JPH07114366B2 - Laser-excited cesium atomic oscillator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a laser-excited cesium atomic oscillator provided with an optical system capable of realizing stable atomic beam excitation operation.

[Prior Art] A cesium atomic oscillator is based on a transition frequency between electron energy levels in a hyperfine structure of a cesium atom.
It is an oscillator that obtains an extremely stable frequency by stabilizing the oscillation frequency of the oscillator. As the transition frequency used in this atomic oscillator, of the hyperfine levels of the cesium 133 in the specified state, the level specified by the total angular momentum quantum number F = 4 and the total magnetic quantum number mF = 0, and the total angular momentum quantum number Number F
= 3, the frequency ν ₀ (9.19263 GHz) corresponding to the energy difference with the level specified by the total magnetic quantum number mF = 0 is used. This is because this transition is least affected by the Zeeman effect due to the external magnetic field. Then, in order to detect the transition of the level difference, the hyperfine level (F
= 3, F = 4), and a cesium atomic oscillator using a deflection magnet is currently used for detecting transition atoms.

In contrast to such a conventional cesium atomic oscillator, a laser-excited cesium atomic oscillator as shown in FIG. 4 has been proposed (for example, see Japanese Patent Application No. 61-241766). In the figure, 1 is an atomic beam generator, which generates an atomic beam having an electron energy level at a ground state level F = 3 or F = 4. This atomic beam is irradiated with the laser beam outputted from the excitation laser 2 in the level selection region D1. That is, the laser light, after being collimated by the lens 2a, by the half mirror 2b, is split into light for level selection and light for resonance detection, the former is sent to the level selection region D1, atomic The atomic beam emitted from the beam generating furnace 1 is irradiated, and the latter is sent to the resonance detection region D2 via the mirror 2c and irradiated to the atomic beam emitted from the cavity resonator 3.

The laser light is linearly polarized and its polarization direction is parallel to the C magnetic field. In this case, the atoms in the sub-levels of the ground state level F = 3,4 repeat light absorption and spontaneous emission, and are concentrated in the ground state level F = 4, mF = 0. Therefore,
Only the atoms of the ground state level F = 4 and mF = 0 reach the cavity resonator 3. The cavity resonator 3 is excited by a microwave having a frequency near ν ₀ . Therefore, the atoms that have reached the cavity resonator 3 resonate with this microwave in the cavity resonator 3 and induce a level F = 4, mF = 0 → level F = 3, mF = 0. Cause release. That is, atoms that have transited from the ground level F = 4, mF = 0 to the ground level F = 3, mF = 0 are emitted from the cavity resonator 3. As described above, this atom is irradiated with the light of the excitation laser 2 in the resonance detection region D2 and excited to F = 4 of the excitation level. Then, the photodetector 4 measures the intensity of the spontaneous emission light when the electrons fall from the excitation level to the ground level again. In this case, the output of the photodetector 4 corresponds to the number of atoms that have caused the stimulated emission, in other words, the resonance output. That is, the photodetector 4 functions as a resonance detector.

The microwave is modulated by the phase modulator 6 by the output of the low frequency oscillator 5 and swept before and after the frequency ν ₀ as the center. At this time, the detection signal output from the photodetector 4 uses the output of the low frequency oscillator 5 as a reference signal,
Synchronous detection is performed by the synchronous detector 7. This synchronous detection output is
It corresponds to the differential value of the resonance output detected by the photodetector 4, and becomes 0 when the microwave frequency matches the frequency ν ₀ , that is, when the resonance output reaches a maximum. When the synchronous detection output is supplied to the VCO control unit 8, the VCO control unit 8 controls the voltage controlled oscillator (VCO) so that the frequency of the microwave matches the value ν ₀ based on the supplied signal. Control 9 The output of the VCO 9 is multiplied by the frequency multiplier 10 and converted into a microwave having a frequency of ν ₀ . Then, the output of the VCO 9 is taken out as a desired output whose frequency is stabilized.

The output frequency of the low frequency oscillator 5 is about 100 Hz. Further, in FIG. 4, the C magnetic field applied to the cavity resonator 3 is for separating the magnetic sub-level mF of the cesium atom, and from the energy level of mF ≠ 0, mF = 0 Separate energy levels.

