The interference patterns between two vortex beams are systematically studied in experiment. Vortex beams with different topological charges (TCs) (±1, ±2, ±3) are generated by modulating the fundamental Gaussian beam with the spiral phase plate, and an improved Mach-Zehnder interferometer is built to study these different interference patterns. When two interference beams are both plane waves, off-axis interference produces fork-shaped interference patterns. The fork direction and the fork number in the fork-shaped patterns are related to the TCs and orientation relation of two vortex beams. When two LG0l vortex beams with different curvature radii interferes coaxially, the interference pattern with a spiral structure is generated, the spiral direction and spiral leaves depend on the curvature radii and TCs of two interfered vortex beams. Coaxial interference of two vortex beams with the same curvature radius produces the spiral-shaped pattern with a petal-shaped (or wheel-shaped) structure (a composite vortex field).
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