Second-order Nonlinear Coefficient Research Articles

Molecular Photonics and Electronics

Molecular Photonics and Electronics

Strength and symmetry of the third-order nonlinearity during poling of glass waveguides

Negative thermal poling introduces second-order nonlinear effects into silica glass. The effects are studied using the charge separation model allowing for the third-order nonlinear effect to be anisotropic. The second-order nonlinear coefficient /spl chi//sup (2)/ is found to be consistent with the results reported previously by Arentoft et al. (1999), Ren et al. (2002), and Marckmann et al. (2001) and the third-order nonlinear coefficient /spl chi//sup (3)/ is found to be anisotropic but constant during poling.

Characterization of thermal poling in silica glasses by current measurements

We present herein a charge migration model that predicts the electric field distribution within a Suprasil™ silica planar sample after poling. The predicted distribution is in agreement with the currents measured at the electrodes during the poling and depoling processes. This electric field is responsible for an apparent second-order non-linear coefficient originating from the third-order one. Numerical values obtained from fits of the experimental curves with the model equations are compatible with the values obtained by optical characterization reported in the literature.

Optical properties of NAEC-PMMA nonlinear polymeric thin film

Novel guest nonlinear optical (NLO) chromophore molecules (4-nitrobenzene)-3-azo-9-ethylcarbazole (NAEC) were doped in poly (methyl methacrylate) (PMMA) host with a concentration of approximately 15% by weight. For a useful macroscopic electro-optic (EO) effect, these NLO molecules NAEC were arranged in a noncentrosymmetric structure in the host polymer by corona-onset poling at elevated temperature (COPET). For applying NAEC-PMMA polymer in optical devices such as EO switch, its optical properties have been investigated. The UV/Visible absorption spectra for the unpoled and poled polymer film were determined. The refractive index of the film was also determined from measurements of the coupling angles with the reflective intensity at 632.8 nm wavelength. Using the simple reflection technique, the EO coefficient 33 value was measured as 60 pm/V at 632.8 nm wavelength. The second-order nonlinear coefficient d(33) was characterized by the second-harmonic-generation (SHG) experimental setup and the calculated d(33) value reached 18.4 pm/V at 1064 nm wavelength. The relation between the second-order nonlinear coefficients d(33) and d(13) for the poled polymer film was also discussed in detail and the ratio d(33)/d(13) value was obtained as 3.3. (C) 2002 Kluwer Academic Publishers.

Dynamics of the second-order nonlinearity in thermally poled silica glass

We study the temporal evolution of both the second-order nonlinear coefficient and of the nonlinear thickness in thermally poled silica-glass slides by using a high-resolution all-optical technique. A time delay in the nonlinearity formation is observed, followed by an increase to a maximum, and a final decrease. The thickness is shown to increase at a rate that differs significantly from that reported for the corresponding ionic charge fronts. Our measurements also show strong dependencies on sample thickness and these can be attributed to different electric fields in the depletion region.

Synthesis and Characterization of Photorefractive Polymer containing Multifunctional Chromophore

The main chain photorefractive polymer (PUA-M) having multifunctional chromophore was synthesized by the step-growth polymerization from N-hydroxyethylcarbazole-4′-[6-(hydroxysulfonyl)]-azobenzene (Azo-2OH) and 1,6-hexamethylene diisocyanate. The molecular weight of the resulting polymer was determined to be Mw=41,300 (Mw/Mn=1.19) by the gel permeation chromatography using polystyrene as a standard, and could be processed into optical quality films. The thermal properties of PUA-M were detected by DSC and TGA. It shows a glass transition temperature of 183°C and an initial decomposition temperature of 223°C. The absorption maximum in UV/vis spectrum of PUA-M film was detected at 416 nm. The second-order nonlinear coefficient (d 33) of PUA-M was about 27 pm/V. The studies into the detailed photorefractive properties for this polymer is in progress.

Second harmonic generation by reflection from vicinal surfaces ofepitaxial layers of cadmium mercury telluride

Reflection second harmonic generation is employed to examine thesurfaces of epitaxial layers of CdxHg1-xTe (CMT) grown on vicinal GaAs(100) substrates. Different vicinal tilts, with respect to the GaAssubstrates, are observed in the epitaxial CMT layers. We also report here onthe measurement of the second-order nonlinear coefficient (d36) of CMT.Because CMT is strongly absorbing at the 1.06 µm wavelength, thismeasurement was performed by comparing the second harmonic intensity reflectedfrom the CMT surface to that measured for a quartz sample in transmission.Directly comparable expressions for the reflected and transmitted secondharmonic intensities are derived from which a value ofd36 = 365±15 pm V-1 is obtained. This value is much larger thanthose reported for similar zinc-blende-type materials and is attributed to anelectronic resonance enhancement.

