Nonlinear Optical Thin Films Research Articles

Coordination-Induced Symmetry Breaking on Metal-Porphyrinic Framework Thin Films for Enhanced Nonlinear Optical Limiting

Structural asymmetry affecting the nonlinear optics (NLO) of metal-organic frameworks (MOFs) is very important in fundamentals and applications but is still a challenge. Herein we develop a series of indium-porphyrinic framework (InTCPP) thin films and provide the first study on the coordination-induced symmetry breaking on their third-order NLO. The continuous and oriented InTCPP(H2) thin films were grown on quartz substrates and then postcoordinated with different cations (Fe2+ or Fe3+Cl-) in InTCPP(H2) (named InTCPP(Fe2+) and InTCPP(Fe3+Cl-)). The third-order NLO results reveal the Fe2+ and Fe3+Cl- coordinated InTCPP thin films have substantially enhanced NLO performance. Moreover, InTCPP(Fe3+Cl-) thin films cause symmetry breaking of microstructures, resulting in a 3-fold increase in the nonlinear absorption coefficient (up to 6.35 × 10-6 m/W) compared to InTCPP(Fe2+). This work not only develops a series of nonlinear optical MOF thin films but also provides new insight into symmetry breaking on MOFs for nonlinear optoelectronic applications.

Effect of growth temperature conditions on the optimization of OH1 single-crystalline thin film by physical vapour deposition

The shape control of 2-(3-(4-hydroxystyry1)-5,5-dimethylcyclohex-2-enylidene) malononitrile (OH1) organic nonlinear optical (NLO) single-crystalline thin film grown by physical vapour deposition (PVD) has been achieved by optimizing the growth temperature condition.

A study of 8 MeV e-beam on localized defect states in ZnO nanostructures and its role on photoluminescence and third harmonic generation

In this article we have explored an effect of electron beam irradiation (EBI) on physical and nonlinear optical properties ZnO thin nano films. Nanostructured ZnO thin films were grown by low cost spray pyrolysis technique. The irradiation dosage has been fixed at 5 kGy, 10kGY, 15 kGy and 20 kGy. The structural investigation by Glancing angle X-Ray Diffractometer (GAXRD) confirms a polycrystalline phase of ZnO with wurtzite structure. The variation in the surface morphology upon EBI has been demonstrated using 2D and 3D Atomic force microscopy (AFM) images. Nanoscope software analysis quantifies the variation in surface roughness and average particle height upon EBI. The defect states created in the films upon irradiation experiments were investigated using UV–visible spectrophotometer, Room temperature Photoluminescence (RTPL), Raman and X-ray photoelectron spectroscopy (XPS). The increase in urbach tail validates the creation of localized defect states in the films The Gaussian fitting on RTPL spectra shows the quenching in the luminescent centers upon irradiation arised as result of recombination of vacancy defects. Phonon confinement model fitting on Raman spectra endorses that shift in the phonon modes observed on irradiation is due to spatial confinement of phonons. The elemental composition and impurity states of the EBI ZnO thin films were studied using XPS spectra. The shift in the binding energy of Zn and O elements infers the electron beam induced changes in the films. The electron beam irradiation has resulted in the increment of third order optical susceptibility χ(3) 3.5 × 10−4 esu to 8.13 × 10−3 esu due to the enhancement of electronic transition to different defect levels formed in the films and through local heating effects arising due to continuous wave (CW) laser illumination. The enhanced THG signal investigated using Nd:YAG laser at 1064 nm and 8 ns pulse width shows the promising features of EBI ZnO films for frequency tripling applications.

Absorption and order parameter dependency to temperature and poling field in polymer-dye films oriented by corona poling

Second-order nonlinear optical (NLO) effects can be observed in materials with noncentro symmetric structures. In order to achieve such structure in the initially isotropic-doped polymer films, they were aligned in an electric field during heating up to the glass transition temperature. In this experimental work, we studied the NLO thin film properties of azo dye as guest molecules oriented in a polymer host by corona-onset poling. Also, the orientational order of nonlinear molecules is measured. We have shown that corona-onset poling at elevated temperature (COPET) is effective in orienting optically nonlinear guest molecules in a host polymer.

