OK, just to clarify - what I want is Z Axis Modulation. The sort of thing you
see on an oscilloscope - a positive voltage makes the trace brighter, a
negative one makes the trace dimmer (or blanks it altogether).

In addition to the Intensity control, I'd like a Contrast control - the
latter basically controlling how much the Z axis input can increase the
brightness of the beam spot.

Thanks.
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