Wavelength selective materials modification of bulk As2S3 and As2Se3 by free electron laser irradiation

In this study we report first measurements of wavelength-selective infrared-induced materials modification of bulk As2S3 and As2Se3. These materials are currently being considered as candidate materials for infrared optical fiber transmission in the range of 1-10 mu m. Our study is aimed at modifying oxygen, hydrogen and carbon impurities bound to chalcogenide constituent elements in the materials to reduce absorption. Tunable infrared radiation from the W.M. Keck Free Electron Laser (FEL) at Vanderbilt was used to excite specific vibrational modes, S-O-H and CHx modes in bulk As2S3 and Se-H, CHx and S-H-2 modes in bulk As2Se3. Changes in vibrational mode amplitudes are monitored by measuring the intensity of the Fourier transform infrared (FTIR) spectra before and after irradiation at appropriate wavelengths. By tuning wavelengths to hydrogen vibrational modes, we find evidence that hydrogen is released and/or redistributed athermally. In particular, following irradiation at specific resonant wavelengths, vibrational mode amplitudes as monitored by FTIR associated with CHx are significantly reduced in bulk As2S3 and As2Se3 samples. In As2S3, the changes in CHx modes are reversed by heat treatment at 115 degrees C for 35 min in nitrogen atmosphere. (C) 2000 Elsevier Science B.V. All rights reserved.