  We introduce a novel time-division multiplexing differential saturated
absorption spectroscopy (TDMDSAS) approach, providing superior accuracy and
stability in Doppler-free spectroscopy. By distinguishing probe and reference
fields in the temporal domain, TDMDSAS efficiently suppresses Doppler
broadening and common-mode optical noise. We utilized this technology to
determine the absolute frequency of diverse neutral Yb isotopes across its
$6s^2\ ^{1}S_0\to 6s6p ^{1}P_1$ transitions. Furthermore, the first-ever
observation of in-situ Doppler-free Zeeman sub-level spectra was accomplished,
enabling the determination of magnetic field gradients. We stabilized a UV
diode laser at 399 nm using an error signal derived from the spectral
first-derivative demodulated signal of $^{174}\mathrm{Yb}$. This technique
yielded a frequency stability of up to 15 kHz with a 40 s averaging time and a
standard deviation of around 180 kHz over a half-hour period. Given its low
cost, straightforward, and scalable nature, TDMDSAS holds excellent potential
in metrology and quantum applications.
