Direct IR excitation in a fast ion beam: application to NO- photodetachment cross sections

Abstract

Abstract Background: Optical access to a travelling ion packet is required in many ion beam experiments that study ion-photon interactions. Methods: An approach is described for carrying out direct infrared excitation of a fast ion beam that uses an optical-quality reflective beam blocker to illuminate a counter propagating pulsed ion beam in a collinear configuration. This arrangement provides optical access along the axis of ion beam propagation by placing a mirror in the beam path at a 25 degree angle. The ion packet is bumped over the mirror, which is also used to block fast neutral particles produced during ion beam acceleration that also propagate along the beam path. Results: The efficiency of this setup is demonstrated in a photodetachment experiment on NO− anions, where a photoinduced depletion of up to 90% of the beam is achieved in a single laser shot. To demonstrate the application of this configuration, the relative photodetachment cross section for NO− has been measured in the range of 2800 – 7200 cm-1. The measured relative cross section shows a set of sharp peaks that are identified as vibrational autodetachment resonances. Conclusion: The new setup paves the way for future experiments where parent anionic species are vibrationally excited via direct infrared excitation first and undergo photodetachment/photodissociation in a subsequent step.