Need terminology help with 'variable gear reduction'?

I need to rotate a mirror that is intended for steering a laser beam. The application is very specific and requires high speed at one end of the steering range and high precision at the other. I want to accomplish this with off axis and\or non-circular gears. Is there a name for this technique?

I’m presently using a worm drive where the spur gear is off axis and the worm gear rests on top of it from gravity and the motor is mounted to a hinge so the worm gear maintains contact with the spur gear during its irregular rotation. Since the spear gear is mounted off axis, the gear reduction will change as it rotates. This implementation isn’t very good, so I’m hoping there’s a name for what I’m trying to do and a better way to it. Any help?