PRECISION LASER SPECTROSCOPY OF H$_3^+$

Abstract

The high-resolution sub-Doppler Lamb dips of the $\nu_2$ fundamental band transitions of H$_3^+$ have been observed using an extended negative glow discharge tube as an ion source and a periodically poled lithium niobate optical parametric oscillator as a radiation source.,{~\bf 109},~263002~(2012)} The absolute frequencies of five transitions were measured to an accuracy of 250 kHz using a fiber optical frequency comb. In addition, we measured the homogeneous linewidths of these lines. Physical significance of these results will be discussed in terms of collisional processes.