MEASUREMENT OF THE STATIONARY THERMAL NONLINEAR REFRACTION LIGHT WAVE-FRONT DISTORTIONS BY IMAGE-PROCESSING

The thermal stationary nonlinear refraction is determined with enhance d sensitivity by measuring the profile distortions of a cw probe light beam in the presence of absorption of a collinearly propagating pump light beam. By measuring the total profile distortion of the probe bea m for different position of the sample cell, a signal similar to the w ell-known Z-scan signal is obtained. Using the Gaussian decomposition method a simple formula is deduced which relates the induced thermal p hase shift to the magnitude of the observed signal. Phase shifts as lo w as lambda/40000 with a signal-to-noise ratio of unity becomes detect able with this technique. (C) 1997 American Institute of Physics.