High-contrast coherent population trapping based on crossed polarizers method

Abstract

A method based on crossed polarizers to observe high-contrast coherent population trapping (CPT) resonance has been developed. Because crossed polarizers have a simple optical system, our method is suitable for chip-scale atomic clocks (CSACs). In CPT, the Faraday rotation in a linearly polarized light field (lin||lin) was calculated using two pairs of Λ-system models; the spectrum of the Faraday rotation is also estimated. After measuring the contrast and linewidth with the crossed-polarizer method, a comparison of the theoretical model and experimental data showed they were in good agreement. Moreover, the experimental results showed that a high contrast (88.4%) and narrow linewidth (1.15 kHz) resonance could be observed using a Cs gas cell and D1-line verticalcavity surface-emitting laser (VCSEL).

Ramsey-coherent population trapping Cs atomic clock based on lin∥lin optical pumping with dispersion detection*

“…Theoretically, the lin lin scheme shows more advantages for miniaturization when compared with the well-developed lin⊥lin scheme because the two interacting, parallel-polarized, and coherent frequency laser beams can be generated easily via an electro-optical modulator (EOM). However, the lin lin scheme provides a way to implement dispersion detection, which further improves the contrast, [13][14][15] whereas the lin⊥lin scheme usually requires the use of two phase-locked lasers or a Michelson interferometer to generate the perpendicular polarized laser beams. We have been developing a Cs atomic clock based on lin lin Ramsey-CPT in our laboratory over the last two years.…”

“…We have been developing a Cs atomic clock based on lin lin Ramsey-CPT in our laboratory over the last two years. [13,16] In this paper, we report the performance achieved by this lin lin Ramsey-CPT atomic clock and describe our in-depth investigation of the current limitations of this clock.…”

Feedback-controlled and digitally processed coherent population trapping resonance conversion in87Rb vapour to high-contrast resonant peak

“…In conventional configurations for excitation of a CPT resonance [5], the resonance contrast defined as the ratio of CPT resonance amplitude to the background is low and ranges from a fraction of a per cent [6] to several per cent [7][8][9]. Various methods were proposed that allow CPT resonance contrast to reach tens [10][11][12][13][14][15] and hundreds per cent [16][17][18]. However, all these methods are either only applicable in special cases or relatively complicated in technical implementation.…”

“…Yudin et al [16] have reported 260% contrast in feedback-spectroscopy method where rubidium atomic fluorescence was measured when scanning the frequency difference of a bichromatic pumping field around the ground-state hyperfine-splitting frequency of 87 Rb, while a feedback loop was used to adjust the pumping radiation intensity in order to maintain a constant level of atomic vapour fluorescence. Contrast exceeding 760% was achieved through the crossed polarisers method [17]. Unfortunately, though, this method relies on resonant Faraday rotation at CPT resonance, and significant contrast enhancement is only possible if the optical cell is placed within a relatively strong and highly stable stationary magnetic field in order to ensure a stable CPT resonance amplitude.…”

Characterization of frequency stability in electromagnetically induced transparency-based atomic clocks using a differential detection scheme

“…Traditionally, this method determines the frequency between hyperfine states of an alkali metal atom via the change in transmitted intensity of a bichromatic optical field. However, recently it has been proposed that a modified detection scheme sensitive to the changes in the light polarization due to magneto-optical rotation (MOR) may increase the performance of such frequency measurements [1,9,10]. In this paper, we experimentally compare two detection schemes (traditional intensity-based EIT and polarization-rotation-sensitive MOR).…”