Interference of Polychromatic Fields

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In the section on basic properties of sensor modules, we introduced the basic rule that governs sensor output when beams from more than one source fall on a sensor.  To review, the essential points were that

(a)  Sensors that report intensity will add the individual intensities.

(b)  Sensors that report complex field (e.g., the fundamental SimpleFieldSensor) will add the individual complex fields.

(c)  Interference between two equal-wavelength beams, assumed temporally coherent, is achieved using the SimpleFieldSensor.

Now, another case of great practical interest is two or more temporally coherent beams of different wavelength.  Such situations arise, e.g., in ladar and heterodyne detection problems.  The interference between such beams, for example the phenomenon of "walking fringes", can be modeled using LightLike library components such as SimpleFieldSensor plus a bit of special modeling setup.  The principles are explained in detail, and a specific example system is constructed, in an auxiliary document.

The User Guide general section on optical propagators also contained quite a few remarks on LightLike modeling with multiple discrete wavelengths and finite continuous bandwidths.  Users may wish to review those comments as well for general context.