  Atomically thin two-dimensional (2D) semiconductors are extensively
investigated for opto-electronic applications that require strong light-matter
interactions. In view of such applications, it is essential to understand how
(photo)excitation alters the non-linear optical response of these materials
under high carrier density conditions. Broadband transient absorption (TA)
spectroscopy is by now a widely used tool to study semiconductor physics in
such highly excited systems. However, the complex interplay between different
many-body interactions in 2D materials produces highly congested spectral
information and an ensuing non-trivial nonlinear photo-response, thereby
masking the desired intrinsic photophysics. Herein, we outline a concise
roadmap for analyzing such congested datasets based on examples of TA analysis
of various 2D materials. In particular, we emphasize the synergy between an
initial qualitative understanding of the transient photo-response based on line
shapes and their derivatives, and a consequent quantitative spectral
deconvolution backed by such insights.
