  We report ultrafast reflectivity measurements of the dynamics of the order
parameter of the charge density wave (CDW) in TbTe$_3$ under anisotropic
strain. We observe an increase in the frequency of the amplitude mode with
increasing tensile strain along the $a$-axis (which drives the lattice into
$a>c$, with $a$ and $c$ the lattice constants), and similar behavior for
tensile strain along $c$ ($c>a$). This suggests that both strains stabilize the
corresponding CDW order and further support the near equivalence of the CDW
phases oriented in $a$- and $c$-axis, in spite of the orthorhombic space group.
The results were analyzed within the time-dependent Ginzburg-Landau framework,
which agrees well with the reflectivity dynamics.
