JPS61233383A - Photomagnetic resonance magnetometer - Google Patents

Abstract

PURPOSE:To reduce the noise accompanied with the variance of the luminance of a light source by setting an absorbing cell in a luminance variance detecting part consisting of a lens, a circular polarizing plate, and a photodetector. CONSTITUTION:An absorbing cell 17 is set additionally in a luminance variance detecting part 16. The cell 17 does not cause magnetic resonance. The cell 17 has the same conditions as a photomagnetic resonance part 19 except it, and the light emitted from a helium lamp 1 is received by a photodetector 16. Consequently, not only the variance of the luminance of the lamp 1 but also that of the absorbing cell 5 is detected by the photodetector 16 of the cell 17. In the output of a photodetector 7 of the resonance part 19, variances of luminance of the lamp 1 and the absorbing cell 5 are detected besides an absorption signal of light due to magnetic resonance. Signals detected by detectors 16 and 17 are cancelled by a differential amplifier 8 to erase the electric noise due to the variance of luminance, thereby reducing considerably the noise due to variances of luminance of the lamp 1 and the cell 5 to improve the measurement precision.

Description

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

[Conventional technology]

A conventional helium frequency tracking type optical magnetic resonance magnetometer will be briefly explained with reference to FIGS. 2 and 3. FIG. 2 shows an example of a conventional improved optical magnetic resonance magnetometer using a 1+B helium lamp.

(2) is the lamp excitation electrode, +31, [+41 is the lens, 141, α is the circularly polarizing plate, (5) is the absorption cell, (61 is the absorption cell excitation electrode, (71, a[i is the photodetection (8) is a differential type amplifier.

(9) is a phase detector, αυ is a one-pressure controlled oscillator, αυ is a buffer resistor, α2 is an RF coil, and (I3 is a high-frequency oscillator).

Note that components not related to this invention are omitted here.

The optical magnetic resonance type is generally a helium lamp (1).

Lens (31, circularly polarizing plate (4), absorption cell (5), photodetector (7).

Differential amplifier (8), 1-phase detector (9), voltage control detector αQ, buffer resistor αml, RF coil α3. The high frequency oscillator (13) is configured with a high frequency oscillator (13), but in order to reduce the noise caused by the change in light intensity caused by the helium lamp (11), the helium lamp (11) is ll'i shared, lens Q
41.

Circularly polarizing plate r19. An improved type of light that newly adds a brightness change detection 1Q11 consisting of a photodetector αe and uses the electric signal gold detected here to electrically offset the light intensity change generated by the helium lamp +11. There was a magnetic resonance magnetometer.

First, the portion of this magneto-optical resonance magnetometer excluding the brightness change detection section αa (hereinafter this portion will be referred to as the magneto-optical resonance section α9) will be explained. Helium lamp (1) is a high frequency oscillator a
The number 10 applied from 3 to the lamp excitation electrode (2)
Discharged by the high frequency voltage of MH2.

Generates light with a wavelength of 1.08μ, which is unique to helium atoms.

This light is made into parallel light beams by a lens (3), changed into circularly polarized light by a circularly polarizing plate (4), and irradiated onto an absorption cell (5).
A high frequency voltage of 0 MHz is applied to the cell excitation electrode (6) to create a glow discharge state. Absorption cell (5
) The completely transmitted light is converted into an electrical signal by a photodetector (7), then amplified by a differential amplifier (8), and then phase detected by a single phase detector (9) to generate an error signal. . The oscillation frequency of the voltage controlled oscillator Ql is controlled by this error signal, and the output flows to the RF coil aa through the buffer resistor (ll'i), generating a high frequency magnetic field H1 and moving it to the absorption cell (5).
is applied to Here, the absorption cell (5) contains H6', which has a very short lifetime (Lif tins) in the excited state.
Assume that atoms are encapsulated.

This movement of helium atoms will be explained with reference to the related energy level diagram in FIG.

