Measurement of Helmholtz wave fields

A simple formalism is found for the measurement of wave fields that satisfy the Helmholtz equation in free space. This formalism turns out to be analo gous to the well-known theory of measurements for quantum-mechanical wave f unctions: A measurement corresponds to the squared magnitude of the inner p roduct (in a suitable Hilbert space) of the wave field and a field that is associated with the detector. The measurement can also be expressed as an o verlap in phase space of a special form of the Wigner function that is tail ored for Helmholtz wave fields. (C) 2000 Optical Society of America [S0740- 3232(00)00906-6] OCIS codes: 040.0040, 030.5630, 030.1670, 260.0260, 350.74 20.