Absolute ion detection efficiencies of microchannel plates and funnel microchannel plates for multi-coincidence detection.

K Fehre,J Stohner,T Jahnke,M Kunitski,D Trojanowskaja,J Gatzke,L Ph H Schmidt,S Zeller,A Czasch,R Dörner,M S Schöffler,O Jagutzki,R Berger,F Trinter

doi:10.1063/1.5022564

Abstract

Modern momentum imaging techniques allow for the investigation of complex molecules in the gas phase by detection of several fragment ions in coincidence. For these studies, it is of great importance that the single-particle detection efficiency ε is as high as possible, as the overall efficiency scales with εn, i.e., the power of the number of detected particles. Here we present measured absolute detection efficiencies for protons of several micro-channel plates (MCPs), including efficiency enhanced "funnel MCPs." Furthermore, the relative detection efficiency for two-, three-, four-, and five-body fragmentation of CHBrClF has been examined. The "funnel" MCPs exhibit an efficiency of approximately 90%, gaining a factor of 24 (as compared to "normal" MCPs) in the case of a five-fold ion coincidence detection.

Highlights

The standard approach to determine the micro-channel plates (MCPs) efficiency is by comparing two detection schemes,9–14 as for example, to measured ion currents in a Faraday cup and the MCP count rate
A method similar to the one in Ref. 15 has been employed in order to achieve this: By measuring the ratio of two contributions which occur intrinsically in the reaction examined by the MCP detector, its efficiency can be deduced without need for an external reference measurement
In order to demonstrate the importance of a high detection efficiency in multicoincident measurements, we compare an efficiency-enhanced “funnel” MCP to a “standard” MCP under identical conditions in an experiment in which we multiply ionize CHBrClF

Summary

INTRODUCTION

The standard approach to determine the MCP efficiency is by comparing two detection schemes, as for example, to measured ion currents in a Faraday cup and the MCP count rate. A method similar to the one in Ref. 15 has been employed in order to achieve this: By measuring the ratio of two contributions which occur intrinsically in the reaction examined by the MCP detector, its efficiency can be deduced without need for an external reference measurement. To this end, the double electron capture from H2 into a fast doubly charged argon projectile (20 keV/u Ar2+ + H2 → Ar0 + H+ + H+) was utilized to create a pair of protons. 86.0 ± 1.2 67.5 ± 3.0 55.6 ± 4.6 employing a strong femtosecond-laser resulting in up to five ionic fragments to be detected

DETERMINING THE ABSOLUTE MCP DETECTION EFFICIENCY FOR PROTONS

Findings

CONCLUSION