Investigation of a Cesium Raman Time/Frequency Standard
Final rept. Mar 1986-Jun 1989
MASSACHUSETTS INST OF TECH CAMBRIDGE RESEARCH LAB OF ELECTRONICS
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The objective of this program was to determine the feasibility of developing an improved portable cesium clock using a semiconductor laser excited resonance Raman interaction. Such a clock has the potential to be smaller, lighter, less expensive, and more accurate than conventional cesium clocks because it does not require a microwave cavity or state selection magnets. To demonstrate this, an experimental Raman cesium clock was constructed. To excite the Raman transition in this beam, a semiconductor laser was amplitude modulated at 4.6 GHz half of the 9.2 GHz cesium hyperfine transition frequency so that the two modulation sidebands were tuned to the resonance Raman transition frequency. The observed signal to noise ratio of about 1800 for a 2 second averaging time was detector noise limited, but only a factor of two smaller than the shot noise limit. For a 15 cm interaction zone separation, such as in the experimental Raman clock, this signal to noise ratio corresponds to a fractional frequency stability of 6xlO-12 for a 100 second averaging time. This compares favorably with commercial cesium clocks. Once detector noise is eliminated, the shot noise limited fractional stability would be 2.7xl0-12 for 100 sec..
- Test Facilities, Equipment and Methods
- Atomic and Molecular Physics and Spectroscopy