Also there's the simple physics view of the same problem. The advantage of scanning is that you can focus all the laser pulse energy into one narrow beam. Non scanning means covering the whole field of view at once with that same laser pulse. Then you have a choice. Either somehow deal with the exponentially weaker return pulse (since it's spread over the whole field of view), or try to increase the pulse energy (and there you're limited by laser safety regulations)

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jlokier 3 days ago | parent | next [-]

From a physics point of view, continuous transmission and correlation detection of a temporally- and spatially-diverse optical signal over the entire field of view addresses the problem of energy being spread out, and gets you better, more robust depth information for less emitted energy than scanning or full-field flashes.

But from an optical and electronics point of view, it's much harder to process the return signal that way, and probably uses a lot more energy due to the processing required (with current tech).

	▲	namibj 3 days ago \| parent [-]
		Actually the same rule as for RADAR also applies to LIDAR: single pulse has better energy efficiency, but requires untenable peak power at any vaguely-state-of-the-art signal quality/reception performance levels. The reason is that you can time-gate the noise out that would otherwise be hitting your correlation accumulators if you have a vague idea of the supposed delay/ToF for the pulse. However, once you add mechanical scanning, at least for systems with not that many orders of magnitude between range resolution and maximum detection range, you can use systems like mode-locked lasers that for example have around 0.1% native duty cycle, circumvent the issue of peak power through the aperture/scanning 's spatial focusing (each pixel only needs a managable amount of energy, and delivering that in a single pulse won't require unreasonable peak power levels), and still get all the energy-efficiency benefits of single-pulse ranging vs. spread-spectrum/correlation ranging. The only but major downside is the requirement of mechanical scanning.

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tubs 3 days ago | parent | prev [-]

Quadratically weaker, not exponentially.

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Animats 3 days ago | parent [-]

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.

	▲	MezzoDelCammin 3 days ago \| parent [-]
		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).