Coherent light source based on collective spontaneous emission
A coherent light source provides spontaneous emission (Dicke superradiance/subradiance) using a dilute and optically thin cloud of disordered atoms. The coherent light source provides improved noise statistics over that of a laser and λ accordingly, may be used in sensitive interferometric applications such as light gyroscopes.
1. A coherent light source comprising:
a chamber for receiving and retaining a group of at least 1000 gaseous state atoms;
a refrigeration system for cooling the group of atoms to a temperature of less than 100 μK; and
an excitation laser directed into the chamber along a first axis for exciting the group of atoms to an excited state from which they decay to generate a transmitted coherent light;
wherein the transmitted coherent light is generated by collective spontaneous emission of the group of atoms decaying from excitation from the excitation laser to provide coherent light; and
wherein the group of atoms has a coherent figure of merit of greater than 1, defined as:
[
N
/
(
R
λ
)
]
2
and an incoherent figure of merit less than 1 defined as:
N
/
(
R
λ
)
2
where N is a number of atoms in the group, R is the radial size of the group along the axis of transmitted coherent light, and λ is the wavelength of the transmitted coherent light.
2. The coherent light source of claim 1 wherein the transmitted coherent light maintains an interference contrast of greater than 0.5 as measured at the output of a Michelson interferometer over a transverse width perpendicular to the axis of transmitted coherent light and substantially equal to 2R where contrast is defined as (n max −n min )/(n max +n min ) and where n max is a maximum count of photons in an interference pattern of the light with itself and n max is a minimum count of photons in the interference pattern of the light with itself.
3. The coherent light source of claim 1 wherein the group of atoms has a width perpendicular to an axis of the transmitted coherent light of greater than 30 μm.
4. The coherent light source of claim 1 wherein R is greater than 5 times a wavelength of the excitation laser.
5. The coherent light source of claim 1 wherein the excitation laser is directed along a first axis and the transmitted coherent light is received along a second axis crossing the first axis.
6. The coherent light source of claim 1 wherein the group has at least 1,000 atoms.
7. The coherent light source of claim 1 wherein transmitted light can have a multiple-photon Fock (photon-number) state to provide an interference pattern with a period less than the wavelength of the transmitted light.
8. The coherent light source of claim 1 wherein the excitation laser excites less than 50% of the group of atoms into excitation at any time.
9. The coherent light source of claim 1 wherein the group is free from feedback from an optical cavity.
10. The coherent light source of claim 1 wherein the atoms are rubidium.
11. The coherent light source of claim 1 further including an interferometer receiving the transmitted light and providing an optical assembly detecting interference of the transmitted light along two different paths and a detector detecting changes in an interference pattern caused by the interference.
12. The coherent light source of claim 11 wherein at least one of the two different paths is a loop and the interferometer provides a gyroscope output indicating rotational angle.
13. The coherent light source of claim 1 wherein the standard deviation of the photon-number statistics is reduced at least by 10%.