Hi Humbleworker,

That sounds like it would work.

What type object? Size? Speed? Distance?

Emitters:
Do you need lasers or would simple infrared (IR) emitters (LEDs) and detectors be okay?

Photo detectors:
IR phototransistors are more sensitive, but photodiodes are much faster reactors.

Do you have bench testing equipment available? A “counter-timer” would allow you to test the idea. Then you could replace it with a PIC that would do the timing and calculate for you.

Have fun.
-Adam-