Ultrafast Laser Volume Nanostructuring of Transparent Materials: From Nanophotonics to Nanomechanics

The capability of ultrashort laser pulses to generate nonlinear absorption in the transparency window of dielectric materials is at the base of volume structuring. The result is a local change of the refractive index, the building block for generating complex embedded optical functions in three-dimensional geometries within a monolith chip. The nonlinearity determines spatial scales on the order of the wavelength. Depending on the rate and the amount of energy deposition, the local refractive index change can be accurately tuned from positive to negative values on variable scales, generating thus new capabilities for processing light within an optical chip in terms of embedded waveguides and micro-optics. New irradiation strategies and engineered glasses permit to go even further in reaching processing super-resolution, i.e., on spatial scales smaller than the optical resolution. The smallest scales achievable nowadays go well below the diffraction limit approaching and even surpassing the 100 nm value, a tenth of the wavelength. We will discuss in this chapter the possibility of obtaining structural features much smaller than the electromagnetic wavelength and the associated methods. Direct focusing and self-organization phenomena will be analyzed, as well as the optical functions originating from these processes, namely in transporting and manipulating light. Achieving extreme scales in the range of 100 nm generates an additional capability to sample the electrical field within the optical chip and thus to process and read out optical signals. We will discuss emerging applications ranging from photonics, such as sensors, spectro-imagers, actuators, or supports for data storage, down to nanomechanical systems, and pinpoint the enabling character of extreme nanostructuring scales using ultrafast lasers.