Fig. 1. Schematic diagram of an end-pumped laser involving a CDG in the pumping unit.

Fig. 2. (a) Top view of second-order CDG taken by microscopy, where the bright rings indicate the ridges, and the dark ones represent the grooves, (b) transverse intensity distribution of diffracted pump light at the far field, (c) schematic cross section of the CDG along the radial direction, and (d) the line profile of pump light along the radial direction.

Fig. 3. Variation of output power of the laser with pump power.

Fig. 4. Intensity distributions of double-ring modes obtained at different pump powers: (a) Pabs=1.06W, (b) Pabs=1.17W, (c) Pabs=1.51W, (d) Pabs=1.65W, (e) Pabs=1.71W, (f) Pabs=1.83W, (g) Pabs=1.95W, and (h) Pabs=2.21W.

Fig. 5. Measured and theoretical intensity distribution of the laser mode along the horizontal direction at Pabs=1.95W. The black triangles represent the measured data points of the double-ring mode, the red line represents the theoretical profile of linear superposition of the LG11 and TEM00 modes, and the green and blue dashed lines represent the respective intensity profiles of theoretical LG11 and TEM00 modes.

Fig. 6. Evolution of beam waist of the laser mode at Pabs=1.95W along propagation distance. M2, quality factors M square.

Fig. 7. Schematic diagram of the Mach–Zehnder interferometer for phase detection. NPBS, non-polarized beam splitter.

Fig. 8. Captured interference patterns of the double-ring mode at Pabs=1.95W.

Fig. 9. Variation of output power of the laser with pump power.

Fig. 10. Intensity distributions of single-ring modes obtained at different pump powers: (a) Pabs=1.37W, (b) Pabs=1.47W, (c) Pabs=1.51W, (d) Pabs=1.64W, and (e) Pabs=1.71W.

Fig. 11. Measured and theoretical intensity distribution of the laser mode along the horizontal direction at Pabs=1.64W.

Fig. 12. Evolution of the beam waist of the laser mode at Pabs=1.64W along the propagation distance.

Fig. 13. Captured interference patterns of the single-ring mode at Pabs=1.64W.