Measurement of the stationary thermal nonlinear refraction light wave-front distortions by image processing

The thermal stationary nonlinear refraction is determined with enhanced 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 beam for different position of the sample cell, a signal similar to the well-known Z-scan signal is obtained. Using the Gaussian decomposition method a simple formula is deduced which relates the induced thermal phase shift to the magnitude of the observed signal. Phase shifts as low as λ/40000 with a signal-to-noise ratio of unity becomes detectable with this technique. © 1997 American Institute of Physics.