Optical beams with spatially variant coherence properties from an unpolarized laser

We generate quasi-monochromatic laser beams with engineered, non-uniform transverse spatial coherence properties using an unpolarized helium–neon laser. This is achieved with a static phase modulating device that spatially modulates the laser’s two orthogonal polarization components, followed by a linear polarizer. Both theoretical and experimental results demonstrate that patterned geometric phase elements or programmable liquid-crystal spatial light modulators, combined with a linear polarizer, can effectively control the spatial coherence properties. This technique exploits the nanosecond-timescale variation of the laser’s emitted polarization ellipse, creating configurable non-uniform coherence patterns that maintain their spatial coherence characteristics down to nanosecond temporal windows.