Alkali vapours, such as rubidium, are being used extensively in many important fields of research. Recently, there is a growing effort towards miniaturizing traditional centimetre-size vapour cells. Owing to the significant reduction in device dimensions, light– matter interactions are greatly enhanced, enabling new functionalities due to the low power threshold needed for nonlinear interactions. Here, we construct an efficient and flexible platform for tailored light–vapour interactions on a chip, and demonstrate efficient interaction of the electromagnetic guided mode with absorption saturation at powers in the nanowatt regime.(read more)