New wide range spectral data on the stress optical coefficient of optical glass

The optical position of optical glasses is fixed by its chemical composition but also by the temperature history of the glass. Therefore, fine annealing of optical glass is an important part in the production process. The temperature profile during cooling of the optical glass from glass transition temperature down to room temperature generates thermomechanical stress in the material. The thermomechanical stress is translated into stress birefringence by means of the stress optical coefficient. The stress birefringence is a measure of the difference in refractive index as a function of the polarization direction. Stress optical coefficient is a function of the wavelength and varies among different glass compositions. For polarization sensitive applications the knowledge of the stress optical coefficient as a function of the wavelength is essential. In this publication a new method of measurement of the stress optical coefficient based on the ASTM C770 procedure C is presented. The new method enables spectral measurements from 245 nm up to 1670 nm. Results of the stress optical coefficient as a function of wavelength for a variety of optical glasses are discussed and compared to measurements from the past based on ISO 10345-2.