Abstract

The hyperfine structures of the P(57)45-0, P(91)48-0, and R(73)46-0 lines of molecular iodine (${}^{127}{{\rm I}_2}$) at 514 nm were studied using third-harmonic generation of a 1542 nm external-cavity diode laser and Doppler-free spectroscopy. The frequencies of the 1542 nm diode laser locked to the hyperfine transitions of these iodine lines are close to those of the P(16) transition in the ${\nu _1} + {\nu _3}$ band of acetylene (${}^{13}{{\rm C}_2}{{\rm H}_2}$), which is used as a wavelength standard for telecom applications. The absolute frequencies of the observed 59 iodine hyperfine transitions were determined with an uncertainty of 5.4 kHz (fractional uncertainty of ${9.3} \times {{10}^{- 12}}$). Highly accurate hyperfine constants were obtained through fitting of the measured hyperfine splittings to a four-term Hamiltonian that includes electric quadrupole, spin–rotation, tensor spin–spin, and scalar spin–spin interactions with an uncertainty of a few kHz. The observed hyperfine transitions provide wavelength standards for telecom applications with various optical frequencies and reduced uncertainties compared with the acetylene wavelength standard.

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