A series of new sulfur-nitrogen ring systems with a neutral radical center were designed for incorporation into liquid crystal molecules and formation of discotic and calamitic phases. It is expected that these materials will display unusual magnetic properties associated with partially oriented bulk liquid crystal structures. Synthetic progress toward new radicals and the first discogen with nr-delocalized neutral radical is described.

The transient absorption, in the visible band, induced by a UV laser pulse at 337nm in three different liquid crystal materials is studied. Two decay channels are observed and assigned to the relaxation of the singlet and triplet excited state populations. The fluorescence is also measured under both UV and two-photon (590nm) excitation and the rate of decay is found to compare well with the rapidly relaxing component of the induced absorption. A strong temperature dependence on both the fluorescence and absorption transients is observed and this is discussed in the context of excimer formation.

This paper presents a design for an optical limiter composed of an optical fiber with a nonlinear interface. Our analysis of this device shows that high linear transmittance is obtained for weak incident light, while at the same time, intense light is attenuated below allowable values through continuous reflection. Moreover, the bandwidth of the device may be quite large when the fibers have small amounts of dispersion. Theoretical calculations are presented along with a characteristic analysis.

Mixed metal clusters (n-Bu4N)3[WCu3Br4S4] (I), (n-Bu4N)3[Wag3Br4S4] (II), (n-Bu4N)3[MoAg3BrCl3S4] (III) and (n-Bu4N)3[MoAg3BrI3S4] (IV) were synthesized by solid state reactions. The cluster anions assume cubic cage shaped structures and possess strong optical limiting capability. At very low fluences the molecules respond linearly to the incident light obeying Beer's law. As light fluence rises their molecular absorptivities increase rapidly exhibiting limiting effect with threshold and saturation fluence of 1.3 J/cm2 and 0.7 J/cm2 for compound I, 0.7 J/cm2 and 0.5 J/cm2 for compound II, 0.6 J/cm2 and 0.3 J/cm2 for compound III, and 0.5 J/cm2 and 0.3 J/cm2 for compound IV respectively. The threshold and saturation values of compound IV are about 3 and 2 times better than those of C60 measured under identical conditions. The optical limiting capability of the clusters is derived from excited state absorption, a process that turns on within nanoseconds and off over milliseconds.

Gradient index or rugate optical filters are continuous generalizations of the familiar quarterwave stack which find widespread applications in sensor hardening. In the design of a filter or mirror there are infinitely many refractive index profiles n(x) whose wavelength-dependent reflectance R(λ) is specified as a design objective. The relationship between R(λ) and n(x) is nearly that of a Fourier-transform pair. Exploiting this relationship, specifically the physically indeterminate phase of the Fourier transforms, permits constrained optimization of rugate designs. In this contribution we outline the approach of optimal phase modulation and indicate by examples its application to problems in optical limiting.

In this paper we describe a technique by which the broadband excited state absorption/emission and dynamics can be measured for materials with either linear or two photon absorption. The technique is applied to two different dyes in solution and to a cyano-biphenyl organic liquid. The ratio of σex/σgr for HITCI in methanol is greater than 1 from 400 to 570nm and at 532nn is determined to be 25; the excited state lifetime is 800ps. For CAP in methanol σex/σgr is greater than 1 from 400–650nm and is 14 at 532nm. Dimer absorption and emission are found to contribute to the excited state response in this material. In the organic liquid broadband (400–570nm) excited state absorption is measured following two photon excitation at 588nm.

There is a recognised requirement for solid-phase, non-linear absorbing devices. We present data for a range of non-linear absorbing dyes in polymer hosts. We identify polycarbonate as a useful host material. We recognise that progress will be required to increase the laser-induced damage threshold of the dyed polymers if practical devices are to be realised.