JPS6255578A - Photomagnetic resonance magnetometer - Google Patents

Abstract

PURPOSE:To achieve a higher measuring accuracy, by providing a photo detector for detecting changes in brightness slantly behind a helium lamp to reduce noises accompanying changes in the brightness of light source. CONSTITUTION:A photo detector 14 for detecting changes in brightness detects changes in the brightness of a helium lamp 1 converted it into an electric signal without intercepting a light incident into an absorption cell 5. After division in the voltage with a voltage adjustor 15, the detected signal is applied to a differential amplifier 16 as input and the difference from an absorption signal of light detected with a photo detector 7 for detecting magnetic resonance as another input is sent to a phase detector 9 as output of the amplifier 16. Thus, even when the photo detector 7 receives changes in brightness of the helium lamp 1 as noise in overlap besides the absorption signal of the light by a magnetic resonance, the level of the signal detected with the photo detector 14 is adjusted with a voltage adjustor 15 and then, the signal is offset with an output signal of the photo detector 7 with the differential amplifier 16. This can cancel electron noises thereby reducing noises due to changes in the brightness of the helium lamp.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is an optical system that 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. This paper concerns improvements to magnetic resonance magnetometers.

[Conventional technology]

Atoms of certain substances such as cesium and helium undergo a change in energy that is proportional to the strength of the surrounding magnetic field, so this energy change is detected using specific light and a high-frequency magnetic field.
There is a magnetometer that tracks the frequency of a high-frequency magnetic field so that the change in intensity of light is maximized. A brief explanation of the magnetic resonance magnetometer will be provided. Figure 2 shows an example of a conventional optical magnetic resonance magnetometer, in which (1) is a helium lamp, (1) is a helium lamp;
2) is a lamp excitation electrode, (3) is a lens, (4) is a circularly polarizing plate, (5) is an absorption cell, +61id absorption cell excitation electrode, (7) is a photodetector, (8) is an amplifier, (9) is a phase detector.

Ol is a voltage control excavator, αυ is a buffer resistor, σ2 is an RP coil, and 13 is a high frequency oscillator.

In the main text, components not related to this invention are omitted.

In this optical magnetic resonance magnetometer, the helium lamp is discharged by a high frequency voltage of several tens of MHz applied from the high frequency oscillator a3 through the lamp excitation electrode (2), and generates light with a wavelength of 1.08 μ, which is unique to -.lium atoms. do. This light is made into parallel light beams by a lens (3) and a circularly polarizing plate (4)
The light is converted into circularly polarized light and irradiated onto the absorption cell (5),
This absorption cell (5) is several tens of MHz from the high frequency oscillator αJ.
A high frequency voltage of 2 is applied via the absorption cell excitation electrode (6) to create a glow discharge state.

The light transmitted through the absorption cell (5) is converted into an electrical signal by a photodetector (7), then amplified by an amplifier (8), and then phase detected by a phase detector (9) to generate an error signal. This error signal controls the oscillation frequency of the voltage-controlled excavator Ql and flows through the output buffer resistor 0υ to the RF coil α3, generating a high-frequency magnetic field H1 and applying it to the absorption cell (5).

Here, the absorption cell (5) has a lifetime (
It is assumed that Hθ atoms having a very short 1life time are enclosed.

This motion of helium atoms will be explained using the related energy level diagram in FIG.

First, the absorption cell (5) is glow-discharged in advance by a high frequency voltage of several tens of MHH and is in a metastable state with the energy of helium atoms of 112S1. The helium atom in this metastable state has a wavelength of 1.0 from helium rung +1+.
Since it is irradiated with 8μ light (Do=D2), it absorbs this and becomes excited state with energy of 2PO,+,2, but the life of the excited state is short.

It loses energy in about 10 seconds and returns to the metastable state of 2 Eli. In addition, when the system shown in Figure 2 is in a quiet magnetic field, the helium atoms in the absorption cell (5) undergo Larmor precession due to the magnetic moment of the atoms themselves being affected by the force of the quiet magnetic field. Since it performs a so-called rotational movement, energy changes occur, and a plurality of Zeman sublevels 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 7-difference motion of the magnetic moments of atoms 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 1.08μ light emitted from a helium lamp (1) from a direction parallel to the quiet magnetic field and circularly polarized by a circularly polarizing plate (4), the helium atoms absorb the light and enter an excited state. It will have an energy of 2F0,1.2. After this, the energy is lost in a short time and returns to the energy of the metastable state 2 sl, but at this time the selectivity of the Zeeman sublevel is preserved and the number of atoms per Zeeman sublevel within the Zeeman sublevel of 2 sl increases. Different skewed distributions are possible.

