A cathode has an emission layer that thermionically emits electrons upon exposure with a laser beam. The material of the emission layer has a product of density (ρ), measured in kg m 3 , heat capacity (Cp), measured in J kg ⁢ ⁢ K and heat conductivity (λ), measured in W mK that is, at room temperature, maximally 500,000 J 2 m 4 ⁢ K 2 ⁢ s . Such a cathode has an improved thermionic emission of electrons.