  LaAgSb$_{2}$ is a rare material, which offers the opportunity to investigate
the complex interplay between charge density wave (CDW) ordering and topology
protected electronic band structure. As both of these phenomena are governed by
the structural symmetries, a comprehensive study of the lattice dynamics is
highly desirable. In this report, we present the results of temperature and
pressure dependent Raman spectroscopy and x-ray diffraction in single
crystalline LaAgSb$_{2}$. Our results confirm that Raman spectroscopy is a
highly sensitive tool to probe CDW ordering phenomenon, particularly the
low-temperature second CDW transition in LaAgSb$_{2}$, which appears as a very
weak anomaly in most experiments. The crystal orientation-dependent
measurements provide the evolution of Raman modes with crystallographic
symmetries and can be further studied through group symmetry analysis. The
low-temperature x-ray diffraction data show the emergence of structural
modulations corresponding to the CDW instability. The combined high-pressure
Raman spectroscopy and synchrotron x-ray diffraction reveal multiple structural
phase transitions through lowering of crystalline symmetries, which are also
expected to lead to electronic topological transitions.
