The spectral phase of a coherent laser beam describes the phase relationship between different frequency components within the beam's spectrum. It's essentially how the phases of the individual colors (or frequencies) of light within the laser beam are aligned with each other. Coherent laser beams have a defined spectral phase, meaning the phases of different frequency components are correlated, while incoherent light sources have random spectral phases.

In essence, the spectral phase is a critical parameter for understanding and controlling the behavior of coherent laser beams, particularly in applications like coherent beam combining where maintaining phase relationships is essential for achieving desired beam characteristics. 

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