JPS6123980A - Optomagnetic resonance magnetometer - Google Patents

Abstract

PURPOSE:To measure a magnetic field without spoiling the high sensitivity of a magnetometer by detecting voltage variation at the output terminal of a high frequency oscillator, and adding this to a photodetection signal and canceling a noise accompanying variation in the brightness of a helium lamp. CONSTITUTION:The output of the high frequency oscillator 12 is applied to the helium lamp 1 through an exciting coil 11 and the lamp 1 turns on. At this time, the output terminal voltage of the oscillator 12 varies according to variation in the discharge state of the lamp 1. The brihtness variation of the lamp 1 appears as a noise in a photodetection signal outputted by an amplifier 6 and is inputted to a differential amplifier 15. Further, variation in the output terminal voltage of the oscillator 12 is level-detected 3 and inputted to the differential amplifier 15 through a voltage regulator 14. Therefore, the noise component in the output of the amplifier 6 is canceled by variation in the output terminal voltage of the oscillator 12 at the output of the amplifier 15 and a high frequency magnetic field H1 by the output of a VCO8 is applied to an absorbing cell 4 without deterioration in the discriminating performance of a phase detector 7, thereby measuring accurately the intensity H0 of a static magnetic field.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention optically detects magnetic resonance absorption of atoms and measures magnetic fields by utilizing the fact that the magnetic resonance frequency is proportional to the strength of the magnetic field. Concerning improvements in optical magnetic resonance magnetometers.

[Prior art]

A brief explanation of the conventional helium frequency tracking type optical magnetic resonance magnetometer will be explained with reference to FIGS. 1 and 2.

In Figure 1, (1) is a helium lamp, (2) is a lens, (3) is a circularly polarizing plate, (4) is an absorption cell, (5) is a photodetector, (6) is an amplifier, and (7) is a helium lamp. is a phase detector, (8
) is a voltage controlled oscillator, (9) is a buffer resistor, and 0■ is an RF coil.

OIl is an excitation coil, and a21 is a high frequency oscillator.

Note that, in the main text, polished products that are not related to this invention are omitted.

In this optical magnetic resonance magnetometer, a helium lamp (1+
is electrodeless discharged by a high frequency electromagnetic field of several tens of MHz applied from a high frequency oscillator nz via an excitation coil αυ,
Generates light with a wavelength of 1.08 μ, which is unique to helium atoms. This light is made into parallel light by a lens (2), converted into circularly polarized light by a 9-circularly polarizing plate (3), and irradiated onto an absorption cell (4). The light transmitted through the absorption cell (4) is converted into an electrical signal by a photodetector (5), then amplified by an amplifier (6), and then phase-detected by a phase detector (power) to produce an error signal. The oscillation frequency of the voltage controlled oscillator (8) is controlled by this error signal, and the output is connected to R via the buffer resistor (9).
Flowing through the F coil H, a high frequency magnetic field H1 is generated and applied to the absorption cell (4).

Here, it is assumed that the absorption cell (4) contains H8' atoms, which have a very short lifetime in an excited state. The motion of helium atoms will be explained using the related energy level diagram shown in FIG. First, a weak high frequency electric field of several tens of MH2 is applied in advance to the absorption cell (4), and the energy of the helium atoms is in a metastable state of 23S1 due to the high frequency excitation. The helium atoms in this metastable state are irradiated with light with a wavelength of 108μ (Do~D2) from the helium lamp (1), so they absorb this and have the energy of 23F0.1.2 in the excited state. However, the lifetime of the excited state is short, and it loses energy in about 10-8 seconds and returns to the metastable state of 23S1. However, when the system shown in Figure 1 is in a static magnetic field, the helium atoms in the absorption cell (4) will move around the static magnetic field like Larmor's grass due to the magnetic moment of the atom itself being affected by the force of the static magnetic field. Since it performs a rotational movement called a rotational movement, a displacement occurs in energy, and a plurality of Zeeman 5ublevels as shown in FIG. 2 are generated. This change in atomic energy due to a static magnetic field is called the Zeeman effect, and the frequency of the thatching motion of the magnetic moment of an atom is called the Larmor frequency (both are proportional to the strength of the static magnetic field. Helium lamp (11 emitted 1,0
When 8μ light is circularly polarized by a circularly polarizing plate (3) and irradiated, 1. Helium atoms absorb light and enter the excited state 2'PO
, 1, and 2, but at this time, the effect of circular polarization selects the Zeeman Sub level within the excited state, and it comes to have energy at a certain Zeeman Sub level. After this, it loses energy in a short time and returns to the energy of the metastable state 26S1, but at this time the Zeeman sublevel selectivity is preserved.
``Within one Zeeman Sub level, there is a biased distribution in which the number of atoms differs for each Zeeman Sub level.

