Trans-4'-(dimethylamino)-N-R-4-stilbazolium hexafluorophosphate (R = Me, Me 1, Ph, Ph 2, 2,4-dinitrophenyl, DNPh 3, 2-pyrimidyl, Pym 4, Scheme 1) were prepd. Their electronic absorption spectra show intense, visible intramol. charge-transfer bands, the energy (Emax) of which decreases in the order R = Me > Ph > DNPh > Pym. This trend arises from the steadily increasing electron deficiency of the pyridinium ring, a phenomenon also obsd. in cyclic voltammetric and 1H NMR data. Fluorescence-free 1st hyperpolarizability .beta. values of [1-4]PF6 were measured by using femtosecond hyper-Rayleigh scattering (HRS) with MeCN solns. and a 1300. nm laser, and static 1st hyperpolarizabilities .beta.0 were obtained by application of the two-state model. The HRS results indicate that the N-aryl chromophores in [2-4]PF6 have considerably larger .beta.0 values than their N-Me counterpart in [1]PF6, with a .apprx. 10-fold increase in .beta.0 obsd. in moving from [1]PF6 to [4]PF6 (25 .fwdarw. 230 .times. 10-30 esu). Stark (electroabsorption) spectroscopic studies in butyronitrile glasses at 77 K allowed the derivation of dipole moment changes .DELTA..mu.12 (10.9-14.8 D), which were used to calc. .beta.0 according to the two-state equation .beta.0 = 3.DELTA..mu.12(.mu.12)2/2(Emax)2 (.mu.12 = transition dipole moment). With the exception of [1]PF6, the Stark-derived .beta.0 values are in reasonable agreement with those from HRS. However, the increase in .beta.0 in moving from [1]PF6 to [4]PF6 is only 2-fold for the Stark data (90 .fwdarw. 185 .times. 10-30 esu). The obsd. trend of increasing .beta.0 in the order [1]PF6 < [3]PF6 < [2]PF6 < [4]PF6 arises from a combination of decreasing Emax and increasing .DELTA..mu.12, with only a slight increase in .mu.12 between [1]PF6 and [4]PF6. Probably the .beta.0 values for [3]PF6 are lower than expected due to the steric effect of the ortho-NO2 group, which causes twisting of the DNPh ring out of the plane of the stilbazolium unit. A single crystal x-ray structure shows that [2]PF6 crystallizes in the space group Cc, with head-to-tail alignment and almost parallel stacking of the pseudo-planar stilbazolium portions of the cations to form polar sheets within a polar bulk structure. [2]PF6 is essentially isostructural with the related Schiff base salt trans-4-[(4-dimethylaminophenyl)iminomethyl]-N-phenylpyridinium hexafluorophosphate ([8]PF6). Second harmonic generation (SHG) studies on [2]PF6 and [8]PF6 using a 1907. nm laser and sieved powd. samples (53-63 .mu.m) afforded efficiencies of 470 and 240 times that of urea, resp. Under the same conditions, the well-studied compd. [1]p-MeC6H4SO3 gave an SHG efficiency of 550 times that of urea. [on SciFinder (R)]

Quadratic Nonlinear Optical Properties of N-Aryl Stilbazolium Dyes**

A device for determining the surface topology and associated color of a structure, such as a teeth segment, includes a scanner for providing depth data for points along a two-dimensional array substantially orthogonal to the depth direction, and an image acquisition means for providing color data for each of the points of the array, while the spatial disposition of the device with respect to the structure is maintained substantially unchanged. A processor combines the color data and depth data for each point in the array, thereby providing a three-dimensional color virtual model of the surface of the structure. A corresponding method for determining the surface topology and associate color of a structure is also provided.

Method and apparatus for colour imaging a three-dimensional structure

We perform a comparative study of second-harmonic generation (SHG) from indium tin oxide (ITO) and from titanium nitride (TiN) nanolayers excited in the near-infrared spectrum. Both materials are compatible with Si technology and are candidate platforms for integrated nonlinear optics. In this work, we fabricate ITO samples with an e-near-zero (ENZ) condition, which can be continuously tailored in the 1150–1670 nm spectral range, and TiN samples with a metallic behavior in the same spectral range. For the ITO nanolayers, we observe tunability and enhancement of the SHG intensity when the samples are excited at their respective ENZ condition, in agreement with the electromagnetic modeling and analogous to its third-harmonic generation studied earlier. On the other hand, we show that the SHG efficiency of TiN nanolayers is lower by a factor of 50. We determine experimentally that the dominant component of the second-order susceptibility for our best ITO nanolayer is χzzz(2ω) = 0.18 pm V–1, and we theoretica...

