JPS6395736A - Laser stimulating cesium atomic oscillator and stimulating laser wave stabilizing method in said oscillator - Google Patents

Abstract

PURPOSE:To eliminate the need for Fabri-Perot interferometer and absorbing cell for stabilizing stimulated laser by stabilizing a voltage controlled crystal oscillator VCXO and a stimulated laser wavelength based on the output of a photodetector. CONSTITUTION:A laser control circuit 12 controls a stimulating laser 2a by the output of a photodetector 5a and as the stimulated laser 2a, a CaAlAs semiconductor laser is recommended because of resonance wavelength, miniaturization and low cost. Moreover, the laser control circuit 12 applies the wavelength control of the laser 2a by injection current control. That is, the laser control circuit 12 detects a change from a frequency where the output of the photodetector 5a is maximized and a current corresponding thereto is fed to the laser 2a to control the laser 2a. Thus, the wavelength of the stimulated laser 2a is controlled so as to maximize the output of the photodetector 5a and the stimulating laser 2a is stabilized to make the device highly stable.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a laser-excited cesium atomic oscillator,
In particular, the present invention relates to a laser-excited cesium atomic oscillator and a method for stabilizing the excitation laser wavelength in the oscillator, which stabilizes the excitation laser using a simple method.

E. Prior Art] A cesium atomic oscillator is based on the transition frequency between electronic energy levels in the hyperfine structure of a cesium atom.
This is an oscillator that obtains an extremely stable frequency by stabilizing the oscillation frequency of a crystal oscillator. cesium 133
Among the energy levels of , those related to transitions used in atomic oscillators are shown in FIG.

Among the base levels shown in Figure 2, the transition frequency is the level specified by the total angular momentum quantum number F = 4 and the total magnetic quantum number mF = 0, and the level specified by the total angular momentum quantum number F = 3 and the total magnetic quantum number mF = 0. Several meters
Frequency ν corresponding to the energy difference between the level specified by F=0. (9,19263 GHz) is used. This is because this transition is least influenced by the Zeeman effect due to external magnetic fields.

A specific example of a conventional cesium atomic oscillator will be described below.

These details can be found in, for example, Gen Otsu-Nishin OHM Bunko, "Laser and Atomic Clock" (Ohmsha, 198 B).
Chapters 7 and 8.

FIG. 3 shows the configuration of a first example of a conventional cesium atomic oscillator. In the figure, an atomic beam generating reactor! The atomic beam generated is sent to the deflection magnet 2. This deflection magnet 2 generates a strong inhomogeneous magnetic field and deflects atoms of degree F=3.4 in the atomic beam. However, since the direction of the magnetic moment of the electron at degree F=4 is opposite to the magnetic moment of the electron at level P=3, the deflection directions of atoms having electrons at both levels are opposite.

In this way, only atoms at level F-4 (or F=3) reach the cavity resonator 3. The cavity resonator 3 has a frequency ν. is excited by microwaves. Therefore, the atoms that have reached the cavity resonator 3 have a frequency ν within the cavity resonator 3. resonates with the microwave, and the level F = 4, mF = 0 →
1st place F=3. Stimulated emission of mF-0 (or level F=3
．． mF=;0→level F=4, mF=0 absorption).

After passing through the cavity resonator 3, the atoms that have undergone stimulated emission and transitioned to the level F=3 (or the atoms that have caused absorption and transitioned to the level F=4) head toward the deflection magnet 4. Since the deflection magnet 4 is the same as the deflection magnet 2, only atoms having electrons that undergo a transition and have their energy levels swapped are deflected in the opposite direction to the deflection in the deflection magnet 2, and are detected by the detector. Reach 5. That is, it resonates with the microwave within the cavity resonator 3, and the level F=4−◆level F=3 (or the level F
Only atoms having electrons that have undergone a transition of =3-F=4) are detected by the detector 5. In other words, the frequency ν. Only atoms that have undergone a transition reach the detector 5, and the detector 5 outputs an electric signal corresponding to the number of atoms. This output is
The microwave frequency is the transition frequency ν of the cesium atom. It is maximum when it matches.

