Abstract

A laser-Stark spectrumeter is described that uses a Lamb-dip-stabilized CO laser to produce saturation Lamb dips in an external cavity containing a precision Stark cell. Spectra of isolated lines, fitted to a Lorentzian line shape show widths of 600 kHz (FWHM), a factor of 250 below the Doppler width. The key parameters needed to obtain such linewidths are the laser-frequency stability, which is found to be ±10 kHz for periods of 1 h or more, and the homogeneity of the Stark field, which is demonstrated through an analysis of broadening mechanisms to be ±1.7 × 10⁻⁴. Spectra showing resolved hyperfine structure on 13 transitions in the ν₄ and 2ν₂ bands of ¹⁴NH₃ are obtained and analyzed. Measurements of the quadrupole-coupling constant eqQ, accurate to about 1% (40 kHz), are obtained from the analyses. To this accuracy, eqQ is the same in the ground and the ν₄ states. The s2ν₂ state, however, shows sizable changes in eqQ, in agreement with the predictions of Spirko [ Mol. Phys. 38, 1761 ( 1979)].

© 1985 Optical Society of America

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