beamcombining

Beam combining refers to methods for merging multiple optical beams into a single beam with higher peak power, brightness, or spectral content. It is used to scale laser systems beyond the capabilities of a single emitter while aiming to preserve beam quality.

Two main approaches exist: coherent beam combining (CBC) and incoherent (power) combining. Incoherent combining simply adds the optical powers of the inputs without controlling their relative phase, providing linear power scaling but little or no improvement in beam quality.

CBC aims to increase both power and beam quality by phasing the inputs so their fields constructively interfere in the target direction. This can be implemented in two spatial architectures: filled-aperture (or single-aperture) in which all beams are overlapped in one common aperture, and tiled-aperture (phased-array) in which separate sub-apertures are phased to form a synthesized, higher-quality output.

To achieve CBC, active phase control is required. Techniques include phase-lock loops, reference beams, and adaptive optics or wavefront sensing to minimize phase errors. Output can be a single, higher-power beam with preserved or improved beam quality; the total output power scales with the number of inputs, while the optimal case yields constructive interference leading to higher peak intensity than any individual beam.

Spectral beam combining uses different wavelengths combined in the same spatial mode, exploiting wavelength diversity; temporal or pulse stacking adds pulses in time to increase energy. Challenges include phase stability, optical losses, nonlinear effects, and sensitivity to environmental perturbations.

Applications include high-power laser systems for materials processing, defense, scientific research, and astronomy, where increased brightness and beam quality are valuable.