Fourth power of the distance, actually. That's the radar equation. You have inverse-square losses going out, as the beam expands with distance. Then you have inverse-square losses coming back when the target is much smaller than the beam. That's the problem flash LIDARs face. It can be overcome with enough laser power out to 20-30 meters.
That's where the beam diameter at the target is much larger than the target, as for aircraft. With a small scanning dot from a LIDAR and a nice big target like a car, almost all the power hits the target, but you still have inverse square losses coming back.
true. My original was just a quick jote on a phone sipping a coffee on Sunday. I admit I simply didn't want to go into the whole "square FOV for the sensor vs. one detector / diode and that combined with the time of flight loss over distance", so I just used "exponential" to mean "it loses power pretty quickly". Apologies for the sloppiness on my part.
Second part of the comment I omitted is was what You mentioned in the beginning. Those 20-30 meters of practical range is why we keep seeing small LIDAR sensors on things like iPhones / iPads (though there I believe the range is even a bit shorter due to the size / power constraints), but not really much beyond that.
For practical demo of what's currently available at the high end of solid state LIDAR (albeit at 40k+ USD), I'd suggest looking at Leica and their BLK2GO PULSE (solid state) vs the rest of the BLK line (rotating laser spot).
That's where the beam diameter at the target is much larger than the target, as for aircraft. With a small scanning dot from a LIDAR and a nice big target like a car, almost all the power hits the target, but you still have inverse square losses coming back.