Lomsadze, BachanaFehrenbach, Charles W.DePaola, Brett D.2013-05-062013-05-062013-05-06http://hdl.handle.net/2097/15745Direct frequency comb spectroscopy is currently one of the most precise techniques for studying the internal structure of atomic and molecular systems. In this technique, a train of ultrafast laser pulses excites states in the target system which then relax, emitting fluorescence. The measured fluorescence is then plotted as a function of the comb parameters. But according to recent theory, the ultrashort pulses from the comb laser can also significantly ionize the target. Here, we test this theory by measuring the ion signal from direct frequency comb spectroscopy. Furthermore, instead of actively controlling the frequency comb parameters, we allow them to drift passively, measuring them and the ion signal simultaneously. The experiments were found to be in satisfactory agreement with theory, and the passive comb approach was found to be functional, though not as convenient as the conventional actively locked comb.en-USThis Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).Direct frequency comb spectroscopyAtomic and molecular systemsArticle (publisher version)