Photoluminescence (PL) and photostability measurements have been made on thin films containing the 2nd order nonlinear optic chromophore, PYR-3, and amorphous polycarbonate (APC). We find that the PYR-3 singlet excited state PL lifetime systematically decreases with increasing PYR-3 concentration, which may be due to PYR-3 excited state energy transfer to non-radiative decay sites. There is no correlation between the PL lifetime and the photostability for low optical intensities, and we find that the photobleaching data cannot be modeled with a single photodegradation quantum efficiency. There is an increase in the photostability with increasing optical intensity, and this enhancement is larger for high PYR-3 concentrations. It can be explained by a reduction in the oxygen content by oxygen-mediated photodegradation for the 5% PYR-3/APC films. This also partly explains the enhancement in the 15% PYR-3/APC films, but there is an additional mechanism as well. The photostability can also be improved by adding beta-carotene, which leads to an enhancement factor of greater than 6.

No abstract

An optically switchable diffraction grating has been made in a thin film containing a photochromic dye and amorphous polycarbonate. We show that a film containing the dye 5-chloro-1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3^'-(3H)naphth[2,1-b](1,4)oxazine] can be optically processed so that a diffraction grating can be completely switched on by ultraviolet light and turned off by thermal relaxation. The ability to switch or modulate the diffraction efficiency has a number of practical applications that include optical switches and add/drop multiplexers.

An optics-based strain sensing system is being developed for quazi-distributed strain sensing in locations and environments that are not accessible to conventional strain sensors. The system comprises an Optical Interrogator that has been designed and constructed by Southern Photonics [1], and optical fibre coupled Bragg grating strain sensors. It has been tested using commercial fibre Bragg gratings [2] that were attached to 2 samples of 316 grade stainless steel and cycled in strain and temperature using an Instron mechanical testing machine and temperature controlled cabinet. The results have been compared to the performance of conventional electrical resistance strain gauges. Pairs of fibre Bragg gratings were simultaneously interrogated at 1540 and 1550 nm centre wavelengths to demonstrate the ability of the system to use multiple sensors for quazi-distributed sensing and temperature compensation. The Optical Interrogator resolution is approximately 4 microstrains, accounting for longer term temperature drift, and it is capable of resolving dynamic strains at rates of up to 90 Hz.

We have made a diffraction grating in an indoline azobenzene/amorphous polycarbonate film by two-beam interference at 532 nm that periodically photodegrades the indoline azobenzene dye. Subsequent illumination of the film with 532-nm light into the trans-isomer band leads to trans-cis isomerization in the indoline azobenzene dye and results in a decrease in the trans-isomer band absorption coefficient. This causes the diffraction efficiency to decrease when probed at 655 nm. The diffraction efficiency returns to its original value when the 532-nm light is blocked by thermal relaxation from the indoline azobenzene cis-isomer to the trans-isomer. Thus, we have been able to optically modulate the diffraction efficiency in a thin film diffraction grating.