If you shine a laser pointer on a rough surface, you will notice that the reflected light creates a constellation of bright spots. However, less visible among these bright spots are threads of darkness known as optical singularites. Historically, these have been challenging to engineer. This month, the Capasso group has published two papers demonstrating powerful new tools to shape these dark regions using metasurfaces.

Christina Spaegele, the lead author of "Topologically Protected Optical Polarization Singularities in Four-Dimensional Space," published in Science Advances, introduces a new class of optical singularities. These fill a missing gap in singular optics: being complete (zero transverse polarization intensity) and robust to perturbations simultaneously. Due to a mathematical feature called topological protection, these singularities exhibit exceptional resilience to stray light and imperfections. Michele Tamagnone, Soon Wei Daniel Lim, Marcus Ossiander, and Maryna Meretska are co-authors on the publication.

In a companion paper, "Point Singularity Array with Metasurfaces," published in Nature Communications, co-first authors Soon Wei Daniel Lim and Joon Suh Park focus on isolated points of darkness with the potential for use in innovative atomic traps. By shaping narrowband light from a single laser source, the team demonstrate that a single meta-optic can produce periodic and aperiodic arrays of point optical singularities with tight intensity confinement.  These compact arrangements could simplify the optical architecture needed for atomic physics experiments. Dmitry Kazakov, Christina Spaegele, Ahmed Dorrah, and Maryna Meretska are co-authors on the publication.

Read "Topologically protected optical polarization singularities in four-dimensional space" in Science Advances and "Point singularity array with metasurfaces" in Nature Communications. Read the press release from Harvard SEAS.