 It facilitates their insertion into vacuum, cleavage to expose clean surfaces, precise manipulation as the extension of a vacuum manipulator (for translations along three axes, and rotations to adjust the sample's polar, azimuth or tilt angles), cooling to temperatures as low as 1 K with the help of cryogenic liquefied gasses, cryocoolers, and dilution refrigerators, heating by resistive heaters (few hundred °C) or e-beam bombardment (up to 2000 °C), precise temperature measurement and control, beam calibration, etc.The role of the electron spectrometer in ARPES is to disperse along two spatial directions the electrons reaching its entrance with respect to their kinetic energy and their emission angle when exiting the sample.In the type most often used, the hemispherical electron energy analyzer, the electrons first pass through an electrostatic lens that 1) picks those emitted from its own small focal spot on the sample, which is, conveniently, some 40 mm away from the entrance to the lens, 2) enhances the angular spread of the electron plume, and 3) serves it to the narrow entrance slit of the energy dispersing element with adjusted energy.