Metal-insulator transition and nonlinear optical responseof sputter-deposited V3O5 thin films

The compound V3O5, a member of the vanadium oxide Magnéli series, exhibits a metal-insulator transition near 430 K, the highest known temperature value among all vanadium oxides. It has been studied before mainly in single-crystal form, and for the very few cases in which thin films have been fabricated before, the procedure has required extensive post-deposition annealing of other oxides or vanadium metal at high temperatures in tightly controlled atmospheres. For the present work, V3O5 films were deposited directly on SiO2 glass substrates, without subsequent annealing, by DC magnetron sputtering. X-ray diffraction study of the samples evidenced oxygen deficiency, accommodated by oxygen vacancies. Resistivity measurements from 300 to 500 K revealed the metal-insulator transition by Tc ∼ 430 K, with an associated resistivity change by a factor of 20, and no detectable hysteresis in heating-cooling cycles, in agreement with most single-crystal studies. Resistivity values obtained were, however, lower than published results for bulk crystal values, particularly at temperatures below Tc. This was attributed to conduction electrons generated by the oxygen vacancies. Gradual resistivity increase in a very thin sample, through heating in air at temperatures up to 500 K, lends support to this argument. Using a pump-probe scattering technique, the V3O5 films were also probed for ultrafast nonlinear optical response. A reduction in the transient relative scattered light signal was recorded, which reached –10% within ∼800 fs. This observed response, likely related to the photoinduced insulator-to-metal phase transition, should stimulate additional interest in this material.

Nonlinear Optical Thin Film Device from a Chiral Octopolar Phenylacetylene Liquid Crystal

A set of chiral discotic phenylacetylenes have been synthesized by 3-fold Sonogashira coupling between different ethynylbenzenes and triiodobenzenes. The resultant bulk materials are fully characterized by polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction. The octopolar nature of the target compounds is studied by UV-vis absorption spectroscopy and hyper-Raleigh scattering in solution. Optimization of the donor-acceptor substitution yields both high hyperpolarizability values and appreciable mesomorphic properties. A simple thin film device for second harmonic generation has been prepared from the nitro-substituted liquid crystalline derivative.

Strongly Nonlinear Optical Chalcogenide Thin Films of APSe6 (A=K, Rb) from Spin‐Coating

The first example of solution-based deposition of strongly nonlinear optical inorganic thin films at low temperatures of 125–250 °C is presented. The obtained glassy and crystalline films of highly nonlinear APSe6 compounds (A=K, Rb; χ(2)≈150 pm V−1) exhibit strong, inherent second harmonic and difference frequency generation (SHG and DFG) in the visible and near-IR spectral region at room temperature without the need of poling (see picture).

Effect of the Interface in Plasmon-enhanced Second Harmonic Generation from Nonlinear Optical Thin Films

AbstractThe second order nonlinear optical (NLO) properties of two different ionic selfassembled multilayer (ISAM) films combined with Ag nanoparticles have been investigated. The plasmon resonances in the Ag particles concentrate the incident light, markedly increasing in the NLO efficiencies of the films. We find that the efficiency enhancement is significantly larger in conventional ISAM films compared to films made using a hybrid covalent ISAM technique (HCISAM), even though the intrinsic bulk second order non-linear susceptibility (χ(2)) is much larger for HCISAM films. We attribute this to the interfaces in HCISAM films being much easier to disrupt by external perturbations such as the metal deposition by which the nanoparticles are fabricated. We conclude that because the plasmon decay length is very short, the plasmonic enhancement of NLO effects primarily occurs at and near the film-particle interface. To discern the importance of the interfaces, we surrounded thin ISAM and HCISAM films with NLOinactive buffer layers, which confirmed this hypothesis, particularly in the case of HCISAM films.

Chemically Selective Analysis of Molecular Monolayers by Nonlinear Optical Stokes Ellipsometry

The application of nonlinear optical Stokes ellipsometry (NOSE) coupled with principal component analysis (PCA) is demonstrated for the chemically selective analysis of molecular monolayers. NOSE allows for rapid polarization measurements of nonlinear optical materials and thin surface films, which in turn benefits from comparably fast data analysis approaches. PCA combined with linear curve fitting techniques greatly reduce the analysis time relative to nonlinear curve fitting. NOSE-PCA is first validated with studies of z-cut quartz, followed by analysis of four thin dye films with similar nonlinear optical properties. The high precision of NOSE measurements combined with the rapid analysis time enabled chemical discrimination between different dyes and the practical realization of NOSE microscopy.

