Since light travels at around 1 foot per nanosecond: at 200 feet = window is 400 nanoseconds, and at 1000 feet = window is 2000 nanoseconds, which is the "time of flight" from the gun to the target and back. The window gets smaller and smaller as you get closer to the gun, and the jammer also sees the window occuring "sooner" in the pulse train.
So for reference, consider a ProLaser III @ 200pps, which sends out one pulse 5000000 nanoseconds. Since the time window is 2000n nanoseconds at 1000 feet, the laser gun will only accept pulses .04 % of the time at 1000 feet, and this gets less and less closer to the gun.
So, jammers can (and do) calculate a time window and then initiate a jamming sequence that is good for several pulses and makes it into the window. But, ultimately the jammer must continue to monitor incoming pulses and calculate the time window as you approach (or move away from) the gun.
And in reality, it gets even more complex: I have been told (but have not verified) that some guns are smart enough to predict (based on the past pulses) when the next reflected pulse is likely to be received back, and then reject any pulses which are outside of that specific range. In this case, the window could be much smaller.
Hope this answers the questions
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