Abstract: A great deal of our understanding of condensed matter comes from observing how materials interact with light. In recent years, the development of novel optical probes has opened yet a new route by which to investigate condensed matter systems, allowing to both interrogate interesting materials that are challenging to study by conventional means and also yielding information in complementary parameter regimes. I will focus on two such probes: exciton spectroscopy in 2D semiconductors and sensing with nitrogen-vacancy (NV) centers in diamond. As a concrete demonstration, I will describe (1) how these probes have been utilized to establish the existence of Wigner crystal phases — the solid phase of the interacting electron gas — in 2D transition-metal dichalcogenide (TMD) systems and (2) how they may further elucidate properties of the electron solid and also shed light on the nature of the corresponding liquid-solid transition, where effects such as frustrated magnetism and impurity interactions are expected to result in exotic and fascinating physics. Finally, I will provide some outlook on the promise of these techniques to investigate more general classes of interesting condensed matter systems.