Theoretical and experimental investigation of the light shift in Ramsey coherent population trapping

Abstract

The ac Stark shift (or light shift) of the 6 2 S 1/2 (F = 3 ↔ 4) transition in 133 Cs, as observed through coherent population trapping under pulsed excitation, is measured using a 133 Cs gas cell and the D 1 -line vertical-cavity surface-emitting laser. This light shift can be calculated using density-matrix analysis. We derive an expression for this shift as a function of light intensity, showing that it varies linearly with respect to light intensity only with intensities higher than 1.0 mW/cm 2 . For pulsed excitation of high laser intensity, the variation in light shift is 20 times lower than that when using a continuous wave. The differences between the results of theory and experiment are discussed, taking into account the difference in conditions assumed; the results from theoretical analysis, taking the attenuation of the first-order sideband into account, approximately agree with the experimental results. The light shift is reduced by shortening the observation times. * Electronic address: yano-yuichiro@ed.tmu.ac.jp

Low-Drift Coherent Population Trapping Clock Based on Laser-Cooled Atoms and High-Coherence Excitation Fields

“…Ramsey spectroscopy [22] has been used to study CPT resonances in many prior studies [10,16,19,[23][24][25][26][27][28][29][30][31][32]. Resonant light shifts have been shown theoretically [18,19] to scale inversely with the Ramsey period, in agreement with recent cold-atom CPT experiments [21].…”

A high-performance Raman-Ramsey Cs vapor cell atomic clock

“…This degradation is generally caused by laser intensity and frequency light-shift effects, cell temperature or pressure effects. In general, light shift is recognized as a major cause and is being studied with significant interest [35][36][37][38][39][40][41][42][43][44] for improvement of atomic frequency standards. As reported in previous literature [23,24], the pulsed interaction presents the advantage to reduce significantly the sensitivity of the clock frequency to laser intensity variations.…”

Two-step pulse observation to improve resonance contrast for coherent population trapping atomic clock

“…The Raman-Ramsey (RR) scheme for enhancing the frequency stability of CPT atomic clocks has been investigated by a number of researchers [3,4,5,6,7]. This scheme simultaneously reduces line broadening and the light shift [6,7,8].…”

“…This scheme simultaneously reduces line broadening and the light shift [6,7,8]. Recently, a short-term stability of 3.2×10 −13 τ −1/2 has been obtained, and stability as low as 3×10 −14 has been achieved at an averaging time of 200 s using a Cs vapor cell with the RR scheme [9].…”

“…In our previous paper, we investigated the light shift in the RR scheme both theoretically and experimentally with the aim of enhancing the long-term frequency stability of CPT atomic clocks [7]. The results showed that the light shift in the RR scheme is lower than that under cw illumination.…”