Nonlinear Optical Properties of the Au-SiO2 Nanocomposite Superresolution Near-field Thin Film

A Au-SiO2 superresolution nanocomposite active nonlinear optical thin film is fabricated reproducibly by cosputtering method with the size of Au nano particles around 2 to 10 nm. Results of the Z-scan indicate that these nanocomposite Au-SiO2 films have nonlinear optical properties and enhanced transmittance at the focusing position. For a 15-nm-thick Au-SiO2 nanocomposite thin film, the transmittance can be 135% for a sample with an average grain size of around 5 nm.

Advantages of polarized two-beam second-harmonic generation in precise characterization of thin films.

Polarized second-harmonic generation using two fundamental beams, instead of one, offers significant advantages for characterizing nonlinear optical thin films. The technique is more precise and allows the internal consistency of the results to be verified. The superiority of the two-beam arrangement over the traditional single-beam arrangement is demonstrated by determining the susceptibility tensors of Langmuir-Blodgett films. We show that, for a well-understood reference sample, the results obtained using two fundamental beams agree qualitatively with those obtained with a single fundamental beam, but are more precise. In a more complicated situation, however, the single-beam technique appears to work well but yields results that are, in fact, incorrect. The two-beam technique, instead, yields clearly inconsistent results, thereby highlighting systematic errors in the experimental arrangement or in the theoretical model used to interpret the results.

Second Harmonic Generation in Barium Titanate Thin Films on Silica Glass by Corona Poling

Among potential inorganic thin films, perovskite-structured barium titanate (BaTiO3) is particularly attractive due to its large ferroelectric response and large optical nonlinear coefficients. SiO2 material is also important in semiconductor processing. Therefore, we study the nonlinear optical (NLO) thin film deposited on a SiO2 substrate. We report our investigation of a BaTiO3 thin film on a silica glass (SiO2) substrate grown by rf magnetron sputtering. We measured the second-harmonic generation (SHG) and calculated the second-order nonlinear optical coefficients from the BaTiO3/glass by using the Maker fringes technique. From our experimental results, we found that by applying corona poling, the nonlinear optical coefficients in BaTiO3/glass can be increased. The SHG of the nonlinear thin film by poling is dependent on temperature.

Self-assembled organic supramolecular thin films for nonlinear optics

We analyze the issues that must be considered on the road towards a practical fabrication method for organic nonlinear optical thin films. The advantages and disadvantages of the most useful techniques for producing nonlinear optical thin films are reviewed. We describe a promising molecular beam deposition techniques that has been developed in our laboratory for the growth of ordered supramolecular self-assembled thin films that are nonlinear optically active and maintain their polar order for large thicknesses.

Fumaryl chloride and maleic anhydride-derived crosslinked functional polymers for nonlinear optical waveguide applications

The synthesis, processing, and characterization of new crosslinked functional polymer thin films derived from fumaryl chloride and maleic anhydride is presented. Experimental data demonstrated that this is a versatile, convenient, and cost-effective method of fabricating ultrastructure crosslinked and functional polymer thin films for potential nonlinear optical (NLO) or other applications where molecular orientation is required. The unsaturated and processable polyester thin films are capable of crosslinking in air to form a hardened lattice under a variety of conditions, including both thermal and photoinitiated crosslinking. The thermal stability of the second harmonic (SHG) signal for a crosslinked NLO thin film was stable at temperatures up to 150°C, which is in contrast to uncrosslinked polymers whose SHG signals typically decreased over 50% below 100°C. Because of the lack of NH/OH groups and their vibrational overtones in the polymer, these crosslinked polyester systems have a great potential for low optical loss applications at 1550 nm communication wavelength. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 317–322, 2004

Hydrogen‐Bond‐Directed Orientation in Nonlinear Optical Thin Films

A simple and effective method for the self‐assembling of thin films with directional ordering perpendicular to the substrate surface (see Figure) is reported. These films are grown on amorphous glass substrates and show second‐order nonlinear optical effects of the order of 5 pm V–1. The ordering in these films can be maintained over large thicknesses (∼800 nm), and they are homogeneous over the area of the thin film.

Formation of channel waveguide with grating in polymer films based on simultaneous photobleaching and embossing

Channel waveguide with grating is fabricated in nonlinear optical (NLO) polymer thin films by means of simultaneous embossing and photobleaching. A combined structure of mask/master consisting of a photomask part and a grating die part which is made of polyimide is fabricated. Then the mask/master is set on the NLO polymer films and both embossing and photobleaching are performed simultaneously. Profiles of the replica grating and the channel waveguide are estimated.

Rh:BaTiO3 thin films with large nonlinear optical properties.

We report the fabrication and the nonlinear optical properties of Rh-doped BaTiO3 thin films. The films were deposited on SrTiO3 (100) substrates by pulsed-laser deposition. The deposited Rh:BaTiO3 thin films were single phase and c-axis orientation investigated by x-ray diffraction. The films exhibited large nonlinear optical effects, which were determined using Z-scan technique at a wavelength of 532 nm with a laser duration of 10 ns. The real and imaginary parts of the third-order nonlinear susceptibility chi (3) were 5.71 x 10(-7) esu and 9.59 x 10(-8) esu, respectively. The value of Re chi (3) of Rh:BaTiO3 films is much larger than those of several representative nonlinear optical thin films. The results show that Rh:BaTiO3 thin films have great potential applications for nonlinear optical devices.

Improved Second Harmonic Generation from Organic-Dye-Doped Polymer/Silica Hybrid Materials

In this study, we investigated the second-order optical nonlinearity and its thermal stability of DR1 (disperse red 1) doped poly(methyl methacrylate) (PMMA)/silica gel films. We found that in situ polymerization of sol−gel precursors (tetraethoxysilane, TEOS) in a polymer generated a hybrid matrix which is a good tradeoff between a silica gel and a polymer matrix. The nonlinear thermal stability of the hybrid system increased significantly compared to that of a poled DR1/PMMA film. Our result proved that the combination of a poled polymer and the sol−gel technique provides a way to increase the thermal stability of nonlinear optical thin films fabricated from existing materials rather than synthesizing new chemical compounds. Several factors which affect the second-order optical nonlinearity of the hybrid system were also examined.

Third-harmonic generation and growth mechanism of vanadyl-phthalocyanine single crystals prepared on KBr substrate by molecular beam epitaxy

Vanadyl-phthalocyanine (VOPc) single crystals were prepared on KBr (1 0 0) substrate by molecular beam epitaxy (MBE). The second and third-harmonic generations of nonlinear optical thin films are proportional to the square of the thickness. Therefore, it is important to prepare a large nonlinear optical single crystal. However, the conditions to prepare a large nonlinear optical single crystal are not well understood yet. In this paper, we succeeded to prepare a large nonlinear single crystal. It was obtained with the control of substrate temp., evap. time and annealing time. The orientation and nonlinear property of VOPc single crystal prepared by the MBE method were also studied. The size of maximum single crystal prepared on KBr is 4×9×0.16 μm. The absorption spectrum of sample has an absorption peak at 790 nm. It reveals that the growth of single crystal gradually grow to a large crystal merging small crystals and also suggest that the VOPc single crystal is monoclinically grown from the results of RHEED pattern and UV/VIS spectrum. We estimated the third-order nonlinear optical susceptibility χ (3) from the TH intensity for VOPc single crystal monoclinically grown on KBr. Its χ (3) value estimated is 8.5×10 −10 esu. The value is 3 times higher than the value reported recently.

Second Order Nonlinear Optical Thin Films Fabricated from Electric Field-Assisted Electrostatic Self-Assembled Monolayer Method

ABSTRACTA new method for the build-up of non-centrosymmetric multilayer thin films has been developed for the first time using an electric field-assisted electrostatic self-assembled monolayer (EF-ESAM) technique. An increase by 116% of the second-harmonic intensity of the films has been observed in comparison with that of ESAM film.