The invariance of vector structured light in complex media

Light is one of the objects of study that has most intrigued humanity, not only from the fundamental point of view, but also due to the large number of applications it has given rise to. In particular, the phenomenon of polarization, associated with the direction of oscillation of the electric field of light, with a history of more than four centuries of study.

This phenomenon, although we do not notice it, is part of our daily life, for example, the sunlight that reaches our eyes through reflection is partially polarized and that is why we use polarized glasses to eliminate that polarized component that bothers our vision. The 3D movies that are often shown in cinemas are another example of the potential of polarization in applications, in this case for entertainment.

Relevantly, the concept of polarization has been taken, for some years, to a much more generalized context, that of light beams with non-homogeneous polarization patterns. This has awakened the general interest of the scientific community, not only in the field of optics, but also in areas as diverse as microscopy or telecommunications. Such beams are generated as an inseparable superposition of spatial degrees of freedom (beam shape) and polarization, giving rise to beams with exotic polarization patterns, which have been called vector beams.

In the field of microscopy, this type of beam has allowed, for example, the development of super-resolution techniques that have allowed us to observe structural details with resolutions impossible to achieve with conventional microscopes, a discovery that culminated in the Nobel Prize in Chemistry in 2014 Awarded to Eric Betzig, Stefan W. Hell, and William E. Moerner for High Resolution Fluorescence Microscopy (STED). In the field of telecommunications, said beams provide an alternative for sending information at higher speeds, with the aim of eventually replacing current communication systems and satisfying the growing demand of society to improve them.

Given the importance that the use of vector beams has awakened, recent research has focused on the study of said beams in media that offer resistance to their propagation. Such is the case of the terrestrial atmosphere, where continuous temperature changes, derived for example from air currents, cause conventional beams to become distorted in propagation. Another example where said beams are affected is propagation in water, very useful, for example, to establish an underwater communications system. As a last example, and perhaps one closer to the reader, we can mention its propagation through the skin, particularly in the detection of subcutaneous diseases, since the light that returns after having interacted with human tissue contains relevant information about of the same.

Until now, the reported results provide contradictory evidence that demonstrates, on the one hand, that the vectorial structure of said beams is more resistant to disturbances in this type of media, but there is also evidence that demonstrates the opposite.

In a recent article published in the journal “Nature Photonics”, Dr. Carmelo Rosales-Guzmán from the Centro de Investigaciones en Óptica, AC (CIO), along with a team of collaborators from Scotland and South Africa provide new information that allows us to resolve this debate. in favor of the fact that vector beams are more resistant to propagation in media such as atmospheric turbulence or water.

These results are invaluable for the scientific community that works with vector beams and their applications, mainly for two reasons.

Encouraging the use of these beams in new applications, for example, in the medical field where beams commonly used for subcutaneous studies immediately become distorted upon entering the skin, vector beams could penetrate the skin at greater depths. Field

Ions in free space would also benefit from the use of this beam, since they are more robust to changes induced by the medium in which they propagate. On the other hand, these results put an end to a fundamental paradigm in optics that somehow limited the study of new types of vector beams, giving rise to their development, not only of new types of vector beams, but also to the development of new techniques. of generation.

In conclusion, the discovery that vector beams are more resistant to disturbances will bring about the improvement and development of new applications that in the not too distant future will have a direct and indirect impact on society. The ones mentioned above are a few, but new applications will undoubtedly emerge that use this inherent property of vector beams.

* CIO Researcher