Abstract

We demonstrate that optical pumping plays a significant role in determining the noise in certain types of laser-pumped vapor-cell microwave frequency standards by changing the way in which the laser’s FM noise is converted to AM noise by the optical-absorption profile. When this FM–AM conversion is the dominant noise source, the noise spectrum of the transmitted intensity can be dramatically altered by the optical-pumping process. FM noise at Fourier frequencies larger than the optical-pumping time is converted to AM noise differently from noise at lower Fourier frequencies. This effect can modify the optimum design of vapor-cell frequency references and adds an additional FM–AM-related noise source that cannot be eliminated with laser tuning.

© 2001 Optical Society of America

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