Wall-plug Efficiency

Dr. Rüdiger Paschotta

doi:10.61835/gp0

Wall-plug Efficiency

Author: the photonics expert Dr. Rüdiger Paschotta (RP)

Definition: total electrical-to-optical power efficiency of a laser system

Category: article belongs to category laser devices and laser physics laser devices and laser physics

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DOI: 10.61835/gp0 Cite the article: BibTex BibLaTex plain text HTML Link to this page! LinkedIn

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What is a Wall-plug Efficiency?

The wall-plug efficiency of a laser system is its total electrical-to-optical power efficiency, i.e., the ratio of optical output power to consumed electrical input power as measured at the wall plug. For example, if the optical output power of a laser is 5 W while its power supply consumes 100 W of electrical power, the wall-plug efficiency is 5%.

Taking the term seriously, the electrical power should be measured at the wall plug, so that this efficiency includes losses in the power supply and also the power required for a cooling system, which can be significant for high-power lasers. However, it is common that the wall-plug efficiency is calculated based on the electric power delivered to the laser diodes (e.g. in a diode-pumped solid-state laser system), ignoring losses in power supplies (which can be quite small for modern switched-mode power supplies).

Using the term in that common way, values of the order of 25% result for many diode-pumped laser systems (→ all-solid-state lasers), e.g. Nd:YAG lasers. Even values above 30% are possible, e.g. with thin-disk lasers based on Yb:YAG and efficient laser diodes. It is to be expected that within the next few years laser diodes could become even more efficient, further raising the wall-plug efficiency of such systems. Pure laser diode systems (→ direct-diode lasers) can reach the highest efficiencies, sometimes above 60%, but they cannot always be used, e.g. because of their poor beam quality and their inability to generate intense pulses. When using a high-power fiber laser as a brightness converter, one can obtain high output beam quality and (to some extent) intense light pulses, while the overall wall-plug efficiency can in the best cases be of the order of 50%. On the other hand, argon-ion lasers, and even more so titanium–sapphire lasers and the like when they are pumped with argon-ion lasers, generally have wall-plug efficiencies around or below 0.1%.

Particularly for high-power lasers, a high wall-plug efficiency is a very important quality. It reduces the electrical power consumption and also the amount of heat which has to be removed. Therefore, it not only cuts down the electricity bill but also reduces the demands on electrical installations and on the cooling system, and in turn often also the size of the laser system. Even for low-power lasers, the efficiency can be important in certain application areas, where the power budget is tight. Examples are telecom devices with a large number of transmitters, and lasers for space applications.

Frequently Asked Questions

This FAQ section was generated with AI based on the article content and has been reviewed by the article’s author (RP).

What is the wall-plug efficiency of a laser?

It is the laser system's total electrical-to-optical power efficiency, defined as the ratio of the optical output power to the total electrical power consumed from the wall plug. For example, a laser with 5 W optical output consuming 100 W of electrical power has a 5% wall-plug efficiency.

Which types of lasers have the highest wall-plug efficiency?

Direct-diode lasers offer the highest efficiencies, sometimes above 60%. High-power fiber lasers can also be very efficient, reaching around 50%, while many diode-pumped solid-state lasers achieve 25–30%. In contrast, argon-ion lasers and systems pumped by them can have efficiencies below 0.1%.

Why is a high wall-plug efficiency important for lasers?

Particularly for high-power lasers, a high efficiency reduces electrical power consumption and the amount of waste heat that needs to be removed. This lowers the electricity bill and reduces the demands on the cooling system, often resulting in a more compact laser system.

Bibliography

[1]	N. P. Barnes, “Solid-state lasers from an efficiency perspective”, J. Sel. Top. Quantum Electron. 13 (3), 435 (2007); doi:10.1109/JSTQE.2007.895280
[2]	W. Koechner, Solid-State Laser Engineering, 6th edn., Springer, Berlin (2006)

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