[Problems to be Solved by the Invention] The laser-excited cesium atomic oscillator described above has the following drawbacks.

Since the laser light is propagated through the air by the individual optical components such as the half mirror 2b and the mirror 2c, it is vulnerable to mechanical vibration from the outside and the operation becomes unstable.

For the same reason as above, the system is lacking in flexibility. Therefore, a laser-excited cesium atomic oscillator using such an excitation optical system is not suitable for a small-sized portable atomic oscillator.

The present invention has been made under such a background, and an object thereof is to provide a small-sized and portable laser-excited cesium atomic oscillator that operates stably even against external vibration.

[Means for Solving Problems] In order to solve the above problems, the present invention irradiates an atomic beam generating furnace for generating an atomic beam of cesium, and irradiates the atomic beam with light in a first irradiation region. A pumping laser, a cavity resonator that resonates cesium atoms in a state of a constant electron energy level by this light using a microwave, and the cesium atom resonated by the cavity resonator Laser irradiation means for re-irradiating the light in a second irradiation region different from the first irradiation region to re-excite the cesium atomic beam, and intensity of spontaneous emission light from the re-excited cesium atomic beam. A photodetector for detecting, an oscillator controller for stabilizing the oscillation frequency of the voltage controlled oscillator based on the output of the photodetector, and the microwave based on the output of the voltage controlled oscillator. In the laser-excited cesium atomic oscillator including the frequency doubler, the light splitting means splits the light output from the pumping laser into two, and the split light is split into the first and the second light splitting means, respectively. And an optical system having an optical fiber that guides light in two irradiation regions.

Further, one of the laser beams split by the optical splitting unit is provided with an optical coupling unit for coupling another laser beam for excitation having a different wavelength from this laser beam, and the two-wavelength laser outputted from this optical coupling unit. It is characterized in that an atomic beam before entering the cavity resonator is excited by light.

[Operation] According to the above means, the laser light for excitation is organically transmitted by the solid-state element. Therefore, it is possible to operate stably against external vibration. Also,
Since the light is transmitted through the optical fiber, the restrictions on the configuration are reduced,
A flexible excitation optical system may be constructed.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the structure of the excitation optical system according to the first embodiment of the present invention. In this figure,
4 is the same as the laser-excited cesium atomic oscillator shown in FIG. The components 5 to 10 are not shown. The present embodiment is different from the atomic oscillator of FIG. 4 in the following points.

A point that an optical branching element 11 is provided and the pumping laser light output from the pumping laser 2 is branched into two lights, one for level selection and the other for resonance detection.

A point where the branched light is guided to the atomic beam tube by the optical fibers 12 and 13.

After the guided light is collimated by the lenses 14 and 15, the level selection light is applied to the atom beam before entering the cavity resonator 3 in the level selection region D1 to generate the resonance detection light. Is a point in the resonance detection region D2 where the atomic beam after exiting the cavity resonator 3 is irradiated.

FIG. 3 (a) is a diagram showing a configuration example of the optical branching element 11, in which a semiconductor laser (LD) is used as the pumping laser 2 and a waveguide device is used as the optical branching element 11, and these are integrated. It was done. LiNb as a waveguide device
There is a waveguide in which Ti is diffused on an O ₃ substrate.

According to such a configuration, the light emitted from the pumping laser 2 is branched into two by the optical branching element 11, and the optical fiber 1
It is sent to lenses 14 and 15 via 2 and 13. Then, the light collimated by the lens 14 is irradiated onto the atomic beam in the level selection region D1, and the light collimated by the lens 15 is irradiated onto the atomic beam in the resonance detection region D2.

In this way, since the excitation light is transmitted by the solid-state element such as an optical fiber, the operation is stable against external vibration,
It can be miniaturized.

Next, FIG. 2 shows the configuration of the excitation optical system according to the second embodiment of the present invention. The second embodiment is a laser-excited cesium atomic oscillator that excites an atomic beam with light of two wavelengths.

The difference between the second embodiment and the first embodiment is as follows.

