Expressions of thermal refractive index coefficients for Ti：Mg：LiNbO3 crystal

The principal refractive indices and the thermal coefficients of LiNbO3 crystal doped with 5mol%MgO and 0.2mol%Ti were accurately measured at the wavelengths of 539.75nm, 632.8nm,1079.5nm and 1341.4nm,and at the tempera-tures of 288K,338K and 423K,It is straightforward to use Sellmeier's equation,modified to suite to LiNbO3 crystal,to solve the parameters Ai, Bi, Ci, and Di of Sell-meier's questions at aforesaid temperatures in an analogy manner of solving the expres-sion of parameter Ci.Then the relationship of parameters Ai,Bi,Ci and Di with tem-peratures T is obtained in terms of least-squares fit.Then the expression of thermal re-fractive index coefficients of LiNbO3 crystal can be inferred.With the expression,the thermal refractive index coefficients of Ti:Mg:LiNbO3 crystal in the wavelength and temperature ranges of 539.75nm～1341.4nm and 288K～423K can be calculated.To examine the practicability of the expression of thermal refractive index coefficients,the noncritical phase matching temperature for 1079.5nm SHG has been calculated,the differences between the calculated and experimented value is less than 1K.Therefore,the expressions are useful for design of nonlinear optical devices of using Ti:Mg:LiNbO3 crystal.