Wavelength variation of the second-order nonlinear coefficients of KNbO_3, KTiOPO_4, KTiOAsO_4, LiNbO_3, LiIO_3, β- BaB_2O4, KH_2PO_4, and LiB_3O_5 crystals: a test of Miller wavelength scaling

We measure second-order nonlinear coefficients using optical parametric amplification and second-harmonic generation over a range of wavelengths for the crystals KNbO3,KTiOPO4,KTiOAsO4,LiNbO3,LiIO3,β-BaB2O4,KH2PO4, and LiB3O5. Combining our new measurements with previously reported values, we compare the wavelength variation of individual dijk’s with Miller scaling, and we conclude that Miller scaling is a useful approximation for these crystals.

Synthesis and nonlinear optical properties of aromatic esters with an electron donor and an electron acceptor end group

We synthesized a series of aromatic esters having an electron donating and an electron accepting end group as a new class of nonlinear optical (NLO) active chromophores (ArESn D-A, n = 2,3, D = MeO (as reference), MeS and Me2N, A = CN). Second-order NLO properties for poled polymer films consisting of poly(methyl methacrylate) (PMMA) doped with 10 wt.-% ArESn D-A (ArESn D-A/PMMA) were investigated. The UV/vis spectra of these polymer films have cutoff wavelengths (λco) of about 350 ˜ 370 nm, which are much shorter than in the case of p-nitroaniline (pNA) (λco = 473 nm) which is a typical strong donor-acceptor (D-π-A) molecule. In addition, some of these polymer films exhibit higher second-order nonlinear coefficients (d33) than a PMMA film doped with 10 wt.-% pNA (pNA/PMMA) (2.8×10–9 esu). Namely, ArES3 Me2N-CN (d33 = 5.6×10–9 esu, 10 wt.-% in PMMA) and ArES2 Me2N-CN (3.8×10–9 esu, 10 wt.-% in PMMA) showed excellent second-order NLO activity as well as transparency in the visible region (λco: 362 nm for ArES3 Me2N-CN and 366 nm for ArES2 Me2N-CN, respectively).

Synthesis and nonlinear optical properties of aromatic esters with an electron donor and an electron acceptor end group

We synthesized a series of aromatic esters having an electron donating and an electron accepting end group as a new class of nonlinear optical (NLO) active chromophores (ArESn D-A, n = 2,3, D = MeO (as reference), MeS and Me2N, A = CN). Second-order NLO properties for poled polymer films consisting of poly(methyl methacrylate) (PMMA) doped with 10 wt.-% ArESn D-A (ArESn D-A/PMMA) were investigated. The UV/vis spectra of these polymer films have cutoff wavelengths (λco) of about 350 ˜ 370 nm, which are much shorter than in the case of p-nitroaniline (pNA) (λco = 473 nm) which is a typical strong donor-acceptor (D-π-A) molecule. In addition, some of these polymer films exhibit higher second-order nonlinear coefficients (d33) than a PMMA film doped with 10 wt.-% pNA (pNA/PMMA) (2.8×10–9 esu). Namely, ArES3 Me2N-CN (d33 = 5.6×10–9 esu, 10 wt.-% in PMMA) and ArES2 Me2N-CN (3.8×10–9 esu, 10 wt.-% in PMMA) showed excellent second-order NLO activity as well as transparency in the visible region (λco: 362 nm for ArES3 Me2N-CN and 366 nm for ArES2 Me2N-CN, respectively).

Analyzing the polarization distribution in poled polymer films by scanning Kelvin microscopy

We present a method for analyzing the homogeneity of the χ(2) distribution in poled nonlinear optical polymer films. The second-order nonlinear coefficient in these polymers is commonly induced by electric-field poling methods which can lead to a χ(2) distribution with poor spatial homogeneity. In this letter, we analyze the χ(2) distribution using scanning Kelvin microscopy. This allows us to detect the height and the direction of the induced polarization through the probing of the countercharges that are present on the polymer surface. We compare the response to that obtained from the scanning second-harmonic microscopy method, in which the direction of the orientation, and thus the phase of χ(2), cannot be seen.

