Virtual orbital angular momentum-based phase clock

A virtual orbital angular momentum (VOAM)-based phase clock is introduced to achieve phase variation metrology, which can be utilized in various conventional interferometry applications. Digital wavefronts possessing VOAM are employed in interference data processing, wherein phase change measurement is converted into image azimuth calculations. With a Moiré technique and a virtual fractional topological charge of l =0.5, a “phase clock” is depicted on a circular dial with a rotational probe indicating the phase change and a stationary probe addressing period ambiguity. The natural 360° reference of the rotation azimuth and the benchmark function of the stationary probe inherently ensure high precision. In the absence of actual OAM beam involvement, this technique harnesses all the benefits of previously reported OAM-based interferometers while overcoming many technological constraints. Factors that disrupt the rotational symmetry of the interferogram are acceptable. Therefore, the method is immune to system errors, alignment errors, and even non-uniformities in the target object under test across the entire aperture. Large-range measurements are attainable due to the stationary probe’s period counting, and remote measurements are feasible without concerns regarding the stability of fractional topological charge propagation. Notably, the phase clock with l =0.5 offers the highest sensitivity to date. This approach can be seamlessly integrated into various traditional interferometers through a straightforward expansion module, incurring zero additional hardware expenses. High resolution can even be achieved with the naked eye. Experiment validation is presented in the form of a displacement measurement interferometer and a temperature sensor. This method introduces a novel paradigm that utilizes OAM for precise interferometry while addressing its inherent limitations.