ARPES spectrometer measures angular dispersion in a slice α along its slit, so in order to map the band structure over a two-dimensional momentum space one needs to turn the sample, changing its roll/polar angle ϑ, pitch/tilt τ, or yaw/azimuth φ. Here, the spectrometer is accepting electrons emitted vertically from the surface and ±8° around: ϑ=0°, τ=0°, -8°≤α≤8°.
<a href="//commons.wikimedia.org/wiki/User:Ponor" title="User:Ponor">Ponor</a>
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