Three-dimensional measurement of a thermal lens in K9 glass using a Mach-Zehnder interferometer

Three-dimensional and time-dependent thermal lens distribution was measured in K9 glass by a Mach-Zehnder interferometer in this paper. The thermal lens was introduced by focusing a millisecond pulse laser into the glass, and the phase information was extracted by Fourier analysis. The specific internal three-dimensional refractive index variation (RIV) was then deduced from phase maps by an inverse Abel algorithm. It is demonstrated that the stress-induced birefringence would lead to negative RIV, which is contrary to results of temperature increment. The method proposed herein would provide a novel idea for measurement of thermal lenses.