  In recent years we are witnessing a flourish in research aimed to facilitate
alkali vapors in guided wave configurations. Owing to the significant reduction
in device dimensions, the increase in density of states, the interaction with
surfaces and primarily the high intensities carried along the structure, a rich
world of light vapor interactions can be studied, and new functionalities, e.g.
low power nonlinear light-matter interactions can be achieved. One immense
remaining challenge is to study the effects of quantum coherence and shifts in
such nano-scale waveguides, characterized by ultra-small mode areas and fast
dynamics. Here, we construct a serpentine silicon-nitride wave guide, having
atomic vapor as its cladding. The unprecedented mode volume of 5e-13 m^3
supported over a length of 17 mm is used to demonstrate efficient linear and
non-linear spectroscopy. Fascinating and important phenomena such as van der
Waals shifts, dynamical stark shifts, and coherent effects such as strong
coupling (in the form of Autler Townes splitting) are all observed. The
serpentine atomic cladding is a promising building block for a variety of light
vapor experiments, as it offers a very small footprint, enables operation with
relatively low density of atoms and extremely strong confinement of light and
vapor. As such it may be used for important applications, such as all optical
switching, frequency referencing, and magnetometry to name a few.
