Characterization Of Optical Materials Research Articles

Optical characterization of semiconductor materials by using FTIR-PAS

In this paper we discuss the procedures for photoacoustic measurements for semiconducting materials, including bulk samples like Gallium Antimonide (GaSb). The optical absorption at photon energies near the band gap was measured at room temperature using Fourier Transform Infrared Photoacoustic spectroscopy (FTIR-PAS). Measurements were performed using a NEXUS 670 FTIR-spectrometer (from Thermo Nicolet) with a MTEC model 300 PA cell (MTEC Photoacoustics, Inc.). Optical properties of the studied samples were determined from their room temperature PA spectra and band gaps were calculated directly from absorption spectra

Electrochromic conducting polymers: optical contrast characterization of chameleonic materials

The optical characterization in the visible wavelength range was obtained for an electrochromic material, poly-3, 4-ethylenedioxy-thiophene (PEDOT), as a function of its redox charge density (charge consumed for the color change between its maximum and minimum absorbance states). The experimental procedure was kept very simple and all the information can be obtained from only one film, including the identification of the maximum achievable contrast for the material. Different films of the electrochromic material were tested in order to check the validity of the predicted values, showing excellent agreement.

An Overview of Recent Advances in Metrology Development for Nanoelectronics at the National Institute of Standards and Technology (NIST)

Nanoelectronics require the introduction of several new uncharacterized material(s) combinations and new processing techniques. The critical metrology and characterization needs of the nanoelectronics industry are being addressed with a broad range of development programs at the National Institute of Standards and Technology (NIST). In this paper, we provide an overview of the recent advances in nanoelectronics enabling metrology developments at NIST. We will discuss a broad range of new techniques, equipment and infrastructure that are being developed to enable atomic and nano-scale measurements. Examples include, but are not limited to: high resolution, low noise techniques and infrastructure for nanoscale chemical analysis; metrology for characterizing device and material intrinsic reliability; electrical, optical and physical characterization of novel materials; and monitoring of processes.

Organic–Inorganic Hybrid Materials for Photonic Applications

Organic-inorganic hybrid materials are derived from the chemical reaction of silane coupling reagents and metal alkoxides, involving O-Si-C bonds in the matrix. They offer superior characters of combined organic groups and inorganic linkages for various optical applications. This paper reviews preparation and characterization of optical devices and materials derived from these hybrid materials. We mainly describe three topics for micrometer-nanometer scale optical components in our laboratories using organic-inorganic hybrid materials: 1) film formation; 2) patterning by the photolithography techniques; and 3) laser emission from dye-doped hybrid spheres and coated glass spheres.

Pump polarization-state preservation of picosecond generated white-light supercontinuum

Supercontinuum (SC) generation is among the most interesting nonlinear optical effects lately discovered, due to the complexity of the mechanisms responsible for its generation. This phenomenon, first demonstrated by Alfano and Shapiro using picosecond pulses in condensed phase, has found novel applications in optical pulse compression, time-resolved spectroscopy and material characterization among many others. Here, we demonstrate that picosecond generated SC white-light in water preserves the polarization state: linear, elliptical and circular of the pump source. Moreover, we were able to determine the SC polarization rotation direction in the circular case. With the generation of pulsed circularly polarized SC, new studies and applications are envisaged in the biological, medical and pharmaceutical field. Amino acids, involved in the origin of life, and other chiral structures represent an attractive target for this type of study.

Tomographic reconstruction of weak, replicated index structures embedded in a volume

Measurements of weak, embedded index structures are important for material characterization of photopolymers, glass and other optical materials as well as for characterization of fabricated structures such as waveguides. We demonstrate an optical diffraction tomography system capable of measuring deeply-buried, weak, fabricated index structures written in a homogeneous volume. High-fidelity cross sections of these weak index structures are constructed by replicating the structure to be measured to form a diffraction grating. The coherent addition of scattering from each of these objects increases the sensitivity of the imaging system. Measurements are made in the far field, without the use of lenses, eliminating phase aberration errors through thick volumes.

Preparation and optical characterization of catalyst free SiO2 sonogel hybrid materials

The synthesis of sol-gel materials induced by ultrasonic irradiation (sonolysis) is implemented as an alternative method for the fabrication of highly pure organic-inorganic composites with good monolithic, mechanical and optical properties. Ultrasonic irradiation, instead of commonly used basic- or acidic-catalyst was used to produce acoustical cavitation within the liquid H2O/tetraethyl-ortosilicate (TEOS) reactants. This procedure forms a hydrolyzed-TEOS colloidal dispersion (sol) which produces, after drying, a highly pure SiO2 network. The resulting SiO2 glass exhibits high porosity and allows the inclusion of several organic compounds in the colloidal sol-state. Novel, optical active synthesized liquid crystalline (LC)-azo-compounds, bent shaped mesogens, cis- and trans-poly(1-ethynylpyrene)s, as well as fullerene (C60) spheres and classical organic dyes were successfully incorporated as dopant agents within the novel catalyst free (CF) SiO2-sonogel host matrix. Absorption and fluorescence spectroscopy studies were carried out in order to characterize the optical performance of both the CF-sonogel and several hybrid composites The pulsed laser photoacoustic technique (LPAT) was implemented to determine thermodynamic phase transitions of LC-based hybrids and laser induced damage (photo-degradation) in dye-based composites. Finally, comparative morphology studies between undoped reference samples and some doped composites were performed by Atomic Force Microscopy (AFM), where an optimal TEOS/dopant concentration ratio, to obtain good mechanical properties among the studied samples, has been found.