Comparative Study of Second-Harmonic Generation from Epsilon-Near-Zero Indium Tin Oxide and Titanium Nitride Nanolayers Excited in the Near-Infrared Spectral Range

A series of hemicyanine dimers, (B3, B5, and B12) whose two chromophores are linked by different numbers of methylene groups, are synthesized. Negative slovatochromic behaviors are observed, and the fluorescence quantum yield is sensitive to the polarity of solvent. In chloroform, the fluorescence intensity is much more intensive than in other polar solvents, and the decay lifetime is much longer. This fluorescence sensitivity to solvent is due to the twisted intramolecular charge transfer (TICT) state formation, which can be blocked in weak polar solvent. The two chromophores in one dimer molecule are correlated and the TICT formation of dimer is relatively difficult compared with monomer. When the linkage is long enough, this correlation can be reduced. The dynamic fluorescence spectra of the chloroform solutions of these dyes support our assumption. The time-resolved fluorescence studies of their LB films provide a new perspective on the excited-state deactive process. The two-dimensional Forster energ...

/pdf/photophysical-studies-on-the-mono-and-dichromophoric-1qq7un7ivp.pdf

Photophysical Studies on the Mono- and Dichromophoric Hemicyanine Dyes II. Solvent Effects and Dynamic Fluorescence Spectra Study in Chloroform and in LB Films

The role of titanium ions on structural, dielectric and optical properties of Li2O–MgO–B2O3 glass system

A novel disc-like amphiphilic molecule, with two-chain nitrogencrown was adopted as a spacer material for fabrication of optical nonlinear Langmuir - Blodgett (LB) multilayers. The intensity of second-harmonic generation (SHG) increased quadratically with the bilayer number (up to 116 bilayers) in Y-type hemicyanine/nitrogencrown interleaving LB multilayers due to improvement of the structural properties by insertion of the long hydrophobic tail of hemicyanine molecules between two chains of nitrogencrown molecules. The second-order susceptibility pM (or esu) was obtained by measuring SHG from the hemicyanine samples.

https://iopscience.iop.org/article/10.1088/0022-3727/30/19/001/pdf

Second-harmonic generation in interleaved hemicyanine/nitrogencrown Langmuir - Blodgett multilayers

Second harmonic generation investigation of indium tin oxide thin films

Second harmonic generation investigation on electric poling effects in fused silica

This paper presents the characteristics of vacuum laser acceleration in circularly polarized (CP) fields with the capture and acceleration scenario (CAS) scheme. Compared with linearly polarized laser fields, the main advantage for using a CP field is that its acceleration channel occupies a relatively larger phase space, stemming from the distribution of the longitudinal electric component, the dependence on the laser initial phase and on the incident polarization azimuth angle, etc. These features can give rise to greater acceleration efficiency. One of the disadvantages is the 'energy saturation' phenomenon if the laser intensity is sufficiently high, which comes from the additional Lorentz force component in the CP field. The output properties of the accelerated CAS electron bunch, such as the energy spectra, the angular distributions, the energy-angle correlations, the acceleration efficiency, the rms emittance and the energy divergence, are also examined. Physical explanations concerning these characteristics are presented.

Vacuum laser acceleration in circularly polarized fields

Concerning laser-driven electron acceleration in vacuum, a comparison was made between using circularly polarized (CP) laser field and linearly polarized (LP) field. It has been found that the main advantage for using CP field is that its acceleration channel occupies relatively larger phase space, which can give rise to greater acceleration efficiency. This feature chiefly comes from the difference in the distribution of the longitudinal electric components of these two kinds of fields. One of the disadvantages with CP field is the “energy saturation” phenomenon as the laser intensity is sufficiently high, resulting from the enhanced Lorentz force component in CP field. Physical explanations of these characteristics are addressed as well.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0263034607000092

Jianhua Xu

Papers

Second-harmonic generation in interleaved hemicyanine/nitrogencrown Langmuir - Blodgett multilayers

Second harmonic generation investigation of indium tin oxide thin films

Second harmonic generation investigation on electric poling effects in fused silica

Vacuum laser acceleration in circularly polarized fields

Polarization effect of fields on vacuum laser acceleration