How to Choose Pulse Energy for a Laser Rangefinder
Energy is the wrong thing to start with. Start with what the instrument has to see, and the energy tier usually picks itself.
The number on the datasheet is measured against a target the supplier chose. Your target may be matte paint at an angle in rain, which is nowhere near it. So the first job is to write down the case you actually care about: distance, target size, reflectivity, weather, and how often you need an answer.
The link budget
Received energy falls with the square of distance. Double the range and you need roughly four times the energy, all else equal. Reflectivity multiplies that: a 10% matte surface returns a fraction of what a road sign does, and a wet or angled surface is worse than either.
Atmospheric transmission takes its share over long paths, and a narrowband filter in the receiver can only recover what the optics deliver. Put the numbers in a spreadsheet before you pick a model.
What each tier buys
Around 100 µJ, in something like the ER100, you're covering a few hundred metres to a kilometre against cooperative targets. Several hundred microjoules reaches further or buys margin against poor reflectivity. Two millijoules and up, ER2000 and above, is where multi-kilometre work against uncooperative targets starts to be realistic.
The cost isn't only money. Energy comes with mass, current and heat. A 10 mJ source is 220 g and pulls 100 A; a 100 µJ one is 7 g and pulls 8 A. If the payload has a 30 g budget, the larger tier isn't on the table.
Rate changes the answer
If you need 100 measurements a second, you're in the high-repetition family at tens of microjoules, and the range budget has to close there. If you need one measurement every few seconds, you can spend the same thermal budget on a much larger pulse.
That's the real trade in this product line: joules or hertz, not both.
Do this before you ask for a quote
Write the maximum range, the target and its reflectivity, the weather case, the required probability of detection, and the update rate. Then ask for a model that meets all five. A supplier who quotes a model without those five is quoting a guess.
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