Analysis of the frequency shift in coherent population trapping resonance’s dynamic continuous-wave spectroscopy at the phase-jump modulation and its comparison with the conventional approach

We present the research of dynamic continuous-wave spectroscopy of the coherent population trapping resonance at phase-jump modulation. Λ system of levels supplemented by a nonabsorbing state and bichromatic optical field, whose spectral components have different intensities, are considered. We demonstrate that the asymmetry leads to an additional nonlinear shift of the error-signal frequency under anisotropic relaxation of the ground-state density-matrix elements. In the opposite case, the resonant light shift of the coherent population trapping resonance frequency is compensated by the one due to asymmetry. We also investigate the conventional approach where the frequency difference of the optical field components is harmonically modulated to obtain the error signal. Comparison demonstrates that in the high-frequency modulation regime, the corresponding frequency shift is more linear than at the phase-jump modulation for nonshort integration times.