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Dive into the research topics where Craig S. Willand is active.

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Featured researches published by Craig S. Willand.


Journal of Chemical Physics | 1990

Second harmonic generation and thermally stimulated current measurements: A study of some novel polymers for nonlinear optics

W. Köhler; Douglas R. Robello; Phat T. Dao; Craig S. Willand; David J. Williams

The relaxation of electric field‐induced polar orientation in novel side and main chain polymers was measured by simultaneous second harmonic generation and thermally stimulated discharge current techniques. Using this combination of experiments, individual microscopic relaxation mechanisms could be discriminated and identified. The relaxation of a polymer bearing polar chromophores on a side chain polymer was found to occur through local reorientation. For polymers containing the polar chromophore within the main chain, both a local rotation of the chromophores and the reorientation of the end‐to‐end vectors of the chains could be detected. Physical aging near the Tg of the polymers greatly increased the stability of the poling‐induced orientation below Tg. Nonlinear dependencies on the poling field were observed for low fields and are discussed in terms of screening due to space charges. Kirkwood–Frohlich correlation factors were found to be very close to unity.


Applied Physics Letters | 1992

Effect of proton exchange on the nonlinear optical properties of LiNbO3 and LiTaO3

Wei‐Yung Hsu; Craig S. Willand; Venkatraman Gopalan; Mool C. Gupta

The effect of proton exchange carried out using benzoic and pyrophosphoric acid on the nonlinear optical coefficient (d) of LiNbO3 and LiTaO3 was studied using a second‐harmonic generation reflectance technique. Significant degradation in the d coefficient of LiNbO3 and LiTaO3 was observed as a result of proton exchange with either benzoic or pyrophosphoric acid under the conditions studied. Some recovery only in the short time proton‐exchanged sample (0.5 h at 180 °C) of LiNbO3 was observed under thermal annealing at 350 °C for 1 h. Results of in situ measurement of second‐harmonic signal recovery under thermal annealing are reported. Results are also presented on theoretical and experimental variations of second‐harmonic generation intensity with an incident polarization angle.


Proceedings of SPIE | 1991

Langmuir-Blodgett films for second-order nonlinear optics

Thomas L. Penner; Nancy J. Armstrong; Craig S. Willand; Jay S. Schildkraut; Douglas R. Robello

Langmuir-Blodgett films have been fabricated of a prepolymerized amphiphile containing a chromophore of high second-order nonlinear optical activity. Thick films, containing as many as 262 layers of noncentrosymmetric structure have been prepared by alternate deposition of the dye polymer and several different materials. In contrast to previous literature reports on Langmuir-Blodgett films of other polymeric dyes, these films show the theoretically expected quadratic dependence of second harmonic generation with film thickness. Polarization studies of the second harmonic generation demonstrate that the chromophores are highly ordered in these films. In addition, by using all-polymeric materials it has been possible to fabricate a waveguide of these films with optical attenuation of about 1 dB cm-1, substantially lower than has been previously reported for Langmuir-Blodgett films even without a noncentrosymmetric structure.


Archive | 1988

Electric-Field Poling of Nonlinear Optical Polymers

Craig S. Willand; S. E. Feth; M. Scozzafava; David J. Williams; G. D. Green; J. I. Weinschenk; H. K. Hall; J. E. Mulvaney

Second-order nonlinear optical (NLO) processes, including harmonic generation and the electrooptic effect, are the result of a nonlinear response in the polarization P of a dielectric which is quadratic in the applied electric field of the light beams E P = X(2):EE.The coupling coefficient x(2) is the second-order electric susceptibility tensor for the material. Maximizing the nonlinear susceptibility coefficients can result in large NLO effects. However, understanding the origins of x(2) often requires examination of these interactions on the microscopic level. Here, the process can be viewed via the molecular polarization p which is induced by an electric field e local to the molecular environment.


Applied Physics Letters | 1992

Correlation between structural and optical properties in proton‐exchanged LiNbO3

Wei‐Yung Hsu; G. Braunstein; Venkatraman Gopalan; Craig S. Willand; Mool C. Gupta

We present a correlation of the structural characterization of proton‐exchanged LiNbO3 provided by ion beam and x‐ray analysis with the optical characterization provided by refractive index and second‐harmonic generation measurements. The process of proton exchange induces disorder in the crystal lattice of LiNbO3. Subsequent thermal annealing removes only partially the lattice disorder and, in particular, the near surface region of the samples generally remains highly distorted. Results of x‐rays studies indicate that the proton exchange induces a strain in the lattice and thermal annealing partially recovers it.


Polymer Bulletin | 1992

New main chain nonlinear optical polymers with high glass transition temperatures

Michael A. Mitchell; James E. Mulvaney; H. K. Hall; Craig S. Willand; Hillary Hampsch; David J. Williams

SummaryVarious 4-methoxy-4′-carbomethoxy-α-amino-α′-cyanostilbenes were prepared as mixtures of E and Z isomers, and polymerized via condensation polymerization using dibutyltin diacetate as catalyst. The resulting low molecular weight homopolymers showed higher glass transition temperatures (168–183°C) than previously reported main chain nonlinear optical (NLO) homopolymers. A high molecular weight (Mn≃30, 200) copolymer possessed an even higher glass transition temperature of 187°C. The hyperpolarizability of the polymers and a model compound were found by EFISH measurements to be in the range of 61 to 79x10-48 esu.


Photochemistry and Photoelectrochemistry of Organic and Inorganic Molecular Thin Films | 1991

Linear and nonlinear optical properties of polymeric Langmuir-Blodgett films

Thomas L. Penner; Craig S. Willand; Douglas R. Robello; Jay S. Schildkraut; Abraham Ulman

We have prepared Langmuir-Blodgett monolayer and multilayer films of a polymeric amphiphile with a side chain containing a chromophore of high molecular hyperpolarizability for second order nonlinear optics. Using optical techniques including polarized transmission and attenuated total reflectance spectroscopies, second harmonic generation, and ellipsometry, we have characterized the orientational order of the chromophore and other polymer groups in the films. The high degree of chromophoric order seen in these films indicates that such polymers are good candidates as materials to fabricate Langmuir-Blodgett films for nonlinear optical applications.


Journal of the American Chemical Society | 1990

New sulfonyl-containing materials for nonlinear optics : semiempirical calculations, synthesis, and properties

Abraham Ulman; Craig S. Willand; W. Köhler; Douglas R. Robello; David J. Williams; Laura Handley


Archive | 1991

Optical article exhibiting a high level of second order polarization susceptibility

Abraham Ulman; David J. Williams; Thomas L. Penner; Douglas R. Robello; Jay S. Schildkraut; Michael Scozzafava; Craig S. Willand


Macromolecules | 1991

Dielectric relaxation study of some novel polymers for nonlinear optics

Werner Koehler; Douglas R. Robello; Craig S. Willand; David J. Williams

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