Field analysis with a mode-tunable local oscillator

Abstract

A novel approach to the measurement of electromagnetic fields is described and demonstrated. The approach is based on the use ofa local oscillator which is tuneable in a spatial mode sense. The technique provides a field analysis capability equivalent to that achievable with a phased array receiver but only requires a single aperture and a single detector. The principle behind the concept is described and successfully demonstrated with a hollow multimode waveguide version ofthe Michelson interferometer, a CO2 laser source and a thermopile detector. Measurements of the waveguide mode spectra excited by the field returned from a tilted plane mirror target positioned at the exit of the interferometer are shown to be in good agreement with theoretical predictions. The technique has the interesting property that the spatial resolution with which fields can be analysed is independent of detector dimensions. In suitable technologies the underlying concepts should be applicable across the electromagnetic spectrum.