The chemical and physical properties of photobleached nonlinear optical (NLO)-polymethacrylates were studied in order to investigate photobleaching mechanisms. We have shown by three key measurement techniques (infrared-spectroscopy, mass spectrometry, and gel permeation chromatography) that the predominant bleaching process is an irreversible decomposition of the NLO moieties accompanied by a broadening of the polymer molecular weight distribution. The quantum yield of the chromophore degradation determined by the evaluation of the bleaching kinetics fit is in agreement with typical data from comparable chromophores. It was found that bleaching causes an increase in surface roughness of NLO-polymer films, causing an increase in waveguide loss. Smoothing of the film surface by an annealing step leads to a lowering of bleaching induced waveguide loss.
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Vydra et al. (1996) studied this question.