A precise spectrophotometric method to determine the refractive index of a semitransparent metallic thin film is presented. This method relies on interference enhancement of the measured spectra, ...employing an opaque substrate with a dielectric spacer layer beneath the absorbing layer of interest to create interference fringes.The resulting spectral oscillations of the stack are highly sensitive to the properties of the top absorbing layer, allowing precise determination of the refractive index via fitting. The performance of this method is verified using simulations in comparison to the typical method of depositing the absorbing thin film directly onto a transparent substrate. An experimental demonstration is made for titanium thin films over the visible range (370-835 nm). The refractive index of these films is extracted from experimental data using a combination of the Modified Drude and Forouhi-Bloomer models. This method showed high repeatability and precision, and is verified for Ti films between 6-70 nm thickness.
The ability of a layer of silver nanoparticles with broad size dispersion to excite coherent acoustic phonon wave-packet in its supporting glass substrate following femtosecond laser excitation is ...tested using time-domain Brillouin scattering in transmission configuration. The generation and propagation over several micrometer distances of gigahertz acoustic phonons in the underlying glass is observed for all investigated samples, involving nanoparticle layers with different morphological properties. The phonon wave-packet exhibits frequency-dependent attenuation rates and amplitudes in the 40–50 GHz acoustic frequency region. The measured attenuation rates are consistent with previous experimental results on silica, indicating that anharmonic interaction of acoustic waves with the thermal phonon bath has dominating contribution to the phonon damping. The features of the acoustic waves emitted by a discontinuous nanoparticle layer are investigated using a simplified theoretical model, allowing to better understand at which condition they are similar to those of the waves emitted by a continuous thin film.
A four‐layer metal–dielectric–metal–dielectric (MDMD) stack design for color control is demonstrated. This stack incorporates Ag, SiO2, and Ti as materials, enabling wide absorbance bands, high ...reflectance peaks, and a strongly tunable color. A wide gamut is obtained by varying the thickness of the SiO2 cavity layer, and the resulting colors exhibit outstanding luminance and chroma. Coatings of red, green, and blue colors are designed and deposited. These coatings demonstrate a very close agreement between the simulated and experimental results. The chroma of the coatings is found to be similar to or exceeded the limits of the Pointer gamut, an empirical gamut of colors in reflectance. This shows that, in the generation of surface color, even for a simple four‐layer stack, the performance of thin‐film coatings can rival or exceed that of traditional paints and dyes.
An overview of the design principles for thin‐film color coatings producing high‐chroma colors is presented. These principles are used to design metal–dielectric–metal (MDM) coatings, which produce bright red, green, and blue coatings in reflectance. The chroma of these coatings is close to or exceeds the previously measured limits of the chroma for surface colors.
A spectrophotometric method is demonstrated for refractive index and thickness determination of thin and ultrathin metallic films. The method involves a three-layer stack where the metallic layer of ...interest is deposited on an opaque Si wafer coated with SiO 2 . This stack creates oscillations in the reflectance spectrum, which are highly sensitive to the index of the metallic film, allowing precise determination of the index of layers down to 1 nm. Experimental index values are given for Ag and Au over the wavelength range of 370–835 nm. These results are correlated with Atomic force microscopy (AFM) images of the films, which reveal dramatic changes in structure for layers of different thickness.
The saturable absorption behaviour associated with chalcogenide thin films has been investigated and optimized using Z-Scan Technique. Huge saturable absorption responses (of the order of 10^-7 m/W) ...were observed for the Bismuth Selenide thin films, which depend on material characteristics and the laser parameters. An approach in which the application of the saturable absorber thin films for super-resolved laser inscriptions has been discussed and a theoretical analysis of the super-resolution efficiency of the thin films has been made.
The growing need for classical as well as quantum optical sensing places increasingly stringent requirements upon the desired characteristics of the engendered fields. Specifically, achieving ...superior field enhancement plays a critical role in applications ranging from chem-bio sensing, Raman and infrared spectroscopies to ion trapping and qubit control in emerging quantum-information science. Due to their low optical losses and ability to exhibit resonant field enhancements, all dielectric multilayers are emerging as an optical material system not only useful to classical photonics and sensing but also of potential to be integrated with quantum materials and quantum sensing. The recently introduced concept of zero-admittance layers 1 within dielectric multilayer materials, enables the creation and control of resonant fields orders of magnitude larger than the exciting field. Here, invoking the zero-admittance concept, we design, fabricate, and characterize an all-dielectric nonabsorbing stack and demonstrate the engendered huge field enhancement. Describing the fields in terms of Bloch surface waves, we connect the surface field to the semiperiodicity in the dielectric domains of the stack. As a specific application of the resonant field, we propose and demonstrate refractive-index sensing for the detection of trace amounts of an analyte. The results include a quantification of the sensitivity of the device with respect to the profile of the exciting field. The experimental results are shown to be in good agreement with theoretical calculations.
Over the last 15 years, there have been tremendous progress in the technology of optical interference filters. Nowadays, it is more and more common to fabricate optical interference filters that can ...combine several tens to several hundreds of layers in order to produce more and more complex optical functions. These progresses are the result of improved multilayer structures modeling and design procedures, the introduction of Virtual Deposition Process, and the development of performant physical vapor deposition machines associated with in-situ optical monitoring. In this paper, we will present actual state-of-the-art of these technologies and some typical examples of filters. We will then present some of the actual challenges and outlook in order to produce more and more performant optical components.
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