Higher Order Processes in Field Emission Spectroscopy from Superconductors

We calculate the energy spectrum of the electrons emitted from a superconductor under an applied field, including two-particle processes. Among these two-particle processes we examine the Andreev processes, in which a whole Cooper pair tunnels out of the superconductor. The Andreev processes are the only ones that can happen with subgap energies. In this range we find an explicit formula for the spectrum of the two-particle processes.