Laser-based continuous-wave excitonic Lyman spectroscopy in Cu₂O

We developed continuous-wave, laser-based excitonic Lyman spectroscopy for sensitive and wide dynamic range detection of 1s paraexcitons in Cu₂O. A single-line tunable carbon dioxide laser was used as a probe light source. The minimum detectable induced transmission change was of the order of 10⁻⁵, allowing us to accurately measure the induced absorption spectra of paraexcitons in thermal equilibrium with the lattice in a low-density limit. Using this spectroscopy technique, we measured important basic parameters, such as the effective mass and lifetime of paraexcitons, that are crucial for discussing the possibility of reaching a Bose-Einstein condensation state with this elementary excitation in a solid.