Narrow-band tunable alexandrite laser with passive $Q$ switching

An alexandrite laser with a self-injection of narrow-band radiation into its cavity was developed. A Fabry – Perot interferometer and a diffraction grating were used as dispersive components in an additional cavity. The cavity was switched by an LiF crystal with $F_3^-$ colour centres. The laser generated a single pulse of $\sim$ 180 ns duration and of 1.5 mJ energy, and with a spectrum 5 $\times$ 10$^{-3}$ cm$^{-1}$ wide. The laser emitted in the spectral range 720 – 780 nm.