Alkali-Metal Vapour Cell, Especially for an Atomic Clock, and Manufacturing Process

• US 20150277386A1
• Filed: 10/11/2013
• Published: 10/01/2015
• Est. Priority Date: 10/12/2012
• Status: Active Grant

• Current Assignee: Centre National De La Recherche Scientifique, Universite De Franche-Comte
• Original Assignee: Centre National De La Recherche Scientifique, Universite De Franche-Comte
• Inventors: Passilly, Nicolas, Gorecki, Christophe, Chutani, Ravinder, Boudot, Rodolphe
• Granted Patent: US 9,488,962 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: C03B 11/14 Pressing laminated glass articles or glass with metal inserts or enclosures, e.g. wires, bubbles, coloured parts
• CPC Class Codes: C03C 15/00 Surface treatment of glass, not in the form of fibres or filaments, by etching etching or surface-brightening compositions, in general C09K13/00
• CPC Class Codes: G04F 5/14 using atomic clocks
• CPC Class Codes: G04F 5/145 using Coherent Population Trapping
• CPC Class Codes: H03L 7/26 using energy levels of molecules, atoms, or subatomic particles as a frequency reference

Abstract

The invention relates to an alkali-metal vapour cell, especially for an atomic clock, and to its manufacturing process. The alkali-metal vapour cell is able to be associated with a laser for emitting an external input laser beam and a photodetector for receiving an external output laser beam, and comprises a housing having an upstream optical window and a downstream optical window and forming an optical cavity filled with an alkali-metal vapour such as a caesium-comprising vapour, and micro-optical means arranged in the optical cavity and comprising an upstream optical reflector and a downstream optical reflector for reflecting the laser beam, which reflectors are inclined relative to each other, the upstream reflector being inclined relative to the plane (P) of the upstream window and to the axis of the input laser beam so that the external input laser beam passes through the upstream window in order to form an internal input laser beam, the latter being reflected by the upstream reflector and deviated towards the downstream reflector so as to form an internal intermediate laser beam that is reflected on the downstream reflector and deviated towards the downstream window so as to form an internal output laser beam, the internal output laser beam passing through the downstream window in order to form the external output laser beam.

Claims

1. A alkali-metal vapour cell, intended in particular for inclusion in an atomic clock, adapted to be associated with a laser for emitting an external input laser beam striking the cell and with a photodetector for receiving an external output laser beam exiting the cell, the laser beam having passed through the cell, said cell comprising, on the one hand, a housing having an upstream optical window and a downstream optical window and forming an optical cavity filled with alkali-metal vapour such as vapour containing cesium, and on the other hand, micro-optical means arranged in the optical cavity and comprising an upstream optical reflector and a downstream optical reflector for reflecting the laser beam, said reflectors being inclined relative to one other, the upstream reflector being inclined relative to the plane (P) of the upstream window and to the axis of the input laser beam, such that:

the external input laser beam passes through the upstream window to form an internal input laser beam, the internal input laser beam is reflected on the upstream reflector and deflected towards the downstream reflector to form an internal intermediate laser beam, the internal intermediate laser beam is reflected on the downstream reflector and deflected towards the downstream window to form an internal output laser beam, and the internal output laser beam passes through the downstream window to form the external output laser beam, said cell further comprising upstream deflection means for deflecting the input laser beam, said means being located upstream of the upstream reflector, and, where appropriate, downstream deflection means for deflecting the laser beam reflected by the downstream reflector, said means being located downstream of the downstream reflector, so as to combine the deflection produced by the deflection means with the deflection produced by the associated reflector.

2. The alkali-metal vapour cell according to claim 1, wherein the upstream reflector and the downstream reflector are arranged symmetrically relative to a transverse mid-plane of the cell.

3. The alkali-metal vapour cell according to claim 1, wherein the input laser beam and/or the output laser beam forms a 90°

angle with the internal intermediate laser beam, and/or the input laser beam and the output laser beam are arranged parallel to one another.

4. The alkali-metal vapour cell according to claim 1, wherein the upstream reflector and the downstream reflector are spaced apart from each other, the spacing between them determining the dimension of the optical cavity and of the cell in the direction (D) of axis (FLII) of the internal intermediate laser beam.

5. The alkali-metal vapour cell according to claim 4, wherein the spacing between the upstream reflector and the downstream reflector is between about 3 mm and about 9 mm, particularly between about 4 mm and about 8 mm, more particularly between about 5 mm and about 7 mm.

6. The alkali-metal vapour cell according to claim 1, wherein the upstream optical window and the downstream optical window are arranged on one and the same side of the cell, in particular are formed by two portions separated by one and the same glass plate—

or wafer.

7. The alkali-metal vapour cell according to claim 1, comprising one and the same side of association with the laser emitting the input laser beam and with the photodetector receiving the output laser beam.

8. The alkali-metal vapour cell according to claim 1, wherein the upstream deflection means, and where appropriate the downstream deflection means, are diffraction means associated with the upstream optical window and where appropriate with the downstream optical window.

9. The alkali-metal vapour cell according to claim 1, wherein the reflectors and the deflection means, in particular the diffraction means, are chosen so as to maintain the circular polarization state of the laser beam during its path.

