Single frequency lasers

A single-frequency laser is a type of laser which operates within a singular resonator mode, achievable when the net gain bandwidth of the laser remains narrower than the frequency spacing of the resonator modes [1]. In cases where the mode spacing isn’t adequately large to support a single resonator mode, single-frequency operation is maintained through the utilization of intracavity filters. This enables the single-frequency laser to possess an exceedingly narrow linewidth, frequently measuring only a few kHz [2], and an extended coherent length. A clear association exists between the coherence length and the spectral width of the laser [3].