HYPERFINE-RESOLVED SATURATION SPECTROSCOPY OF METASTABLE N$_2$ IN THE (1-0) BAND OF THE $\tilde{B}^3\Pi_g-\tilde{A}^3\Sigma^+_u$ ELECTRONIC TRANSITION

Abstract

A spectrometer for measuring sub-Doppler saturation spectra in a discharge flow cell has been built and tested on the (1-0) band of the $\tilde{B}^3\Pi_g-\tilde{A}^3\Sigma^+_u$ electronic transition of $^{14}$N$_2$ near 11250 cm$^{-1}$. A cw Ti:sapphire laser is stabilized relative to a single frequency HeNe laser and offset scanned with a RF synthesizer. An amplitude-modulated bleach beam is counter-propagated with a phase-modulated probe beam through the discharge cell. Absorption and dispersion phase signals are demodulated in a probe beam receiver, then demodulated at the lower bleach modulation frequency and finally averaged with lock-in detection at the audio frequency of the AC-discharge. Isolated hyperfine lines are observed with a FWHM of about 7 MHz and the splittings can be recorded with a precision of a few hundred kHz. Comparisons will be made with more extensive prior work by Giesen et al.