So you would like to make an IR radar, i.e. point it at something and it will say if its in the way? Like a collision detector for a car? Light travels at a very high speed, so a reflection from a target 4m away will take 13 nanoseconds to return. This means that you have to operate the IR transmitter extremely fast to capture a reflection and its not a good place to start from. if you use ultra sound, sound travels at 720MPH so the time delay for your target will be 12 mS, which is low enough to be useable.
Frank