In this work we present reactive sputtered SiOxNy films with a variable refractive index as a convienent solution for contrast improvement of liquid crystal diffuser multi stacks in near-to-eye AR/VR displays. The focus concerns minimization of light reflections between internal structures, in particular ITO, by optimizing internal layers through tailored properties of thin film coatings, as well as subsequent laser patterning of thin film stack. Inorganic thin films have been deposited on glass by physical vapor deposition. Corresponding refractive index, thickness, uniformity and dielectric characteristics and other electro-optical properties have been measured and their impact on the resulting optical performance of the final integrated element stack has been compared against counterparts utilizing traditional polyimide and SiOx films.
We demonstrated a new approach to measuring third-order nonlinear optical effects using an experimental setup incorporating both Z-scan and Mach-Zehnder interferometer methods. This method could be especially purposive for thermo-optical effect studies as it can simultaneously probe thermal gradient profile as well as absolute temperature changes induced by an optical beam. The experimental setup was tested using chloroform. Experimental measurements were carried out using 1064 nm Nd:YAG laser with 8 ns pulse width and 40 kHz pulse repetition rate. The measured nonlinear refractive index of chloroform was mainly induced by the thermo-optical effect. As thermo-optical response depends on beam size at focal length, measurements were carried out with 35 mm and 125 mm focal length lenses. Measured nonlinear refractive index values of Z-scan and interferometric measurements gave the same value indicating that this method can be used for thermo-optical effect studies.
In this paper we report the results of studied nonlinear optical properties of DMABI-Ph6 in form of solutions with chloroform as solvent and guest-host thin films with poly(methyl methacrylate) as host material. We implemented the Zscan method for studies of Kerr and two-photon absorption of selected material. During experimental measurements we used 1064 nm Nd:YAG laser with 30 ps pulse duration and 10 Hz repetition rate. From acquired values of Kerr coefficients we calculated values for real part of third-order susceptibility, as well as second-order hyperpolarizability. Acquired data for DMABI-Ph6 were compared with data for other ABI derivatives studied previously to describe how different donor and acceptor groups influence third-order nonlinear optical properties.
We studied nonlinear optical properties of two different aminobenziliden-1,3-indandione derivatives – DDMABI and DMABI-OH by employing the Z-scan method. Through this we described how different donor and acceptor groups influence third-order nonlinear optical properties such as Kerr effect and two-photon absorption. During experimental measurements we used 1064 nm Nd:YAG laser with 30 ps pulse duration and 10 Hz repetition rate. From acquired values of Kerr and two-photon absorption coefficients we calculated values for real and imaginary parts of third-order susceptibility, as well as second-order hyperpolarizability. Quantum chemical calculations were carried out for secondorder hyperpolarizability to study how well calculations correlate with experimental values. Acquired data for DDMABI and DMABI-OH were compared with data for other ABI derivatives studied previously.
We describe the sample preparation and experimental setup for second harmonic generation measurement of electro-optical (EO) chromophore/polymer system at the time of contact-poling. Different types of spacers for avoiding electric breakdown due to avalanche multiplication are compared. Electric field threshold values for second harmonic generation are observed in all samples.
Fast liquid crystal optical shutters due to fast switching, vibrationless control and optical properties have found various applications: substitutes for mechanical shutters, 3D active shutter glasses, 3D volumetric displays and more. Switching speed depends not only on properties of liquid crystal, but also on applied electric field intensity. Applied field in the shutters can exceed >10 V/micron which may lead to dielectric breakdown. Therefore, a dielectric thin film is needed between transparent conductive electrodes in order to reduce breakdown probability. In this work we have compared electrical and optical properties of liquid crystal displays with dielectric thin films with thicknesses up to few hundred nanometers coated by flexo printing method and magnetron sputtering. Dielectric breakdown values show flexographic thin films to have higher resistance to dielectric breakdown, although sputtered coatings have better optical properties, such as higher transmission and no coloration.
Triphenylmethyl and triphenylsilyl structural fragments can be used to obtain glass forming, solution processable materials from polar chromophore molecules. Large number of compounds has been synthesized taking advantage of this approach, making it possible to identify some structure-property relations. Regarding the non-linear optical (NLO) properties of the given materials it is evident that triphenylmethyl groups help shielding unwanted NLO efficiency limiting dipolar interactions between polar chromophores in solid films. Chromophore stacking is still observed for compounds with large dipole momentum values. The glass transition temperatures of the compounds increase with the molecular weight for the studied material class, reaching values up to 130°C.
