Abstract
BackgroundOptical access to a travelling ion packet is required in many ion beam experiments that study ion-photon interactions.MethodsAn 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.ResultsThe 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.ConclusionThe 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.PACS33.15.Ry; 33.80.Eh; 33.80.-b
Highlights
Optical access to a travelling ion packet is required in many ion beam experiments that study ion-photon interactions
The work presented here was inspired by the need to illuminate an outstretched ion packet (~30 cm) in a completely collinear ion beam experiment, in which photoelectrons and photofragments created from a fast moving ion beam are collected in coincidence (PPC) [7]
As part of an effort to expand the present set of experiments towards direct infrared excitation of the parent anionic species prior to the photodetachment step, it has become essential to irradiate the entire outstretched ion packet with the output of a 10 Hz infrared (IR) optical parametric oscillator/optical parametric amplifier (OPO/OPA) laser system before it enters the Electrostatic ion beam trap (EIBT)
Summary
To demonstrate the capabilities of the reflective beam blocker design for coupling a light source with a travelling ion packet, a photodetachment experiment using a beam of NO− molecules was carried out. These experiments exploit the low electron affinity of NO− that allows for efficient photodetachment at wavelengths between 2 – 5 μm. The depletion of the beam caused by photodetachment of the NO− was derived from consecutively measuring the IR on and IR off ion signals (denoted as NIR and N0 respectively) at a given wavelength. RC conceived of the study, participated in design and coordination and helped draft the manuscript.
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