  In this paper, we examined the effects of proximity-induced interactions such
as Rashba spin-orbit coupling (SOC) and effective Zeeman fields (EZFs) on the
optical spectrum of $n$-type and $p$-type monolayer (ML)-MoS$_2$. The optical
conductivity is evaluated using the standard Kubo formula under Random phase
approximation (RPA) with including the effective electron-electron interaction.
It has been found that there exists two absorption peaks in $n$-type
ML-MoS$_{2}$ and two knife shaped absorptions in $p$-type ML-MoS$_{2}$ which
are contributed by the inter-subband spin flip electronic transitions within
conduction and valence bands at valleys $K$ and $K'$ with a lifted valley
degeneracy. The optical absorptions in $n$-type and $p$-type ML-MoS$_{2}$ occur
in THz and infrared radiation regimes and the position, height, and shape of
them can be effectively tuned by Rashba parameter, EZFs parameters, and carrier
density. The interesting theoretical predictions in this study would be helpful
for the experimental observation of the optical absorption in infrared to THz
bandwidths contributed by inter-subband spin flip electronic transitions in a
lifted valley degeneracy monolayer transition metal dichalcogenides (ML-TMDs)
system. The obtained results indicate that ML-MoS$_{2}$ with the platform of
proximity interactions make it a promising infrared and THz material for optics
and optoelectronics.
