Real-time holographic heterodyne spatial filtering

Traditionally, homodyne and heterodyne are a combination of a frequency mixer followed by a low-pass filter. Mixing two signals of frequencies f(1) and f(2) generates signals of frequencies f(1) + f(2) and f(1) - f(2) and their integer multiples. Both multiplication heterodyne and phase-sensitive detection have been demonstrated optically by using photorefractive, four-wave mixing (FWM). The multiplicative characteristic of FWM was used for mixing, and the response time of the photorefractive medium is used for low-pass filtering. If one of the input beams is both spatially and temporally modulated using a controlled oscillating membrane, depends on which model is heterodyned, one can generate an orthogonal set of Bessel bandpass filters. This scheme can be integrated part within parallel data acquisition systems for applications involved in nondestructive testing.