Fig. 1. Illustration of the basic idea of the ring laser cavity using a cascaded modulation scheme. (a) Overall beam propagation of the intracavity oscillation mode and the extracavity output mode; (b) beam propagation of the self-reproduction Gaussian field; (c) beam propagation of the output field with controllable amplitude and phase.

Fig. 2. Equivalent diagram of the beam propagation in the ring laser resonator.

Fig. 3. Experimental setup of the ring laser resonator.

Fig. 4. The cascaded phase holograms, 2D intensity profiles, and axial intensity distributions (at the white dashed line) of different output structured fields. (a)–(c) HG₂₂ mode; (d)–(f) LG₀₈^* mode; (g)–(i) flat-top mode; (j)–(l) pattern of letter “A.”

Fig. 5. A series of HG and LG modes generated directly from the ring laser resonator.

Fig. 6. (a) Diagram of the interference experiment to detect the topological charge of the output LG mode. The cascaded phase holograms, 2D intensity profiles, and interference patterns of (b)–(d) LG_0,+1 mode and (e)–(g) LG_0,−1 mode.