Imaging of nonlinear optical response in biopolyesters via second harmonic generation microscopy and its dependence on the crystalline structures

Nonlinear optical response in various polyhydroxyalkanoates (PHAs) was investigated via second harmonic generation microscopy (SHGM). It was revealed that the second harmonic generation (SHG) efficiency depended on both the polymer chemical structure and the crystalline structure. Among the PHAs studied, the microbial polyesters, poly(R-3-hydroxybutyrate) (PHB) and poly(R-3-hydroxyvalerate) (PHV) showed strongest SHG activity, which could be attributed to hydrogen bonding that enhanced hyperpolarizability of the carbonyl groups in the crystalline lamellar core, and the noncentrosymmetric arrangement of the SHG moieties. The β- and γ-type poly(β-propiolactone) demonstrated different SHG efficiency due to the different packing scheme of the chain stems in the crystal lattice despite the same chain conformation. In addition, SHG response in the banded spherulite varied with the lamellar orientation. Furthermore, SHGM was applied for 3-D imaging of PHB spherulite in PHB/poly(ɛ-caprolactone) blends via optical sectioning of the thick film at different depths. For PHB/poly(l-lactide) (PLLA) blends, SHGM revealed that the PHB twisting lamellae formed from the melt confined between the preformed PLLA twisting lamellae had the same twisting period as the latter, which could not be observed under polarized optical microscope. Due to the advantages, SHGM is expected to find more applications in characterization of nonlinear optical (NLO) materials with heterogeneous structures.

Spectrometric Determination of the Refractive Index of Optical Wave Guiding Materials Used in Lab-on-a-Chip Applications

The design and optimization of light-based analytical devices often require optical characterization of materials involved in their construction. With the aim of benefiting lab-on-a-chip applications, a transmission spectrometric method for determining refractive indices, n, of transparent solids is presented here. Angular dependence of the reflection coefficient between material-air interfaces constitutes the basis of the procedure. Firstly, the method is studied via simulation, using a theoretical algorithm that describes the light propagation through the sample slide, to assess the potentially attainable accuracy. Simulations also serve to specify the angles at which measurements should be taken. Secondly, a visible light source and an optical fiber spectrometer are used to perform measurements on three commonly used materials in optical lab-on-a-chip devices. A nonlinear regression subroutine fits experimental data to the proposed theoretical model and is used to obtain n. Because the attainable precision using this method of refractive index determination is dictated by the uncertainty in the transmission measurements, the precision (with 95% confidence) for mechanically rigid samples, namely glass and poly(methyl methacrylate) (PMMA), is higher than those estimated for the elastomer sample (in-house-molded poly(dimethylsiloxane) (PDMS)). At wavelengths with the highest signal-to-noise ratio for the spectrometer setup, the estimated refractive indices were 1.43+/-0.05 (580 nm) for PDMS, 1.54+/-0.02 (546 nm) for glass, and 1.485+/-0.005 (656 nm) for PMMA. Accurate refractive index estimations with an average precision equal to 0.01 refractive index units (RIU) were obtained for PMMA and glass samples, and an average precision of 0.09 RIU for the PDMS molded slide between 550 and 750 nm was obtained.

Synthesis and Optical Characterization of Novel Imidazole-Based Azo Materials

We synthesized novel imidazole-based azo compounds and their optical properties were investigated. In the course of recrystallization, pink-orange and violet products were obtained. The violet one shows poor solubility for most organic solvents except polar aprotic solvents such as dimethylsulfoxide (DMSO) and dimethylfolmamide (DMF). The spectra of NMR in DMSO-d6 and UV–vis absorption spectra in DMSO for both products were found to be identical. However, there were differences in FT-IR absorption spectra. The violet solid compound exhibited broad bands that could be attributed to N–H…N hydrogen bonding. These results show that the violet product consists of an aggregation of molecules formed via intermolecular hydrogen bonding. Additionally, imidazole-based azo copolymers containing liquid crystalline side chain groups were also synthesized. The photoinduced birefringence of these copolymers was observed by irradiation of a linearly polarized 532 nm laser beam as a pumping light. It was confirmed that the material exhibited photoisomerization properties and the observed birefringence was attributed to photoinduced molecular reorientation. Moreover, the dipolar effect in photoinduced birefringence was briefly discussed.

