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Beam Combining

Definition: a class of techniques for power scaling of laser sources by combining the outputs of multiple devices

Categories: lasers, methods

How to cite the article; suggest additional literature

Various laser architectures allow the development of high-power laser sources with high beam quality, i.e., high brightness. However, all of these approaches have their limitations, and some envisaged laser applications would require a higher laser power and brightness than appears to be feasible with any known laser technology. Another problem is that very high-power laser systems are developed and built only in small numbers, making the devices fairly expensive.

A viable solution to these challenges could be the principle of beam combining, which essentially means combining the outputs of multiple laser sources (often in the form of laser arrays) so as to obtain a single output beam. The use of a scalable beam-combining technology leads to a power-scalable laser source, even if the single lasers are not scalable.

The goal of beam combining is generally not only to multiply the output power, but also to preserve the beam quality, so that the brightness is increased (nearly) as much as the output power. Therefore, it is generally not sufficient, e.g., to combine mutually incoherent beams side by side, because this would increase the beam area while not decreasing the beam divergence, consequently increasing the beam parameter product and reducing the beam quality.

There are many different approaches for beam combining with increased brightness, but these can all be grouped into one of two categories:

These techniques are discussed in more detail in the corresponding articles. They can be applied to various laser sources, e.g., based on laser diodes (particularly diode bars) and fiber amplifiers, but also to high-power solid-state bulk lasers and VECSELs.

Comparison of Coherent and Spectral Beam Combining

Coherent and spectral beam combining techniques are substantially different in various respects:

In conclusion, it is to be expected that methods of spectral beam combining will find more widespread application, although coherent methods will in some cases be required, e.g. due to constraints concerning the optical spectrum.


It is expected that beam-combined laser systems will in the near future reach output power levels of tens to hundreds of kilowatts. Possible applications of such systems are often in the military sector, e.g., in the context of anti-missile and other directed energy laser weapons. There are also possibilities for long-distance free-space optical communications [1] and laser-based manufacturing.


[1]G. S. Mecherle, “Laser diode combining for free space optical communication”, Proc. SPIE 616, 281 (1986)
[2]T. Y. Fan, “Laser beam combining for high-power, high-radiance sources”, IEEE J. Sel. Top. Quantum Electron. 11 (3), 567 (2005) (an excellent review paper)
[3]Special issue on beam combining: IEEE Sel. Top. Quantum Electron. 15 (2) (2009)

(Suggest additional literature!)

See also: coherent beam combining, spectral beam combining, power scaling of lasers, high-power lasers, high-power fiber lasers and amplifiers, coherence
and other articles in the categories lasers, methods

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