New results on the temperature coefficient of the refractive index for various optical materials

The refractive index, a property of optical materials, fluctuates with changes in temperature. This means that any temperature variations in a lens, whether it's made from optical glass, infrared material, or even a filter, can cause changes in the refractive index. This, in turn, leads to distortions in the wavefront that are dependent on temperature in the application. However, these temperature-dependent variations in the refractive index can be offset by thermal expansion, which allows us to define what we call athermal glass behavior. A crucial element for designing athermal optics is a dependable database that contains the thermal coefficient of the refractive index for the optical materials. ISO has released two standards, ISO 6760-1 and 6760-2, which focus on measuring the temperature coefficient of the refractive index. For many years, reliable data on these temperature coefficients have been a key component of the data sheets for optical glass. More applications need broadband dn/dT evaluations up to 2325 nm. Current measurement capabilities are limited to 1060 nm wavelength. Questions arise if extrapolation of dn/dT data from 1060 nm to 2325 nm is a valid approach.