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Spaceborne MEMS atomic clock frequency stabilization system optimization and experimental study

By: frbiz man

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1 Introduction
Coherent population trapping CPT (Coherent Population Trapping) is the interaction of atoms with coherent light produced by a quantum interference. CPT developed a high resolution spectrum of passive CPT atomic frequency standard is small, low power consumption and quick start feature. CPT frequency standard is the only theory can be made of chip-scale atomic frequency standard size, not only in the basic research of great significance, but also in deep space exploration, satellite navigation, aerospace, digital communications, synchronization systems for time and frequency demanding field has a wide range of applications. Since the 90s of the 20th century, the rapid development of laser cooling, greatly promote the cold atomic clock, and the optical clock based on coherent population trapping CPT atomic clock development. Here are a kind of atomic clock onboard MEMS resonator system optimization and experimental study.
2 CPT atomic clock works
2 with frequency 1 and the two laser beams and the two excited state hyperfine levels and composition of A three-level role, when the two laser beams to meet the two-photon resonance conditions, the atomic population trapped in the ground state of the two super- on the fine level. Not absorb photons; when the frequency of one beam of light near the atomic resonance frequency scanning, the light transmission in the atomic medium strength signal rendered as electromagnetically induced transparency, electromagnetically induced transparency signal after processing, can be used as error signal to lock and modulation drive signal the local oscillator signal in order to achieve atomic clock loop. Have high precision and high stability frequency standard, the evaluation indicators: short-term stability and frequency drift. CPT effect is produced by the laser interaction with atoms, and its narrow bandwidth, high laser frequency stability of the proposed requirements. Only when the laser frequency stability to meet the requirements, continue to produce CPT effect, to ensure measurement accuracy of atomic clocks.
3 Frequency Stabilization System Optimization
Usually refers to laser frequency stability when in continuous operation. Within a certain time interval the average frequency v and the time variation of v frequency ratio, that is S = v / v, it is clear that the smaller the variation of v, then S greater, the more that the stability of frequency good. In the engineering, sometimes referred to as the inverse of S stability. Frequency stability can be divided into short-term stability and long-term stability, the former refers to sampling time observing the frequency change within 1 s, and greater than 1 s observation time on average as a long-term stability. Frequency reproducibility is that laser at a different time, place and other conditions, frequency of repetition or reproduction accuracy.
This shows that the frequency stability and replicability are two different concepts. Therefore, a laser frequency stabilization, not only depends on its stability. And it depends on how the frequency reproducibility. As the laser frequency on the environmental temperature, mechanical vibration, extremely sensitive to outside interference, even if strict measures, free-running laser frequency stability and reproducibility can not meet the order of magnitude. Servo system to control the use of electronic laser, when the outside influence to make a specific laser frequency deviation from the reference frequency, by Kam-frequency signal from the electronic servo system to automatically adjust the laser's frequency response to a specific reference frequency in order to achieve stable frequency purpose.

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