Characterization of Nanometric Thin Films with Far‐Field Light

Abstract The characterization of ultrathin transparent films is paramount for various optoelectronic materials, coatings, and photonics. However, characterizing such thin layers is difficult and it requires specialized clean‐room equipment and trained personnel. Here, a contact‐less, all‐optical method is introduced and validated for characterizing nanometric transparent films using far‐field optics. A series of nanometric, smooth, and homogeneous layered samples are fabricated first, alternating transparent spacer and fluorescent layers in a controlled manner. Fluorescence radiation pattern originating from the thin fluorophore layers is then recorded and analyzed and quantitative image analysis is used to perform in operando measurements of the refractive index, film homogeneity and to estimate axial fluorophore distances at a sub‐wavelength scale with a precision of a few of nanometers. The results compare favorably to measurements obtained through more complicated and involved techniques. Applications in nanometrology and biological axial super‐resolution imaging are presented. It is demonstrated in live cells the precise axial localization of single organelles in cortical astrocytes, an important type of brain cell. The approach is cheap, versatile and it will have applications in various fields of photonics.