Knowledge Bank

The cavity ring-down technique has recently been developed in our laboratory for the study of pulsed molecular beams. In the ring-down approach, molecular absorption is deconvoluted from the measured decay time of a high finesse optical resonator which is tailored to overlap a molecular beam in both space and time. The approach is inherently insensitive to laser output power fluctuations and allows molecular beams to be probed with 100% duty cycle. Initial studies performed in our laboratory focused on the electronic spectra of transition metal and carbon clusters. In several of these species we have achieved rotational resolution employing a pulsed dye laser of .$04cm-1$ bandwidth and have exhibited sensitivities on the order of parts per million (fractional absorption). In the copper trimer system we have measured states previously unobserved by either R2PI or LIF techniques. In addition to the transition metal systems we have obtained rotationally resolved spectra of small carbon cluster. Currently, we are working on obtaining the electronic spectra of small silicon clusters, focusing on $Si3$. We have demonstrated that the cavity ring-down technique is ideally suited to the study of pulsed molecular beams, especially in the case of systems which are difficult to probe with techniques which can suffer from rapid molecular internal conversion or predissociation.