Optical Material Homogeneity

An important property of an optical component is the variation of the refractive index of the material from which it is made, broadly referred to as homogeneity.  Material inhomogeneity causes variation of the refractive index in a glass, which can be in the form of sharp, cord-like regions called striae or it can occur as a gradient of the refractive index through a larger region of the sample.  Material index variations must be qualified to ensure their impact is within tolerance for a particular optical design where the material is used.

ZYGO laser interferometer products offer a range of capabilities for qualifying optical material homogeneity as well as built-in analyses in our comprehensive Mx data acquisition and analysis software.

Verifire MST – Multiple Surface Test interferometer is well suited to qualify material homogeneity of plane parallel windows by simultaneously measuring the transmitted wavefront of the window and removing the effects of surface deformation (required to achieve precise material measurements).  The simultaneous nature of measurement using the MST reduces measurement uncertainty for the most precise results, and maintains the important linear component of homogeneity, information lost with other metrology methods.

Verifire and Dynafiz interferometers enable similar measurement capabilities of wedged optics with an acquisition and analysis software package designed specifically for material homogeneity measurements.