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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?

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It is generally the case that neutral particles are detected by observing the results of further physics (decays, captures, inelastic scattering events and so on). Because I don't know anything about the experiments you are describing I won't venture an opinion as to exactly what is going on, but MCPs are often sensitive to optical band photons, so the decay of excited molecular states is one possible guess. –  dmckee Apr 24 '13 at 16:07
    
It is not by the decay of excited molecular states. As and example you can see in this article O.Aviv et..al. PHYSICAL REVIEW A 83, 023201 (2011) [link: pra.aps.org/pdf/PRA/v83/i2/e023201], that the MCP#3 is used to record the neutral fragments. So, I think, if it hits with sufficiently high energy the the channels in the MCP can emit electrons thereby detecting the neutrals. –  albedo Sep 24 '13 at 8:38
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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.

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Lot of articles says the use of MCP to detect neutrals. Just as an example:O.Aviv et..al. PHYSICAL REVIEW A 83, 023201 (2011) [link: pra.aps.org/pdf/PRA/v83/i2/e023201]. In this article the MCP#3 is used to record the neutral fragments! –  albedo Sep 24 '13 at 8:33
    
@albedo: in the paper, Al clusters are accelerated to 4.2 keV, this is why it works. I will clarify my answer. –  gigacyan Oct 15 '13 at 15:12
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