Systems and methods of observing a sample using a charged-
particle beam apparatus in
voltage contrast mode are disclosed. The charged-
particle beam apparatus comprises a charged-
particle source, an optical source, a charged-
particle detector configured to detect charged particles, and a controller having circuitry configured to apply a first
signal to cause the optical source to generate the optical pulse, apply a second
signal to the charged-
particle detector to detect the second plurality of charged particles, and adjust a time
delay between the first and the second signals. In some embodiments, the controller having circuitry may be further configured to acquire a plurality of images of a structure, to determine an electrical characteristic of the
structure based on the rate of
gray level variation of the plurality of images of the structure, and to simulate, using a model, a physical characteristic of the
structure based on the determined electrical characteristic.