Sellmeier parameters for ZnGaP2 and GaP

Sellmeier parameters are determined for the birefringent material ZnGaP2 an d the singly refractive material GaP by the minimization of chi-square empl oying the Levenberg-Marquardt method. The distinguishing feature of the pre sent work is that all five Sellmeier parameters are treated as adjustable. In previous work the Sellmeier parameter related to the restrahlen frequenc y was fixed and set equal for both ordinary and extraordinary waves in the birefringent material. The fitted results show there is approximately an 8% difference between the two. Taking this parameter as adjustable allows for a better fit on all other parameters. (C) 2000 American Institute of Physi cs. [S0021-8979(00)00103-1].