  Atomically thin cuprates exhibiting a superconducting phase transition
temperature similar to bulk have recently been realized, although the device
fabrication remains a challenge and limits the potential for many novel studies
and applications. Here we use an optical pump-probe approach to noninvasively
study the unconventional superconductivity in atomically thin
Bi$_2$Sr$_2$Ca$_{0.92}$Y$_{0.08}$Cu$_2$O$_{8+{\delta}}$ (Y-Bi2212). Apart from
finding an optical response due to the superconducting phase transition that is
similar to bulk Y-Bi2212, we observe that the sign and amplitude of the
pump-probe signal in the atomically thin flake vary significantly in different
dielectric environments depending on the nature of the optical excitation. By
exploiting the spatial resolution of the optical probe, we uncover the
exceptional sensitivity of monolayer Y-Bi2212 to the environment. Our results
provide the first optical evidence for the intralayer nature of the
superconducting condensate in Bi2212, and highlight the role of double-sided
encapsulation in preserving superconductivity in atomically thin cuprates.
