  This paper describes the Light-Shift Laser-Lock (LSLL) technique, a novel
method intended for compact atomic clocks that greatly simplifies the laser
setup by stabilizing the pumping-laser frequency to the atoms involved in the
clock, without the need of an external reference. By alternating two clock
sequences with different light shifts, the method estimates and cancels out a
controlled amount of induced light shift, acting on the laser frequency. The
LSLL technique is compatible with state-of-the-art 3-level clocks and was
demonstrated with FPGA-based electronics on a pulsed-optically-pumped (POP)
vapor-cell clock developed at INRIM. The results have shown that the LSLL
technique operates robustly, having a capture range of gigahertz without
significantly compromising clock stability. In our tests, the clock exhibited a
white frequency noise of $3.2 \times 10^{-13}$ $\tau^{-1/2}$ for averaging time
up to 4000 s, reaching a floor below $1 \times 10^{-14}$ up to 100 000 s. These
performance levels meet the requirements of future Global Navigation Satellite
Systems (GNSS) on-board clocks, and offer the added benefits of a reduced clock
footprint, as well as increased reliability and robustness.