Small D-π-A type organic molecules with incorporated 4H-pyan-4-ylidene (pyranylidene) fragment in their structures show potential in organic photonics - such as materials for organic light emitting diode application studies and organic solid state lasers. Additional incorporation of bulky triphenyl- groups in their structures gives them the ability to form thin amorphous solid films from volatile non-polar organic solvents. Unfortunately, there is still no clear relation between compound organic structures and their thermal and optical properties. In order to investigate the above mentioned regularities we have synthesized a series of tripheyl- group containing derivates of 2,6-bis-styryl-4H-pyran-4- ylidene with different stryryl- substituents and investigated their physical properties. The thermal decomposition temperatures of the obtained glassy 4H-pyran-4-ylidene compounds are in range from 198o to 312oC and depend from electron acceptor and styryl-groups while their glass transition temperatures are in range from 104o to 132oC and are mostly influenced by the electron acceptor fragment. The light absorption of synthesized 4Hpyran- 4-ylidene compounds in solutions of dichloromethane as well as in their solid state are in range from 400 nm to 550 nm. Their photoluminescence spectra in the solid state (from 600 nm to 800 nm) are red-shifted by approximately 50 nm comparing to their photoluminescence spectra in solutions of dichloromethane (from 550 nm to 750 nm) and mostly depends on the N,N-ditrityloxyethyl-aminostyryl-electron donor substituent, 4H-pyran-4-ylidene π-system and on the electron-acceptor group. Synthesized compounds could be used as potential materials for light amplification.
Thin organic waveguiding layers are applied more and more frequently as optical components in novel optoelectronic devices. For development of such devices it is important to know the optical properties of the used waveguides. One of the most important parameters is optical propagation loss in the waveguide. In this paper we present optical propagation loss measurements in planar electro optical waveguides using travelling fiber method. Using this method attenuation coefficient α at 633 nm as a function of chromophore concentration for the first two guiding modes in the slab waveguide was determined.
Molecular organic compounds with electron donating fragment bounded through π-conjugated system with electron acceptor fragment, as well as with incorporated triphenyl groups in their molecules show potential for creating cheap and simple solution processable materials with nonlinear optical properties. Additional insertion of azobenzene fragment in their structures makes them also possible to form holographic volume and surface relief gratings (SRG) after exposure to laser radiation, which could be useful for holographic data storage. For these purposes polymers are generally used. However, their application is complicated and challenging task as in every attempt to obtain the same polymer it will have different physical properties. On the other hand, the synthetic procedure of molecular glasses is more simple as their structure and physical properties are strongly defined. Unfortunately, there is still no clear relation between compound organic structures and their thermal, glass-forming and optical properties.
In order to investigate the above mentioned regularities, we have synthesized and investigated ten molecular glassy organic compounds with three different fragments as main backbones of the molecules: indene-1,3-dione (WE-1, WE-2, WE-3), isophorene (IWK-1D, IWK-2M, IWK-2D) and pyranylidene (DWK-2TB, ZWK-2TB, JWK-2TB, ZWK-3AZO). Compounds containing isophorene fragment in their molecules had the highest NLO efficiencies (d33 up to 125.7 pm/V for IWK-2D) and also were the most effective holographic data storage compounds with holographic self diffraction efficiency 13% and holographic diffraction efficiency 20%, also for IWK-2D, but their thermal stability (Td from 288°C to 295°C) and glass transition (Tg from 90°C to 105°C) values were just average. Pyranylidene type compounds had the highest thermal stability and highest glass transition (Tg from 115°C to 180°C). But their ability to form and maintain amorphous structure were low and they had average NLO efficiencies (d33 up to 66.2 pm/V for ZWK-2TB) and average holographic self diffraction efficiency 2% and holographic diffraction efficiency 8% for ZWK-3AZO. The molecules with just azobenzene fragment and indene-1,3-dione as electron acceptor has the lowest thermal (Td from 250°C to 282°C, Tg from 70°C to 98°C) and also the lowest holographic properties with holographic diffraction and self diffraction efficiencies at 4% for WE-1 and lower for other compounds. Nevertheless, some of the investigated molecular glasses show potential as multifunctional optical materials.
