Light shift of coherent population trapping resonances

We have measured the spectral position of the absorption minimum in a coher ent population trapping resonance in thermal cesium vapor as a function of light intensity. The dependence of position on intensity is found to be alm ost linear. We have furthermore studied the dependence of this light shift on neon buffer gas pressure and find a strong reduction for higher pressure s. So the addition of a buffer gas not only reduces the linewidth of the re sonance but also a very important systematic effect for precision measureme nts.