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: 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 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 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.