Quantum interference can play an important role in laser spectroscopy of unresolved transitions. This has been observed at NIST in studying comb-based measurements of the D lines in the spectra of stable lithium isotopes. Improved resolution and accuracy of this comb-based measurement has helped to resolve the long-standing discrepancies that hampered stringent tests of few-electron atomic theory.
(a) Can. J. Phys. 89:59-62 (2011): DOI:10.1139/P10-096