We report on the development of a handheld three-dimensional (3D) terahertz scanning system with an aspherical telecentric 3D-printed f-θ lens using selective laser sintering. The lens covers a broader scan line of 50 mm with its larger aperture, compared to the 20 mm range in our initial work, which was presented at the European Microwave Week 2021. In order to evaluate the adaptability of the optomechanical components with different sensor units, two different integrated frequency-modulated continuous wave radar modules based on monolithic microwave integrated circuit technology, operating in W- and D-bands are tested within the measurement scheme. The optomechanical part consists of a galvanometer scanner mirror and the f-θ lens. The optical system enables B-scans perpendicular to the manual translational movement of the sensor unit by its user. An integrated guiding wheel system with rotary encoder makes it possible to correlate the measurement points to their respective locations, enabling complete 3D volumetric inspection of the corresponding structures, which is particularly useful for the inspection along cracks and welds.

We demonstrate monochromatic and white light optical amplification of the photo-oxidation of adsorbed methylene blue using an inverse colloidal photonic crystal fashioned from anatase nanocrystals, denoted i-nc-TiO2-o. Enhanced photo-activity that drives the oxidation of the dye is attributed to slow photons in i-nc-TiO2-o. When the slow photon wavelength is optimized with respect to the electronic excitation energy of i-nc-TiO2-o, the photo-oxidation rate of the dye is doubled compared to conventional nc-TiO2. By increasing the probability of absorbing photons in i-nc-TiO2-o relative to nc-TiO2, a larger population of electron-hole pairs is generated enabling more efficient photo-oxidation. Slow photons in photonic crystals portend a myriad of opportunities for amplified photo-processes in chemistry and biology.

We present a bottom-up approach for the construction of "Smart" active defects in colloidal photonic crystals (CPCs). These structures incorporate polyelectrolyte multilayer (PEM) planar defects embedded in silica CPCs through a combination of evaporation induced self-assembly and microcontact transfer printing. We show how the enormous chemical diversity inherent to PEMs can be harnessed to create chemically active defect structures responsive to solvent vapor pressures, light, temperature as well as redox cycling. A sharp transmission state within the photonic stopband, induced by the PEM defect, can be precisely, reproducibly and in some cases reversibly tuned by these external stimuli.

These materials could find numerous applications as optically monitored chemical sensors, adjustable notch filters and CPC-based tunable laser sources.

We here demonstrate the use of semiconductor chalcogenide nanocrystals as single-source precursors for the one-step formation of flexible functional films. By taking advantage of the surface chemistry of these “zero-dimensional” building blocks we obtain close-packed three-dimensional arrays of nanocrystals interconnected by oxide sheaths. The films are obtained by exposing oxidation-resistant nanocrystals to an air plasma treatment. This treatment does not significantly influence the photoluminescence efficiency of the individual nanocrystal building blocks but confers them resilience to bending as well as resistance to acidic environments, hot solvents, annealing, and UV irradiation.