Micro-channel plate (MCP) detectors are used to detect photons, electrons or charged particles. But how can MCPs be used to detect neutral particles? In ion traps, the neutral molecules (after being irradiating with a laser, the ions fragment or lose electrons to produce neutral molecules or fragments) are detected with MCPs. I didn't understand the principle of how MCPs work for neutrals! Can anyone please explain this?
To produce secondary electrons in an MCP detector, a particle has to hit it with very high energy. Charged species are accelerated towards MCP through high difference in electric potential (like 5 kV) and when they hit the surface, they produce a cloud of plasma that includes other electrons that follow the amplification cascade.
You cannot accelerate neutral particle in this way, but if the particle is moving very fast already, it will also produce a cloud of plasma when it hits the surface, ejecting secondary electrons. In the paper that you cite, negatively charged clusters were accelerated to 4 keV and then they lost an electron through photodetachment.