Characterization of Quantum-Enhanced Photon Sources in Plasma Spectroscopy

Quantum-enhanced light sources, such as spontaneous parametric down-conversion (SPDC) and squeezed light, offer improved two- and multi-photon absorption capabilities. In particular, SPDC-generated light supports entangled two-photon absorption (ETPA) that scales linearly with pump power, in contrast to the quadratic scaling observed with classical fields. We investigate the feasibility of ETPA for impurity detection in a helicon plasma using singly-ionized argon (Ar+). Using spectral line data and collisional-radiative modeling, we identify viable ETPA transitions and calculate associated cross sections, transition rates, and absorbed powers. For a non-degenerate ETPA case with near-resonant intermediate states, we obtain a peak absorbed power of 0.6 nW/cm along the beam path. These values suggest the potential for ETPA-based fluorescence detection in low-flux environments. We conclude by outlining a proposed experimental demonstration in an Ar+ helicon device and present preliminary results from our entangled photon source characterization.