Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/24—Arrangements or instruments for measuring magnetic variables involving magnetic resonance for measuring direction or magnitude of magnetic fields or magnetic flux
  • G01R33/26—Arrangements or instruments for measuring magnetic variables involving magnetic resonance for measuring direction or magnitude of magnetic fields or magnetic flux using optical pumping
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
  • G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
  • G01C19/58—Turn-sensitive devices without moving masses
  • G01C19/60—Electronic or nuclear magnetic resonance gyrometers
  • G01C19/62—Electronic or nuclear magnetic resonance gyrometers with optical pumping

Definitions

• the present invention relates to an atomic or molecular vapor cell for optical pumping by an optical pumping wave as well as a magnetometer or gyroscope using such a cell.
• the use of the optical pumping properties of atomic or molecular gases such as helium-3 and helium-4 is now well known for the detection of weak magnetic fields.
• atomic or molecular gases such as helium-3 and helium-4
• atoms in the metastable 2 3 S state are created by a gentle electrical discharge.
• One or more components of the transition 2 3 S-2 3 P are excited by a resonant light towards 1.08 ⁇ m suitably polarized.
• the metastable atoms are thus oriented or aligned by optical pumping in the 2 3 S state.
• helium-3 which has a non-zero nuclear spin
• This helium polarization method is used in particular in magnetometers to measure magnetic induction.
• the helium-4 magnetometer is based on the measurement of the electronic magnetic resonance in the magnetic field to be measured.
• the resonant frequency gives the value of the field to be measured.
• Electronic resonance is detected by the variation in the absorption coefficient induced on a beam of light circularly polarized at 1.08 ⁇ m or in the polarization of fluorescent light.
• Another object of the present invention is a new atomic or molecular vapor cell for optical pumping, making it possible to use a low power laser source while having a pumping efficiency greater than that of direct pumping of metastables of helium-3.
• the laser source is preferably tuned to one of the 2 3 S-2 3 P transitions of helium-4.
• a sensitive cell formed of an enclosure at least partially transparent, containing a gas, - one or more laser sources directed towards the cell, and
• FIG. 1 is a diagram of a magnetometer according to a first embodiment
• FIG. 2 is a diagram of a magnetometer according to a second embodiment.
• the same elements have the same references.
• magnetometers described below are given by way of example of use of a cell in accordance with the present invention.
• present invention can be applied to other types of magnetometers and also to gyroscopes comprising as main element a cell of the type described in the invention.
• the cell 1 is lit by a pumping light beam coming from a light source 2 constituted by a laser source.
• the laser source 2 is preferably constituted by a semiconductor laser which can be of any kind, single mode or multi ode, with standard double heterostructure or with quantum wells or any other structure. However, other laser sources can be envisaged such as NN-doped LiNbO-lasers or even LNA lasers.
• the laser source 2 is constituted by a laser tunable on one of the 2 3 S-2 3 P transitions of helium-4. The light coming from the laser therefore has a wavelength of approximately 1.08 ⁇ m.
• the pumping beam F 1 from the source 2 is polarized linearly and a quarter-wave plate 3 therefore provides a circularly polarized pumping beam illuminating the cell 1.
• two electrodes 4, 5 or excitation rings are brought to an alternating voltage by a generator 6 high frequency providing a signal of the order of MHz, which allows to maintain a gentle discharge necessary for obtaining metastable atoms.
• the metastable helium atoms created by the discharge are thus oriented lon itudinally in the direction D of the magnetic field B.
• the orientation rate is higher than with pure helium-4, because of the indirect couplings between Zeeman populations of helium-4 (2 3 S-) induced by the cross-exchanges and the hyperfine coupling.
• the actual measurement of the magnetic induction is carried out as follows: two windings 7, 8 situated in planes parallel to the direction of propagation of the pumping beam F. and on either side of this beam are supplied by a radio frequency generator 9 and provide a radio frequency field.
• the radio frequency field thus created perpendicular to the longitudinal component of the magnetic induction B induces the electronic magnetic resonance of helium-3 or helium-4 between sub-levels Zeeman 2 3 S 1 , when the radio generator frequency 9 is frequency modulated around an adjustable value.
• the radio-frequency field can be adjusted from the radiation transmitted by cell 1.
• a detection cell 11 receives the radiation transmitted by the cell 1 and allows, using a processing circuit 10, to act on the radio-frequency generator 9.
• FIG. 2 another embodiment of a magnetometer with optical helium pumping in which the measurement of the magnetic induction returns to that of the precession frequency of the nuclear magnetization of helium -3 by nuclear magnetic resonance.
• the atomic or molecular vapor cell 1 is, in accordance with the present invention, filled, as for the embodiment of FIG. 1, with a mixture of helium-3 and helium-4 with a proportion of helium-3 greater than that of the device described above, for example between 1/3 and 1/10.
• the optical pumping of cell 1 is carried out, as for the embodiment of FIG. 1, by a laser source 2 emitting light F., at a wavelength of approximately 1.08 ⁇ m linearly polarized on a blade quarter wave 3 which polarizes it circularly before sending it to cell 1.
• Cell 1 is subjected to a gentle discharge created by a high frequency generator 6 connected to two excitation coils 5, 4.
• the atomic or molecular vapor cell for optical pumping used is therefore a cell containing a mixture of helium-3 and helium-4.
• the absorption of the pumping beam by helium-4 is more effective than by helium-3, because the oscillator forces are greater (there are 3 sub-levels of fine structure and not much more because of hyperfine structure); while the efficiency of electronic -> nuclear orientation transfer mechanisms remains comparable to that of pure helium-3.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• Engineering & Computer Science (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Measuring Magnetic Variables (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Cites Families (6)

• 1989
  • 1989-11-14 FR FR8914894A patent/FR2654570A1/fr active Pending
• 1990
  • 1990-11-06 WO PCT/FR1990/000796 patent/WO1991007668A1/fr not_active Application Discontinuation
  • 1990-11-06 EP EP19900916758 patent/EP0453544A1/de not_active Withdrawn

Non-Patent Citations (1)

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