findroot 指定变量为实数

c = 3*10^8;
la = c/10^(9);
k0 = 2*\[Pi]/la;
u0 = 10^(-7)*4*\[Pi];
t1 = -0.36297;
t2 = -0.67188;
r1 = +0.53693;
r2 = -0.26594;
re = r1 + r2*I;
tr = t1 + t2*I;
Clear[dz];
Clear[k];
$Assumptions = dz \[Element] Real && dz > 0;
$Assumptions = k \[Element] Complex && k > 0;
pp = 59;
FindRoot[{I*Sin[k*dz]*(k0/k - k/k0) + re*(2*Cos[k*dz] + I*Sin[k*dz]*(k/k0 + k0/k)), tr*(2*Cos[k*dz] + I*Sin[k*dz]*(k/k0 + k0/k)) + 2}, {{k, 49 - 0.36 I}, {dz, 0.10821}}]
错误显示为：The second argument Real of Element should be one of: Primes, Integers, Rationals, Algebraics, Reals, Complexes, or Booleans
变量为dz和k
计算机好像无法找到精确的值