Photoionizaton of Pure and Doped Helium Nanodroplets

TL;DR

This review discusses recent advances in photoionization spectroscopy of pure and doped helium nanodroplets, highlighting new experimental techniques and insights into their quantum and relaxation properties.

Contribution

It provides a comprehensive overview of recent experimental progress in photoionization studies of helium nanodroplets, including time-resolved spectroscopy and high-energy radiation sources.

Findings

Photoionization reveals detailed relaxation dynamics of helium nanodroplets.

High laser fields enable formation of highly ionized nanoscale matter.

Recent techniques improve understanding of quantum properties and excitation processes.

Abstract

Helium nanodroplets, commonly regarded as the "nearly ideal spectroscopic matrix", are being actively studied for more than two decades now. While they mostly serve as cold, weakly perturbing and transparent medium for high-resolution spectroscopy of embedded molecules, their intrinsic quantum properties such as microscopic superfluidity still are subject-matter of current research. This article reviews recent work on pure and doped He nanodroplets using PI spectroscopy, an approach which has greatly advanced in the past years. While the notion of the ideal spectroscopic matrix mostly no longer holds in this context, photoionization techniques provide detailed insights into the photo-physical properties of pure and doped He nanodroplets and their relaxation dynamics following electronic excitation. Exploiting nowadays available high laser fields, even highly ionized states of matter on the nanoscale can be formed. Our particular focus lies on recent experimental progress including fs time-resolved spectroscopy, photoion and electron imaging, and novel sources of highly energetic radiation.