How to detect the duty cycle of a laser pointer
This will give you some clues to answering your assignment (but not everything). ;^)


You have correctly identified the problem with signal strength. You're going to have to figure out a way to detect a signal and extract the pulses and make them the same amplitude.
Detecting pulse width with a micro would be straightforward but that's not on your list of components so you'll have to go analog. If you low-pass filter the pulses you'll get a DC signal that varies with pulse width and now you just have to ... 


Do your research and update your question (rather than add comments) with one clear question when you get stuck. Show your research. Show schematics.