The microwave is modulated by the phase modulation circuit 7 using the output of the low frequency oscillator 6, and has a frequency ν. The center is swept after the building. Then, a detection signal outputted from the detector 5 according to the number of atoms reaching the detector 5 is detected by a synchronous detection circuit 8 using the output of the low frequency oscillator 6 as a reference signal. This detection output shows that the microwave frequency is the value ν
. When it matches, it becomes O, and this is supplied to the vcxo control circuit 9. The vcxo control circuit 9 determines that the frequency of the microwave is set to a frequency ν based on the supplied signal.
. Voltage controlled crystal oscillator cv c x to match
Control month O. vcxo t.

The output of is multiplied by the frequency conversion circuit 11, and the frequency is ν. is converted into microwave. And vcxo
The output of to is taken as the desired frequency stabilized output.

Note that the output frequency of the low frequency oscillator 6 is approximately 100H.
It is z. In addition, in FIG. 3, the C magnetic field applied to the cavity resonator 3 is for separating the magnetic side level mP of the cesium atom. Specifically, from the energy level of mFfo, the C magnetic field is applied to the cavity resonator 3. =0 energy level is separated.

Next, FIG. 4 shows a second example of a conventional cesium atomic oscillator. This uses a laser instead of the deflection magnet 2.4 for energy level selection and resonance detection, and is called a laser-excited cesium atomic oscillator.

In this figure, components 1, 3.6-11 are similar to those in FIG. Frequency ν output from laser 2a
As shown in FIG. 2, the laser beam of , has a ground level F=4
to the excited level F-4 (or from the ground level F=3 to the excited level F=3). Further, the laser beam is linearly polarized, and the direction of polarization is parallel to the C magnetic field. Electrons in each magnetic level of level F=4 (or F=3) repeatedly absorb light and spontaneously emit light, and concentrate at the ground level F=4, mF=0.

When the electrons state-selected in this way pass through the cavity resonator 3, they cause a transition between levels in the same manner as in the first example, and change from the ground level F = 4, mF = O to the ground level F
= 3, the atom that has transitioned to mF=O is in the cavity resonator 3
released from. This atom is irradiated with light from the laser 2a to excite it to an excitation level of F=3, and the intensity of spontaneous emission when the atom falls from this level to the ground level again is detected by a photodetector 5.
Measure at a. Hereinafter, in the same manner as in the first example, the photodetector 5
The output of a is detected by the synchronous detection circuit 8, and with this detection output v
The VCXOIO is controlled via the cxo control circuit 9.

In addition to the first and second examples, atomic oscillators have also been proposed that use two types of laser beams when selecting an energy level, and that use a recycling transition laser for resonance detection.

[Problem that the invention seeks to solve]

The conventional laser-excited cesium atomic oscillator described above can be highly stabilized compared to other conventional atomic oscillators,
Furthermore, since no deflection magnets are used, it is expected that the device will be more compact. However, this requires high stability in the wavelength of the excitation laser. Additionally, a Fabry-Bérot interferometer and an absorption cell are required for stabilization. Therefore, the device does not necessarily become smaller, and there are drawbacks such as an increase in price.

The present invention was made against this background, and an object thereof is to provide a highly stable, compact, and inexpensive laser-excited cesium atomic oscillator and a method for stabilizing the excitation laser wavelength in the oscillator. do.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides an atomic beam generation reactor that generates a cesium atomic beam, and a laser beam irradiating the atomic beam to a certain electron energy level. an excitation laser that creates a state of a first control circuit that stabilizes the oscillation frequency of the voltage controlled crystal oscillator based on the output; a frequency conversion circuit that generates the microwave based on the output of the voltage controlled crystal oscillator; and a second control circuit that stabilizes the oscillation wavelength of the excitation laser based on the above.

In addition, the cesium atomic beam is irradiated with excitation laser light to bring it to a constant electron energy level, and microwaves are used to cause the cesium atoms at the constant energy level to resonate, and the intensity of this resonance is detected. In the laser pumped cesium atomic oscillator that stabilizes the frequency of the microwave based on the output of the photodetector, the oscillation wavelength of the excitation laser is stabilized based on the output of the photodetector. Features.

