Fig. 1. (a) Diagram of diamond Brillouin laser structure:（EOM: electronical optical modulator, OA: optical amplifier, ISO: isolator; (b) Stokes linewidth measurement structure for Brillouin laser)

Fig. 2. Stokes linewidth corresponding to the reflectivity of the three sets of coupling mirrors. (a) Power spectrum of the corresponding delayed self-heterodyne amplitude difference; (b) Linewidth and envelope amplitude difference curves calculated by the coherent envelope method