In-situ differential spectroscopy

A spectrometer comprising:

• an electron beam generator for generating an electron beam that is directed at a sample,
• an electron beam positioner for directing the electron beam onto a position of the sample and thereby producing a secondary emitted stream from the sample,
• a secondary emitted stream positioner for positioning the secondary emitted stream onto a detector array,
• the detector array for receiving the secondary emitted stream and detecting both amounts and received positions of the secondary emitted stream, where the secondary emitted stream includes at least one of electrons and x-rays,
• a modulator for sinusoidally modulating at a frequency the position of electron beam that is directed onto the sample, and thereby repeatedly sweeping the electron beam between a first position and a second position on the sample, and
• an extractor in signal communication with both the modulator and the detector array, for extracting a differential signal by applying a Fourier filter in a time domain at the frequency of modulation, representing a difference between signal frames received from the first position during the repeated sweeps of the electron beam and signal frames received from the second position during the repeated sweeps of the electron beam.