased in Q. However, since the thickness of the cell is reduced, the strength as the CPT is weakened, and there is a problem that the S / N (signal / noise) after detection is reduced.

In addition, since the gas cells of the invention described in Patent Document 3 are individual, when a plurality of gas cells are arranged between the optical pumping light source and the photodetector, the number of transmission glasses of light emitted from the optical pumping light source is “ The number of gas cells × 2 ”. For this reason, when the number of gas cells is increased, the amount of attenuation of light increases. Further, since a gas pressure difference due to the difference between the internal pressure and the external pressure is generated in the gas cell, a glass thickness that can withstand this pressure difference is required. Further, since it is inevitable that the buffer gas pressure in each gas cell varies in production, it is impossible to have the same center frequency of atomic resonance (EIT phenomenon) at a certain temperature of each gas cell. For this reason, the center frequency at which the EIT characteristic is obtained is shifted between the gas cells, and the convex characteristic of the EIT as a whole of the plurality of gas cells becomes broad, so that the frequency stability as an oscillator eventually deteriorates. . Furthermore, this rubidium atomic oscillator requires a metal case (microwave resonance part). In addition, since the dielectric must be disposed in the metal case together with the gas cell, the corresponding volume becomes an obstacle and cannot be reduced in size.

  In addition, in the gas cell of the invention described in Patent Document 4, light is incident through a light incident hole provided in the cavity, but an adjustment rod inserted in the cavity (where two spheres communicate with each other). ) To prevent light from being blocked by light, it is not possible to pass light near the adjusting rod. That is, the portion into which the adjustment rod is inserted has a problem that the volume of the gas cell cannot be used efficiently because the waist portion of the glass sealed body is narrowed. In addition, since the gas cell has a structure that narrows the waist portion of the glass sealing body, fast-velocity atoms (atoms distributed on the side with fast thermal vibration) collide with a surface that is not perpendicular to the optical axis. For this reason, there is a problem that the rate of occurrence of relaxation due to collision is reduced. In addition, this rubidium atomic oscillator requires an adjustment rod.

  Therefore, an object of the present invention is to provide an atomic oscillator that can obtain a CPT phenomenon strongly and secures a high S / N.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

Application Example 1 A light-emitting element, a gas cell that transmits resonance light output from the light-emitting element, and a light-receiving element that detects light transmitted through the gas cell are provided, and the gas cell is arranged in a direction in which resonance light is transmitted. An atomic oscillator characterized in that it has a partition portion and the interior is divided into a plurality of rooms.
Since the atomic oscillator has a configuration in which the interior of the gas cell is divided into a plurality of rooms by the partition portion, the CPT phenomenon can be strongly obtained, and high signal / noise (S / N) can be secured. Moreover, since the partition part is shared by the adjacent rooms, the number of partition parts through which resonance light passes can be reduced as compared with the case where a plurality of gas cells having one room are provided. For this reason, the attenuation amount of light can be reduced.

Application Example 2 The atomic oscillator according to Application Example 1, wherein the rooms provided in the gas cell are connected by an opening provided in the partition part.
Since such an atomic oscillator can make the pressure of the gas inside the gas cell uniform, it is possible to eliminate variations in characteristics between rooms.

Application Example 3 The atomic oscillator according to Application Example 2, wherein the opening is provided in a part of the partition where the resonant light passes.
Thereby, since the resonance light does not pass through the partition portion, it is possible to prevent the light from being attenuated, and it is not necessary to increase the intensity of the resonance light, so that the line width can be prevented from widening. Furthermore, since the pressure of the buffer gas is common in each room, it is possible to eliminate variations in characteristics between the rooms.

Application Example 4 The atomic oscillator according to Application Example 1, wherein the room provided in the gas cell is narrower on the incident side of resonance light than on the emission side.
With such a room width (width in the direction in which the resonance light passes), the thermal motion speed of the atoms is slower in the room on the incident side of the resonance light than in the room on the emission side. Further, the resonance light is transmitted through the partition portion, so that the intensity on the incident side is smaller than that on the emission side. For this reason, even if the room on the emission side of the resonance light is wider than the incidence side, the intensity of the resonance light is attenuated, so that the half width of the signal can be prevented from becoming wide.

Application Example 5 The atomic oscillator according to any one of Application Examples 1 to 4, wherein a plurality of the partition portions are provided.
As a result, at least three or more rooms are provided inside the gas cell. For this reason, the CPT phenomenon can be obtained more strongly, and a high signal / noise (S / N) can be secured.

