Recording of a hologram by using the second-order nonlinearity

The observation of “spatial-modulation” resonances of saturated absorption in the interaction of iodine-127 vapors with a superposition of frequency-nondegenerate TEM₀₁ and TEM₁₀ transverse modes of a linear laser is reported. The modulation of the total radiation power of the probing wave, recorded at twice the beating frequency of transverse modes of the laser, is interpreted to be the result of the transformation of modulation of the spatial distribution of the field into its amplitude modulation under the action of nonlinearly absorbing iodine vapors. Resonances of saturated absorption of the weak line R(127)11-5 of iodine-127 (633 nm) in an extracavity cell are observed by the method proposed.