A self-assembled polytetrafluoroethylene (PTFE) nanostructure is deposited on microcrystalline diamond (MCD) films, by use of physical and chemical vapor deposition in a two-step process, to produce (fully) superhydrophobic surfaces: high water contact angle (static, 165±2 deg ), very low hysteresis (dynamic, ∼4 deg ), and associated sliding angle (1 deg 5 ′ ±15 ′ ), thus combining the diamond infrared transparency and self-cleaning properties. These are interpreted in light of Wenzel and Cassie-Baxter wetting models, associated with structural microscopy of nano-micro rough PTFE/MCD surfaces, and present a promising perspective for self-cleaning infrared optics applications.
Superhydrophobic surfaces were produced on glass with self-cleaning and wide-angle anti-reflection in the near-infrared
(1.0-2.1μm). These properties resulted from a combination of surface energy and nano/micro-structured topology based
on silica nanoparticles (NPs), index grading and interference. In a two-layer approach (glass/silica NPs/PTFE), a water
contact angle (WCA) of 169°±2°was attained with very low hysteresis (≤ 2°), as well as high transmittance (93-94% at normal incidence). In a three-layer approach (glass/silica NPs/silica aerogel/PTFE), surfaces were produced with WCA of 158°±2°, also very low hysteresis (< 5°), and significant antireflection. This allowed for a normal transmittance of 99.5% or higher, which decreased less than 2% at +20° incidence. These results show that pronounced wide-angle antireflection and self-cleaning properties can be simultaneously attained by proper glass coating. Present advantages and limitations for potential applications are discussed.
Optical properties of transparent polymer thin films, produced by spin-coating on silicon and constituted of polycarbonate (PC), poly(methyl methacrylate) (PMMA), and PC/PMMA, were investigated with regard to integrated thermo-optical (TO) device applications. Refractive index dependences on wavelength, temperature, and film composition were measured by spectroscopic ellipsometry with a dedicated autocontrolled heater setup, in the ranges of 400 to 800 nm, 25 to 85 °C and 0 to 100 wt % PC, respectively, with determination of Cauchy and Lorentz-Lorenz parameters. Within these intervals, thermomechanical compatibility and pronounced index contrast of around 0.12 between PC and PMMA, as well as their TO coefficients one order of magnitude higher than that of silica, allow convenient tailoring for specific TO requirements. In addition, wide-range fine-tuning of refractive index variation is found to be facilitated by the weak dependence of isothermal dispersion curves and TO coefficients on film composition.
KEYWORDS: Coating, Liquids, Refractive index, Kinematics, Minerals, Interferometry, Reflectivity, Atmospheric modeling, Signal processing, Process control
This work briefly reviews recent progress in interferometric monitoring of spin and of dip coating, from a unified point of view, and its application for contactless viscometry of liquid films. Considering the associated models and measurement uncertainties, the method was validated for both coating processes with oil standards of known viscosities and constant refractive indices. Limitations and perspectives for application of the laser viscometer to liquid films with a varying refractive index are also discussed.
A brief overview of optical monitoring for vacuum and wet bench film deposition processes is presented. Interferometric and polarimetric measurements are combined with regard to simultaneous real-time monitoring of refractive index and physical thickness. Monitor stability and accuracy are verified with transparent oil standards. This double optical technique is applied to dip coating with a multi-component Zirconyl Chloride aqueous solution, whose time varying refractive index and physical thickness curves indicate significant sensitivity to changes of film flow properties during the process.
A significant part of film production by the coating industry is based on wet bench processes, where better understanding of their temporal dynamics could facilitate control and optimization. In this work, in situ laser interferometry is applied to study properties of flowing liquids and quantitatively monitor the dip coating batch process. Two oil standards -- Newtonian, non-volatile, with constant refractive indices and distinct flow properties -- were measured under several withdrawing speeds. The dynamics of film physical thickness then depends on time as t-1/2, and flow characterization becomes possible with high precision (linear slope uncertainty of ±0.04%). Resulting kinematic viscosities for OP60 and OP400 are 1,17 ± 0,03 St and 9,9 ± 0,2 St, respectively. These results agree with nominal values, as provided by the manufacturer. For more complex films (a mutli-component sol-gel Zirconyl Chloride aqueous solution) with a varying refractive index, through a direct polarimetric measurement, allowing also determination of the temporal evolution of physical thickness (uncertainty of ± 0,007 microns) is also determined during dip coating.
