An analytical description for the field of a harmonic focusing source is derived. It is valid for spherically concave sources with small aperture angle and high ka, under conditions of quasilinear distortion (strong shocks precluded). The solution furnishes access to the phase and amplitude of second harmonic sound. Underwater experiments conducted with an f/2 lens coupled to a low-density source array are discussed. The results support the utility and validity of the analytical model for describing the amplitude and phase distribution of the second harmonic along the acoustic axis. It is shown that phase shifting in the focal region differs from that of linear radiations, and that both nonlinear propagation and diffractive effects are important in determining phase properties.