Effect of Stoichiometry and Absorption on Self-Pumped Two-Beam Coupling Gain and Photovoltaic Fields in LiNbO$_{3}$:Fe

The variation of self-pumped two-beam coupling gain in LiNbO$_3$:Fe crystals is investigated, using a CW Verdi 532 nm laser, as a function of absorption coefficients, $\alpha $, and stoichiometry. The 81 crystals tested contain either 0.02{\%} or 0.05{\%} Fe concentrations and are either stoichiometric, intermediate, congruent, or Li deficient. These compositions include a range of $\alpha $ varying between 0.1 and 16 cm$^{-1}$. Experimental coupling efficiency results exhibit a dependence on both composition and $\alpha $; these parameters influence the photovoltaic field, which plays a large role in coupling efficiencies. Experimental results are compared with a mathematical model using a focused geometry, and values for the photovoltaic fields as a function of composition are extracted.