Abstract: A technique for determining the modulation index of a frequency-modulated laser source from the absorption spectrum that is produced when light from the laser passes through an alkali metal vapor cell. The absorption spectrum contains a primary minimum and a number of satellite minima and the modulation index is determined using ratios of the minima. The technique is used to calibrate the laser source of a CPT frequency standard so that it operates at a desired modulation index. Ways are disclosed of using the technique to calibrate the CPT frequency standard either manually or automatically. The calibration may be done when the CPT frequency standard is built, when the frequency standard is initialized, or during normal operation of the CPT frequency standard.

Abstract: A technique for determining the modulation index of a frequency-modulated laser source from the absorption spectrum that is produced when light from the laser passes through an alkali metal vapor cell. The absorption spectrum contains a primary minimum and a number of satellite minima and the modulation index is determined using ratios of the minima. The technique is used to calibrate the laser source of a CPT frequency standard so that it operates at a desired modulation index. Ways are disclosed of using the technique to calibrate the CPT frequency standard either manually or automatically. The calibration may be done when the CPT frequency standard is built, when the frequency standard is initialized, or during normal operation of the CPT frequency standard.

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 the ground state hyperfine resonance line observed by means of coherent radiation fields creating Coherent Population Trapping (CPT) in an alkali metal atomic ensemble contained in a cell. The radiation fields are created by frequency modulating a laser at a subharmonic of the hyperfine resonance frequency of the alkali atomic ensemble chosen or by using two lasers whose frequency difference is equal to the hyperfine frequency of the alkali atoms. The hyperfine resonance signal is observed either on the fluorescence emitted by the alkali atoms contained in the cell or on the light transmitted through the same cell. This signal is used, through synchronous detection, to lock the frequency of the microwave generator used to modulate the laser (or to maintain the frequency difference between the two lasers), to the hyperfine resonance frequency of the alkali atoms, thereby implementing an atomic frequency standard.

Abstract: An atomic frequency standard is disclosed where optical pumping of the resonance cell is achieved by coherent light and the pumping results in Coherent Population Trapping of the resonant alkali metal atoms. The fabrication of frequency standards of substantially reduced size and weight is permitted by use of solid state laser sources having certain integrated optical modifier elements and a resonance cell of metallic construction.

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.

Abstract: The invention disclosed herein is a cell construction for use in optically activated atomic frequency standards. The cell includes a stiff non-magnetic metallic chamber body having an integral cold weldable tubulation through which the atomic source material may be charged and the tubulation pinched off to seal the chamber. Optically transparent windows for introducing light radiation into the chamber and receiving light signals generated therein are sealed to the chamber.

Abstract: An ion pump is described which includes a vacuum housing, a unique, readily removable and replaceable magnet system which makes it possible to measure leakage current alone and a unique, readily removable and replaceable reactive metal cathode for reacting with gaseous ions impinging thereon for their collection. It also includes a novel tandem sputter shielding arrangement for preventing deposition of sputter products on the anode insulator. Both power supply and current metering means which may be mounted on and directly connected to the ion pump are also described.