Optical Second Harmonic Generation and Relaxation Dynamics of Aligned Azo-Dyes in Sol-Gel Derived Organic-Inorganic Film

An Azo-dye doped organic-inorganic hybrid film was prepared by the sol-gel technique, and optical second-harmonic (SH) nonlinearities were measured as a function of the poling conditions. Azo-dye molecules dispersed in poly-vinylpyrrolidone were complexed with the hydrolyzed silicon-alkoxide. The Maker-fringe pattern composed of a fine oscillating pattern on a broad component, and the highest second-order nonlinear coefficient, d 33, was 0.83 pm/V when poled at 175°C and 4 kV. The analysis of the decay curves of the SH intensities at 150–190°C predicted the relaxation time of about 3 years at room temperature.

Thermally stable second-order nonlinear optical addition-type polyimides functionalized by diamine chromophore

A series of chromophore-functionalized polyimide prepolymers with excellent processibility were prepared by a Michael addition reaction of diamine chromophore 2 with structurally different bismaleimide (BMI) monomers. The effects of the BMI moiety's structure and thermal curing condition on glass transition temperature (Tg) and thermal stability of the polyimides were studied by DSC, TGA, and FTIR. Among the five cured polyimides, PI3, bearing a sulfone moiety, exhibited the highest Tg and thermal decomposition temperature (Td). Its corresponding prepolymer, PP3, was selected to evaluate NLO properties in a simultaneously poling and thermal polymerization process. A relatively large poling-order parameter was observed. The second-order nonlinear coefficient, d33, was 25 pm/V at 1064 nm fundamental wavelength. The second harmonic generation signal was almost without decay up to 170°C. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3598–3605, 1999

Second-harmonic generation in silicon carbide polytypes

We report simultaneous measurements and ab initio calculations of the second-order nonlinear coefficients for SiC polytypes. Our measured values for χzzz (χzxx) are 18 (−4) pm/V for 4H SiC and 24 (−4) pm/V for 6H SiC. They are in good agreement with our theoretical results.

Synthesis of azo chromophores containing a perfluorocyclo-alkenyl moiety and their second-order optical nonlinearity

1,2-Bis[4-[4-[ N-ethyl- N-(2-hydroxyethyl)amino]phenylazo]phenylthio]perfluorocyclopentene, having two independent intramolecular push-pull chromophores in a molecule, showed the highest second-order nonlinear coefficient ( d 33) among the cyclobutenyl, -pentenyl, -hexenyl, and cyclopentenyl nitro derivatives in both doped poly(methyl methacrylate) (PMMA) and polycarbonate (PC).

A new NLO polyurethane with a tricyanovinyl group

A new functionalized polyurethane structure with a heteroaromatic thiophene ring having a tricyanovinyl group in the polymer side chain was synthesized. The resulting polymer was soluble in N-methylpyrrolidinone and could be processed into good optical quality films by spin casting at ca. 100 °C. The second-order nonlinear coefficient, d33, was determined to be 51 pm/V from measuring the second harmonic generation (SHG) for a thin polymer film. The outstanding orientational stability of the aligned chromophores was observed up to about 150 °C, which originated from the rigid polymer backbone and the stabilizing function of the hydrogen bridges formed between the neighboring polyurethane chains.

Second-Harmonic Generation in Oriented CdSe-Nanocrystal-Doped Indium Tin Oxide Film and its Application to an Infrared Detector

AbstractSecond-harmonic generation in CdSe nanocrystals doped in indium tin oxide ( ITO ) films has been examined. The thin film samples were prepared by r.f. magnetron sputtering with ITO target on which CdSe chips were placed. The X-ray diffraction patterns of as-deposited films indicate that CdSe crystallites are precipitated in an amorphous ITO matrix, and they are preferentially oriented in the direction of (111) plane of zinc blende structure or (002) plane of wurtzite structure. The mean diameter of CdSe crystallite was estimated to be 3-5 nm using Scherrer's equation. Moreover, the CdSe crystallites grew with keeping its initial orientation when a dc voltage of 50 V/cm was applied in the direction parallel to the film surface. The application of the electric field effectively enhanced the second-harmonic intensity by two orders of magnitude compared to that of the as-deposited films. The second-order nonlinear coefficient d(2) for the electrically-treated specimen calculated on a basis of a modified Maker fringe theory is d31 = 3.0 × 10 pm/V at the wavelength of 1064 nm, which is comparable to d values reported for CdSe single crystal, d31 = 25 pm/V at 1054 nm and d33 =76 pm/V at 1064 nm.

