Time-dependent thermal lensing in lead oxide–modified silicate glass

Abstract

The detection and characterization of the thermal-lensing effect is measured for a lead oxide–modified silicate glass material. The self-modulation of the exciting beam is measured with a simple experimental setup on both millisecond and nanosecond time scales. The results of our analysis indicate that to first order the operative mechanism of self-focusing is the same on both time scales, namely, the time-dependent modulation of the refractive index that is due to thermal heating. On a millisecond time scale we recognize the occurrence of multiple focal points within the sample. Although these undulations in the beam waist have been reported previously by others, our experimental methods allow these undulations to manifest themselves in new ways, namely, in Z scans and transmittance versus power profiles. These are indicative of a strong thermo-optic effect and are consequences of Maxwell’s equations. With our model a dn/dT value of 1 × 10−5 K−1 is extracted.