When an electromagnetic wave with an energy equal to the energy difference between the Zeeman-Zab levels of 2381, that is, a high-frequency magnetic field at the Larmor frequency, is applied to this unevenly distributed state in a direction perpendicular to the static magnetic field, magnetic resonance occurs between the high-frequency magnetic field and the magnetic moment of the atoms. As a result, energy conversion occurs, and the above-mentioned uneven distribution is eliminated. In other words, the helium atom is in the metastable state 23S1 3
This returns to the initial state in which the number of atoms is approximately equal to the Zeeman-sub level of the book.

The above process, that is, the energy change of the helium atom from 23S1 → 26AQ, 1,2 → 23S1, occurs every time the frequency of the high-frequency magnetic field matches the Larmor frequency because the 1.08μ light is continuously irradiated. returned. The system shown in Figure 1 uses the fact that light parallel to the static magnetic field is absorbed during the above process, and as a result, the light that passes through the absorption cell is reduced, so that the frequency of the high-frequency magnetic field always matches the Larmor frequency. It is controlled so that At this time, the relationship of equation (1) is established between the high frequency magnetic field, the atomic constant, and the static magnetic field.

ω = ω0 = rho ... il + ω: Angular frequency of high-frequency magnetic field ω0: Larmor frequency of atoms r: Magnetic rotation ratio (constant) of atoms Ho: Strength of static magnetic field In this way, the system in Figure 1 becomes static. Lock-on to the Larmor frequency proportional to the strength of the magnetic field aHo,
The frequency of the high-frequency magnetic field at this time, that is, the voltage-controlled oscillator (
Since the oscillation frequency of 8) matches the Larmor frequency, by measuring this, the static magnetic field strength HO can be measured in ft#.

This conventional optical magnetic resonance magnetometer has extremely high sensitivity.

It has many features such as being able to measure minute magnetic field fluctuations and continuously determining the total magnetic force of one surrounding magnetic field.

However, the conventional optical magnetic resonance magnetometer uses a photodetector (5
), the amount of light absorbed by magnetic resonance, that is, the absorption signal, is only about 0.1%, so when the brightness of the helium lamp (1) fluctuates, the fluctuation is reflected in the light detector
), the signal-to-noise ratio of the absorbed signal deteriorates, the discrimination performance of the phase detector (7) deteriorates, and high sensitivity is ultimately impaired.

[Outline of invention]

This invention was made with the purpose of improving this drawback, and utilizes the fact that the output change of the high frequency oscillator and the brightness change of the helium lamp are related to each other, and detects the output change of the high frequency oscillator, and detects the output change of the high frequency oscillator. The present invention aims to provide an optical magnetic resonance magnetometer that adds to the output and reduces noise accompanying changes in brightness of a helium lamp.

[Embodiments of the invention]

FIG. 3 shows an embodiment of the present invention.