First, the absorption cell (5) is preliminarily glow-discharged by a high frequency voltage of several tens of MHz, and the energy of helium atoms is in a metastable state of 23S1. Helium atoms in this metastable state have a wavelength of 1.08μ from a helium lamp +11.
Since the light (Do~D2) of and returns to the metastable state of 23S1. In addition, when the optical magnetic resonance sa9 is in the static 8 field, the magnetic moment of the helium atoms in the absorption cell 15+ is affected by the force of the static magnetic field, and the motion is called 9t-Larmour's motion around the static magnetic field. Since the rotational movement is performed, a displacement occurs in energy, and a plurality of Zeeman sublevels (Zeman8ubbvel) shown in FIG. 3 are generated. The change in atomic energy caused by such a static magnetic field is called the Zeeman effect, and the frequency of the atomic movement of the magnetic moment of the atom is called the Larmor frequency, both of which are proportional to the strength of the static magnetic field.

Therefore, when a helium atom in a quiet magnetic field is irradiated with a 1.08μ element emitted by a helium lamp +11 from a direction parallel to the quiet magnetic field, the helium atom absorbs the light and enters the excited state 2. ``It will have an energy of 0, 1.2, but at this time, the Zeeman sublevel is traced within the excited state due to the effect of circular polarization, and it will have an energy of a certain Zeeman sublevel.'' After this, it loses energy in a short time and becomes metastable WM2.
We return to the energy of 81, but at this time, the trace selection note of the Zeeman sublevel is preserved, and within the Zeeman sublevel of 2s81, a biased distribution in which the number of atoms differs for each Zeeman sublevel is created.

The *i1i wave has energy equal to the energy difference between the Zeeman sublevels of 25S1 in this unevenly distributed state.

That is, when a high-frequency magnetic field at the Larmor frequency is applied 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, causing energy exchange, and the above-mentioned uneven distribution is eliminated. In other words, the schihelium atoms return to the initial state in which approximately equal numbers of atoms are distributed in each of the three Zeeman sublevels of the metastable state 25S1.

The above process, 2s81 → 2sPO of helium atoms
, 1, 2 → 2581 is repeated every time the frequency of the high-frequency magnetic field matches the Larmor frequency because the 1.08 μ light is continuously irradiated, but the electronic circuit system of the optical magnetic resonance section a9, ie. Photodetector (7).

Differential type amplifier (8) 1-phase detector (91, 11E pressure-controlled oscillator [11, buffer resistor αυ, RF coil a) The light parallel to the field is absorbed during the above process, and as a result, The frequency of the high-frequency magnetic field is always controlled to match the Larmor frequency by utilizing the decrease in the light transmitted through the absorption cell.At this time, the relationship between the high-frequency magnetic field, the atomic constant, and the static magnetic field is expressed by the following equation. holds true.

ω = ω0 rHo - (tlω: Angular frequency of high-frequency magnetic field ω0: Larmor frequency of the atom r: Magnetic rotation ratio (constant) of the atom Ho: Strength of the static magnetic field Thus, the optical magnetic resonance part uIIa, the strength of the static magnetic field Lock-on to Larmor frequency proportional to HQ
) However, since the frequency of the high-frequency magnetic field at this time, that is, the oscillation frequency of the voltage controlled oscillator αl, matches the Larmor frequency, by measuring this, the strength of the silent magnetic field HOt can be accurately measured. However, of the light received by the photodetector (7), absorption due to magnetic resonance, that is, the absorption signal, accounts for only 0.1% of the total, so the brightness of the helium lamp (1) will fluctuate due to the optical magnetic resonance field a alone. This fluctuation appears on the photodetector (7), which lowers the signal-to-noise ratio of the absorption signal and deteriorates measurement accuracy. Therefore, as shown in FIG. 2, the same lenses (1:l) as the lens (3), 9-circularly polarizing plate (4), and 1-element detector (7) used in the magneto-optical resonance section 119 are used.

