Patent Number: 
Section: claims

1. A method comprising:arranging a detector and an optical component such that a surface of the detector and a surface of the optical component receive similar levels of contamination, wherein the surface of the detector is separate from the surface of the optical component;subjecting the surface of the detector and the surface of the optical component to a cleaning treatment;irradiating the surface of the detector such that secondary electrons are emitted by the surface of the detector; anddetecting at least one of a resulting secondary emission voltage and current. 2. The method of claim 1, wherein the cleaning treatment comprises subjecting the surface of the detector and the surface of the optical component to hydrogen radicals. 3. The method of claim 2, wherein the cleaning treatment further comprises:providing hydrogen gas in at least part of the hydrogen radical supply system;producing hydrogen radicals from the hydrogen gas; andsubjecting the surface of the detector and the surface of the optical component to at least part of the hydrogen radicals. 4. The method of claim 3, wherein the producing the hydrogen radicals from the hydrogen gas comprises using at least one of a filament, a plasma, radiation, and a catalyst. 5. The method of claim 1, wherein the cleaning treatment removes at least part of a deposition from at least one of the detector surface and the optical component surface, and wherein the deposition comprises at least one of B, C, Si, Ge, and Sn. 6. The method of claim 1, further comprising: comparing a voltage or current corresponding to the resulting secondary emission to a stored secondary emission voltage or current. 7. The method of claim 1, further comprising: storing the resulting secondary emission voltage or current.