A multi-line laser is a semiconductor-based laser comprising emitters for multiple laser wavelengths and an optical coupler.
In a multi-line laser, individual lasers emit beams at different wavelengths, which are combined by an optical coupler to form a single, high-quality laser beam. Because the spectral linewidth of each individual laser is very narrow, the resulting laser beam possesses a very narrow spectrum, achieving a high degree of monochromaticity and coherence.