In this paper we present a new approach for thermal lens analysis using a two-wavelength DSPI (Digital Speckle Pattern
Interferometry) setup for wavefront sensing. The employed geometry enables the sensor to detect wavefronts with small
phase differences and inherent aberrations found in induced lenses. The wavefronts was reconstructed by four-stepping
fringe evaluation and branch-cut unwrapping from fringes formed onto a diffusive glass. Real-time single-exposure
contour interferograms could be obtained in order to get discernible and low-spacial frequency contour fringes and obtain
low-noise measurements. In our experiments we studied the thermal lens effect in a 4% Er-doped CaO-Al2O3 glass
sample. The diode lasers were tuned to have a contour interval of around 120 μm. The incident pump power was
longitudinally and collinearly oriented with the probe beams. Each interferogram described a spherical-like wavefront.
Using the ABCD matrix formalism we obtained the induced lens dioptric power from the thermal effect for different
values of absorbed pump power.