Coherent-population-trapping resonances in buffer-gas-filled Cs-vapor cells with push-pull optical pumping

Abstract

We report on a theoretical study and experimental characterization of coherent population trapping (CPT) resonances in buffer gas-filled vapor cells with push-pull optical pumping (PPOP) on Cs D1 line. We point out that the push-pull interaction scheme is identical to the so-called lin⊥lin polarization scheme. Expressions of the relevant dark states, as well as of absorption, are reported. The experimental setup is based on the combination of a distributed feedback (DFB) diode laser, a pigtailed intensity Mach-Zehnder electro-optic modulator (MZ EOM) for optical sidebands generation and a Michelson-like interferometer. A microwave technique to stabilize the transfer function operating point of the MZ EOM is implemented for proper operation. A CPT resonance contrast as high as 78 % is reported in a cm-scale cell for the magnetic-field insensitive clock transition. The impact of the laser intensity on the CPT clock signal key parameters (linewidth -contrastlinewidth/contrast ratio) is reported for three different cells with various dimensions and buffer gas contents. The potential of the PPOP technique for the development of high-performance atomic vapor cell clocks is discussed.

Ramsey spectroscopy of high-contrast CPT resonances with push-pull optical pumping in Cs vapor

“…(1) yields σ y (τ) ≃ 9 × 10 −15 at 1 s averaging time. This value is about one order of magnitude better than shot-noise estimations in the CW regime [19]. In real life, this result will be degraded by various noise mechanisms such as the detector noise, the laser intensity and frequency noise or the oscillator phase noise through Dick effect [25].…”

“…In a recent study, we investigated CPT resonances in Cs vapor cells with PPOP [19]. Resonance contrasts as high as 78 % were demonstrated in continuous regime in cm-scale cells.…”

“…The EOM is driven at 4.596 GHz with a stabilized RF power of 22 dBm by a low noise microwave oscillator to generate first-order optical sidebands frequency-separated by 9.192 GHz. The EOM bias electrode dc voltage V is actively controlled using a microwave synchronous detector technique [19] to the so-called dark point to stabilize the carrier suppression. This carrier suppression is inherently limited by the EOM extinction ratio parameter measured to be 24 dB with our device.…”

Characterization of Cs vapor cell coated with octadecyltrichlorosilane using coherent population trapping spectroscopy

“…The optical carrier is actively rejected with an extinction ratio of 24 dB using the lock-in microwave detection technique described in Ref. 39. At the output of the EOM, light is sent through a Michelson delay-line and polarization orthogonalizer system to produce the so-called push-pull optical pumping interaction scheme.…”

“…As observed in buffer-gas filled Cs vapor cells using push-pull optical pumping technique, the resonance contrast is measured to increase with the laser power while a saturation value is expected to be observed at higher intensities. 39 The short-term relative frequency stability of an atomic clock, in terms of Allan deviation r y (s), is given by…”