Calculating Fluence and Fluence rate of images from Metadata

[TimothyLambdenCambridge]

It may be helpful to incorporate a function that looks up the metadata to calculate the fluence (electrons per unit area) and fluence rate (electrons per unit area per unit time).

• dp.getfluence()
• dp.getfluencerate()

The function would look up the metadata or give an error asking you to input the data if it is missing:

• Beam current/Faraday cup reading/Screen current reading
• Dwell time
• Electron beam energy/wavelength
• Probe Size/Convergence angle

Note: In STEM, the dose would be higher if your probe size is larger than the step size (supersampling), so you would need to output either the probe size limited dose and the step size limited dose.

It could also have a setting to output in different units e.g. "e^-nm^-2", "e-A^-2", "Ccm^-2" etc.

Think this function would be helpful for many users who often have separate scripts that calculate the fluence themselves, and would be easy to implement given most of the information is available in the metadata anyway.

[CSSFrancis]

@TimothyLambdenCambridge Great to talk to you a couple of weeks ago! I've been a little bit busy with this but it would be good to see about implementing some of this stuff! I think a good first step would be a small PR for setting the gain for some dataset.

Maybe something similar to how the beam energy is set currently.

pyxem/pyxem/signals/electron_diffraction2d.py

Lines 75 to 84 in 4c8de4c

	@property
	def beam_energy(self):
	try:
	return self.metadata.Acquisition_instrument.TEM["beam_energy"]
	except AttributeError:
	return None
	@beam_energy.setter
	def beam_energy(self, energy):
	self.metadata.set_item("Acquisition_instrument.TEM.beam_energy", energy)