  Light-shifts are known to be an important limitation to the mid- and
long-term fractional frequency stability of different types of atomic clocks.
In this article, we demonstrate the experimental implementation of an advanced
anti-light shift interrogation protocol onto a continuous-wave (CW) microcell
atomic clock based on coherent population trapping (CPT). The method, inspired
by the Auto-Balanced Ramsey (ABR) spectroscopy technique demonstrated in pulsed
atomic clocks, consists in the extraction of atomic-based information from two
successive light-shifted clock frequencies obtained at two different laser
power values. Two error signals, computed from the linear combination of
signals acquired along a symmetric sequence, are managed in a dual-loop
configuration to generate a clock frequency free from light-shift. Using this
method, the sensitivity of the clock frequency to both laser power and
microwave power variations can be reduced by more than an order of magnitude
compared to normal operation. In the present experiment, the consideration of
the non-linear light-shift dependence allowed to enhance light-shift
mitigation. The implemented technique allows a clear improvement of the clock
Allan deviation for time scales higher than 1000 s. This method could be
applied in various kinds of atomic clocks such as CPT-based atomic clocks,
double-resonance Rb clocks, or cell-stabilized lasers.