An optical coupling element 21 is interposed between the output end of the optical branching element 11 and the optical fiber 12, and the first laser beam for level selection outputted from the optical branching element 11 is supplied to the optical coupling element 21. The point that it is supplied to one input terminal.

The configuration is such that the second light for level selection output from the pumping laser 22 is input to the second input end of the optical coupling element 21.

The wavelengths of the first and second lights are different, and for example, the first laser light excites a cesium atom at the ground level F = 3 to the excitation level F = 4, Laser light of the cesium atom at the ground level F = 4
= 4 is excited.

FIG. 3B shows a device in which a semiconductor laser is used as the pumping lasers 2 and 22 and a waveguide type device is used as the optical branching device 11 and the optical coupling device 21, and these devices are integrated. This device is also manufactured in the same manner as the waveguide type device of FIG.

In such a configuration, the laser light output from the excitation laser 2 is split into two in the optical branching element 11. Of the branched light, the level selection light is combined with another laser light from the pumping laser 22 in the optical coupling element 21, and then guided by the optical fiber 12 and the lens 14 Are collimated by and are irradiated with the atomic beam before entering the cavity resonator 3 in the level selective region D1. On the other hand, the light for resonance detection is
The light is guided to the resonance detection region D2 via the optical fiber 13 and the lens 15, and is irradiated with the atomic beam that has exited the cavity resonator 3.

In each of the above embodiments, if polarization maintaining fibers are used as the optical fibers 12 and 13, it is possible to irradiate the atomic beam with light with the polarization maintained reliably.

[Advantages of the Invention] As described above, according to the present invention, the excitation light output from the excitation laser is guided by using an optical fiber or the like to irradiate the atomic beam, so that the operation is stable. It is possible to make a small laser-excited cesium atomic oscillator.
Therefore, it can be widely used as a portable atomic oscillator that is easy to handle.

[Brief description of drawings]

1 and 2 are blocks showing the construction of a pumping optical system of a laser pumped cesium atomic oscillator according to the first and second embodiments of the present invention, and FIG. 3 is a semiconductor laser and optical branching and optical coupling. 2A and 2B are diagrams showing an example in which elements are integrated. FIG. 1A is used for the first embodiment, and FIG. 2B is used for the second embodiment.
It is used in the examples. FIG. 4 is a block diagram showing the configuration of a known laser-excited cesium atomic oscillator. 1 ... Atomic beam generator, 2, 22 ... Excitation laser, 3 ... Cavity resonator, 4 ... Photodetector, 5 ... Low frequency oscillator, 6 ... Phase modulator, 7 ... Synchronization Detector, 8 ... VCO control unit, 9 ... VCO (voltage controlled oscillator), 10 ... Frequency multiplier, 11 ... Optical branching element, 12,13 ... Optical fiber, 14,15 ... Lens, 21 ...... Optical coupling element.

Claims (2)

[Claims] 1. An atomic beam generator for generating an atomic beam of cesium, an excitation laser for irradiating the atomic beam with light in a first irradiation region, and a constant electron energy level state by the light. A cavity resonator that resonates cesium atoms using microwaves, and re-illuminates the light in the second irradiation region different from the first irradiation region in the cesium atoms resonated by the cavity resonator. Laser irradiation means for irradiating and re-exciting the cesium atomic beam, a photodetector for detecting the intensity of spontaneous emission light from the re-excited cesium atomic beam, and a voltage based on the output of the photodetector. Laser-excited cesium including an oscillator controller that stabilizes the oscillation frequency of a controlled oscillator, and a frequency multiplier that generates the microwave based on the output of the voltage-controlled oscillator. In the atomic oscillator, an optical device having an optical branching unit for branching the light output from the pumping laser into two, and an optical fiber for guiding each of the branched lights to the first and second irradiation regions. A laser-excited cesium atomic oscillator, comprising: 2. An optical coupling unit for coupling one of the laser beams branched by the optical branching unit with another pumping laser beam having a different wavelength from this laser beam is provided. The laser-excited cesium atomic oscillator according to claim 1, wherein an atomic beam before entering the cavity resonator is excited by a laser beam having a wavelength.