Optical rubidium atomic frequency standard
An optical atomic clock includes a fiber-coupled electro-optic modulator to phase modulate and suppress residual amplitude modulation of a frequency-doubled laser; a rubidium-enriched vapor cell configured to perform a two-photon transition of rubidium atoms to generate a fluorescence signal from the laser; and a differential lock mechanism to stabilize a frequency of the fluorescence signal to a resonance frequency of the two-photon transition of the rubidium atoms.
1. An apparatus comprising:
a laser source to generate a light beam at a predetermined frequency;
a frequency comb device to generate an optical beat note from a first portion of the light beam;
an optical waveguide to modulate a phase of a second portion of the light beam, wherein the optical waveguide comprises a fiber-coupled electro-optic modulator, and wherein residual amplitude modulation is suppressed in the optical waveguide;
an erbium doped fiber amplifier to amplify the frequency of the second portion of the light beam;
a vapor cell assembly comprising rubidium atoms, the vapor cell assembly configured to perform a two-photon transition of the rubidium atoms to generate a fluorescence signal from the second portion of the light beam;
a controller to lock a frequency of the fluorescence signal to a resonance frequency of the two-photon transition of the rubidium atoms;
a frequency counter to count the optical beat note; and
a processor to compare the locked frequency of the fluorescence signal to the optical beat note.
2. The apparatus of claim 1 , comprising a voltage source to apply a DC offset voltage to the electro-optic modulator.
3. The apparatus of claim 1 , comprising:
an optical filter to filter a portion of the fluorescence signal; and
a photomultiplier tube in conjunction with a current pre-amplifier to detect a magnitude of the portion of the fluorescence signal filtered by the optical filter.
4. The apparatus of claim 1 , comprising a magnetic shield comprising dual-zone temperature regions surrounding the vapor cell assembly.
5. The apparatus of claim 1 , comprising a thermo-generating device to heat the vapor cell assembly to approximately 100° C.
6. The apparatus of claim 1 , wherein the photomultiplier tube and the current pre-amplifier are configured to monitor laser power of the portion of the fluorescence signal filtered by the optical filter.
7. The apparatus of claim 1 , comprising a splitter to split the light beam into the first portion and the second portion.
8. An optical atomic clock comprising:
a fiber-coupled electro-optic modulator to phase modulate and suppress residual amplitude modulation of a frequency-doubled laser;
a rubidium-enriched vapor cell configured to perform a two-photon transition of rubidium atoms to generate a fluorescence signal from the laser;
a differential lock mechanism to stabilize a frequency of the fluorescence signal to a resonance frequency of the two-photon transition of the rubidium atoms; and
a photodiode to detect the residual amplitude modulation of the laser, wherein the electro-optic modulator is to undergo voltage biasing to remove the residual amplitude modulation of the laser.
9. The optical atomic clock of claim 8 , comprising:
a detector to detect a magnitude of the fluorescence signal; and
a retro-reflector that is positioned facing the detector.
10. The optical atomic clock of claim 9 , wherein the detector is to detect light comprising an optical wavelength of approximately 776 nm emitted from the rubidium atoms.
11. An optical atomic clock comprising:
a fiber-coupled electro-optic modulator to phase modulate and suppress residual amplitude modulation of a frequency-doubled laser;
a rubidium-enriched vapor cell for performing a two-photon transition of rubidium atoms to generate a fluorescence signal from the laser; and
a differential lock mechanism for stabilizing a fractional frequency instability of the laser to 1×10-13 at one second.
12. A method comprising:
providing a light beam at a predetermined frequency;
splitting the light beam;
generating an optical beat note from the light beam using a frequency comb device;
modulating the frequency of the light beam;
suppressing a residual amplitude modulation of the light beam;
performing a second harmonic generation of the light beam;
performing a two-photon transition of rubidium atoms in a vapor cell to generate a fluorescence signal from the light beam;
stabilizing a frequency of the light beam to remain on a resonance frequency of the two-photon transition of the rubidium atoms; and
detecting a repetition rate output of the frequency comb device.
13. The method of claim 12 , comprising using multiple spatially dislocated light beams to increase an interaction of the rubidium atoms with the light beams.
14. The method of claim 12 , comprising detecting colors of the fluorescence signal other than at a wavelength of 420 nm.
15. The method of claim 12 , comprising applying a AC Stark shift cancellation laser to the light beam.
16. The method of claim 15 , comprising using an atom fluorescence detector to monitor a laser power of the fluorescence signal.
17. The method of claim 16 , comprising simultaneously modulating the laser power and frequency of the fluorescence signal, wherein a frequency shift of the fluorescence signal and the AC Stark shift are equal.
18. The method of claim 12 , comprising stabilizing a power of the light beam prior to delivery into the vapor cell at approximately 30 mW, wherein the light beam is delivered into the vapor cell at a wavelength of approximately 778 nm.
19. The method of claim 12 , comprising stabilizing a fractional frequency of the light beam to 1×10 −15 at one day.