Distance is about 3m. IR or visible light - does not matter.
It is possible that object/obstacle can be shiny, so for correct detection necessary large amount of reflected light.
Maybe for this task better to use specific retroreflector?
there will be two sensors with distance about 3-4 cm between. Object must cross 1st sensor's reflector but do not cross the 2nd one.
But the use will be this: