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Refractive Index Drop Observed After Precision Molding of Optical Elements: A Quantitative Understanding Based on the Tool–Narayanaswamy–Moynihan Model
Author(s) -
Fotheringham Ulrich,
Baltes Andrea,
Fischer Peter,
Höhn Petra,
Jedamzik Ralf,
Schenk Christian,
Stolz Claudia,
Westenberger Gerhard
Publication year - 2008
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2007.02238.x
Subject(s) - refractive index , thermodynamics , materials science , differential scanning calorimetry , drop (telecommunication) , molding (decorative) , relaxation (psychology) , logarithm , optics , chemistry , composite material , mathematics , optoelectronics , physics , mechanical engineering , psychology , social psychology , mathematical analysis , engineering
The room‐temperature refractive index is measured for three different prior cooling rates (approximately 10, 50, and 250 K/h) for two glasses especially developed for precision molding. The empirical logarithmic relationship between the cooling rate and the refractive index is also reproduced for the comparatively high cooling rate of ca. 250 K/h. The same relationship is found in a simulation of these cooling rates by the semiempirical Tool–Narayanaswamy–Moynihan model for structural relaxation, with the necessary parameters obtained from differential scanning calorimetry and temperature jump experiments. The measured and the simulated refractive indices coincide within the limits of experimental error. The results demonstrate that the index drop, which is observed when these glasses are first cooled at a regular optical cooling rate (e.g., 2 K/h), and then precision molded (typical cooling rate 1000 K/h), can be understood considering the concepts of structural relaxation.