  We consider exciting surface plasmon polaritons in the Kretschmann
configuration. Contrary to common belief, we show that a plane wave incident at
an angle greater than the angle of total internal reflection does not excite
surface plasmon polaritons. These excitations do arise, however, if the
incident light forms a narrow beam composed of an infinite number of plane
waves. The surface plasmon polariton is formed at the geometrical edge of the
beam as a result of interference of reflected plane waves.