As a complement to the standard m-line method, where an analytical curve is fitted to the measurements of waveguide modes and extrapolated to provide the refractive index in the zero-depth limit, we review our polarimetric approach to a direct-near surface measurement of graded-index films, and present its new and more straightforward version, which is applicable to existing samples without masking procedures prior to ion exchange.
Integrated optics components based on second-order nonlinearities are provided by structures presenting departure from centrosymmetry, both at microscopic and at macroscopic levels.
In a non-exhaustive review, we consider optical methods for the evaluation of molecular first hyperpolarizabilities, presenting Hyper-Rayleigh Scattering (HRS) as a more direct method than inference from the standard Electric Field-Induced Second Harmonic Generation (EFISH). From a macro perspective on films, also alternatively to EFISH, we consider determination of second-harmonic susceptibilities from the Maker fringe technique, as well as of electro-optic (EO) coefficients by several methods, using a dc/modulated electric field and light in either transmission or reflection, external or internal.
As a case study from our laboratory, with the standard p-nitroaniline as reference, we illustrate application of HRS to the newer 2-(2’-hydroxy-4’-aminophenyl)-6-nitrobenzoxazole (HBO-BO6) molecule. The guest-host systems formed by its incorporation, as well as of commercial chromophores, into silicate sol-gel film matrices, were subjected to Corona poling. Application of the Poling Optical Polarimetry (POP) method to these systems during poling has revealed significant birefringence. For the resulting oriented structures with high-hyperpolarizability ingredients, such as the HBO-BO6 molecule, POP results have indicated the importance of EO characterization methods with explicit consideration of anisotropy, associated with very high EO coefficient materials.
Direct near-surface (DNS) and m-line techniques for the measurement of surface refractive index of ion-exchanged waveguides are compared. Measurements are also compared to direct investigation of ion concentration profiles by energy dispersion spectroscopy (EDS). Good agreement is obtained for the Ag+, K+, and Ag++K+ exchanged samples, but not for the K++Ag+ sample. The index profile approximately follows in a linear proportion the concentration profile after a single Ag+-exchange, while this is not observed for all other samples involving K+-exchange. These results on ion-exchange and refractive-index profiles are discussed, towards a comprehensive and accurate characterization of graded-index waveguides.
Optical monitoring (OM) during film production is considered for thermal vacuum and spin coating processes. During spin coating, OM has allowed identification of several phases during film formation, and characterization of the temporal dynamics may improve control and reproducibility in film production. For films grown under high vacuum, optical monitoring allows continuous inspection of the interference signal, with typical determination of optical thicknesses in multiples of quarterwaves. Long trial-and-error procedures are avoided, even under presence of density fluctuations during deposition. Instrumentation and metrologic aspects are presented. Examples are given of liquid film deposition for silicate sol-gel films and silicone oils, as well as of thermal evaporation of ZnSe and ZnS films. In these, we also performed an intercomparative analysis with the post- process, spectrophotometric envelope method. Optical interferometry monitoring is non-destructive, can be integrated to film manufacturing processes, allows precise metrological procedures, and can be applied to the real-time and in situ characterization of a wide variety of non- opaque, liquid or solid, films.
Optical interferometric monitoring during spin coating of fluid coatings has allowed close observation of their temporal evolution. When the fluids are non-volatile, kinematic viscosity data can be determined using a simple analytical model. Validity of the method was tested with a standard nominal kinematic viscosity v equals 37 +/- 1 cS for which the optospinography method, combined with Abbe refractometry, provided v equals 36.1 +/- 0.1 vS. This is an indication that we now have available an absolute, contactless optical viscometry method for thin fluid films in small samples.
