Bias-Variant Photomultiplier Tube

A method for biasing a photomultiplier tube (PMT) comprising:

• generating an initial set of photoelectrons through secondary emission via the absorption of photons with a photocathode;
• directing the initial set of photoelectrons to a plurality of dynodes;
• amplifying the initial set of photoelectrons to form a second set of photoelectrons with a first pair of dynodes having a first bias difference;
• amplifying the second set of photoelectrons to form at least a third set of photoelectrons with at least a second pair of dynodes having at least a second bias difference greater than the first bias difference;
• and
• receiving the at least a third set of photoelectrons with an anode.

An optical system comprising:

• an illumination source configured to generate illumination;
• a set of illumination optics configured to direct and focus the illumination onto the sample surface;
• a bias-variant photomultiplier tube (PMT) sensor configured to detect at least a portion of light scattered, reflected, or defracted from the surface of the sample;
• and
• a set of collection optics configured to direct and focus at least a portion of light scattered from the surface of the sample to an input of the bias-variant PMT sensor.