New electron-photon coincidence technique using enhanced photon detection probabilities

High detection efficiencies are the crucial parameters for successful coincidence measurements. Typically, photons are excluded from coincidence experiments due to the small solid angle accessible for detection. We present an approach how to drastically enhance the photon detection probabilities using optics assemblies.

Sketch of the basic rotational symmetric mirror system. The rotation axis is indicated by a gray dashed line. Three different possible trajectories of the emitted photons are indicated. All photons following path 1 (blue) are guided onto the active detector surface by a parabolic mirror which also parallelizes the respective trajectories. While photons following path 2 (red) are reflected by the inner spherical mirror, photons following path 3 (violet) are first reflected by the outer spherical mirror and then guided onto the detector by the parabolic mirror.

In general, relaxation processes of matter involve different de-excitation steps, where multiple particles can be emitted. Coincidence detection methods allow the measurement and of multiple particles and their correlation to follow a distinct relaxation path of the system of interest.

In this publication, we show how the coincidence method can be optimized for time-efficient detection if charged particles like electrons as well as photons are detected. Experiments including photon detection typically suffer from poor countrates. This fact often prohibits the coincidence measurement of processes involving photon emission, which will now be accessible with the presented setup. We especially emphasize the optimization of the accessible solid angle for the photon detection using customized optical systems which mainly consist of mirrors to detect photons in the wavelength range from 120 nm to 320 nm.

The presented setups were characterized by measuring electron-photon coincidences after the excitation of noble gases with narrow-bandwidth synchrotron radiation of appropriate exciting-photon energies. The results illustrate the benefits of the usage of such systems to investigate a variety of different deexcitation pathways involving the emission of photons, e.g. in more complex and dilute prototype systems like clusters.

A. Hans et al. Review of Scientific Instruments  90 093104 (2019)

DOI: 10.1063/1.5109104

Andreas Hans  @ AGE – Spectroscopy