0 is a level detection circuit, α gradient is a voltage regulator, and 01 is a differential amplifier. In this thread, the output terminal voltage of the high frequency oscillator (12) is detected and rectified by the level detector θm, and after being appropriately divided by the voltage regulator 04, it becomes one input of the differential amplifier +151. The difference between the optical absorption signal and the input optical signal is sent to the phase detector (power) through the output of the differential amplifier a9.In this way, the output signal of the amplifier (6) is used as the output terminal of the high frequency oscillator Q2. A voltage proportional to the voltage variation is removed.

Here, high frequency oscillator 0? The output of is applied to the helium lamp +11 by the excitation coil aI), causing the helium lamp (1) to emit light by electrodeless discharge.

When the output changes, the brightness of the helium lamp (11) also changes.In other words, if the output of the high frequency oscillator 0? changes due to factors such as changes in the power supply voltage, the brightness of the helium lamp (1) changes.

Further, since the helium lamp (1) is a discharge tube, the discharge state changes minutely due to external factors such as photography or temperature, and the brightness changes. At this time, the change in the discharge state is accompanied by a change in the electrical impedance of the helium lamp +11, so an impedance mismatch occurs between the helium lamp (1), the excitation coil at+, and the high-frequency oscillator aZ, and a part of the high-frequency power is transferred to the helium lamp +11. The output terminal voltage of the high frequency oscillator O2 changes as it is reflected.

In this way, a change in the brightness of the helium lamp (1) always appears as a change in the output terminal voltage of the high frequency oscillator O2.

Moreover, it was confirmed through experiments that they are almost proportional.

On the other hand, since the output of the amplifier (61), that is, the light absorption signal [, changes in the brightness of the helium lamp +11 appear as noise, the voltage division ratio of the voltage regulator +141 should be adjusted appropriately.
It becomes possible to significantly reduce noise caused by changes in brightness of the helium lamp (1) from the output signal of the n-amplifier (6).

As described above, according to the magneto-optical resonance magnetometer of the present invention, it is possible to reduce the noise associated with changes in the luminance of the rungs, thereby providing a device that measures magnetic fields without impairing the high sensitivity of the magneto-optical resonance magnetometer. can do.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of a conventional helium optical magnetic resonance magnetometer, Fig. 2 is an energy level diagram for explaining the principle of a helium optical magnetic resonance magnetometer, and Fig. 3 is an illustration of the magnetometer of the present invention. FIG. 2 is a configuration diagram showing an example. In the figure (1) hahelium lamp, (21fl lens, (
3) is a circularly polarizing plate, (4) is an absorption cell, (5) is a photodetector, (6) is an amplifier, (7) is a phase detector, (8) is a voltage controlled oscillator, and (9) is a buffer resistor. 00) is an RF coil, Qll is an excitation coil, i+21 is a high frequency oscillator, 031 is a level detection/rectification circuit, 1141 is a voltage regulator, (one is a differential amplifier. Note that the same or equivalent parts in Figure 1 are indicated by the same reference numerals.

Claims (1)

[Claims] A lamp that generates a light beam used for optical detection of magnetic resonance, a high-frequency oscillator that causes the lamp to discharge and emit light, an absorption cell containing a substance that generates magnetic resonance, and a high-frequency magnetic field applied to the absorption cell to generate magnetic resonance. R to produce
an F coil, a photodetector that detects the absorption of the light beam resulting from magnetic resonance in the absorption cell and converts it into an electrical signal, an amplifier that amplifies the electrical signal of the photodetector, and a phase detector that detects the output of the amplifier. a phase detector that generates an error signal, a voltage controlled oscillator that controls the oscillation frequency with the error signal and generates a high frequency voltage with a frequency equal to the Larmor frequency, and converts the high frequency voltage into a current and supplies it to the RF coil. In an optical magnetic resonance magnetometer, which consists of a buffer resistor that generates a high-frequency magnetic field, the voltage change at the output end of the high-frequency oscillator is detected, and this is added or subtracted from the electrical signal of the photodetector. An optical magnetic resonance magnetometer, characterized in that it is provided with means for canceling out noise accompanying changes in brightness of a lamp.