6. Conclusion

Light is the main tool with which we probe our material environment. As a result, it has always been a precious ally for human techniques, long before we could, as proposed here, speak of the optics of material media as a rich and varied scientific and technical field.

Deciphering how matter interacts with light relies heavily on understanding the electronic energy levels in atoms, molecules and solids.

In a coarse-grained vision, it is undoubtedly the separation of different light frequencies that has been the foundation of spectroscopy, detailing information that the eye could not see, and giving more or less direct access to the relevant electronic energies of matter (mainly "transitions"). The classic tools of this separation, such as prisms and gratings, can be increasingly integrated into compact systems, and over a wider and wider...