[Operation] According to the above means, the wavelength of the excitation laser is stabilized by the output of the photodetector. Therefore, a Fabry-Perot interferometer and an absorption cell, which were conventionally necessary, are no longer necessary for stabilizing the excitation laser. As a result, the device becomes highly stable,
It becomes possible to downsize and lower the price.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, components 1 and 2a.

3.5a, 6~! (2) is similar to the conventional laser-excited cesium atomic oscillator shown in FIG. This embodiment differs from conventional atomic oscillators in that a laser control circuit 12 controls an excitation laser 2a based on the output of a photodetector 5a.

Here, as the excitation laser 2a, a GaA 12A s semiconductor laser is preferable because of its resonance wavelength, miniaturization of the device, and low cost. Further, the laser control circuit I2 controls the wavelength of the laser 2a by controlling the injection current. That is, the laser control circuit 12 detects the amount of change from the frequency at which the output of the photodetector 5a becomes maximum, and controls the laser 2a by supplying a current corresponding to this to the laser 2a.

By the way, the output of the photodetector 5a essentially depends on the following factors.

■Amount of cesium vapor sent from atomic beam generator 1,■
Input microwave frequency of cavity resonator 3, ■Input microwave level, ■Oscillation wavelength of excitation laser 2a, and ■Oscillation intensity of excitation laser 2a.

Among these factors, the microwave frequency of
The purpose of the atomic oscillator is to stabilize the 10 oscillation frequencies. Therefore, the above factors ■, ■～■
It is important to keep constant. In particular, it is most important to keep the oscillation wavelength of the excitation laser 2a constant, and this is the difference between this embodiment and the prior art.

Now, according to the above configuration, the wavelength of the excitation laser 2a is controlled so that the output of the photodetector 5a becomes maximum. This stabilizes the excitation laser 2a. Therefore, the device can be highly stabilized. In addition, a Fabry-Perot interferometer and an absorption cell are not required, making it possible to downsize and lower the cost of the device.

[Effects of the Invention] As explained above, this invention aims to stabilize the VCXO and the excitation laser wavelength based on the output of the photodetector, so it is possible to use a Fabry-Perot interferometer for stabilizing the excitation laser. and absorption cells are not required. As a result, a highly stable, compact, and low-cost atomic oscillator can be realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a laser-excited cesium atom oscillator according to an embodiment of the present invention, FIG. 2 is a diagram showing the photon energy of electromagnetic waves related to the energy level and transition of cesium-133 atoms, and FIG. 4 is a block diagram showing the configuration of a conventional cesium atomic oscillator, and FIG. 4 is a block diagram showing the configuration of a conventional laser-excited cesium atomic oscillator. ! ...Atomic beam generator, 2.4...
Bending magnet, 2a...Excitation laser, 3...
...Cavity resonator, 5...Detector, 5a...
...Photodetector, 6...Low frequency oscillator, 7...
... Phase modulation circuit, 8 ... Synchronous detection circuit, 9
...VCXO$lJ1 circuit, IO...
VCXO (voltage controlled crystal oscillator), 11... frequency conversion circuit, 12... laser control circuit.

Claims (2)

[Claims] (1) An atomic beam generation reactor that generates a cesium atomic beam, an excitation laser that irradiates the atomic beam with laser light to create a state at a certain electronic energy level, and cesium atoms at the certain electronic energy level. a cavity resonator that resonates using microwaves, a photodetector that detects the intensity of this resonance, and a first control that stabilizes the oscillation frequency of the voltage-controlled crystal oscillator based on the output of the photodetector. a frequency conversion circuit that generates the microwave based on the output of the voltage-controlled crystal oscillator, and a second control circuit that stabilizes the oscillation wavelength of the excitation laser based on the output of the photodetector. A laser-excited cesium atomic oscillator comprising: (2) Irradiate the cesium atomic beam with excitation laser light to bring it to a constant electron energy level, use microwaves to cause the cesium atoms at the constant energy level to resonate, and detect the intensity of this resonance. In the laser pumped cesium atomic oscillator that stabilizes the frequency of the microwave based on the output of the photodetector, the oscillation wavelength of the excitation laser is stabilized based on the output of the photodetector. A method for stabilizing the excitation laser wavelength in a laser-pumped cesium atomic oscillator.