Can an optical mouse be used to measure distance down to 1-10μm?
I have tried this before, using an Avago sensor harvested from an optical mouse.

It doesn't work.

The resolution is excellent but the accuracy is terrible.  And the calibration varies with distance from material to the sensor.

I arranged a test with a 3" diameter wheel and the sensor reading the outside "tread" of the wheel.  I also put a flag on the wheel, passing through an optical interrupter sensor.  The number of counts read per revolution varied by a few tenths of a percent, nowhere near good enough repeatability for machining.

I guess you could use the optical mouse sensor in combination with an accurate but low-resolution sensor to fill in the in-between points.  But really, I think other sensor technologies are more appropriate for this.