KEYWORDS: Chromophores, Systems modeling, Nonlinear optics, Polymers, Molecules, Monte Carlo methods, Polarization, 3D modeling, Picosecond phenomena, Computer simulations
One of the possibilities to create organic molecular material for NLO applications are polymers with dispersed NLO
active chromophores. These molecules must be acentrically ordered by applying an external electric poling field. The
NLO efficiency depends on dipole moment, molecular hyperpolarizabilities, concentration of the chromophores and
external poling field strength. Calculating, from first principles, the extent of the alignment and via this NLO efficiency
has proven to be challenging. One approach to solve this problem is pure analytic statistical mechanics treatment, what
could be enhanced by Monte Carlo (MC) statistical mechanical modelling. The chromophore molecules usually have
been treated as point dipoles embedded in some kind of realistic molecular shape – prolate spheroid. Another possibility
is fully atomistic molecular modelling with classical force field MD methods. This method allows obtain extent of
alignment and observing kinetics of poling and relaxation. Unfortunately, in case when host and chromophores are
represented at atomistic level, MD approach requires huge amount of computations. One of the solutions is to reproduce
the motion of the molecules of interest (chromophores) using Langevin dynamics (LD). This method simulates the effect
of molecular collisions and the resulting dissipation of energy that occur in real host, without explicitly including host
molecules. In this contribution chromophore load, dipole moment and poling field impact on extent of alignment and
poling / relaxation dynamics of model system obtained by LD simulations will be presented. On a basis of these results
we would like to come forward with some inspirations for EO polymer design.
New molecular design of obtaining molecular glasses has been developed by linking triphenylmethyl moieties to
chromophore core by flexible C-C bridge. Compounds capable of forming stable amorphous phase with good optical
quality have been acquired with increased chemical and thermal sustainability compared to the previously reported
design. NLO activity of compounds has been measured after corona discharge polling. Compared to previously
synthesized trityloxy fragment containing compounds increase of d33 coefficient by up to 17 times was achieved for the
same chromophore core containing compounds.
A simple method for measuring bilayer system refractive indexes and thicknesses in the low absorbing part of
spectra is demonstrated. The method is based on application of Savitzky - Golay smoothing filters and interference
fringe separation in the reflected or transmitted spectra of the bilayer system. The refractive indexes and thicknesses are
extracted from the wavelengths corresponding to extreme points in the spectrum. Due to the fact that wavelength
difference of extreme points in the analyzed spectrum is defined by the product of both, the layer thickness and refractive
index, one must generate an appropriate initial guess of these parameters. For refractive index approximation two
different methods have been used - point by point and Sellmeier dispersion relation. The final optimization procedure is
based on a priori assumption that the thickness calculated from permutations of all extreme points in the spectrum
should be the same. Thus the optimal penalty parameter for finding the solution is the standard deviation of calculated
thicknesses. In order to demonstrate the effectiveness of this simple method, results of thin organic film thicknesses and
refractive indexes are presented.
In this work we present simple preparation of original trityl group containing glassy luminescent 6-styryl substituted
derivatives of 2-(2-tert-butyl-4H-pyran-4-ylidene)malononitrile
(DWK-1TB), 2-(2-tert-butyl-4H-pyran-4-ylidene)-2-
ethyl-2-cyanoacetate (KWK-1TB),
2-(2-tert-butyl-4H-pyran-4-ylidene)-1H-indene-1,3(2H)-dione
(ZWK-1TB) and
5-(2-tert-butyl-4H-pyran-4-ylidene)pyrimidine-2,4,6(1H,3H,5H)-trione (JWK-1TB). Their optical properties have been
investigated. The absorption maxima of synthesized glasses is in region from 425 nm to 515 nm and emission maxima is
from 470 nm to 625 nm in solution of dichloromethane. But absorption maxima of their solid films is from 425 nm to
500 nm and emission maxima is in range from 570 nm to 710 nm.
Incorporation of bulky trityloxy ethyl groups combining with existing tert-butyl groups results in thin solid films
formation of synthesized glasses from volatile organic solvents (chloroform, dichloromethane) without them being doped
in any polymer. This makes them perspective for potential applications in organic light-emitting diodes and organic
lasers by simple luminescent layer composition with cheap
wet-casting approaches.
All glasses show good thermal stability with thermal decomposition temperatures from 264° to 318°C and glass
transition values up to 158°C for DWK-1TB. These thermal properties of synthesized glasses could make them also
useful for potential applications in other optical materials such as materials for nonlinear optics.
In given study a new structural design of molecular NLO materials is presented where amorphous phase formation is
achieved by introduction of bulky trityl and triphenylsilyl substituents. Obtained materials formed stable organic glasses
with good optical quality and glass transition temperatures notably exceeding ambient. NLO activity was successfully
measured in samples that underwent corona discharge poling. The comparison of both enhancer groups revealed, that
trityl group increases thermal sustainability of material, while triphenylsilyl group better promotes formation and
stability of amorphous phase.
