US3675067A - Optical resonance cell with means for regulating internal vapor pressure - Google Patents

Optical resonance cell with means for regulating internal vapor pressure Download PDF

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Publication number
US3675067A
US3675067A US124974A US3675067DA US3675067A US 3675067 A US3675067 A US 3675067A US 124974 A US124974 A US 124974A US 3675067D A US3675067D A US 3675067DA US 3675067 A US3675067 A US 3675067A
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Prior art keywords
envelope
cell
temperature
bulb
atoms
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US124974A
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English (en)
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Henri Brun
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Thales SA
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CSF Compagnie Generale de Telegraphie sans Fil SA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J65/00—Lamps without any electrode inside the vessel; Lamps with at least one main electrode outside the vessel
    • H01J65/04—Lamps in which a gas filling is excited to luminesce by an external electromagnetic field or by external corpuscular radiation, e.g. for indicating plasma display panels
    • H01J65/042—Lamps in which a gas filling is excited to luminesce by an external electromagnetic field or by external corpuscular radiation, e.g. for indicating plasma display panels by an external electromagnetic field
    • H01J65/048—Lamps in which a gas filling is excited to luminesce by an external electromagnetic field or by external corpuscular radiation, e.g. for indicating plasma display panels by an external electromagnetic field the field being produced by using an excitation coil
    • 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
    • G04—HOROLOGY
    • G04F—TIME-INTERVAL MEASURING
    • G04F5/00—Apparatus for producing preselected time intervals for use as timing standards
    • G04F5/14—Apparatus for producing preselected time intervals for use as timing standards using atomic clocks

Definitions

  • ABSTRACT An optical resonance cell containing an alkali vapor to be optically pumped, the transparent walls of which are coated with a layer of paraffin while a bulb containing the reserve of alkali metal is connected to the cell in such a manner as to decelerate the alkali vapor flow between the bulb and the cell.
  • the present invention relates to optical resonance cells which can be used, for example, in atomic clocks or optically pumped magnetometers.
  • cells are available which are capable of operation only at very low optimal temperatures.
  • these cells can operate only with an optimum density of a saturating alkaline metal vapor; if this density is too low in the cell, too few atoms are involved in the phenomenon of optical pumping and resonance, and the resonance signal disappears.
  • the vapor density is too high, there is too high a degree of absorption of the pumping light wave, due to the fact that, because of the relaxation phenomenon, the atoms of a vapor are never all oriented, and the output signal reaching the optical detector is too weak.
  • the optimum temperature of operation of a resonance cell is for example 35 C in the case of caesium vapor and 45 C in the case of rubidium vapor.
  • the regulation of the temperature of such cells, at ambient temperatures which may be higher than these temperature levels, requires the use of thermoelectric devices (such as frigatrons) which take a relatively large amount of power.
  • a specific property of absorption of atoms of the alkali vapor is exploited.
  • This property is exhibited for example by a layer of substance, such as paraffin, deposited upon the walls of the cell, which layer has already been used in certain known cells with a purpose similar to that for which a filler gas is used, that is to say in order to prevent disorientation of the vapor atoms as a consequence of direct collision with the cell walls (the mean free trajectory of the vapor atoms being greater than the cell dimensions).
  • This property is again exhibited by the glass of the wall itself, if a filler gas is being used.
  • an optical resonance cell comprising an envelope having transparent walls; a bulb containing an alkali metal and communicating with said envelope; first means for decelerating the alkali vapor flow between said bulb and said walls; and second means for absorbing on said walls a predetermined number of alkali atoms of said vapor flow.
  • FIG. 1 illustrates an optical resonance cell in accordance with the invention
  • FIG. 2 is an explanatory graph.
  • the cell according to the invention illustrated in FIG. 1, comprises an envelope 1 of any desired shape, the walls of which are covered with a fine layer or film 2 of a substance which, on the one hand, prevents any disorientation of the vapor atoms as a consequence of collision with the walls, and, on the other hand, has a certain capacity for absorption of said atoms.
  • This layer will be, for example, of paraffin.
  • the cell likewise comprises an exhaust stem 3 and a bulb communicating with the cell and containing alkaline metal 5, the vapor of which is to be optically pumped.
  • the bulb 4 is connected to the envelope 1 through a tube 6 having a neck 7 of very small diameter.
  • the layer 2 should be sufficiently thin to enable the envelope to retain its transparency to the pumping light.
  • the operation of the cell is based upon a specific property of the paraffin layer 2, namely that it absorbs per second, a certain number of atoms of the alkaline vapor, which number is a function of the temperature and of the number of atoms in the envelope.
  • the envelope 1 and the bulb 4 thus being brought to this temperature while maintaining within the envelope the optimum vapor pressure P,,, assuming that the alkaline metal is rubidium.
  • the paraffin layer 2 absorbs n atoms per second for a number n of rubidium atoms in the envelope corresponding to a vapor pressure of P
  • N is the Avogadro fa ctor
  • R the gas constant
  • T the absolute temperature 0 273.15 of the vapor
  • M the atomic mass of the vapor.
  • FIG. 2 shows by way of example curves which respectively illustrate the variations in 11, and n, for a given paraffin layer and a given diameter of the neck 7, the rubidium vapor pressure in the envelope being Pm.
  • the transition point at around 77 C, for n, corresponds to the melting point of the particular paraffin.
  • an operating temperature no higher than the melting temperature of the parafiin will be used, because absorption then becomes very fast and this means that a substantial alkaline metal reserve is then required. Accordingly, the
  • curve n is modified by reducing the diameter of theneck 7, in order to produce curves for n and n, which are substantially coincidental between 45 and 77 C.
  • the envelope will tend to empty itself of vapor.
  • the absorption factor of the paraffin is proportional to the number of atoms present in the envelope:
  • n is therefore low at the start and n, is much higher because of the pressure difference between the bulb and the envelope. Accordingly, the envelope starts to fill up. As filling progresses, n rises and n, reduces, until an equilibrium (n, n is reached, where the number of atoms in the envelope remains the same and this condition maintains in the envelope the desired optimum vapor pressure.
  • operation at 70 C was made possible using a 3/ 100 mm diameter for the neck 7.
  • the filler gas is by itself adequate to produce the desired decelerating effect, due to the diffusion of the alkaline vapor through the gas.
  • all that is necessary is to vary the length and width of the neck 7 connecting the bulb 4 with the envelope 1, the gas flow being highly sensitive to these parameters.
  • the cells according to the invention have, among others, further advantages:
  • the invention is inno, way limited to the examples described hereinbefore.
  • the alkaline metal used need not necessarily be rubidium.
  • the arrangement for decelerating the gas flow between the bulb 4 and the envelope 1 is not necessarily a small-diameter orifice or neck (in the case of envelope lined with an absorbent layer), and other arrangements having the same function, may be placed at 7, for example a porous wall or a capillary tube, may be used, the gas flow then depending not only upon the diameter of the capillary tube but also upon its length.
  • An optical resonance cell adapted to substantially maintain an optimum alkali metal vapor pressure therein over a range of temperatures, said cell comprising;
  • said first and second means being constructed relative to each other and cooperating with each other to cause said firstand second functions of temperature to be substantially matched over a range of temperature thereby resulting in a dynamic equilibrium of vaporized alkali atoms at substantially said optimum vapor pressure over said range of temperature,
  • said first means cooperating with said second means for preventing the absorbing means from losing its absorbing efficiency and for decelerating said atoms supplied from said reservoir to obtain within the envelope the desired atomic density.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Stabilization Of Oscillater, Synchronisation, Frequency Synthesizers (AREA)
US124974A 1968-02-02 1971-03-16 Optical resonance cell with means for regulating internal vapor pressure Expired - Lifetime US3675067A (en)

