Thomas A. Barr

Theoretical and experimental study of the second-order polarizabilities of Schiff's bases for nonlinear optical applications

Abstract A series of twenty-four Schiffs bases was synthesized and nonresonant static molecular second order polarizabilities (β) of these compounds were theoretically calculated and compared with experimental values. The computational method employed obtained: (a) values of polarization versus static electric fields using a semiempirical Hamiltonian; (b) all tensor elements of β by performing polynomial fits of the former data, within the finite-field approach. The experimental values were obtained using a modified electric field induced second harmonic generation (EFISH) experiment with 1,4-dioxane as the solvent. The measured quantities were the projection of β on μ (the permanent dipole moment), relative to MNA (2-methyl-4-nitroaniline). The correlation between the predicted static molecular quantities and their corresponding experimental values was 0.95 (based on a simple least-squares regression forced through the origin). A factor of 8.7 ± 0.3 was determined to be the adjustment parameter for Schiffs bases to account for the solvent and dispersion effects at the fundamental wavelength of 1064 nm.

Investigation of the solvent effect on the hyperpolarizability-structure relationship of optically nonlinear organic molecules

The characterization of organic materials for their nonlinear optical properties involves the use of samples in the liquid phase. The most convenient way to prepare samples for such investigations at room temperature is to dissolve the materials in a suitable solvent. However, the influence of the solvent on the measurements may depend on the physical and chemical properties of both the solvent and the solute. If the solvent effect is not properly taken into account in relating measured macroscopic quantities to the microscopic properties of solute molecules, the comparison of the experimental results of hyperpolarizabilities with the theoretical predictions may be invalid. In this study, a set of molecules with different sizes of conjugated ir-electron structure designed in a systematic order was used to investigate the structure-property relationship and its dependence on the environment using solvents of varying polarity. The materials used include vanillin Schiffs base derivatives. Experimental techniques such as electric field induced second harmonic generation, hyper-Rayleigh scattering and solvatochromic method were employed in this study.

Investigation of solvent effect on optical nonlinearity of organic molecules

Experimental methods based on nonlinear optical processes such as electrical field induced second harmonic generation and hyper-Rayleigh scattering are often used in measuring the second order microscopic susceptibility of optically nonlinear organic molecules in solution. One of the fundamental problems in these experimental procedures is the influence of the presence of solvent molecules on the optical nonlinearity of solute molecules. We have investigated this solvent effect experimentally and our preliminary results are presented.

Hydrogen triplet laser as a high average-power laser

In 1967, Herzberg predicted the existence of the hydrogen triplet series lasers and noted that the far infrared laser ((Delta) V equals 0) transitions should produce very strong laser action. A laser in the hydrogen triplet spectrum was discovered and reported by Barr and McKnight in 1982. Dabrowski and Herzberg confirmed the spectroscopic assignments of the laser lines, and restated that there should be a strong laser on the triplet transitions. The experimental work was strictly oriented to discovering the existence of these lasers. Thus the deductions we make concerning power capability are limited by the type of data available. The experiments show that: (1) the laser is on the triplet series lines as stated above, (2) the three lines start emission within a fraction of a microsecond of one another and terminate at approximately the same time, and (3) the lines seem to be self terminating.

Re-Analysis Of The CS2-O2 Flame As An Infrared Light Source

A computer code has been assembled to analyze the CS2-O2 flame as an infrared light source. The particular application is to experiments performed at Sanders, Inc., Nashua, New Hampshire, USA in 1987. The code contains calculations of fourteen chemical populations in the flame and eighteen excited states of carbon monoxide. CO* is the vibrationally excited CO produced in the reaction, CS+O=S+CO*. We find that the radiation from the experiments at 30 torr can be approximated by the model when the deactivation, third body term, is minimized. The match between experiment and calculation was somewhat obscured by apparent recirculation of spent gases in the experiment observation chamber. Our conclusion is that the CS2-O2 flame can be used as an infrared light source up to at least a pressure of one atmosphere.