A circularly polarizing plate (I5. A brightness change detection unit α8 with the photodetector side placed at the same position in the optical axis direction is newly added, and the brightness change of the helium lamp (1) detected here and the optical magnetic resonance part a
By electrically canceling out changes in the brightness of the helium lamp (1) caused by S using a differential amplifier (8), noise accompanying changes in brightness is reduced.

[Problem that the invention seeks to solve]

Changes in the brightness of the light source vary not only depending on the lighting state of the lamp but also on the glow discharge state of the absorption cell. In the conventional improved outdoor magnetic resonance magnetometer, although the change in lamp brightness can be canceled out, the change in brightness of the absorption cell is not detected in the brightness change detection section. Since there is no function to detect changes in brightness, it is impossible to cancel out changes in the brightness of the absorption cell, and therefore there is a problem in that noise accompanying changes in brightness cannot be sufficiently reduced. The present invention was made to solve these problems, and aims to improve measurement accuracy by reducing noise caused by changes in brightness of a light source.

[Means for solving problems]

An absorption cell is added to the conventional brightness change detection section, which consists of a lens, a circularly polarizing plate, and a photodetector. That is, in order to avoid stimulating optical magnetic resonance, the lenses, circularly polarizing plates, absorption cells, and photodetectors that are the same as those of the optical magnetic resonance section except for the RF coil are arranged in the same direction as the optical magnetic resonance section in the optical axis direction. In addition, by lighting the above-mentioned absorption cell with a high-frequency voltage to create a light emission state that is almost the same as that of the optical magnetic resonance section, except that magnetic resonance is not caused, not only changes in the brightness of the lamp but also changes in the brightness of the absorption cell are detected. Then, the detected electrical signal t-electronically cancels out the brightness change occurring in the magneto-optical resonance section, thereby reducing noise accompanying the brightness change.

[Effect]

Conventionally, only lamp brightness changes were detected to reduce the noise associated with brightness changes, but in this invention, an absorption cell is newly added to the conventional brightness change detection section to prevent FFI resonance from occurring. The optical system of the magneto-optical resonance section is operated under almost the same conditions as the optical system, except for By electrically canceling out the brightness changes of the helium lamp and absorption cells generated in the magnetic resonance section, the noise associated with brightness changes is reduced.

Noise accompanying brightness changes can be further reduced.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the present invention.

aω is the absorption cell (5) used in the optical magnetic resonance section αl
This is the same absorption cell as the lens 036 circularly polarizing plate I.

The above-mentioned absorption cell a? ) T-A new addition is made so that the arrangement of these parts in the optical axis direction is the same as the optical parts of the optical magnetic resonance section 11. Furthermore, except that no high-frequency electric field is applied to the absorption cell αη to prevent magnetic resonance from occurring, the high-frequency voltage that is the output of the high-frequency oscillator Q3 is transmitted via the absorption cell excitation electrode (6). The operating state of the glow discharge is the same as that of the absorption cell (5) of the magneto-optical section a9, except that no magnetic resonance occurs due to the applied light, and the light emitted here is the same as the light of the helium lamp (1). The light is also received by the photodetector αe. The photodetector (Ie detects the luminance change of the helium lamp +11 and the absorption cell aη, and is one input of the differential amplifier (8). The photodetector (7) is the other input. The difference between the optical absorption signal and the optical absorption signal is detected by the phase detector (9) as the output of the differential amplifier (8).
) will be sent to.

Here, in the helium lamp (1) and absorption cell (5) of the optical magnetic resonance section 0, a high frequency voltage, which is the output of a high frequency oscillator (13), is applied to the lamp excitation electrode (2) and the absorption cell excitation electrode (6), respectively. Therefore, when the output of this high frequency oscillator Q3 changes, the helium lamp (1
), the absorption cell (5) changes in brightness. High frequency oscillator 0 due to fluctuations in the power source voltage or external vibrations.
When the output of the helium lamp (1) and the absorption cell (5) fluctuate, the brightness of the helium lamp (1) and the absorption cell (5) fluctuate. Also, helium lamp (1)
Since the absorption cell +5) is a -rice discharge tube, the discharge state changes depending on external factors such as temperature, and the brightness changes.