In the characterization of graded-index glass waveguides, use of the standard m-line method by several laboratories has produced increasing discrepancies in the refractive index profile with decreasing film depth. We have addressed this very critical problem by a direct near-surface (DNS) approach, where the polarimetric Abeles-Hacskaylo method was extended as an admittance-matching condition for inhomogeneous films. In this paper, we review the measurement procedures of the same Ag+-exchanged waveguides by the DNS approach and by the m-line method, whose result showed significant disagreement at the film-air interface. We search the underlying reasons for this disagreement and test them against non-optical measurements of the ion-concentration profile, to reach a better understanding of the near-surface region, as well as of the distinct probing range of the m-line and DNS techniques.
Results form our near-surface approach for inhomogeneous films are compared with those from the standard m-line technique in K+ and Ag+ ion-exchanged, graded- index waveguides. We focused our attention on the determination of the refractive index at the film-air interface, and we conclude, from fundamental reasoning as well as from experimental evidence, that the direct near- surface approach can provide higher accuracy than the usual extrapolation from the modal effective indices.
We consider application of the in situ poling optical polarimetry method to guest-host systems consisting of a Corona-poled, sol-gel, porous silicate film matrix doped with Disperse Red 1 (DR1) chromophores. Refractive indices, and physical thicknesses are consistently determined by ex situ null ellipsometry, atomic force microscopy and Abeles- Hacskaylo characterization. Due to the pronounced poling- induced birefringence we found in the composite films, in opposition to previous approaches, we could not disregard it with respect to refractive index values. Even for the case of strong birefringence, this procedure and associated modeling allow estimation of electro-optic coefficients and second-order susceptibilities of poled dielectric films doped with DR1, or with other high hyperpolarizability chromophores.
First results are presented of optical interferometric monitoring during dip coating in real time, as applied to mineral oil OP10 and multi-component zirconyl chloride aqueous solution films. Resulting new perspectives are considered.
Monitoring of electrical field poling processes by optical polarimetry (EFPOP) is presented as a simple alternative method for the study of induced noncentrosymmetry, related to nonlinear optical second-order effects in organic chromophore-doped sol-gel films. Dynamics of EFPOP has been closely followed in guest-host systems, consisting of porous sol-gel silicate film matrices doped with p-nitroaniline, as evidence of the EFPOP sensitivity to chromophore orientational order.
Optical interferometric monitoring of spin coating (optospinography) has allowed close observation of a thin liquid film temporal evolution (at 500 -2500 rpm, 100 Hz data acquisition), from which its kinematic viscosity can be determined. The data obtained from this procedure is in good agreement with known values for two oil standards, indicating that the method is valid in the range of approx. 0.4 to 150 Stokes. Advantages and limitations are discussed.
Temporal evolution during spin coating is interferometrically monitored, with close regard to gelation at the final stages of the process. Uniform silica films on silicon were produced from an established sol composition, from which slight deviations were taken to produce nonuniform, cracked films. A distinct evolution of the sol to gel transition could then be detected, at speed of rotations of 1000 - 3000 rpm and data acquisition at 100 Hz. Interpretation of a set of experimental results is discussed in terms of a two-phase system, in the light of, and as a test of, current theoretical models.
The aim of the present work was developing of a simple in use laser modulation set-up of the high fidelity and fully controlled by the personal computer. That allows to broad the area of application of the gas and solid state lasers in such fields as medicine, therapy, biology, environment control etc. where the staff without the deeper knowledge in non-linear optics can successfully solved the problems of their own speciality. To build up the electrooptic element of the modulator such advanced material as transparent PLZT ceramics was chosen. Advantages of this ceramics as compared with mainly used for the same purposes electrooptic single crystals - as extremely high values of the electrooptic coefficients, the broad range of transparency, a high resistance to optical damage and the relative cheapness of its producing allow to use PLZT ceramics in a variety of electrooptic devices 1. In the last years cheap portable PLZT modulators - small in size, with minimum of optical length (1-2 mm), simple in adjusting and use were offered for didactic purposes to demonstrate in schools and universities the electrooptic effect and the use of this effect for information transmitting via laser beam 2,3.
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