  A physically transparent unified theory of optically and plasmon induced hot
carrier generation in metals is developed with all the relevant mechanisms
included. Analytical expressions that estimate the carrier generation rates,
their locations, energy and direction of motion are obtained. Among four
mechanisms considered: interband absorption, phonon and defect assisted
absorption, electron electron scattering assisted absorption, and surface
collision assisted absorption (Landau damping), it is the last one that
generates hot carriers which are most useful for practical applications in
photo detection and photo catalysis.
