Phase-conjugate backward stimulated emission from a two-photon-pumped lasing medium

Optical phase conjugation of the two-photon-pumped frequency upconversion backward stimulated emission of a new dye solution has been demonstrated. When the 1064-nm pump intensity reaches a certain threshold value, a highly directional and phase-conjugate backward stimulated emission at ∼616-nm wavelength can be observed. After backward passage through an aberration plate placed in the input pump beam path, the introduced aberration influence (1.6-1.8 mrad) can be entirely compensated by backward stimulated emission with a final beam divergence of only 0.23 mrad. The net conversion efficiency from the absorbed IR pump energy to the backward visible stimulated emission energy can reach 10%.