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Simulation Code for the paper "The effect of the electric trapping field on state-selective loading of molecules into rf ion traps"

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posted on 10.11.2020, 14:57 by Laura Blackburn, Matthias Keller
Simulation code for paper published in Scientific Reports [28/10/2020]

See reference below for other datasets for this publication.

These files should enable the user to reproduce simulations in the paper.

This code can also be adapted to explore the effects of varying trap, laser and molecular beam parameters on the achievable state-selectivity of ionisation inside an rf ion trap.

The Matlab (.m) files contain the simulation code for calculating the ionisation-probability-weighted distribution of ionisation thresholds in an ion trap. The four files included each consider a different case:

(1) Axially_applied_electric_field_molecular_beam.m
This file considers the special case of only a dc voltage applied to the axial electrodes of a linear Paul trap. The molecules are ionised from a molecular beam.

(2) Axially_applied_electric_field_background_gas.m
This file considers the special case of only a dc voltage applied to the axial electrodes of a linear Paul trap. The molecules are ionised from a homogeneous background gas.

(3) Radially_applied_electric_field.m
This file considers the special case of only a rf voltage applied to the radial electrodes of a linear Paul trap.

(4) Axially_and_radially_applied_fields_molecular_beam.m
This file considers the general case of both a dc voltage applied to the axial electrodes and a rf voltage applied to the radial electrodes of a linear Paul trap. The molecules are ionised from a molecular beam.

Abstract:
Trapped molecular ions in pure rovibronic states are desirable in experiments ranging from cold chemistry to searches for physics beyond the Standard Model. Resonance-enhanced multiphoton ionisation (REMPI) can be used to prepare molecular ions in specific internal states with high fidelities. However, in the presence of electric fields, ionisation spectra exhibit frequency shifts and the ionisation thresholds are broadened. For this reason, REMPI studies are normally conducted in low and highly homogeneous electric fields, whereas the operating principle of rf ion traps requires electric fields that vary in space and time. In order to investigate the impact of this on the state-selectivity of REMPI in ion traps, we have simulated the expected broadening of the ionisation threshold under various operating conditions of a typical linear Paul trap. In many cases, the width of the ionisation threshold exceeds the separation between rotational energy levels, preventing state-selective ionisation. Careful choice of the trapping and laser parameters during loading can reduce this broadening, enabling state-selective ionisation in some instances. Where this strategy is not sufficient, the broadening can be reduced further by rapidly switching the trapping voltages off and on again during loading. This has been demonstrated experimentally for a Coulomb crystal of 40Ca+ ions without descrystallising it.

Funding

Low temperature Ion - Radical Collisions

Engineering and Physical Sciences Research Council

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