Determination of orientational distribution function of organic molecular surfaces using the modified maximum-entropy method

The determination of the surface orientational distribution function for organic molecules such as liquid crystals has been studied using the maximum-entropy method with second-order optical nonlinear coefficients. Systematic simulation revealed that the conventional maximum-entropy method does not give sufficient information about the axial ordering $(〈{\mathrm{cos}}^{2}\ensuremath{\theta}〉)$ along the surface normal direction $(\ensuremath{\theta}$ is the angle between the molecular axis and surface normal direction). We propose a modified maximum-entropy method that involves an additional constraint function of $〈{\mathrm{cos}}^{2}\ensuremath{\theta}〉$ and gives more realistic distribution functions. Distribution functions were determined for several previous experimental results using these conventional and modified methods. From the comparison of these distribution functions, it has been shown that the distribution densities of molecules oriented at tilt angle $\ensuremath{\theta}=180\ifmmode^\circ\else\textdegree\fi{}$, which appear when using the conventional maximum-entropy method, are artifacts.

Synthesis and nonlinear optical properties of end-group modified aromatic esters as chained chromophores

We synthesized aromatic ester derivatives with some electron accepting groups at molecular ends as new class of nonlinear optical (NLO) active chromophores (ArESn-X, n = 2, 3, X = CN, CF3, NO2, DCV). Some second-order NLO properties for poled polymer films consisting of poly(methyl methacrylate) (PMMA) doped with 10 wt.-% ArESn-X (ArESn-X/PMMA) were investigated. UV/vis spectra of these polymer films have cutoff wavelengths (λco) of about 300∼380 nm, which are much shorter than in the case of p-nitroaniline (pNA) (λco = ca. 450 nm) as a typical strong donor-acceptor (D-A) molecule. In addition, some of these polymer films exhibited larger second-order nonlinear coefficient (d33) values than PMMA film doped with 10 wt.-% pNA (pNA/PMMA) (2.8 × 10−9 esu). Namely, ArES3-CN (d33 = 3.1 × 10−9 esu, 10 wt.-% in PMMA), ArES3-NO2 (3.0 × 10−9 esu, 10 wt.-% in PMMA) and ArES2-DCV (4.0 × 10−9 esu, 10 wt.-% in PMMA) showed not only excellent second-order NLO activity but also excellent transparency in the visible region (λco = 304 nm (ArES3-CN), 340 nm (ArES3-NO2) and 370 nm (ArES2-DCV), respectively). Consequently, these compounds are believed to be promising chromophores for second-order nonlinear optics.

Synthesis and nonlinear optical properties of end-group modified aromatic esters as chained chromophores

We synthesized aromatic ester derivatives with some electron accepting groups at molecular ends as new class of nonlinear optical (NLO) active chromophores (ArESn-X, n = 2, 3, X = CN, CF 3 , NO 2 , DCV). Some second-order NLO properties for poled polymer films consisting of poly(methyl methacrylate) (PMMA) doped with 10 wt.-% ArESn-X (ArESn-X/PMMA) were investigated. UV/vis spectra of these polymer films have cutoff wavelengths (λ co ) of about 300-380 nm, which are much shorter than in the case of p-nitroaniline (pNA) (λ co = ca. 450 nm) as a typical strong donor-acceptor (D-A) molecule. In addition, some of these polymer films exhibited larger second-order nonlinear coefficient (d 33 ) values than PMMA film doped with 10 wt.-% pNA (pNA/PMMA) (2.8 x 10 -9 esu). Namely, ArES3-CN (d 33 = 3.1 x 10 -9 esu, 10 wt.-% in PMMA), ArES3-NO 2 (3.0 x 10 -9 esu, 10 wt.-% in PMMA) and ArES2-DCV (4.0 x 10 -9 esu, 10 wt.-% in PMMA) showed not only excellent second-order NLO activity but also excellent transparency in the visible region (λ co = 304 nm (ArES3-CN), 340 nm (ArES-NO 2 ) and 370 nm (ArES2-DCV), respectively). Consequently, these compounds are believed to be promising chromophores for second-order nonlinear optics.