Laser-Induced Fluorescence Spectroscopy (LIFS) of Trapped Molecular Ions in Gas-phase

TL;DR

This review discusses Laser-Induced Fluorescence Spectroscopy (LIFS) of trapped gas-phase molecular ions, highlighting experimental challenges, recent advancements in instrumentation, and techniques for improving signal detection in fluorescence measurements.

Contribution

It provides a comprehensive overview of LIFS techniques for gas-phase ions, emphasizing recent improvements in signal-to-noise ratio and spectral characterization methods.

Findings

Integrated high-finesse optical cavities enhance SNR by an order of magnitude.

High numerical aperture optics improve fluorescence collection efficiency.

Recent techniques enable detailed spectral analysis of weak gas-phase fluorophores.

Abstract

This review presents the Laser-Induced Fluorescence Spectroscopy (LIFS) of trapped gas-phase molecular ions. A brief description of the theory and experimental approaches involved in fluorescence spectroscopy, together with state-of-the-art LIFS experiments employing ion traps, is presented. Quadrupole ion traps are commonly used for spatial confinement of ions. One of the main challenges involved in such experiments is poor Signal-to-Noise Ratio (SNR) arising due to weak gas-phase fluorescence emission, high background noise, and small solid angle for the fluorescence collection optics. The experimental approaches based on the integrated high-finesse optical cavities provide a better (typically an order of magnitude more) SNR in the detected fluorescence than the single-pass detection schemes. Another key to improving the SNR is to exploit the maximum solid angle of light collection by choosing high numerical aperture (NA) collection optics. The latter part of the review summarises the current state-of-the-art intrinsic fluorescence measurement techniques employed for gas-phase studies. Also, the scope of these recent advances in LIFS instrumentation for detailed spectral characterisation of a fluorophore of weak gas-phase fluorescence emission is discussed, considering fluorescein as one example.