High-power narrow-linewidth tunable external-cavity laser based on biaxial focal discrepancy.

A high-power narrow-linewidth Littman external-cavity laser utilizing biaxial focal discrepancy has been proposed. In the Y-direction, an object-image conjugate structure is introduced to enable beam circulation along a symmetric path. The mechanical installation complexity is reduced, and the system output power is enhanced. In the X-direction, a non-conjugate scattering path is formed to facilitate effective feedback of the near-axis beam at the target wavelength. The adjacent mode crosstalk is suppressed, and the mode selectivity is improved. Experimental results demonstrate that the external cavity output power is 277.7 mW, representing an increase by a factor of more than five. The side mode suppression ratio is 65.68 dB. A spectral linewidth of 2.62 kHz is estimated in short-delay recirculating beat-frequency tests. This research offers insights for designing high-power narrow-linewidth tunable lasers.