When an electromagnetic wave with energy equal to the energy difference between the Zeeman sublevels of 28i, that is, a high-frequency magnetic field at the Larmor frequency, is applied to this uneven distribution 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 uneven distribution is eliminated. Finally, υ helium atoms return to the initial state in which roughly equal numbers of atoms are distributed in each of the three Zeeman sublevels of metastable state 2 Sl.

The above process, that is, 2 S1 → 2 P of helium atom
The energy change of o 12-+ 2131 is 1.08μ
Since the light is irradiated in series, it is repeated every time the frequency of the high-frequency magnetic field matches the Larmor frequency, but the photodetector (7), amplifier (8), 1-phase detector (9+, !pressure-controlled oscillator QQ) , buffer resistor αυ, and RF coil α2, the electronic circuit system always maintains a high frequency by taking advantage of the fact that light parallel to the silent magnetic field is absorbed during the above process, and as a result, the light transmitted through the absorption cell is reduced. The frequency of the magnetic field is controlled to match the Larmor frequency.At this time, the following relationship holds between the high frequency magnetic field, the atomic constant, and the static magnetic field.

ω-ωO-rHo ・・・－・・・(
1) ω: Angular frequency of high-frequency magnetic field ωo Larmor frequency of two atoms γ: Magnetic rotation ratio of atoms (constant) Ho: Strength of static magnetic field In this way, the system in Figure 2 is proportional to the strength MO of static magnetic field. Lock on to the Larmor frequency,
The frequency of the high-frequency magnetic field at this time, that is, the voltage-controlled oscillator Q
(The oscillation frequency of I coincides with the Larmor frequency, so if this is measured, the strength of the static magnetic field HO can be accurately measured. However.

Of the light received by the photodetector (5), the absorption due to magnetic resonance, that is, the absorption signal is only about 0.1 inch. [Problems to be solved by the invention] Conventional optical magnetic resonance magnetometers lack the ability to detect changes in the brightness of helium lamps. Therefore, there was a problem in that it was not possible to reduce the noise caused by changes in the brightness of the helium lamp.This invention was made to solve this problem. The purpose is to reduce this and improve measurement accuracy.

[Means for solving problems]

A photodetector for detecting brightness changes is placed diagonally behind the helium lamp (closer to the absorption cell) to detect changes in the brightness of the helium lamp without blocking the light entering the absorption cell, and the detected electrical signal is transmitted. It is used to electrically cancel out changes in the brightness of the light source that appear on the other photodetector for magnetic resonance detection, thereby reducing noise associated with changes in the brightness of the helium lamp.

[Effect]

Conventionally, there was no function to detect changes in the brightness of a helium lamp, so the photodetector that detects magnetic resonance detected changes in the brightness of a helium lamp as an electrical signal, which caused measurement accuracy to deteriorate. By placing a new photodetector for detecting brightness changes diagonally behind the helium lamp, changes in lamp brightness can be detected without blocking the light from the helium lamp heading toward the magnetic resonance system, and the electrical signals detected here can be used to detect changes in the brightness of the lamp. By electrically canceling out changes in the brightness of the helium lamp, it is possible to reduce noise associated with changes in brightness. Another advantage is that it only requires adding a photodetector for detecting changes in brightness near the helium lamp and changing part of the electronic circuit system.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the present invention.
) is a photodetector for detecting brightness changes, αS is a voltage regulator, αe
is a differential amplifier, and the photodetector I for detecting brightness changes is placed diagonally behind the helium lamp (1) so as not to block the light incident on the absorption cell (5).

