Abstract: An optically-excited atomic frequency standard that subjects alkali metal atoms (111) to circularly-polarized optical radiation. The atomic frequency standard is improved by the use of a circular polarizer (202) to control the intensity of the circularly-polarized optical radiation. The circular polarizer includes a linear polarizer (203) and a quarter-wave retarder (205), with the light to be circularly polarized passing first through the linear polarizer (203) and then through the quarter-wave retarder (205). In the atomic frequency standard, the optical radiation (105) to which the circular polarizer (202) is applied is itself linearly polarized, and the intensity of the circularly polarized light produced by the circular polarizer (202) is controlled by rotating (303) the circular polarizer. The degree of rotation determines how much of the linearly-polarized optical radiation passes through the linear polarizer, and thus how much circularly-polarized light is produced.

Abstract: Adaptive noise reduction techniques used in devices that pass light from a laser through a quantum medium such as a rubidium vapor cell. A CPT frequency standard that employs the techniques has a first channel in which the laser light passes through the quantum medium and to a photodetector to produce a first signal and a second channel in which the light passes to a second photodetector without passing through the quantum medium to produce a second signal. The first and second signals are processed in a signal processor to produce an enhanced output signal in which the noise has been reduced. The signal processor implements noise predictor and noise remover. In a preferred embodiment, the noise predictor employs a FIR filter in which the coefficients are set in response to feedback from the enhanced output signal.

Abstract: An atomic frequency standard based on coherent microwave emission from an ensemble of hydrogen or alkali metal atoms at their ground state hyperfine frequency. Hydrogen or alkali metal atoms are prepared in a coherent state by means of a radiation field resonant with the atoms at their hyperfine frequency prior to their entering into the emission region. The coherent microwave radiation emission results from the phenomenon of stimulated emission of radiation in a storage bulb placed in a cavity tuned to the hyperfine frequency. Because the atoms enter the cavity already prepared in a coherent state, radiation is emitted without threshold regarding the atomic flux or the cavity quality factor. The atoms emit their energy at their natural frequency perturbed only slightly by secondary effects such as spin exchange collisions, wall collisions and second order cavity pulling.

Abstract: An improved optically pumped atomic frequency standard in which excitation light intensity entering the resonance cell is controlled and maintained independently of the optical pump.