  The best embodiment of the atomic oscillator according to the present invention will be described below. FIG. 1 is a block diagram illustrating the configuration of an atomic oscillator. The atomic oscillator 10 uses CPT and controls the frequencies of the two lights so that the frequency difference between the coupling light and the probe light is within this narrow region. For this purpose, the atomic oscillator 10 includes an optical system 12 and a frequency control circuit 18. The optical system 12 includes a gas cell 20, a coherent light source 14 (light emitting element) that supplies resonance light (incident light) to the gas cell 20, and a photodetector 16 (light receiving element) that detects transmitted light that has passed through the gas cell 20. I have. The frequency control circuit 18 controls the oscillation frequency based on the signal detected from the photodetector 16.

  FIG. 2 is a sectional view of the gas cell. The gas cell 20 has a partition portion 22 that intersects the direction in which resonance light is transmitted, and the interior of the gas cell 20 is divided into a plurality of rooms 24. The partition portion 22 can transmit resonance light and is designed to be perpendicular or substantially perpendicular to the optical axis through which the resonance light is transmitted. For this reason, the atoms encapsulated in each room 24 are efficiently relaxed for those having a high velocity.

  That is, each chamber 24 is sealed with a gaseous gas atom together with a buffer gas (filling gas for buffering), and these atoms have various speeds from fast to slow. Are mixed and distributed. Among these, when fast-velocity atoms (excited atoms) contribute to the EIT phenomenon, the wavelength of light seen from the atoms apparently changes due to the Doppler effect, so the detection width (Δω) in the EIT phenomenon is expanded by this Doppler effect. (See FIG. 3). FIG. 3 is a diagram showing the relationship between the frequency difference between the resonant light (coupling light ω1) and the resonant light (probe light ω2) and the EIT signal intensity. Therefore, in order to prevent the detection width from expanding due to the Doppler effect, it is necessary to reduce the number of fast atoms contributing to the EIT phenomenon as much as possible. For this reason, in this embodiment, the partition part 22 is provided in the inside of the gas cell 20, and by making a fast atom collide with the partition part 22, it transfers to a ground state (slow speed state) rapidly.

Then, the fast-velocity atoms immediately collide with the partition portion 22 and the time related to light is shortened, so that the probability of shifting to the ground state (slow speed state) without causing light absorption increases. On the other hand, the time for the atom having a reduced velocity to collide with the partition portion 22 becomes longer, and the time related to light becomes sufficiently longer, so that the probability of absorbing light is increased. In other words, by providing the partitioning portion 22 perpendicular to the optical axis, the probability that fast-velocity atoms remain on the optical path is lowered.
In the case shown in FIG. 2, since there are seven partition portions 22, there are eight rooms 24. The metal atom may be an alkali metal such as rubidium or cesium.

  Further, the width (cell thickness) of the room 24 in the direction in which the resonant light is transmitted may be set so that the velocity of the atoms enclosed in the room 24 is reduced. That is, atoms that are in thermal motion in the room 24 decelerate when they collide with the partition 22 and the like, so that the proportion of slow atoms increases when the cell thickness is reduced. For this reason, the detection width (Δω) is narrowed, and a very sharp EIT signal intensity is obtained.

  FIG. 4 is a diagram showing the relationship between the cell thickness and the half width of the EIT spectrum. As shown in FIG. 4, it can be seen that when the cell thickness is reduced, the full width at half maximum is reduced from about 1 mm. For this reason, in the gas cell 20 of this embodiment, the cell thickness is set to 1 mm or less, the velocity of atoms in each room 24 is slowed, and the signal line width is prevented from widening due to the Doppler effect between the atoms and the resonance light. is doing.

In this way, the interior of the gas cell 20 is divided into a plurality of rooms 24, and the partition part 22 provided between the adjacent rooms 24 is shared. For this reason, in the gas cell 20 shown in FIG. 2, the number of the partition portions 22 through which the resonance light is transmitted can be reduced as compared with the case where a plurality of gas cells 20 that do not have the chamber 24 are arranged in the direction in which the resonance light is transmitted. it can. That is, in the gas cell 20 shown in FIG. 2, it is possible to prevent the resonance light from being attenuated by the partition portion 22.
The gas cell 20 is kept at a high temperature because it is necessary to keep the atoms in a gas state when utilizing energy transition of atoms.

  Such an atomic oscillator 10 that uses the quantum interference effect of two types of laser light detects how much light incident on the gas cell 20 is absorbed by the atomic gas by the photodetector 16 provided on the opposite side. Thus, the atomic resonance is detected, and the control system synchronizes a reference signal such as a crystal oscillator with the atomic resonance to obtain an output. In the atomic oscillator 10, the two ground levels receive resonance light, and two resonances irradiated simultaneously in a three-level system (for example, a Λ-type level system) that is resonantly coupled to the common ground level. When the frequency of light exactly matches the energy difference between the first ground level and the second ground level, the three-level system becomes a superposition of the two ground levels, and excitation to the excitation level. Stops. CPT uses this principle to detect and use a state where light absorption in the gas cell 20 stops when one or both wavelengths (frequency) of two resonance lights are changed.

