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To enable the functioning of a laser which delivers--on average--100 watts of energy in its beam, how much power does it take?

(Does the 2nd law of thermodynamics dictate that the average power supplied must be at least twice that of the average power delivered?)

Edit: Please include the power supplied to the cooling system in your calculations if it is required for the laser's continued functioning.

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The total electrical to optical power efficiency of a laser system is sometimes termed wall-plug efficiency. It is the ratio of

$$\eta = \frac{\text{optical output power}}{\text{consumed electrical input power}}$$

The values vary a lot, and also there are other factors like cooling system power which might or might not be included, in which case the calculation will be completely different. (Usually, the cooling system effect is greater in high power laser system e.g. 1GW pulsed laser systems)

The following table summarizes some laser types, to show how variable the efficiency can be (source)

laser type efficiency
Pure laser diode systems ~ 60%
thin-disk lasers based on Yb:YAG close to 30%
Nd:YAG lasers about 25%
argon ion lasers ~ 0.1%
titanium–sapphire lasers ~ 0.1%

NOTE This is not an exhaustive list. There are many more types of lasers (chemical, solid state, phtonoic crystal, dye etc), and implementations and I am by no means an expert in the field (someone like OpticalResonator will have a more authoritative answer to this question).

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