SHG efficiency of the poled guest - host polymer system is proportional to the concentration and orientation degree of
NLO active molecules (chromophores). Corona poling realized at elevated temperatures could cause concentration
decrease of NLO- active molecules due to centrosymmetric crystallization. Our studies showed that number density of
crystallites is depending on orientation procedure. To obtain the best orientation procedure for guest - host systems
containing four different chromophores based on dimethylaminobenzylidene 1, 3 - indandione we have compared
optical images and SHG efficiency of corona poled films. According to our observations external poling electric field
applied from the very beginning of the sample heating process can reduce crystallite grow. The optical quality is
improved and SHG efficiency in some cases is up to 1.6 (depending on molecule structure) times larger after our
suggested orientation sequence compared to classic corona poling procedures.
The optically induced switching of material properties is important for investigations of opto-electronic effects and optomechanical
properties. Investigated organic materials contain chromophore dipole consisting of acceptor and donor
groups bridged by a delocalized &pgr;-electron system. Both calculations and experimental data show a reversible highly
dipolar photoinduced intra molecular charge transfer in indandione type molecules (DMABI) accompanied by change of
the sign and the value of the dipole moment. Investigations of optical properties of thin host-guest polymer films show
that the photoinduced process of DMABI is related to the photoinduced switching between two equally stable states of
the molecule. In this work first results of formation of the surface relief in polymer films incorporated with DMABI
derivatives will be presented. The refractive index gratings of DMABI host-guest films show that red light is less
diffracted than blue one. The reversible surface potential changes on irradiation in photoinduced intramolecular electron
transfer band in polymer host-guest films is observed. The DMABI molecules in solid state have nonlinear optical
properties, which can be used and investigated in host-guest polymer matrix. The influence of concentration of DMABI
molecules on photoinduced processes is discussed.
Many organic compounds in solid state have nonlinear optical properties due to the orientation of the molecules in a
polymer matrix. In this work, all-optical poling and second harmonic generation in a composition consisting of 1 mass%
of N,N-dimethylaminobenzylidene 1,3-indandione (DMABI) compound in poly(methyl methacrylate) (PMMA) matrix
were studied. Thin films were prepared by solvent casting. The 1.064-μm fundamental and 532-nm second harmonic
wavelengths of a Nd:YAG laser were used. It is shown that DMABI molecules can be oriented by the method of all-
optical poling, and that the process is related to the photoinduced switching between two equally stable states of the
molecule.
Second order non linear optical (NLO) properties of sPMMA based host-guest systems containing eight dimethylaminobenzylidene -1, 3 - indandione (DMABI) related chromophores have been investigated by means of quantum chemical calculations and SHG experimental characterization. Ab initio calculations with basis set 6-31G were used for molecular geometry determination as well as in the calculations of molecular hyperpolarizability by FF approach. Influence of the chromophore concentration on the host-guest film NLO performance was obtained by SHG Maker fringe experiments. The highest value of d53233 =80 pm/V (frequency corrected value d033 =12 pm/V) at chromophore concentration 15 %wt have been recorded for tret-butyl substituted DMABI chromophore.
Molecular structure and optical properties of the novel amphiphilic derivative of dimethylaminobenzylidene 1,3- indandione (C17DMABI), have been studied as the monolayer on a water surface (Langmuir films) and Langmuir-Blodgett (LB) multilayers of Y-type structure using optical absorption techniques. The compression (pi) - A isotherms of the C17DMABI monolayer show two different phases. Phase transition takes place at surface pressures 1 less than (pi) less than 20 mN/m. The compression-induced changes of the monolayer spectra in the region 330 - 600 nm have been analyzed using deconvolution of spectra of Gaussian shaped bands. At least three different transitions takes place at approximately 395, approximately 445 and approximately 505 nm. Analysis of deconvoluted band spectral shifts, intensities and dichroism confirms a molecular packing rearrangement and change of the tilting angle at the phase transition pressure interval.
Five amphiphilic alpha- or beta-amino acid derivatives containing photoactive azobenzene moiety and bearing amide or sulfonamide functional groups were synthesized and mono- and multilayers, prepared by Langmuir-Blodgett technique, were investigated. The reversible photoisomerization processes in solutions of these derivatives were observed. Reversible trans/cis photoisomerization of 4-[4-(hexyl- palmitoylamino)- phenylazo]benzenesulfonyl-(beta) -alanine in multilayer assemblies has been observed on alternate irradiation with UV light (centered at 360 nm) and visible light (452 nm).
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