= Exciton absorption experiment in copper(I) oxide
In <Giant Rydberg Excitons in Cuprous Oxide by Tomasz Kazimierczuk and others>, a polished $34\,\mathrm{\mu m}$ <copper(I) oxide> crystal was mounted without strain at $1.2\,\mathrm K$. A tunable single-frequency dye <laser> scanned <photon> <energy>; balanced detection compared transmitted light with a reference beam. Transmission dips resolved <spectral lines> assigned to bound <excitons> through <principal quantum number> $n=25$. Their convergence towards an unbound threshold supports a hydrogen-like internal series, with small systematic deviations.<Giant Rydberg Excitons in Cuprous Oxide by Tomasz Kazimierczuk and others>[pp. 3–5, figures 1–2; supplement, Experimental setup, pp. 3–5 and figure S2]{ref}
Controls mattered: restricting broadband illumination improved resolution of high-$n$ <excitons>; lowering <laser> power or expanding its spot reduced interaction-induced suppression. Balanced detection suppressed source fluctuations. The measurement probes optical resonances, not individual <Electron>-<electron hole> trajectories or directly imaged radii. <Electric-dipole selection rules> favor P-envelope states in this material, unlike the hypothetical permitted lowest-state transition above. Finite resolution and crystal inhomogeneity affect <spectral lines>; the inferred binding series requires a continuum threshold and a model.<Giant Rydberg Excitons in Cuprous Oxide by Tomasz Kazimierczuk and others>[pp. 3–5; supplement pp. 2–4 and 6–7, figure S3: selection rules, illumination tests, line corrections and deviations]{ref}
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