10. The alkali-metal vapour cell according to claim 1, further comprising, in the optical cavity, one or more masks preventing the passage of the laser beam into unwanted area(s).

11. The alkali-metal vapour cell according to claim 1, wherein the upstream reflector and the downstream reflector are formed by shaping, particularly by etching, a plate—

or wafer, and comprise a reflective coating, particularly of metal, more particularly of aluminum.

12. The alkali-metal vapour cell according to claim 1, comprising, in addition to the optical cavity, a dispenser cavity adjacent to and in communication with the optical cavity, suitable for receiving a dispenser of alkali metal such as cesium, the alkali-metal vapour which is generated by heating after sealing the cell migrating towards and into the optical cavity through the communication between the two cavities.

13. The alkali-metal vapour cell according to claim 1, wherein the optical cavity is filled with alkali-metal vapour and a buffer gas.

14. The alkali-metal vapour cell according to claim 1, having associated optical means for shaping the external input laser beam, in particular a quarter-wave plate and a collimating lens.

15. The alkali-metal vapour cell according to claim 1, wherein the housing comprises, on one hand, a shapeable plate—

or wafer shaped so as to form the recess of the optical cavity, the upstream reflector, the downstream reflector, if appropriate the recess of the dispenser cavity and the cleared area of the communication between the two cavities, and on the other hand, a glass plate—

or wafer so as to form the upstream optical window and the downstream optical window and to close off the optical cavity, where appropriate the dispenser cavity, and with which are associated deflection means, in particular diffraction means, the glass plate—

or wafer and the recess-shaped plate—

or wafer being arranged opposite each other and sealed to one another, in particular by anodic bonding.

16. The alkali-metal vapour cell according to claim 1, comprising a shapeable plate—

or wafer etched so as to form the recess of the optical cavity, the upstream reflector, the downstream reflector, if appropriate the recess of the dispenser cavity and the cleared area of the communication between the two cavities, the upstream reflector and the downstream reflector being etched along the crystal planes of the constituent material of the shapeable plate—

or wafer.

17. The alkali-metal vapour cell according to claim 16 as dependent on claim 8, comprising a shapeable silicon plate—

or wafer, etched with a pyramid shape along the crystal planes [111] at 54.7°

so as to form the upstream reflector, the downstream reflector, and the recess of the optical cavity, and, in combination, upstream diffraction means for diffraction towards the adjacent outer edge of the cell and if appropriate downstream diffraction means with an angle of 19.48°

.

18. A method for manufacturing an alkali-metal vapour cell according to claim 15, wherein:

a shapeable plate—

or wafer—

is provided and is shaped to form a recess or recesses, in particular is etched, so as to form the recess of the optical cavity, the upstream reflector, the downstream reflector, if appropriate the recess of the dispenser cavity and the cleared area of the communication between the two cavities,

a glass plate—

or wafer—

is provided that is suitable for forming the upstream optical window and the downstream optical window and for closing off the optical cavity, if appropriate the cavity dispenser,

the recess-shaped plate—

or wafer—

and the glass plate—

or wafer—

are placed facing each other and are sealed to one another, in particular by anodic bonding,

the optical cavity is filled with alkali-metal vapour,

and the glass plate—

or wafer—

is associated with deflection means, in particular diffraction means.

19. The method for manufacturing an alkali-metal vapour cell according to claim 18, wherein:

an etchable silicon plate—

or wafer—

is provided, and is etched with a pyramid shape along the crystal planes [111] at 54.7°

by wet etching so as to form the upstream reflector, the downstream reflector, and the recess of the optical cavity,

the glass plate—

or wafer—

is associated with deflection means, in particular diffraction means.

20. The method for manufacturing an alkali-metal vapour cell according to claim 18, wherein a dispenser cavity is formed, adjacent to and in communication with the optical cavity, a dispenser of alkali metal such as cesium is placed in the dispenser cavity, and once the recess shaped plate—

or wafer—

and the glass plate—

or wafer—

are sealed to one another, heating is performed so as to generate alkali-metal vapour which migrates towards and into the optical cavity via the communication between the two cavities.

21. The method for manufacturing an alkali-metal vapour cell according to claim 18, comprising at least one of the following operations:

placement of one or more masks in the optical cavity in order to prevent the passage of the laser beam into undesired area(s),

placement on the upstream reflector and downstream reflector of a reflective coating, particularly of metal, more particularly of aluminum,

introduction of a buffer gas into the optical cavity,

association with the alkali-metal vapour cell of optical means for shaping the external input laser beam, in particular a quarter-wave plate and a collimating lens.

22. An atomic clock comprising an alkali-metal vapour cell according to claim 1, associated in a compact manner with a laser for emitting an external input laser beam striking the cell and with a photodetector for receiving an external output laser beam exiting the cell.

23. The atomic clock according to claim 22, wherein the laser for emitting the input laser beam and the photodetector for receiving the output laser beam are associated with the cell on one and the same side of association.

24. The atomic clock according to claim 22, wherein the input laser beam and the output laser beam are arranged parallel to one another, one next to the other.

25. The atomic clock according to claim 22, wherein the laser is a VCSEL vertical cavity laser.