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FR138532 1968-02-02

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US (1) US3675067A (enrdf_load_stackoverflow)
FR (1) FR1573924A (enrdf_load_stackoverflow)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3904260A (en) * 1973-07-23 1975-09-09 Us Navy Method for producing magnetic resonance cells
US4337998A (en) * 1980-04-15 1982-07-06 Hughes Aircraft Company Variable transmittance window
US5256995A (en) * 1992-07-17 1993-10-26 Ball Corporation Low helium permeability atomic frequency standard cell and method for forming same
US20090039881A1 (en) * 2007-08-07 2009-02-12 John Kitching Compact atomic magnetometer and gyroscope based on a diverging laser beam

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2030404A (en) * 1930-12-03 1936-02-11 Gen Electric Electric discharge device
US2081247A (en) * 1928-03-09 1937-05-25 Philips Nv Electric discharge tube
US2280618A (en) * 1938-03-25 1942-04-21 Gen Electric Electric gaseous discharge device
US3084257A (en) * 1959-01-19 1963-04-02 Lab For Electronics Inc Low pressure pumping
US3242423A (en) * 1962-01-10 1966-03-22 Csf Resonance cells for optical pumping
US3331977A (en) * 1965-03-15 1967-07-18 Westinghouse Electric Corp High output discharge lamp with vapor pressure control means
US3353037A (en) * 1964-05-11 1967-11-14 Bbc Brown Boveri & Cie Apparatus for separately adjusting the vapor pressures of two or more substances in a common vapor chamber
US3486058A (en) * 1967-09-12 1969-12-23 Rca Corp Sputter resistive cold cathode for low pressure gas discharge device

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2081247A (en) * 1928-03-09 1937-05-25 Philips Nv Electric discharge tube
US2030404A (en) * 1930-12-03 1936-02-11 Gen Electric Electric discharge device
US2280618A (en) * 1938-03-25 1942-04-21 Gen Electric Electric gaseous discharge device
US3084257A (en) * 1959-01-19 1963-04-02 Lab For Electronics Inc Low pressure pumping
US3242423A (en) * 1962-01-10 1966-03-22 Csf Resonance cells for optical pumping
GB1036002A (en) * 1962-01-10 1966-07-13 Csf Improvements in resonance cells for optical pumping
US3353037A (en) * 1964-05-11 1967-11-14 Bbc Brown Boveri & Cie Apparatus for separately adjusting the vapor pressures of two or more substances in a common vapor chamber
US3331977A (en) * 1965-03-15 1967-07-18 Westinghouse Electric Corp High output discharge lamp with vapor pressure control means
US3486058A (en) * 1967-09-12 1969-12-23 Rca Corp Sputter resistive cold cathode for low pressure gas discharge device

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3904260A (en) * 1973-07-23 1975-09-09 Us Navy Method for producing magnetic resonance cells
US4337998A (en) * 1980-04-15 1982-07-06 Hughes Aircraft Company Variable transmittance window
US5256995A (en) * 1992-07-17 1993-10-26 Ball Corporation Low helium permeability atomic frequency standard cell and method for forming same
US20090039881A1 (en) * 2007-08-07 2009-02-12 John Kitching Compact atomic magnetometer and gyroscope based on a diverging laser beam
US7872473B2 (en) * 2007-08-07 2011-01-18 The United States of America as represented by the Secretary of Commerce, the National Institute of Standards and Technology Compact atomic magnetometer and gyroscope based on a diverging laser beam

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Publication number Publication date
FR1573924A (enrdf_load_stackoverflow) 1969-07-11

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