  In the atomic oscillator 10 described above, since the inside of the gas cell 20 is partitioned into a plurality of rooms 24 in the optical axis direction, the CPT phenomenon can be strongly obtained and a high S / N can be secured. In addition, even when a plurality of thin cells are stacked, the CPT phenomenon can be strongly obtained, and a high S / N can be secured.

  In addition, since an object (for example, an adjustment rod for tuning microwaves) that blocks resonance light is not inserted into the gas cell 20, the resonance light can pass through any part of the partition portion 22. For this reason, all the volume (cube, cylindrical shape, etc.) of the whole gas cell 20 can be utilized efficiently.

  The gas cell 20 is provided with a common partition portion 22 between adjacent rooms 24. For this reason, the number of partitions 22 (glass) through which the resonance light passes may be “the number of rooms + 1”, so that the attenuation amount of the resonance light can be reduced. For example, in the gas cell 20 having two chambers 24, the number of transmitting glasses while the resonant light passes through these chambers 24 is 3, so that the attenuation of light is reduced.

  If the glass plate constituting the partition 22 is glass (transparent material), it is not necessary to withstand the difference between the atmospheric pressure outside the gas cell 20 and the gas pressure in the room 24 (atmospheric pressure difference). The strength is not limited. Therefore, the thickness of the partition part 22 can be reduced within a manufacturable range.

  Further, since the atomic oscillator 10 according to the present embodiment is a CPT method, a dielectric for shortening the wavelength of the microwave is not required as in the prior art, and a metal case is not required.

The gas cell 20 may have a form described below as well as the form shown in FIG. FIG. 5 is a cross-sectional view illustrating a first modification of the gas cell. In the gas cell 30 of the first modification, an opening 32 is provided in the partition part 22, and each room 24 is connected by the opening 32. As a result, the buffer gas can flow into each room 24 and the pressure and temperature of the buffer gas in each room 24 become uniform, so that variations in characteristics between the rooms 24 can be eliminated.

  And the opening part 32 can be provided in the arbitrary positions of the partition part 22. FIG. For this reason, as shown in FIG. 6, the opening part 32 can also be provided in the position through which resonant light passes. As a result, the resonance light does not pass through the partitioning portion 22, so that attenuation of the light can be prevented, and it is not necessary to increase the intensity of the resonance light, so that the line width can be prevented from widening. Furthermore, by sharing the buffer gas pressure among the rooms 24, it is possible to eliminate variations in characteristics between the rooms 24.

  FIG. 7 is a cross-sectional view illustrating a second modification of the gas cell. In the gas cell 36 of the second modified example, the cell thickness on the side where the resonant light is incident is narrower than the cell thickness on the side where the resonance light is emitted. With such a width of the room 24, the speed of the thermal motion of the atoms is slower in the room 24 on the incident side of the resonance light than in the room 24 on the outgoing side. Further, the resonance light is transmitted through the partition part 22, so that the intensity on the incident side is smaller than that on the emission side. For this reason, even if the room 24 on the emission side of the resonance light is wider than the incidence side, the intensity of the resonance light is attenuated, so that it is possible to prevent the half width of the signal from becoming wide.

It is a block diagram explaining the structure of an atomic oscillator. It is sectional drawing of a gas cell. It is a figure which shows the relationship between the frequency difference of resonance light (coupling light (omega) 1), and resonance light (probe light (omega) 2), and EIT signal intensity | strength. It is a figure which shows the relationship between cell thickness and the half value width of an EIT spectrum. It is sectional drawing explaining the 1st modification of a gas cell. It is sectional drawing of the gas cell which provided the opening part in the passage part of resonant light. It is sectional drawing explaining the 2nd modification of a gas cell.

Explanation of symbols

10 ......... Atomic oscillator, 20, 30, 36 ......... Gas cell, 22 ......... Partition, 24 ......... Room, 32 ......... Opening.

Claims (5)

A light emitting element, a gas cell that transmits resonance light output from the light emitting element, and a light receiving element that detects light transmitted through the gas cell,
The gas cell has a partition part with respect to the transmission direction of the resonance light, and the inside thereof is divided into a plurality of rooms.
An atomic oscillator characterized by that.   The atomic oscillator according to claim 1, wherein the rooms provided in the gas cell are connected by an opening provided in the partition.   The atomic oscillator according to claim 2, wherein the opening is provided in a portion of the partition where the resonant light passes.   2. The atomic oscillator according to claim 1, wherein the chamber provided inside the gas cell has a narrower incident side of resonance light than an outgoing side.   The atomic oscillator according to claim 1, wherein a plurality of the partition portions are provided.

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