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Final Report

An investigation of the technical feasibility of using pulsed optical pumping to eliminate the light shift and improve the longterm stability of passive rubidium frequency standards

Thomas C. English, E. Jechart, T. M. Kwon

Published Aug 31, 1978• 0 citations
OpenAlex

Abstract

A pulsed optical pumping rubidium frequency standard has been constructed for the purpose of eliminating the light shift and investigation the long-term frequency stability in the absence of light shifts. The device used employs a very small physics package that occupies a total volume of only 260 cc. Initial measurements of the light shift for this device showed that the light shift was reduced by about an order of magnitude: to approximately -1.5 times 10 to the -10th power fractional frequency shift for a 30$ reduction in light intensity. Under these conditions, the square root of the Allan variance was determined to be of the order of parts in 10 to the 12th power for averaging times of 24 hrs and 48 hrs.

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Device of pulse optical pumping and pulse sampling optical detection is presentedto reduce the light shift in Rb87 atomic frequency standard. The 0-0 transitionlineshape and light shift is calculated. It is qualitatively, inagreement with the experimen-tal results. With this device, one may expect to improve the long term frequency sta-bility of the passive Rb87 atomic frequeney standard.

Acta Physica Sinica•Jan 1, 1981•0 citations

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We have realized and studied a rubidium atomic frequency standard based on a paraffin-coated cell, exhibiting a short-term frequency stability <3 × 10−12 τ−1/2 between τ = 1 and 100 s. Characterization of the wall-coating is performed by measuring the T1 and T2 relaxation times. Perturbations of the medium- to long-term clock stability, due to variations in the laser-intensity, laser frequency, the microwave power shift, and the shifts due to temperature variations are measured and analyzed. A method for reducing the intensity light-shift by detuning the laser frequency and the resulting improvement in clock stability is demonstrated. This work is of relevance for further improvements on Rb cell standards using anti-relaxation wall-coating technology.

Journal of Applied Physics•Jun 15, 2012•37 citations
A pulsed optical pumping rubidium frequency standard has been constructed for the purpose of eliminating the light shift and investigation the long-term frequency stability in the absence of light shifts. The device used employs a very small physics package that occupies a total volume of only 260 cc. Initial measurements of the light shift for this device showed that the light shift was reduced by about an order of magnitude: to approximately -1.5 times 10 to the -10th power fractional frequency shift for a 30$ reduction in light intensity. Under these conditions, the square root of the Allan variance was determined to be of the order of parts in 10 to the 12th power for averaging times of 24 hrs and 48 hrs.
The paper describes work done on the Passive Rubidium Frequency Standard in order to identify and possibly improve its frequency stability in the short and long term region. In relation to the short term region, experiments are described which permit the identification of the major sources of noise and measurements are reported. A theoretical model is developed and conclusions are drawn relative to the optimization of the various parameters. In relation to the long term region, earlier work has shown that the power shift created by inhomogeneous broadening in the presence of a buffer gas and light shift could be a cause of instabilities. To avoid that effect we have started experiments on a wall coated cell without buffer gas and we report results on the wall shift and its temperature dependence. Although that type of cell avoids the power shift, it is observed that the temperature dependence of the wall shift is relatively large. These results are discussed in terms of earlier data obtained on rubidium masers.
It is experimentally demonstrated that, using diode lasers for optical pumping and RF /spl pi/-pulses for population transfer, nearly all of the ground state Rb atoms in a vapor cell can be concentrated into one of the two M/sub F/ = 0 sublevels. The fractional population difference /spl Delta/ between the two M/sub F/ = 0 levels can be made as high as 1. This should result in a very significant improvement (about a factor of 100) in the S/N over the conventional discharge-lamp-pumped rubidium frequency standards (RFSs). This would lead to a substantial improvement in the short-term stability of the RFS. This is a pulsed population transfer scheme. The microwave interrogation takes place in the absence of strong pumping light. This has the potential for eliminating the light shift and thereby improving the long-term frequency stability of a an RFS.>
The /sup 87/Rb cell frequency standard, optically pumped by a laser diode, is of great interest in the development of high short-term stability oscillators. We report experiments performed on a rubidium cell prototype aiming at evaluate the transfer of the laser noise to the hyperfine clock transition via the light shift effect, which appears to be the main contribution to the observed short term frequency stability in this kind of standard. Pulsed optical pumping will also be examined in order to strongly reduce the light shift effect and to achieve the theoretical limit never approached up to now despite the strong detected microwave signals.
We have realized and studied a rubidium atomic frequency standard based on a paraffin-coated cell, exhibiting a short-term frequency stability <3 × 10−12 τ−1/2 between τ = 1 and 100 s. Characterization of the wall-coating is performed by measuring the T1 and T2 relaxation times. Perturbations of the medium- to long-term clock stability, due to variations in the laser-intensity, laser frequency, the microwave power shift, and the shifts due to temperature variations are measured and analyzed. A method for reducing the intensity light-shift by detuning the laser frequency and the resulting improvement in clock stability is demonstrated. This work is of relevance for further improvements on Rb cell standards using anti-relaxation wall-coating technology.