At this time, the brightness change detection member uses the absorption cell aη, unlike in the past.
is added, and the light emitted under the same conditions as the magneto-optical resonance section aS, except that it does not cause magnetic resonance, is received by the photodetector ae, so unlike the conventional method, only the brightness change of the helium lamp (1) can be detected. (The brightness change of the absorption cell (5) can also be detected in almost the same state by detecting it with the brightness change photodetector ae of the absorption cell aη.

The output of the photodetector (7) of the optical magnetic resonance unit aS includes the helium lamp (11) in addition to the light absorption signal due to magnetic resonance.
Since changes in the brightness of the absorption cells (51 and 51) appear as noise, by canceling the signals detected by the photodetector (7) and αe with the amplifier (8) of the differential board, electrical noise due to changes in brightness can be eliminated. It is possible to significantly reduce noise caused by changes in brightness of the helium lamp (1) and absorption cell (5).

As described above, according to the magneto-optical resonance magnetometer of the present invention, it is possible to reduce not only the brightness changes of the lamp but also the noise accompanying the brightness changes of the absorption cell. Equipment to measure! ct- can be provided.

〔Effect of the invention〕

As explained above, this invention is 1! Source fluctuations and vibrations.

Conventionally, changes in the brightness of helium lamps and absorption cells, which fluctuated due to external factors such as temperature, were detected only by changes in the brightness of the helium lamp, and the noise associated with these changes in brightness was reduced. Changes in the brightness of the absorption cells are also detected, and noise caused by these changes in brightness is reduced, which has the effect of making the sensor even less susceptible to external factors such as power fluctuations and vibrations.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing an embodiment of the present invention, Figure @2 is a diagram showing an example of the configuration of a conventional improved magneto-optical co-% magnetometer, and Figure @3 is a diagram showing the energy level of helium atoms. This is a diagram. In the figure, (1) is a helium lamp, (2) is a lamp excitation electrode, 13+, +14 is a lens, 14+,
[9 is a circularly polarizing plate, +51. aη is an absorption cell, (61 is an electrode for excitation of the absorption cell, (7
1, (lle is a photodetector, (8) is a differential amplifier,
(9) is a phase detector, Kasumi is a voltage controlled oscillator, and αυ is a buffer resistor. a2 is an RF coil, (13 is a high-frequency oscillator, αa is a brightness change detection section, and a!J is an optical magnetic resonance section. In the figure, the same or corresponding parts are denoted by the same reference numerals.

Claims (1)

[Claims] an absorption cell containing a lamp that generates light M used for optical detection of optical magnetic resonance and a substance that generates magnetic resonance;
a high-frequency oscillator that causes the lamp and the absorption cell to discharge and emit light; an RF coil that applies a high-frequency magnetic field to the absorption cell to generate magnetic resonance; and detecting absorption of light rays resulting from magnetic resonance in the absorption cell; A photodetector that converts into an electrical signal, an amplifier that amplifies the electrical signal of the photodetector, a phase detector that detects the phase of the output of the amplifier and generates an error signal, and controls the oscillation frequency with the error signal. A voltage controlled oscillator that generates a high frequency voltage with a frequency equal to the Larmor frequency, and a voltage controlled oscillator that converts the high frequency voltage into a current and generates a
In a magneto-optical resonance magnetometer consisting of a buffer resistor that is applied to the F coil to generate a high-frequency magnetic field, an absorption cell and a photodetector for detecting brightness changes are newly added, and the high-frequency magnetic field is not applied to the absorption cell. By detecting the luminance changes of the lamp and absorption cell with the added photodetector and subtracting this electrical signal from the electrical signal of the photodetector, the lamp and absorption cell are An optical magnetic resonance magnetometer characterized by canceling out noise caused by changes in brightness of an absorption cell.