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Base-induced cycloadditions of tosylmethyl isocyanide to a series of isothiocyanates have been investigated. Depending on the reaction conditions, thiazoles 5 and/or imidazoles 7 are obtained, with the thiazoles, in particular, being obtained with high regiospecificity. During the course of this work a high-yield ring transformation of 5-amino-1,3-thiazoles (5) to imidazole-5-thiols (7) was discovered, which has not been previously reported. A number of reactions of 7 are described.

We report the implementation and operation of novel superhigh-reflectivity negative-dispersion dielectric mirrors for use in tunable ultrafast laser systems. The mirror structure is divided into two distinct regions: an underlying superhigh-reflectivity dielectric quarter-wavelength stack and an overlying negative-dispersion section consisting of only a few layers and forming simple multiple Gires-Tournois interferometers. The example that we present was designed for operation from 800 to 900 nm and has a near-constant group-delay dispersion of -40 fs(2) and a peak reflectivity greater than 99.99%. We show a comparison of the predicted and the measured mirror performance and application of these mirrors in a mode-locked Ti:sapphire laser tunable from 805 to 915 nm.

Propagation of intense femtosecond pulses in solids and liquids is investigated experimentally and numerically. A brief review of experiments in fused silica that reveal complicated spatio-temporal dynamics including temporal pulse splitting is presented. Experiments in methanol show the expected effects of linear dispersion and an instantaneous Kerr nonlinearity as well as a contribution from a noninstantaneous nonlinearity with a response time on the order of 10 femtoseconds. Propagation in these two systems is modeled using a modified (3 + 1)-dimensional nonlinear Schroedinger equation (NLSE) that includes nonlinear shock and space-time coupling terms and a (1 + 1)-dimensional NLSE that includes a response time of the nonlinear part of the refractive index.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Summary form only given. Because of the broad bandwidth of femtosecond laser pulses, dispersion coefficients are important parameters in femtosecond pulse propagation. Dispersion coefficients of dielectrics and nonlinear materials such as barium borate (BBO) are measured over an extended wavelength range, and improved equations are sought for these materials. Using a white light Michelson interferometer, we measure dispersion coefficients of materials placed in one arm of the interferometer for wavelengths from 0.4-1.1 /spl mu/m.

Amorphous alloys of the type A1−xFex, where A represents B, Ge, or Sn, were prepared by two‐source coevaporation in the ranges 0.3⩽x⩽0.9, 0.30⩽x⩽0.65, and 0.45⩽x⩽0.64. The magneto‐optical properties of these alloys were examined by means of the polar Kerr effect. The magnetic properties of the alloys with B and Ge were also studied. The concentration dependence of the Fe moments in the Fe metalloid alloys is analyzed in terms of a model in which due account is taken of the fact that the variation of the heat of alloying in the various iron metalloid alloys entails a variable degree of intrinsic compositional short‐range order.

TE‐TM mode conversion was studied in LPE‐grown garnet films with high Faraday rotation (up to 1800 °/cm at 1.15‐μm wavelength) and positive uniaxial anisotropy. High conversion ratios (80–90%) were found for several modes. The phase matching is satisfactorily explained by the birefringence in the film resulting from the misfit stress.

Results are reported of polar magneto‐optical Kerr effect measurements performed at room temperature on the Heusler alloy PtMnSb in the wavelength range 280–2000 nm. The double Kerr rotation has a maximum in excess of 2.5° at 720 nm, which is to our knowledge the highest room‐temperature Kerr rotation reported thus far for any material in the wavelength range under consideration. In order to assess the influence of composition the related materials PdMnSb, NiMnSb, and PtMnSn were also investigated. Here the Kerr effect was considerably lower.

Some of the common questions that confront the classroom teacher in regard to arithmetic are closely related to measurement and based on what should be taught. A few of the questions might be stated: How can tests be improved so that fundamental concepts, reasoning and estimation can be measured? Do people who have ability in computation also have ability in reasoning and estimation? Would arithmetic have a better carry-over into real life if the reasoning type of arithmetic were stressed?