Abstract
In high-resolution molecular spectroscopy, precise measurements of the optical frequency are crucial to
evaluate minute shifts and splittings of the energy levels. In this study, we developed a frequency
measurement system of cw lasers scanning the wide range employing an optical frequency comb. We
demonstrated the frequency measurement of a scanning dye laser, and analyzed the spectral
characteristics during the laser scan. The developed system was applied to Doppler-free two-photon
absorption spectroscopy of S1
1B1u(v4 = 1)←S0
1Ag(v = 0) transition of naphthalene. We obtained wellresolved
rovibronic spectra with the linewidth of 2.48 MHz, and determined absolute frequencies with
the uncertainty of several tens of kHz. For the Q(K)Q(J) transitions, the rotational lines were assigned, and
molecular constants in the excited state were determined.
