Magnetic field measuring apparatus

• US 20090001979A1
• Filed: 06/12/2008
• Published: 01/01/2009
• Est. Priority Date: 06/27/2007
• Status: Active Grant

• Current Assignee: Hitachi High-Technologies Corporation (Hitachi, Ltd.)
• Original Assignee: Hitachi High-Technologies Corporation (Hitachi, Ltd.)
• Inventors: Kawabata, Ryuzou
• Granted Patent: US 7,652,473 B2
• Time in Patent Office: Days
• US Class Current: 324/244.100
• CPC Class Codes: G01R 33/032 using magneto-optic devices, e.g. Faraday or Cotton-Mouton effect
• CPC Class Codes: G01R 33/26 using optical pumping

Abstract

Providing: quickly brining a vapor cell 119 to a desired temperature when retaining the heat of the vapor cell 119 to enhance the magnetic field detection performance of an optically pumped magnetometer; preventing adherence of atoms in the vapor cell 119 to a laser irradiation light passing-through part of the vapor cell 119; downsizing the periphery of the vapor cell 119; and suppressing the effect of a magnetic field from a heater used to retain the heat of the vapor cell 119. The present invention includes: a transparent film heater 118 provided to a laser irradiation light passing-through part of a vapor cell 119, the vapor cell 119 being a magnetic detection part of the optically pumped magnetometer; a temperature detector 115 provided at a center part of a side of the vapor cell 119; a temperature regulator 111 that sets a desired temperature for heat retention of the vapor cell 119 and compares the desired temperature and the actual temperature of the vapor cell measured by the temperature detector 115; an operation unit 112 that upon receipt of a PID control signal for temperature control from the temperature regulator 111, performs a temperature adjustment and switches on/off, in a pulsed manner, current applied to the transparent film heater 118 after the desired temperature is reached; and a heater power supply 113 that upon receipt of an operation signal from the operation unit 112, applies current to the transparent film heater 118.

Claims

1. An optically pumped magnetometer comprising:

a glass cell with an alkali metal enclosed therein, the cell having a conductive part through which laser irradiation light applied to the cell passes;

a temperature detector for measuring a temperature of the cell;

a control part that applies current to the laser irradiation light passing-through part to perform temperature control, based on the temperature measured by the temperature detector; and

a magnetic field measurement part that performs magnetic field measurement.

2. The optically pumped magnetometer according to claim 1, wherein the laser irradiation light passing-through part is made of conductive glass.

3. The optically pumped magnetometer according to claim 1, wherein the laser irradiation light passing-through part includes a film heater that is transparent to the laser irradiation light.

4. The optically pumped magnetometer according to claim 1, wherein the control part receives from the temperature detector a signal to the effect that the cell has reached a set temperature, and switches on/off the current applied to the laser irradiation light passing-through part in a pulsed manner to make the magnetic field measurement part perform magnetic field measurement when the current is off.

5. The optically pumped magnetometer according to claim 4, further comprising:

a beam splitter that splits the laser irradiation light; and

a correction part including a second cell to which the laser irradiation light split by the beam splitter is applied, and corrects a deviation of a frequency of a magnetooptical resonance signal, the deviation being caused by a magnetic field during the current applied to the laser irradiation light passing-through part of the cell being on, by controlling current applied to the laser irradiation light passing-through part of the second sell to be constantly on.

6. The optically pumped magnetometer according to claim 1, wherein the control part sets a cycle of a temperature control signal to be longer than a feedback control cycle for magnetic field measurement, the feedback control cycle being determined by a phase comparator, a loop filter, a voltage-controlled oscillator and a frequency divider included in the magnetic field measurement part.

7. The optically pumped magnetometer according to claim 4, wherein the magnetic field measurement part corrects a magnetic field detection sensitivity during the current applied to the laser irradiation light passing-through part under pulse control being on, based a ratio between a line width of a magnetooptical resonance signal obtained by sweeping a frequency of a RF magnetic field from a RF coil and an S/N ratio of the magnetooptical resonance signal, the S/N ratio being a ratio between a resonance value of the magnetooptical resonance signal and an output value fluctuation of a first derivative of the magnetooptical resonance signal at a resonance frequency.

8. The optically pumped magnetometer according to claim 1, wherein a set temperature for a temperature controlled by the control part is a temperature at which a ratio between a line width of a magnetooptical resonance signal obtained by sweeping a frequency of a RF magnetic field from a RF coil and a S/N ratio of the magnetooptical resonance signal is minimum.

9. The optically pumped magnetometer according to claim 1, wherein the metal is one of kalium, rubidium or cesium.

10. The optically pumped magnetometer according to claim 1, wherein the glass cell is made of heat-resistant glass or quartz glass.