We have investigated, theoretically as well as experimentally, the relative merits and demerits of using three different optical configurations for a compact coherent population trapping (CPT) vapor clock using 87 Rb. These correspond to the following choices of polarizations for the two Raman beams: ∥ lin lin, ( σ σ , ), and push-pull optical pumping (PPOP), applied on the D1 manifold. We have used a multi-level atomic model to study the dependence of the CPT spectrum on axial as well as transverse magnetic fields for these three schemes. Corresponding experimental studies have been performed using a laboratory scale CPT clock employing a two cm long, isotopically pure rubidium cell, loaded with a buffer gas. We observed a CPT contrast close to 20% with a sub-kilohertz linewidth by adopting the PPOP scheme. We discuss the strengths and weaknesses of each of the three optical excitation schemes, and present frequency-stability measurement data for the prototype clock.

Determining light shift in Raman-Ramsey interference is important for the development of atomic frequency standards based on a vapor cell. We have accurately calculated light shift in Raman-Ramsey interference using the densitymatrix equations for a three-level system without invoking the adiabatic approximation. Specifically, phase shifts associated with coherent density-matrix terms are studied as they are relevant to the detection of Raman-Ramsey interference in transmission (or absorption) through the medium. For the single-velocity case, the numerically computed results are compared with the analytical results obtained using the adiabatic approximation. The result shows light shift suppression in conformity with the closed-form analytic solutions. The computational studies have also been extended to investigate Raman-Ramsey interference for a Doppler-broadened vapor medium. Importantly, a velocity-induced frequency shift is found at the fringe center as an additional source of frequency error for a vapor cell Raman clock.

A repeated query technique has been demonstrated as a new interrogation method in pulsed coherent population trapping for producing single-peaked Ramsey interference with high contrast. This technique enhances the contrast of the central Ramsey fringe by nearly 1.5 times and significantly suppresses the side fringes by using more query pulses (>10) in the pulse cycle. Theoretical models have been developed to simulate Ramsey interference and analyze the characteristics of the Ramsey spectrum produced by the repeated query technique. Experiments have also been carried out employing a repeated query technique in a prototype rubidium clock to study its frequency stability performance.

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