In such a configuration, the photodetector α41 for detecting brightness changes
Changes in the brightness of the helium lamp [1] are detected and converted into electrical signals without blocking the light incident on the U absorption cell (5). The brightness change signal of the helium lamp detected here is divided into voltages appropriately by the voltage regulator a9, and then becomes the manual power of one side of the differential amplifier and is input to the photodetector (7) for magnetic resonance detection, which is the input of the other side. The difference between the detected light and the absorption signal is sent to the phase detector +9) as the output of the differential amplifier.

Here, the helium rung (1) is the lamp excitation electrode (2).
A high-frequency voltage, which is the output of high-frequency oscillator 0, is applied to the oscillator 0 to emit light, so if the output of this high-frequency oscillator changes, the brightness of the helium lamp changes.Also, since the helium lamp +11 is a discharge tube, it may cause vibrations or The discharge state changes slightly due to external factors such as temperature, and the brightness changes.

At this time, the photodetector α for detecting brightness changes placed diagonally behind the helium lamp (11)
Detects changes in brightness as electrical signals. Therefore, even if the brightness change of the helium lamp (11) is superimposed as noise in addition to the absorption signal of light due to magnetic resonance, the photodetector (7) for detecting magnetic resonance detects it by the photodetector a4 for detecting brightness change. After level-adjusting the level of the detected signal using the voltage regulator αS, this signal and the output signal of the photodetector (7) are canceled by the differential amplifier αe, thereby canceling out the electrical noise. Noise can be reduced.

As described above, the optical magnetic resonance magnetometer of the present invention detects and reduces the brightness change of the helium lamp that occurs in the magnetic resonance system, so it does not impair the high sensitivity of optical magnetic resonance (measuring the magnetic field). It is possible to provide a device for

〔Effect of the invention〕

As described above, this invention makes it possible to detect changes in the brightness of the helium lamp without blocking the light incident on the absorption cell by providing a photodetector for detecting changes in brightness diagonally behind the helium lamp. It is possible to reduce the noise associated with changes in the brightness of the helium lamp without adversely affecting the resonance detection signal. Therefore, it has the effect of making it less susceptible to external factors such as temperature and vibration, and fluctuations in power supply.

In addition, in order to realize the device of B's invention, it is only necessary to add a photodetector for detecting brightness changes to the side of the helium lamp of the conventional optical magnetic resonance magnetometer, and to slightly change the electronic circuit system. The advantage is that no changes need to be made.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an embodiment of the structure of a conventional optical magnetic resonance magnetometer, and FIG.
The figure shows the energy level of helium atoms. In the figure, (1) is a helium lamp, (2) is an electrode for exciting the lamp, and (3) is a lens. (4) is a circularly polarizing plate, (5) is an absorption cell, (6) is an absorption cell excitation electrode, (7) is a photodetector, (8) is an amplifier, (
9) is a phase detector, αl is a voltage controlled oscillator, and αυ is a buffer resistor. α is an RF coil, 0 is a high-frequency oscillator, α is a photodetector for detecting a change in brightness, 4 is a voltage regulator, and αe is a differential amplifier. Note that the same or corresponding parts in the two figures are designated by the same reference numerals.

Claims (1)

[Claims] A lamp that generates a light beam used for optical detection of optical magnetic resonance, an absorption cell containing a substance that causes magnetic resonance, a high-frequency oscillator that causes the lamp and the absorption cell to discharge and emit light, and a high-frequency magnetic field that applies a high-frequency magnetic field to the absorption cell. an RF coil for applying an RF signal to generate magnetic resonance; a photodetector for detecting absorption of the light beam resulting from the magnetic resonance in the absorption cell and converting it into an electrical signal; and an amplifier for amplifying the electrical signal of the photodetector. a phase detector that detects the phase of the output of the amplifier and generates an error signal; a voltage-controlled oscillator that controls the oscillation frequency using the error signal and generates a high-frequency voltage with a frequency equal to the Larmor frequency; In the magneto-optical resonance magnetometer, which consists of a buffer resistor that converts into RF and applies it to an RF coil to generate a high-frequency magnetic field, a new photodetector is added near the lamp to detect changes in the brightness of the lamp. 1. An optical magnetic resonance magnetometer, characterized in that noise accompanying changes in brightness of a lamp is canceled out by detecting the electrical noise with a photodetector and subtracting this electrical noise from the electrical signal of the photodetector for magnetic resonance detection.