An elastomeric grating coupler

We report on a novel nondestructive and reversible method for coupling free space light to planar optical waveguides. In this method, an elastomeric grating is used to produce an effective refractive index modulation on the surface of the optical waveguide. The external elastomeric grating binds to the surface of the waveguide with van der Waals forces and makes conformal contact without any applied pressure. As a demonstration of the feasibility of the approach, we use it to measure the refractive index of a silicon oxynitride film. This technique is nondestructive, reversible, low cost and can easily be applied to the characterization of optical materials for integrated optics.

Near-Field Optical Characterization of Nanocomposite Materials

We present a near-field optical technique which makes use of the strongly enhanced optical field at a laser-illuminated metal tip. The enhanced field is used to locally excite the sample under investigation by multiphoton absorption. An optical scan image with spatial resolutions down to 20 nm is established by detecting the emitted fluorescence. The principle of the method is described and experimental results are demonstrated for samples of J-aggregates of PIC dye molecules. Ongoing experiments on nanocomposite, Er 3+ -doped oxyfluoride glass-ceramics are discussed.

High-resolution and easily implemented spectral measured system used for optical characterization of optoelectronic materials and devices

We set up a compact high-resolution linear charge-coupled-device (CCD)-based spectrometer for the characterization of optoelectronic materials and devices. The spectrometer is controlled by a personal computer. Detailed design diagrams of the mechanical structure and electronic hardware are described. Spectral resolution of the CCD measurement system of ~0.7 A/pixel is determined from spectral calibration using two laser sources. Electroluminescent measurements of several selective optoelectronic components, as well as the transmission measurements of GaSe and GaSe 0.9 S 0.1 layered semiconductors, are performed utilizing the new spectrometer. The experimental results are analyzed and discussed.

Automatic Instrumentation with a PC-based Data Acquisition System for Experiments in Optical Characterization of Materials

A simple automatic control for applications of optical characterization of materials using theoptical Z-scan technique is presented in this paper. The emphasis is placed in the automation process. For this purpose, a communication I/O port of a PCI-MIO-16E data acquisition card (from National Instruments) was used and the graphical programming language LabVIEW.

Structure Property Characterization of Nonlinear Optical Materials

ABSTRACTThis research is comprised of understanding the linear photophysical properties of various dyes to better understand the more complicated nonlinear optical properties. Determining structure property relationships of a series of structurally closely related chromophores is the key in understanding the drivers for the various photophysical properties. In this paper we survey the effect of physically changing the Pt poly-yne structure on the S0-S1 and T1-Tn absorption properties for each of the chromophores. A series of structurally modified platinum poly-ynes have been studied using experimental methods including UV/Vis absorption and nanosecond laser flash photolysis. We found that with extension of the ligand length both the ground and triplet excited state absorption shift to lower energies. Comparing the absorption properties of the ligands and butadiynes with the platinum containing versions reveal that the S1 and Tn exciton is localized on one portion of the ligand with extension and not conjugated through the whole molecule. Changing the phosphine R group results in little effect to the absorption properties except when the R group is conjugated in the case of phenyl. However, changing the R group results in varied materials properties.

Quantitative characterization of aqueous solutions probed by the third-harmonic generation microscopy

Third-harmonic microscopy is one of the emerging techniques for noninvasive microscopic imaging of biological structures. We use a novel technique for nonlinear optical material characterization and study the effect of different environment and the structural sensitivity of the third harmonic. In particular, a transformation of collagen in solution is observed for the first time using third-harmonic generation. We also study the ultimate limits of the third harmonic to detect micro- and nanoscopic features inside living cells and find that structures as small as 50 nm can be detected using the current level of technology.

ChemInform Abstract: Preparation and Characterization of Nonlinear Optical Crystal Materials: Cadmium Mercury Thiocyanate and Its Lewis Base Adducts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Chemical characterization of optical data storage materials by EPMA

Chemical characterization of optical data storage materials by EPMA

Investigation of thermal transport in n-type porous silicon by photo-acoustic technique

Non-destructive thermal and optical characterization of materials can be successfully performed by the photo-acoustic technique. In this work, this technique has been applied to the measure of thermal conductivity in porous silicon by considering the photo-acoustic response at fixed frequency of samples having the same porosity but different thicknesses. Experimental data are interpreted in terms of a model which takes into account both scattering effects and the contribution to the photo-acoustic signal of the interstitial gas expansion. The measured thermal conductivity is found to be lower than the one reported for crystalline silicon by two orders of magnitude. A discussion of the photo-acoustic signal dependence on the morphology of the porous medium is also presented.

Novel techniques for the optical characterization of photovoltaic materials and devices

By means of newly designed optical instrumentation, mainly based on the use of integrating spheres, the fundamental optical properties of photovoltaic materials and devices (solar cells, modules) have been investigated. Relevant results concerned the optical loss (reflectance) of devices and the transmittance of semitransparent materials, used in the window sheets, under both direct and diffuse light. All the developed techniques are non-destructive and allow the characterization of selected areas of the samples. The use, however, of automatic translation stages makes easy to perform an optical and, in some cases, electrical mapping of the entire sample.