Measurement of internal strain in polymers by means of optical hole burning

Spectral holes were investigated in polymers doped with octaethylporphine and other tetrapyrrolic chromophores. A single hole was burned at a fixed temperature (T) or pressure (P) and its width has been examined when T or P was subject to a change. The width of a hole created at higher T (30–45 K) shows surprisingly little variation upon cooling to 5 K. It even broadens slightly at the lowest T. The cooling produces negligible deviation from the Lorentzian hole shape. By contrast, the hole broadening under the He gas pressure leads to a Gaussian distortion. The reversible, non-dynamical broadening is discussed in terms of local stress affecting a small number of atoms adjacent to the dye molecule.